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.

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.

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.

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.


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.

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!

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!

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.

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.

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.

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

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.