Category: TUBE AMPS

Fender Prosonic Re-Revisited: Reunited

And it feels so good!

My never ending quest for that Fender ‘sparkle’ may just have ended. For the Fender Prosonic, anyway.

After a couple of years of mixing and matching speakers, i discovered the best speakers to make the Prosonic sound like a TRUE Fender amp were the 25W Greenbacks in tandem.  I’m quite aware that it’s underpowered compared to the amp, but man if you got it, you gotta get it. For me it’s all about tone. I hardly crank the amp so there’s hardly any fear of blowing the Greenbacks.

Now by Fender clean sparkle i mean the bell-like tones you get, especially when you play a Strat in positions 2 and 4. I’ve heard this distinct Strat tone on a Bassman, and on a Twin Reverb, hell even on a Princeton and a Champ.

I knew the Prosonic can sound like a true Fender amp, and the Celestion Greenbacks simply has it. It disproves the critics saying the amp is too hot to be a Fender. It still is hot with the Greenbacks, but it finally has the identifiable clean Fender sound.

But this configuration also has a disadvantage- there are no cases for a 2×12 Fender Prosonic. You can have it custom made, but it’s expensive. So i re-housed the chassis in an empty Twin Reverb case. Worked well, but its not aesthetically pleasing. The gap on either ends of the front panel bothered me.

The original case held 2×10 ‘vintage 30 flavored’ speakers, but i was able to make a baffle that held a 1×12 speaker. I originally had a WGS Veteran 30 in it and it sounded good, but it lacked that Fender clean sound. A single Greenback is way underpowered (25W vs the Prosonic’s 60W). Even set to 30W the amp is still too much for the Greenback. I needed a beefier 1×12 speaker that sounds like the  2 greenbacks, but does it exist?

Yes. Yes, it does.
And it comes in the form of the 75W G12H-75 Creamback.

I FINALLY can stop the nagging feeling about the amp not looking presentable. It’s superficial, but having a mismatched chassis and case just bugged the heck out of me. I could have saved myself a lot of trouble and time if i had just simply studied and compared the Frequency Response of the 25W Greenback G12M versus the other 12″ Celestions.

Courtesy of Celestion’s website, the charts below show the 75W Creamback’s frequency response approaching 20KHz held at above 70dB, meaning there’s more emphasis on those frequencies and they’re essentially louder compared to the Greenback which slopes downward below 70dB:

Greenback G12M
G12MGreenback

Creamback G12H-75G12H-75CREAMBACK

superimposed (Greenback is appropriately in GREEN):
G12H75-G12M-merged

From around 100Hz is when the frequencies coincide, but you can see the higher frequencies on the 75W Creamback stays above 70dB, in contrast to the Greenback. This would explain the initial icepick-y impression i had, coming from a greenback setting (read on for my fix for it below).

I had the G12m-65 Creamback before, and though it sounded normal, it didn’t have the sweet Fender clean sparkle. Check out the difference between that and the 75W Creamback (65W in Blue):

G12H75-G12M-65-merged
The most important factor were the high frequencies. You can see the drop off of the 65W just before 20KHz, while the 75W retains it above 70dB.

You can also see a drop in the original Greenback, but not as drastic (compared to the 65W Creamback):

G12m-G12M-65-merged
Though the Greenback and the 65W Creamback almost looks identical, that dissimilar high frequencies emphasis  made all the difference in getting the Fender clean tone.

Just a disclaimer, its not just the speaker change that made this Prosonic finally sound like it’s venerated Fender tube amp ancestors (the Prosonic was made in the mid 90s). Stock, the Prosonic is a hot-lava-spewing high-gain beast. I had to experiment with tube swaps in the preamp and the amp stages to raise the headroom for it, as well as a couple of tried-and-true well-publicized (online) mods coming from the original Prosonic designer himself Bruce Zinky. But if there was just one change that could have the most effect on it, it was the speaker change.

Also, when it comes to the dirty tones, the 75W Creamback seems to have a much tighter response than the Greenback. There’s more boomy bottom end on the greenbacks (possibly because there are 2 of them?), and sounds more loose, almost a sponge-y feel to it. Though the tight response may also be due to the Creamback being brand new and hardly broken in yet. That the creamback already sounds great out of the box is a good indication it can only get better as it’s played on.

The highs are also more apparent on the Creamback (in high gain), which the graphs earlier confirms. On the same settings as the greenbacks, the Creamback is almost icepick-y, but this is easily tamed. Instead of rolling back on the Treble (i maxed it out), i roll back a bit on the Bass (was at 7 on the greenbacks, now at 4), and to my own surprise, by increasing the mids (sounds great between 3 and 7). Sounds counter-intuitive, though it does make sense to do this. Instead of subtracting the levels of higher frequencies, other frequencies are tweaked to achieve the balance that provides the most harmony in your ear.
Also, the Creamback is perceptibly louder on the same greenback settings. Either clean or on high gain, i found myself rolling back a bit on the volume to achieve the same dB level i had on the greenbacks.

Well, THE PROSONIC IS HOME. Looks as it should be, far less bulkier. Relatively small, it’s compact and heavy. Deceptive in sound as well, it looks and sounds like a quintessential Fender amp when played clean, but kick in to high gain, and you swear it’s NOT a Fender amp – it’s a hellacious fire-breathing monster!

Last thing i need to do now is to apply the Fender logo. It’s like pinning a medal on a rookie that struggled and prevailed and came out on top, more versatile than ever before. It’s now ready for the big leagues. It’s now earned the name of the badge itself.

2005 VOX AC30 CC2X

This is IT.
Save for the Prosonic, this amp has made every other amp i own (and still want to own) almost irrelevant. Not that i don’t want anymore amps (i still would like a Marshall!), but it makes me feel like i dont NEED them as much.
The AC30 pretty much rounds up the tube tone i personally have been looking for. There’s not one tube amp that can nail EVERY tube sound authentically. Each amp specializes itself to a particular sound and tone. Though the Prosonic grabs the top prize for unparalleled versatility (goes from Fender CLEAN to hot bluesy tone to scorching red hot shred machine), the AC30 CC2X takes the niche of the sweet clean chime and the un-imitatable Top Boost tone. Think about it – almost every amp manufactured these days either imitates or clones a Fender or a Marshall (which by the way, as every tube amp afficionado knows, Marshall amps originally imitated and cloned a Fender Bassman!). But not very many (if at all) clones an AC30. It is unique!

THE PURCHASE

ebay- it’s a dirty jungle! It’s a bane for sellers, but a boon for buyers. Being careful and knowing what you’re looking for helps in making an educated purchase.
I saw this AC30 with a Buy It Now price and a Best Offer, with free shipping. The description read that the seller “does not have the power cord to test it”. Which means IT DOES NOT WORK! I saw the blue AlNiCo speakers and thought, well, maybe i can use those speakers instead if the amp is completely dead- they do command a good price. Plus it looks clean, the grill cloth looks straight (most grill cloths are either sagging or out of place already with amps this old and used). I can also part away with the cab easily.

So unknown if it works or not, if its fixable or not, i went and got it. Took over a week to arrive, and man! did it look like it was going to be a disaster!
The box it came in was super beatup, tape all over, flaps not even p[roperly closed, some holes thats bleeding with (gasp!) peanut packaging!!! Damn you people who use peanuts for packaging. You can never take anything out of the box without spilling any peanut on the floor. So DAMN YOU TO HELL!!!
I didnt even bring it inside- i took pictures all around without touching the beatup package. I even took a video of me taking the amp out of the box.
Aside from the awful peanuts, the amp was also wrapped tightly with almost 2 inches of bubblewrap. Good! it wasnt all just peanuts. slowly i took the buble-wrapped amp out, but to no avail- i STILL had peanuts spilling out. DAMN YOU TO HELL, PEANUT PACKAGERS!!!
As soon as i got the amp out, i started to SLOWLY cut through the bubble wrap. It was tightly wrapped that it took sometime to completely remove all of it. and then i saw the amp in its entirety.

CLEAN AS CLEAN CAN BE!!! WOW! that 2-inch thick bubblewrap made up for the crummy packaging! HALLELUJAH!!!
I can’t see any breaks anywhere, no dents, no huge scratches, no tears, no structural damage at all. PRISTINE!!!
After cleaning up all the peanuts and packaging and bubblewrap in the trash (this is still outside, mind you), i hauled the monster up a flight of 17-step stairs to my apartment. backbreaking motherfucker!

THE INSPECTION
a much thorough inspection indeed confirmed that there were no breaks or dents or structural damage to the amp. It WAS missing the power cord (which is the same as what you have on a PC, which is easily acquirable. It also just means that the seller must’ve tested it,. saw it didnt work, and made a poor excuse of “unable to find a cord” for it. Whatever, it’s now in my possession).
The bell covers of the Blue AlNiCo celestions had dust on it, indicating its been around a while. It did have the footswitch to go with it, but also was missing the 1/4 stereo cable that connects it to the amp. no big deal, i have both missing cable and power cord.
Plugging in the amp, it did NOT light up at all when it was turned on. I opened the fuse holder, and it didnt look like it blew. So my first thoufght was the Power Transformer. Damn. That’s not cheap. Oh well- im handy with the solder, we may be able to fix this.

THE FIX
So i got the drill/driver and went to town opening up the back. Not the easiest chassis to take out- there were 6 MORE screws that help the chassis to the amp after the back was removed. and then it revealed the tubes (its like a peek of heaven! he he).
JJ EL84s, a Sovtek GZ34, and 2 JJ 12ax7 and 1 chinese-made 12ax7 preamp tubes. Not bad, but it can be better- if i do fix these there’s going to be some tube-rolling happening. Maybe. IF i even fix it.
After tooling around, it seems nothing was done, no noticeable changes, upgrades or mods done at all. GOOD! that means no one really did anything to it. It’s worse if someone did- you don’t know what they’ve done, which could have caused or even contributed to it not working.
I also found ANOTHER fuse that’s blown- right under the IEC receptacle (where you plug in the power cord to). I had to wait a few days to get the replacement fuse, as i didnt have the right value AND size for it. Online technical manual and schematics revealed what it needed.
Once the fuse came in, i replaced the blown one, and once i turned the power switch on, there was light!!! The tubes were glowing! HELLOOOO, NURSE! it was a fuse issue! Or so I thought.
Then as quick as my elation, the amp blew the new fuse. huh. Something is making it blow. I over-ordered a lot of fuse, with different ratisgs. Probably not the correct rating. Putting a higher rated fuse STILL blew it though. But with the chassis out and the tubes glowing, i saw the tube rectifier (GZ34) flash briefly just before it blew the fuse. AHA!
I quickly turned the amp off, waited for the tube to cool down, and pulled the Sovtek rectifier out. Let’s see if it is indeed just the tube or something else making it flash bright briefly and also blowing the fuse. I have another amp (the Epiphone Blues Custom 30) that uses an old stock U.S.-made GZ34 rectifier, so i pulled that off of it, and plugged it in the AC30. Put a new fuse, plugged it in, and turned it on.

This time it stayed on. YES!!! It was a bad tube rectifier. After a few minutes of warming up, i slowly turned the volume all the way up (to 11!) and can hear a slight unmistakeable overdriven amp hum. I plugged in my 12-string Gretsch, and KERRANG!!!!
WE HAVE SOUND! AND MAN, HOW SWEET IT IS!!!

I spent no time putting the chassis back in and the back panel on. I’m playing this now!

KNEE-BUCKLING AND ALL THAT GOOD STUFF
Wow. this beast is jaw dropping! I knew what i was gonna get, but i never knew how good it really sounds. I spent a good hour just turning knobs, fiddling with tones, finding out what does what, getting myself familiar with the amp. So much tonal variety, but so unique-sounding! Everything works! And the Vox chime – heaps and heaps of it! So much so that there is even a tone cut knob that tames it back, if you so desire. Overdriven, the Top Boost is so sweet you can almost taste it. mix both that and the Normal channel, and the grit just gets grittier. The reverb has a switch that makes it sound hauntingly cavernous, perfect for deep retro-surf sounds. And the tremolo is not just useable and passable- it adds a flavorful dimension to the already magnificent sound.

and all it took to fix it was a tube rectifier and a fuse change. This was one chance i took that could’ve turned into a nightmare waste of a purchase, instead became one of the best fixes ive ever done.

So now we have The Keepers: The Fender Prosonic, this Vox AC30 CC2X, the Fender Bassman Ten, the Plush P1000-s, The Kalamazoo line (Reverb 12, Model One, Model Two, Bass 50), The Peavey Windsor 100W head, the projector amps (RCA and Bell & Howell), and… that’s it. Maybe the cheap solidstate no-name 100W bass amp just so i have something for my bass guitar.

This is IT. now let’s JAM!!!

1996 FENDER PROSONIC

You know when a dream becomes real? This is one of them.
Ive been lusting after a Fender Prosonic ever since i learned about it a couple of years ago. At that time ive been searching for a “modern” tube amp that employs tube rectifiers. A good 95%+ of all tube amplifiers made today have solid state rectifiers. Why tube rectifiers? “SAG”. To put it simply, when a signal goes thru an overdriven amp with a tube rectifier, the signal undergoes something similar to compression. Instead of dying quickly, it dies slowly, and the sound sustains for a little longer. The impression is that it “blooms”, the sound seem like its getting louder instead of softer as it decays. This is know as ‘sag’. Awful for jazz and metal or anything you need fast articulated notes, but perfect for blues and anything that needs sustain. Which i LOVE.

THE PICKUP
Ive been on the lookout for a cheap one for months now, scouring eBay, always finding them priced beyond what i’d like to pay (and afford!). Until one day on Craigslist, an ad was up for one. It normally goes for an average of $700 to as much as $1600 for the “custom shop” (which after much research really has no circuit difference with the production model – only the kitsch of having an early model makes it appealing to collectors…). $600 is relatively cheap for it. This was LESS!
I immediately emailed the guy with an offer, and he replied back saying he agreed with it as long as i pick it up that same day. No problem! As soon as work was done, i withdrew money, and headed there.
This is the most ive spent on ANY one guitar-related purchase (im poor! and im poorer now!). My heart was racing – i will have to cut back on lunches and dinners in the next 2 weeks! 😀 But as soon as i took it home and plugged in, it was well worth above what i paid for.

HOME
The first was to test how it sounds with my guitars. I test-drove it when i was at the guys’ place, and it sounded great, but its always different when you have your own comfortable axe to use, and you have all the time to futz around.

On the front has the unusual set of controls ive seen on a 2-channel amp. There is one Volume knob for channel 1, and a Master Volume, not for over the 2 channels, but Master for channel 2 only. Both channels share the same 3-band EQ and Reverb. In addition to a Gain knob for the 2nd channel, there is an ADDITIONAL Gain 2 knob, also for channel 2 only.  The front also displays the green jewel light and the 2 inputs (1 is high, 2 is low, about -3dB lower per the manual).
On the back are the Power switch, as well as the standby switch, and the WONDERFUL 3way selector switch which sets it to Class A tube rectifier (30W), Class A/B tube rectifier (50W), and Class A/B Solid state (60W). Most of my testing was done on Class A. The back also sports the Effects Loop Send and Return jacks, the occupied jack for the combo speakers, an additional output speaker jack to wire an external cab, and the footswitch jack.

Inside are the two Celestion speakers (supposedly the 10″ version of Celestion Vintage 30’s). Hello!

I used my ’88 Gibson SG Special to test for humbucker sounds, a Korean-made 90’s Squier Strat, and a Danelectro Mod 6  (modded with a Baritone neck) for single coils.

Channel 1 sounds clean only up to 2, but man its LOUD! Past 2 and it starts to break up. NICELY! mmmm…. tube breakup…..
Channel 2 is just a firebreathing monster eating jalapenos and drinking capsacin in molten lava. HOT!!!

Not going to elaborate further, all i know is this beast needs a bit fo taming. Its over-the-top cascading dual Gain settings is WAY more than what even the most aggressive metalhead needs. After several hours over a couple of days, it was time.

THE SWITCH
Stock tubes sounded ok, but i never did like new production tubes very much (only if necessary). So i went about changing them, and dug up what NOS and used vintage tubes i got, but not before looking at the tube amp chart, the schematics, and forum-trolling. There isnt one definitive place i found that outlines exactly which preamp tubes do what, so i traced the harder ones using the schematic i found online.
left to right facing the back:
V9 = rectifier
V8, V7 = power tubes
V6 = Phase Inverter (PI)
V5 = 1/2 pushing the PI, 1/2 Reverb recovery
V4 = Reverb driver
V3 = 1/2 effects loop, 1/2 unused
V2 = 1/2 Gain 2, 1/2 channel 2 master volume (and looks like the EQ section)
V1 = 1/2 Gain 1, 1/2 Channel 1 volume

Now this is interesting. I double-checked to make sure i read the schematics right, but it seems V1 which controls Channel 1 Volume, ALSO controls Gain1 of Channel 2. V2 seems to control Channel 2 Master Volume and the EQ section, AND Gain 2. One would think that V2 should have both GAIN levels hooked to it, and maybe have V1 used for Channel 1 and the EQ section. The Master Volume for channel 2 could have dedicated itself on the unused section of the FX Loop.

At any rate this is what i ended up putting in at first try:
V9 = stock chinese 5AR4 (had to order something else for it)
V8, V7 = GE 6L6GC
V6 thru V3, V1 = GE 12AT7
V2 = RCA 12AX7A cleartop
Though it gave the amp a better sweep and a it more headroom, this also gave the amp a better sounding drive, on both Channel 1 (when turned up), and on Channel 2, which has less distortion, but still fizzy when dialed up. I usually turn this up when i want something more thrash chunky riffing.

One thing it certainly did was clean up the noisy reverb. Amazing what bad tubes can do, and how easy it is to fix them. No more AM radio static. The 12AT7 in the reverb recovery also made the reverb less swampy. Though truth  be told, i LIKE swampy! but putting a 12AX7A in the reverb recovery also added back a bit more drive and less headroom.

Now i mentioned ive always wanted to have a Prosonic since ive learned of it, but i didnt go into too much research on it -i didnt want to get an impression until i got one, so i can judge for my own. I do know that tube rectifiers give a tube amp a sweet sound when the tubes are cookin’, as evident in the old Bell & Howell tube amps ive owned that used tube rectifiers. The chinese rectifier was doing its job, but it sounded stiff and thin to me. I have an Epiphone Blues Custom 30 that uses a 5AR4 tube rectifier also, and the sound improved when i replaced the chinese tube rectifier in it with a Richardson-branded US tube that was made in the 80s. It looked like a Bendix with the off-color base, but i wasnt sure. All i know is that the sound of the Epi BC30 was rounder and had more depth with the change.
So i went about looking for used old stock 5AR4 tubes, and was prepared to get even japanese made if i cant find relatively cheaper 5AR4 tubes. Everyone points to a British Mullard, but seriously what blue-collar person can afford a $100 tube? At any rate i ended up with a couple of Japanese (looked like Matsushita) 5AR4 tubes, and one GE.
Dropping one of the Japanese tubes in, the change was immediately apparent. There was more volume, or at least the bottom end was more evident, and it was tighter. Before the change, the overdriven sound was too loose-sounding, a bit too hairy. There was less fizz now, and the overdrive is more focused. YUMMY! That one stays!

Only now that ive owned A Prosonic that ive gone in and read as much as i can about it on forums and boards, just to get an idea what people are hearing, and compare notes, so to speak. So far what ive been reading is consistent with what im hearing – this amp when given a little work, becomes much more of a jewel than it already is!

One tube ive been meaning to play with are 5751 tubes – a lower gain 12AX7, but slightly more than a 12AT7. The SRV tube, which i guess lends to its expensiveness. I was able to find some old stock online that were relatively cheap. At least compared to the new production 5751’s the ones i got were just slightly cheaper, which for old stock is a GOOD price! I also got a pair of Sylvania JAN 6L6GB’s to try.

As soon as the 5751 and 6L6GB’s came in, i swapped and moved tubes around. I ended up with this configuration:
V9 = japanese old stock 5AR4
V8, V7 = JAN Sylvania 6L6GB
V6 = GE 6679/12AT7
V5 = GE 5751
V4 = GE 12AT7
V3 = GE 12AT7
V2 = RCA 12AX7A
V1 = GE 5751

This seemed the most musical-sounding combination for me.
V9 = japanese old stock 5AR4 – gave it a better bottom end ( i can hear it now! so much so i can dial back the Bass and still sound great)
V8, V7 = JAN Sylvania 6L6GB – higher headroom, better, louder cleans before CH1 starts overdriving
V6 = GE 6679/12AT7 – clean-sounding tube for the PI, less hairiness on pushing the power tubes
V5 = GE 5751 – instead of 12AX7, the 5751 doesnt make the reverb too swampy, and also pushes the PI less
V4 = GE 12AT7 – tames the reverb well, maybe TOO well. im thinking of changing this back to an RCA 12AX7A cleartop
V3 = GE 12AT7 – FX loop. easily the most useless tube in the chain to me – i dont use it. why waste a 12AX7 tube in it? just an old stock quiet 12AT7 to keep the chain going. Cant NOT put anything, since removing it makes the amp go silent.
V2 = RCA 12AX7A – keep Gain 2 real hot, and also drive the EQ section strong. Also debating on putting a 5751 (swap with V4)
V1 = GE 5751 – 12AX7A was too hot, didnt give Channel 1 much sweep, and overdrives too soon when turned up. 12AT7 seemed like a blanket was on channel1, 5751 opens it up and brings back that chime without losing clarity at higher volumes.

One thing ive also wanted to use are 7581 tubes, an industrial version of the 6L6GC. Known for its higher plate voltage, it can be subbed without worries. One strong tube. Thats the thing though- i have only ONE. it came out of a mismatched pair (with a 5881!) in a Bassman 10 i got a couple of years ago. Tested in my Hickok 600, it tested very strong. But without a pair, its been sitting on the shelf. So i went on ebay to find one. Its a dicey move, since who knows what condition tube i was going to get. But i went ahead and placed a bid.

While waiting for the auction to end, i decided to swap out speakers. Granted the stock celestions are loud and had character, but it seemed too midrange-y to me. From what ive been reading, Brice Zinky had intended for the Prosonic to contain 1 12″ Vintage 30. I almost bought one, until dug up my speaker overstocks, and found a WGS Veteran 30. DAMN! i forgot about this baby. Similar to a Vintage 30, but supposedly a fuller sound. I did a quick and dirty hookup, and it sounded promising. This led me to measuring the baffle and looking at options. Either i can get a custom-made 1×12 baffle for $100, or i can just order a half-yard grill cloth for $16 and make one myself. Im pretty handy with a jigsaw and i have 1/2″ birch ply materials in my basement, this shouldnt be too hard. As im cheap, i ordered the grill cloth.

There was also a THIRD option: get another pair of 10″ speakers. AS i dug thru my speaker overstocks, i also spotted a pair of CTS speakers dating to the 18th week of 1973. I remembered this being an early replacement for the  Kalamazoo Bass 50 projects i had some years back. Theyre essentially derivatives of  ceramic Jensen C10N speakers. Oddly enough Weber doesnt make this specific model (they do have C12N copies), so i was forced to scour ebay for something old stock thats similar.
Wouldnt you know it – the midrange-heavy sound was definitely less, the bottom end was MUCH tighter, and the clean sound has more shimmer to it! I like!

One mod i did do was to cut the cap found on the preamp tube socket of V1. Supposedly for more headroom. Man, the clean sparkle got MUCH better!

For a couple of days ive played with this configuration, and im finding it sweeter each day. Until i got the 7581 tube i won. Crossing my fingers i tested it, and wow – this one was as strong as the one i got. A GOOD PAIR! I immediately dropped it in the amp and fired the amp up.

JAW DROPPING.

What i started out for this amp – trying to get that overdriven tube-rectifier laced sound, i ended up loving the clean sound of it. With the 7581 tubes in place and on CLASS A, the sparkle that i thought was better got so much more clearer. If they were talking about a real Fender clean, these tubes in this amp certainly got it there. And it made the sweep wider, there is much more clarity in the notes in higher volumes before overdriving in Channel 1. And When it DOES overdrive, the sound is much more defined and less scattered.
Switching to Channel 2, its even more eye-popping. The distortion isnt fizzy with just playing on Gain 1, and only gets to that point when turning up gain 2.
UN. REAL.

its turned from a high-gain beast to a multi-faceted, multi-horned monster! Cleans are sparking (and louder!) on the Danelectro single coil lipsticks, brittle overdrive gone with the humbuckers, fizziness virtually gone in lower gain settings, and the squawk is back on the lowly strat!

SPEAKERS
Ive come to find that this versatile amp can work wonders on different speakers. I still like the inherent sound of the stock Celestions, and id like to still use them. For that i have a 2×12 closed back speaker cab on the way. I plan on putting 10″ conversion baffles for it too.
whether id put the stock celestions in it, or put the celestions back in the combo and move the CTS speakers in the cab, im still not sure. There is still the 12″ option.
What i truly want is to have the prosonic in a 2×12 combo, but from what ive canvassed online, it will push me back close to $300 to have a custom-made 2×12 cab for it. I can simple get a Twin cab, and adjust the chassis to it (Twin cab is about 2 to 3 inches longer). Then i thought, thats can be a lot of work!Especially when im already getting AMAZING tone now.
Ill wait til the cab comes in. For now, ill enjoy and keep playing this wonderful amp!

DATING THE AMP
One thing that intrigued me was WHEN the amp was made. Its certain that this was a production model from Corona, not from Lake Oswego. Though some people put a lot of weight into where their prosonic was made, i could care less in this matter. There were NO circuit difference from the ones made in the custom shop in lake Oswego with the ones made in Corona. The only real difference is that (supposedly) the first few Prosonics were made with “better” PCBs, and higher grade components. Be that as it may, These “higher grade” components arent that much different with what was in the production models. Now if it was the use of different TYPE of capacitors (say, orange drops Vs. Paper in oil), or resistors (say carbon comp Vs metal film), id allow a good leeway that the tone would be vastly different. Its not (ive seen the innards of a lake Oswego made Prosonic and a production Corona Prosonic), and to me, i couldnt tell major differences. Not even any differences in the values used. To me, its just a matter of corksniffing now, and at worst, a peeing contest. But thats just my humble opinion. Some people hold in high regard the Kitsch of something Collectible. Im not a collector, im a guitar player.

That said, the production code should have been stamped on the tube chart, but its blank. The QA Inspection sticker does have two handwritten initials, one scribble in black next to Electronic Test, and what looks to be 6K or GK next to Sound Test. Looking at a couple of pictured samples online, GK seems to be a better decipher. According to fender’s own reference, this dates it to 1996, November.I must say, this amp has been pretty well-kept, considering its  made during the first year of production.

SOME THOUGHTS (for now)
Save for a couple of tweaks, i must say, im DONE! Ive arrived to where i want to go with this amp. I didnt expect to get Fender-clean sounds, i was content to get something decent, but that just blows me away each time i strum my lowly squier and my baritone Mod 6. The blazing hot gain i first experienced was acceptable, but now its more easily controlled. If i want to let it loose, i just turn up both GAIN knobs!

In the process of doing the cap cut on V1, i was able to inspect the innards of the amp. I must say, its relatively simple layout on the PCB. Ive opened the Epiphone Blues Custom 30, and just getting to the PCB was a pain. Once open, the Prosonic chassis reveals a clean layout where you can follow the schematics easily. Another plus for this amp is that the pots arent directly soldered onto the PCB, like some modern amps that ive seen. This makes for easier pots replacement. This is significant because apparently the pots are linear, not audio taper. This is one reason why the sound JUMPS from full silence to a loud volume when going from zero to 1 on the dials.  An audio taper allows you to open the amp SLOWLY from silence to a more gradual increase in perceived volume. This looks to be a good mod for Channel 1, to make the clean sweep a little better. Maybe for Gain 1 also, but i think its control is ok.

The amp didnt come with a footswitch, just the cover. It wasnt hard to get a footswitch, its just a matter of expense. The stereo 1/4″ type it uses isnt available from Fender anymore, and no one sells it. But apparently the REV/VIB version works well. I got the REV/VIB footswitch i used for the other Plush amp i got (P-1000S), used a 1/4″ stereo plug to dual RCA adapter, and i was in business. I did order a footswitch with had the direct streo 1/4″ plug to dedicate to this amp.

Playing mostly in Class A, this has been truly amazing. But switching to Class A/B, ad even solid-state rectifier, it even makes for a more versatile amp. The dough i dropped for this doesnt hurt anymore – im glad for the little sacrifices i have to make, now that i have this tone machine to play with.
🙂

UPDATE: MORE SPEAKER OPTIONS!
This week came the 2 used 2×12 cabs i got online.
1) Black Tuck n roll – no brand, one handle on the longer side top. looks like a cab made by Kustom with their tuck n roll line of amps (or the plush/ Earth amps of the early 70s), though the silver (turning brown from dust and age) grill cloth gives it away – all the grill cloth ive seen Kustom and Plush use is black. Inside the cab the construction seems home-made (gobs of glue  lining the edges), but exhibit no wiggle – this cabinet feels, looks, and IS solid. Outside the cushioned soft vinyl  sets it apart from  the usual rectangular 2×12 cabs, while the inside reveals a unique speaker positioning – the speaker panel is ANGLED. the speaker baffle/panel is separate from the grill cloth panel, and the left side is set about 1/3 of the way back into the cab. In effect the speaker on this side is further back when facing it, while the other is closer to you. This didnt make any sense until i inspected the outside of the cab further. One short side is FLAT – it didnt have the cushioned tuck n roll cover on it, just a soft tolex. It seems it can convert to a VERTICAL cab! When in this position, the ANGLED speaker panel inside projects it at an upwards angle, much in the same way a fender combo front is a bit angled back upwards, or how the tilt-back legs of some fender combos allow it to lean back a little further. THAT’S WHY!
I ended up installing the WGS Veteran 30 12″ speaker on the more angled side, and a fender branded speaker on the other side (it looks like a jensen C12N, but it has a slightly smaller magnet. Im still researching its make and model. Both Are 16ohm speakers, and i decided to just wire them parallel for 8ohms. The cab has a panel to fully close it up, but has a 4″ diameter hole in the center.

2) Empty 70’s Fender Twin Combo Cabinet – came with caster, fender logo on the silver grill, back panels, and even the tube layout diagram. This is EXACTLY what i was planning to transplant the Prosonic chassis into, even if it was about 2 inches wider. It just cost too much money to get a NEW custom made combo cabinet. This too was structurally SOLID.
I put in vintage 12″ Pyle Speakers from 1968 and 1969 (what looks like Jensen C12N’s). Though not from the same batch and year, it is exactly the same model. Both are 8ohms wired in series for 16ohms total.

UPDATE #2:
After an exhaustive testing of the different speaker options, it’s been decided: the 10″ Celestion speakers in the Prosonic are getting changed out. Its too mid-range-y for my tastes, and it lacks the sparkle and top end cleans that the jensen ceramics (C10N or C12N) have, and lacks the overdriven smoothness and depth of the 12″ WGS Veteran 30 (which is supposed to be an improved Celestion Vintage 30, with a better clarity on its higher midrange).  The Celestions just did not have enough chime in the clean sound, and was too brittle-sounding when switching to channel 2’s overdriven sections. Hell, even the WGS had that elusive Fender chime when played clean! A very versatile speaker.

And that’s whats going in as a replacement in the Prosonic combo. Ive already started cutting up a 1/2″ thick birch ply to its baffle dimensions, and im about to cut the hole for the single 12″ WGS speaker (from the tuck and roll 2×12 cab). If i was able to find the jigsaw tonight id have been done with the rough cut.
The silver grill cloth is ready, and i finally got a matching fender logo with the sweeping tail taken out of an empty ’69 Fender Bandmaster Reverb head (which will then house a Bassman 10’s chassis – yes, another project).
$8 – 2’x2′ 1/2″ thick birch ply
$16 – 1/2 yd Fender Grill cloth
$15 – used fender logo
$1 – set of screws for speakers
[u]  $0 -[/u] some elbow grease and existing tools (jigsaw, circular saw, sander, drill/driver, staples, glue, black paint)
$40 – Total
compared to $100 if i had it done professionally, with the same results. And it doesnt even have a Fender Logo!

Im excited about this mod, as it makes the combo my favorite among all my amps. Its versatility, its tone, and its unassuming look that betrays its monstrous capability… and now its lighter! My back is thanking me already. 🙂

Update #3: Just changed out the Japanese 5AR4 rectifier with a used old stock Gibson-branded Holland-made Amperex 5AR4 that tested well above new. It retained the clarity and depth of the Japanese 5AR4, with a better bass response. And still provides that “bloom” on overdriven settings. Mmmmmm…. delicious!

UPDATE #4: 1×12 conversion DONE!
didnt really take that long – its the planning and measuring that took some time. Preparation is necessary to make sure errors and mistakes are avoided or minimized. Its a professional tube amp -it should NOT look sloppy!
What exactly is involved in the prep?
1) Direct tracing the original baffle onto the 2’x2′ birch ply.
2) Deciding WHERE the 12″ speaker will be located. Centered seem ideal, but the heavy transformers are off to the right side more (facing the amp). Centered will make the amp heavier on one side and awkward to carry.  I set the speaker hole about an inch and a half from the left, top, and bottom edge.
4) Tracing the speaker hole. I used a twin reverb’s speaker hole as the guide, traced it onto a stiff cardboard, and cut the cardboard out. Or if you have a compass you can use that instead. Also traced the screw holes. I just used 4.
5) Once all the measurements are traced, i double checked. Measure twice…

After the prep starts the cut. First is the dimensions of he baffle itself. Once thats done, the speaker hole is next, using a jigsaw with the smallest width blades i can find. The circle cut wont be perfect, but at least the smaller width makes the curving cuts easier. Slowly following the trace makes it look less sloppy. It wont really be seen once the grill and speakers are on, but as a perfectionist on denial, i will know, and it will nag at me if i didnt do the best job i can. Gotta hold yourself accountable.

after the cut is a spray of flat black enamel all over. Not to really color it but just enough to cover it. Its subtle  but it makes the silver grill cloth sparkle more against the dark background. Think about it – stars are visible more in the dark night sky. Same principle.

Once its dry, its on with the grill cloth. Ive only done this once before, and what i can remember, the grill cloth need to be pulled taut and as tight as possible, so it wont bulge or sage, and must be done square, or it would look uneven, with random diagonal patterns. By following the straight rows and columns of black and silver threads and folding them according to the baffle’s dimensions, it allowed me to align the straight pattern squarely with the baffle frame itself. Doing about 2 inches at a time, i pulled and aligned the grill cloth square, and then stapled it.

Once thats done, the next thing i put on was the Fender logo. I got the fender logo from a 69 Bandmaster head, with the tail. But before i did this, i decided to follow the exact placement of the Prosonic logo. I took a letter size paper, and aligned it at the top right angle of the original baffle. i then took a pencil and traced the logo from the top, more so where the 3 screws were. I then transferred this trace over to the new baffle, and punched a guide hole where the screws would be. I then screwed in the fender logo.

Last was the 12″ speaker. Using the screw guide from the template i also bore some guide holes fot the speaker screws. Once thats done, its a simple matter of aligning the speaker right and secure.

I took the wires with the right angled 1/4″ plug from the Bassman 10 cabinet and used those for the connection between the speaker and the amp. Looked more original with the round Fender “F” plug cover.

Some thoughts: It came out well! In hindsight i should have used a 3/4″ thick birch ply instead of the 1/2″ i got now, but i dont hear anything rattling or buckling from a loud setting. Its holding up well! I may make a second one, this time using laminated pine. I know exactly what to do now.

Im definitely MUCH MORE satisfied now with this 1×12″ configuration using the WGS Veteran 30 speaker. It;s 3:30AM and im more inspired o keep riffing away! Sleep beckons though, but its gonna be a nice slumber, knowing when i wake up i can play again, and mre time to play thru this amp. 🙂

UPDATE! July 03, 2013
CLOSE TO 3 YEARS LATER… WE FINALLY HAVE THE PERFECT COMBO!

it took til the early months of 2013 to finally nail down the perfect speakers for the Prosonic. and wouldn’t you know it, the winners are CELESTION GREENBACKS!

what made the Greenbacks THE speakers for the Prosonic is the emergence of the TRUE FENDER CLEAN. The overdrive channel will always be THE hallmark of this gem of an amp, but not until i attached the Greenbacks to it did it finally show the TRUE Fender clean sound, the unmistakeable chime a Fender is known for, and only a Fender can provide. You know, when you play a strat clean thru a Fender amp you get that trademark Fender Strat ‘squawk’ in the 2 and 4 positions – this amp finally got that going for it with the Greenbacks. I thought the 1×12 WGS Veteran 30 speaker had it, man! i was so wrong.

Going from 1×12 WGS:
Instead of dedicating a separate 2×12 cab for the prosonic combo, i ended up using the empty 2×12 twin combo i mentioned. I had already drilled the holes on the twin cab for the Prosonic chassis before, so it was (relatively) easy to transfer it. It does have about an inch of space on either side of the front panel, though at first glance it doesnt look as funny as it first did before. a closer look does show the gaps. Im still in the process of thinking a way to cover them.

1972 PLUSH CONGRESS IV

Another great craigslist find, this vintage all tube amp hails from the early 70s (01/05/1972 to be exact, as penciled in under the chassis itself).
As a background, Plush amplifiers were made from 1969 thru 1973, apparently direct copies of either a fender showman or a twin reverb. Its main striking feature is the now identifiable “tuck and roll” covering not unlike that of Kustom amps, instead of the regular tolex coverings. Not surprisingly they were sued, either by Kustom or Fender (not sure), and its been said they went out of business due to bankruptcy from these litigations (but the story goes that they went on to become Earth Sound Amplifiers, who in their early life also had tuck and roll covering on their early amps, though nothing real conclusive to support this Plush-Earth Sound connection other than whats been generated thru forums and posts). Earth Sound also went the way of the dinosaurs eventually.

THE FIND:

Trolling craigslist one night, the ad “PA tube head – $100” immediately caught my eye. “Tube” and “$100” together are usually a good indicator of a possible good deal, so i checked it out. Two things stood out – the tuck and roll covering, and a bunch of knobs to match several inputs. Whoa! Mixer? it said PA, so i googled the name, and sure enough most results were about asking the same question i have: what is a Plush Amplifier?
A website about plush amps did answer most of that question, so i called the number on the ad right away, and left a message. As a follow up i also emailed. I got a response the next morning, and proceeded to arrange for pickup. A little drive out to the country on a sunny early sunday afternoon is a nice change – one of the cool things i enjoy about out-of-the-way weekend drives.

The guy was nice, and spoke about how being a drummer, he had not much use for the amp anymore. It did power on, but didnt hook it up to a cab or even try it out – we spoke at length about the virtues of vintage and analog instruments. In the end i almost got an unloaded 2×18 ampeg cab, but having a small car, it wasnt going to be an easy transport (and i have no  more space in my house!). i DID get a project solidbody guitar also for cheap – a double cutaway setneck Aspen brand, no pickups and with a bad paintjob, all other hardware included. for $5 with a harshell case also included, i couldnt turn it down. But that’s another story….

INITIAL START-UP AND RESTORATION:

As soon as i got home, i plugged the head into a 2×12 cab loaded with Carvin British Series US-made speakers. The tubes glowed and warmed up, and sound came thru once i plugged a guitar in.
It sounded clean, though several knobs wont turn, and some are stiff. The reverb didnt work, and channel 4 sounded weaker than the other 3. No big hum or extraneous noise were heard (other than what i was making thru the guitar), so the guitar is functional as is, just needs work.

A couple of contact cleaner sprays allowed the stiff pots to twist easier, but there were 6 that were completely stuck and frozen – no amount of clamping and pliers twisting freed it loose. I ended up replacing them temporarily with my own stock of Alpha pots, eventually ordering the correct size (i had the correct values, but they were mini pots – it works great, but it just looked odd to keep it that way). Reading the stamped code on the back showed they were Centralab pots, and man – NOS are expensive! So i got the next best thing – CTS pots. as soon as they arrive, ill be opening up the amp again.
I ended up changing two pots, and moving the current pots around to get all of the untwistable ones on one channel – at least i can have 3 usable channels til i get the orders in.
Workng without schematics (there were NONE found anywhere online), i made sure the values are correct for the gain and master volume pots (1 Meg), but i didnt inspect the tone pots – i thought they were all 250k. I realized it later when i saw the midrange control pots were 100k. oops! oh well, thats a lesson for me, plus its not that big of a deal – it will be corrected when i get the order in.
but for now, the goal is to get it to full working condition. After the pots were properly cleaned with contact cleaner, i proceeded to check the preamp tubes by removing one at a time and playing each channel- with a pencil, i marked each preamp tube that corresponded to what channel, and to what sockets they were in. Doing this i found out each channel had its own preamp tube. More on that later…

It had a reverb in and out RCA connectors in the back, and seeng no reverb tank inside the cab, i hooked up a working spare reverb tank i had lying around, and didnt have any reverb response either. Bummer.

So on to the next step – I removed the preamp tubes (6 12AX7’s, one 12AT7, and one 12AU7), and replaced them for now with new production EH 12AX7’s, 1 NOS RCA 12AT7 and 1 RCA 12AU7.
THE SPRING REVERB CAME TO LIFE!!! I dont know where its coming from, but its there alright. The old preamp tubes must be in their last legs. The dry sound is now much stronger, and the reverb sounds quite lush.
The 4 power tubes were  Japan 6L6GC’s, and were all branded the same (Realistic), looking like they were all from the same batch, a good chance they are matched. Ive seen several plush amps online pictured with non-matching pairs. I havent tested these yet, but they sounded strong. I may tube-roll with my own old stock 6L6’s, but i I see no need to replace them at this time.

After a few more sound checks, i decided to replace the bigger electrolytic caps. After almost 40 years, even though it sounds strong and there were no tell-tale signs of impending burnup or blowout or simple failure, its best to be on the safe side.

Unscrewing what looked to be non-original non-matching screws, the bottom easily fell off, and revealed not just point to point wiring with most of the smaller components on a slim turret board, but the reverb tank as well – THERE IT IS! It looked exactly like my other non-working accutronics tank, only the Plush’s tank had pitting and some rust on it.

There were 3 big caps in the under side, and one cap can on top of the chassis. I had to snap a picture of the cap can’s side where the cap values are stamped on since it was in an awkward unreadable spot. 3 20uF/500V were needed for this cap can, and 2 80uF/350V and 1 40uF/450V (in series with one of the 20uF caps) under the chassis.
I kept close to the same values, only substituting a 100uF cap on the 80uF ones, and a 47uF for the 40uF. I figured i can replace with a bigger value, but i wanted to hear as close as possible to how the original amp sounded. I can always up the values later on if i see fit (this can also raise the headroom, which for a PA system is paramount, then again im mostly going to plug in a guitar here anyway).

THE JAM TEST

So now that most of the amp is in working, its time to put it thru the Jam Test.  😉 I must say – this is one LOUD MONSTER! Cleans are excellent, and not ice-picky at all. It barely overdrives! To most modern-day guitarist looking for “breakup” or high gain sound, this is a drawback, and not for them at all. This is after all a P.A. amplifier, so its setup NOT to distort. I guess thats one reason the Plush engineers thought best to copy a dual showman or a twin reverb, all for their clean headroom. This one has it! and i thought thats all it had.

My buddy came over for our regular jam, and we put it thru the paces, and lo and behold, he dialed it enough to get real overdrive. WHERE THE HELL IS THAT COMING FROM?!? we took a look at the settings. He was plugged in to Channel 1, gain at 8, bass at 2, mids at 9, and treble at 3. Main volume is at 8. DAMN! turning up the mids and lowering the bass and highs, made this a promising dirty rockin machine!

Further tests revealed the amp is picky about what to get it to overdrive – it wanted bright pickups. The guitar he played was a Luna brand, while i tested a dean Evo (both humbucker equipped). The Evo sounded dark on the Plush (detuned to D). I plugged in a Squier ’51 that had a GFS Dream 180 bridge Humbucker (described on their site as having “…the sparkle and chime of our Retrotron Nashville, along with the fat warm bottom of our Alnico PAF pickups”,  “…made to combine the chime and jangle of vintage Filtertrons with the warmth and body of a great pair of vintage PAF’s). It worked well – the biting overdrive pushed the amp to sound grittier at higher volumes.

For about 3 hours of jamming we used it, plugging different guitars and in different settings. Everything worked, even the 4 frequency cut/bost switches. All 3 hours were earcandy!

On  a separate note: You can tell we used “cheap” guitars. It only goes to show that even low-end guitars can sound amazing if you use a great-sounding tube amp. You can have a super high end guitar that costs a couple thousand dollars, but it will still sound like crap if you pair it with a bad-sounding amp. This is one reason why i shifted to tube amps from being a simple guitar-tech. Knowing tube amps completes the circle of a great electric guitar sound.
And it DOES helps to play decent too. 😉

ONE BIG SAFETY ISSUE

I’m putting a 3-prong cord in.
The amp came with the original power cord, but with a replacement 2 prong plug (must have worn off, as ive seen pictures with the original plug wearing out right at the plug base). This is then hooked up inside the chassis to a standby switch and a separate 3-WAY toggle switch that has the ON setting up, the OFF setting in the middle, and a Reverse Polarity in the down position.

Back in the day, there used to be NO standard for grounding electrical appliances and equipment. When you have several amps plugged in to the same mains, hum can occur, which can be mitigated by turning the plug around. In this case, you just flip the switch down to set it to the correct polarity.

The problem here is that one you flip down the switch, the chassis or any metal part of it becomes HOT instead of the Ground, and electricity will pass through it. and once you plug your guitar in, it will pass through YOU as well. touch a metal part of another amp that isnt in the same polarity, and you complete a circuit – YOU GET ELECTROCUTED! happened to me. On THIS amp. I flipped the switch down too hard, and kept it ON (reversed polarity), and touched a different properly grounded amp. YIKES!

Im tempted to make the all-in-one bypass/off/on mod with the 3way toggle switch, but i much prefer a separate bypass switch. Seems more traditional, plus might as well use whats on it.

DEDICATED CHANNELS

During the jam test, after we figured out how to coax a crunchy tone out of the 1st channel, we copied the same settings over to channel 2, but it didnt sound as good, and didnt crunch as hard. At first i thought it was the overstated midrange value (250K instead fo 100K), but later on i figured it out with an experiment.

A clue was in one of the post of another Plush owner about modding it, who mentioned that “…each of those channels have a separate section”. Preamp? Hmmm…. so i went to town and one by one took out a preamp tube and turned the amp on. Lo and behold, it revealed the tubes that were responsible for getting the sound thru each channel (duh), and even for the reverb! Looking at what i thought was the correct layout, the tubes did NOT line up. I had a high-gain 12AX7 tube in the reverb section, and a 12AU7 in for channel 2. No wonder it sounded weak! a quick change of tubes effectively brought up the volume AND gain, now at level with the rest of the other channels. This also made for a much tamer reverb with a 12AU7 in it.

Now that i know which tube sockets control which channel correctly, there will be preamp tube rolling! I do have a stash of used old stock Mullards, RCAs, Sylvanias, and GEs i can try – heck, i may just simply put a different preamp tube for each channels, and then do an ABCD test.

FURTHER THOUGHTS

Pots will be set back to stock values as soon as the order comes in. Later on one channel will possibly be converted to a twin reverb tone stack. Im thinking another can be set to blackface bassman tone values. along with mods as well (maybe). Im keeping at least ONE channel stock.

A review of the schematics for a dual showman and twin reverb shows that there IS a difference with the pot values, at least the mids. Dual Showman and Twin reverb mid pots show a value of 10K, while the mids on the Plush are set to 100K. The Bass and Treble are all the same at 250K. Bassmans have theirs at 25K.

This was one of my oversights – i assumed the gain and master volume were all 1Meg, and all the tone controls were all 250K, so for the tone, i just simply transposed some over to the other channels without checking. So for channel 2, the mids are set at a higher range (250K), though the difference is noticeable only at much higher gain – the overdriven sound has that thick discernible midrange tone. at lower gain settings the clean tone sounds the same as the other channels, though this is only a preliminary test. Most of the Jam Test were in full overdrive on channel 1, and clean tones across the other channels.

SOME FINAL THOUGHTS (FOR NOW)

This is THE most interesting amp ive acquired, hands down. 100W via 6L6GCs, FOUR DEDICATED CHANNELS (!!!), and an excellent-sounding reverb. ON ALL 4 CHANNELS, SWITCHABLE! It even has 4 frequency boosts/cuts (though i leave them all ON, and just futz with the tone controls). Its simple when you boil it down to what it does, but it does it 4 times! This has the potential to be a versatile guitar amp. And who can deny its quaint soft tuck and roll cover? Its almost perfect – there arent any noticeable tears, just a little nick here and there – pretty clean for something thats been around over the 38 years.
Almost looks like a foot stool. i beter make sure this is NEVER put on the floor – people may think its furniture to sit on!

Great amp, even better price! 😉

Some more pics: