Pro Reverb Issues- High Plate Voltage- Rectifier Tubes

Hey there tdpri,

I've got an early silverface pro reverb that I'm having some issues with. It has been crackling and humming for some time now, it's pretty minor (low volume) enough that I can play over it, and it mostly goes away after the amp is on for a while (20 minutes) I replaced a ton of parts in the amp as I am going for a jerry garcia modded twin type sound. Using some nice quality components- replaced all electroltyics in the amp, all tone and coupling caps, all plate resistors (didnt change slopes- maybe that's it) used PRP metal films, orange drop 400v tone caps (maybe too low with my high plate voltage???) I did use high voltage F&T filter caps and used 1watt PRP's in the can.

I had a solid state plug rectifer in the amp for a while because I really dig that quick attack and higher headroom of a twin reverb... really does change the sound a lot and it was great on low volumes... but terrible turned up to distort. So I replaced the rectifier with a gz34 still only lowered the plate voltage to like a little more than 480v. I thought a 5ar4 was the same as 5u4 but i guess it's closer to a gz34... but the 5ar4 did introduce more sag (or so i think it sounds that way) and my plate voltage is now an even 480v (doubt my meter is that accurate though)... The 5ar4 sounds the best with the amp cranked up- much better dirt than the SS and even better than GZ. But I'm not a fan of the super saggy sound... I feel like I experience the sound of sag more intensely than most people or something, because I'm really not thrilled with the idea of getting anymore sag.

Anyways, I'm just wondering if a 5u4 will drop my plate voltage enough to get this amp sounding when cranked? Could it be something else? Where should I begin checking voltages? I'm not that fluent in knowing what all the voltages mean or where to check exactly, but I know enough to not kill myself... I've checked wires over and over and moving them doesnt seem to get change the crackle at all. There are no ceramic caps in the amp, I replaced them with films or polystyrenes.

I've also read and heard quite a few times recently while researching my problem that you should just install the 5u4 and get on with it. The transformers in my amp seem to be exactly the same as the blackface pro reverbs with the gz34 rectifiers (the amp has been completely modded to blackface specs... including resistors in the dog house and all that) So why are the blackface pro's able to take the gz34 and my amp isnt?

Is there any way I could drop the plate voltage with the zener diode method or whatever so that I could be able to use a solid state diode rectifier? That's my ultimate goal really... I feel like the ****ty overdriven sound of the amp is coming from this high voltage...

Any help would be greatly appreciated!! Thanks a bunch!

Do you still have the tube chart in the cabinet? I think it was shipped with a 5U4GB.
If it was, then having a GZ34/5AR4 (same thing) or solid state rectifier will make for higher plate voltage.
Not sure how that affects a Pro Reverb with 6L6's, but on my Silverface DR with 6V6's it was bad news.
Fender changed the transformers a little when they switched from GZ34/5AR4 to 5U4GB. So even if the amp is Blackfaced the transformer is still different.

Ok, first of all, a 5AR4 is the same as a GZ34. Any differences you have noticed are due to differences in individual tubes. Secondly, though a 5U4 type tube will lower your B+, it may harm your power transformer due to it's increased draw on the 5 volt filament winding- 3 amps as opposed to 2 amps for a 5AR4/GZ34. A saver tube to use to lower your B+ would be a 5V4, 5R4 or an old stock 5Y3GT. Don't use a new production Sovtek 5Y3GT, as it performs more like a 5AR4 than a true 5Y3GT.

400v rated caps should be fine in the early preamp but for the tremolo circuit & phase inverter, as well as later preamp stages, that's not enough voltage rating.

5AR4=GZ34- same tube.

Perusing various SF Pro Reverb schematics I see that they sometimes came w/ a GZ34. Sometimes with a 5U4. Never a SS rectifier. Your voltages are high, then, even for a silverface.

Your main (power tubes), screens, PI, tremolo & reverb filter caps should be 500v rated at least, if you're seeing that kind of voltage on your plates.

There is a trick wherein you place a diode in series on the B+ feed to the preamp, which supposedly stiffens the preamp power supply. But I'd double check my connections & replace the 400v ODs w/ 630v caps first.

okay... I've got some 600v mallorys I can use... So phase inverter coupling caps... Tone stack .1, .047 are okay at 400v? should I replace the normal and reverb coupling caps with 600v? or are they okay with the 400v? I'm sure the tremolo's are 600v (the little red caps metallized polyprop caps)... my filter caps are as follows... the 22uf ones are rated at 500v and the 100uf's are rated at 450v (they used to be 350v and I paid extra for the extra voltage- thought I'd be okay there)

the model numbers of my transformers all matched up with the same numbers on the blackface schematic... and the early silverface schematic... so this reminded me that the early silverface and late blackface pro's have the same model number power tx, but they were actually different. My tube chart has a 5u4 listed- so i guess that's what i should go with...

My amp has a newer output transformer as well... but it's the proper model number- dont know if that would make it different than a silverface or blackface or similar... gah that's annoying!

what if i got a new power transformer say from heyboer or somewhere... wouldnt that be more likely to be similar to the blackface power tx? and would I then want to use a GZ34? What is the actual cause of higher voltages in amps?

I REALLY like the sound of the solid state rectifier (tubedepot.com advertises it as a replacement for tons of tubes- and i've heard its okay that fender's can handle 500v+ easily) but my amp definitely sounds better at higher volumes and associated overdrive with the gz34 and 5ar4 than the SS... and i'm assuming even better with the 5u4... but really I want that SS rectifier sound!!! it's so much snappier and bad ass for my style (i have a weber california in the amp and play a strat with d allen 69's) I love a snappy, responisve, dynamic, clean fender with a little bit of grit on tap for digging in. So should I try the Weber V Dump method? Or should I really get a variac? Would getting a blackface power transformer... or maybe a twin power transformer allow me to use an SS rectifier? Also, I've heard of people getting larger output transformers (right?) would that be useful for what i'm going for (higher headroom, more responsiveness, dynamics, etc etc?)

Thanks a bunch guys!

Wow! You are ready to dig in. All over the place.

You know the sound you want. You get it with SS rectification, for the most part with what you already have, as far as transformers & such. Keep them.

First make it safe to use & not prone to failure.

If your 100uF 450v main caps are wired in series, & correctly (parallelled w/ some voltage divider resistors, correct polarity) you have a 50uF 900v main cap. More than enough voltage rating. You should be good. Make sure it's right.

If you want to know what voltage rating your coupling caps should be, (all caps for that matter) check your nominal voltages with no tubes. The voltages will be higher but the caps have got to be able to take the higher voltage.

If I were you I'd use the GZ34 but a 5u4 will be safe too & you won't blow anything up or exceed heater ratings. A GZ34/5AR4 has very little sag. At lower volumes there should be very little difference in the way it sounds vs. a SS recto. 10-20 plate volts is about it. At max volume you like the GZ34 better- that's all I would need to know, really.

Do not use a Variac when operating tubes. Just don't. Bad news.
A Twin PT will give you even higher voltages than you have now. With your current PT, you are "allowed" to use any method of rectification you want. You might try an OT upgrade for more headroom.
I don't know what the V-dump method is. I have tried the zener diode thing & ultimately scrapped the idea, it seemed like a weak link in my power chain ("prone to fail").

Every amp seems to "like" a different rectifier, it sounds like yours likes the GZ34. If you must go SS, make sure your caps can take the voltage.

So I just changed the phase inverter caps and coupling caps to 630v mallory 150's. Seems a little better. I like the SS rectifier better, but yeh it does increase the voltage by like 10v or a little more... I'm thinking I'm not liking the way the preamp tubes are reacting to the high voltages in my amp. I need to order some more 12at7's (some good NOS 6201's or 4024's) there was once upon a time I liked 12at7 in v1 or v2 and a 12ax7 in my phase inverter best. Could the high voltages be causing my preamp to distort earlier? I know I like the way the SS rectifier makes my amp sound- i like it a lot better, until my volume knob hits 5 or so and the amp starts breaking up... then i like the gz34 or the 5ar4 better, I dont think its because of the tube vs SS rather its because of the voltage. with the higher plate voltage of the SS the breakup sounds kinda ring modulated... or kind of like it has crossover distortion or something... it doesnt sustain properly (and really this goes for all of these rectifiers in this amp) it just sounds off... nothing like a fender blackface should sound when cranked (and I know they have a different flavor of breakup than other amps) The high notes on my e and b strings sound especially terrible. When I bend my B string or E string at the 12th fret and above and pick it hard... it is NASTY. Just a not good sound. The cleans are amazing right now though- which is weird... I guess they could always be better though. I do feel like i'm not getting enough of THAT strat sound out of this setup. I'm getting more spank than I should be getting (which I actually like) I feel like my power tube dirt sounds okay, but my preamp is distorting more than it should and it sounds like crap. Oh it also sounds even worse when I switch my strat pickups to series mode and get more output (I have a special little rotary knob pickup selector for all kinds of pickup combos) and running a boost into it is pretty gross. It's like the clean is blended with this terrible metallic distortion. I was thinking for a while that the reverb circuit was getting hit too hard- or the reverb driver or recovery was running much too hot because the reverb was extremely sensitive and metallic sounding... For some reason that's cooled off a bit... but maybe a 12au7 in the reverb driver? should I go back to 12at7 in v2? Right now I have a 5751 in v1 and stock tube choices everywhere else- so I didnt think itd be a huge difference... really thought it would be better being an rca blackplate triple mica and hearing so many people say 12at7's arent made for the first gain position.

I know this is a lot of speculation by a guy that doesnt know much at all about amps. But it really just does feel that way!! haha... let me know if i'm completely off.

I'm thinking lower plate voltage would help this altogether. But I dont know... hah! Could it just be I dont like the power tubes in my amp?

How much voltage will the 5u4 take off my plates? It might be worth it to see if that does it for the overdrive tones... then maybe I can try the V dump with the SS rectifier?

I just realized that my amp's stock circuit has 2 70uf 250v filter caps... instead of the 100uf 450v's I have... I know the higher voltage is fine, but what about the value?

oh yeh- it seems like some of the crackle and pop went away with the upgraded PI and coupling caps- I rearranged some wires while in there too... but it comes and goes anywyays, and it was still there, just a bit quieter.

Should I post pics or sound clips?

A little more capacitor in the mains supply isn't a bad thing IMHO. You're increasing it from 35uf @ 500v to 50uf @ 900v. That will translate into a bit more available to the output tubes, which will firm up the low E and open e power chords. If it were my choice, I'd leave them in.

... The high notes on my e and b strings sound especially terrible. When I bend my B string or E string at the 12th fret and above and pick it hard... it is NASTY. Just a not good sound. The cleans are amazing right now though- which is weird...

Not weird at all. What you describe may not be caused by the circuit, but by the speakers. Do you have a suitable external cab you could try?

Not weird at all. What you describe may not be caused by the circuit, but by the speakers. Do you have a suitable external cab you could try?

Always a good idea.
If that doesn't help, check your lead dress, especially the wires to the tubes. I fixed the reverb on my drummer's TRRI and when I was done, it sounded horrible, hollow & just overall nasty at high volumes, like a ring modulator.

What had happened was that the wires to one of the preamp tubes had poor lead dress, which was causing an oscillation. I moved the offending wires just a little bit- problem solved.
On V1, V2 & V4, make sure the wires from pins 1,2 & 3 are bundled together & away from the wires from pins 6,7 & 8. You'd be amazed at how easily these wires can interfere with each other & create problems.

Well... I found some interesting stuff with the amp. The reverb tank was causing a lot fo the microphonics sounds! brand new and it was broken- just a loose transducer (I think that's what it is at least) put my old reverb tank in and good as new. I've isolated the snap crackle pop to the reverb channel... when I just use v1 and PI preamp tubes the snap crackle pop is gone. I redid solder joints and have tested caps and everything, just cant find it anywhere! The ****ty high e sound was the reverb tank and maybe some other parts and a slightly microphonic tube.

Stuffs starting to sound good here!!! thanks for the help guys!

on a different question- i've heard its a good idea to decouple the shared cathode bypass cap between the normal and vibrato channel. Is this a good thing to do? (i've read all over it is...)

anyways, just wanna make sure I'm gonna do it right... to do this I would...
cut the wire connecting pin 8 of v1 and v2. and from pin 8 i would just wire up a typical bypass cap value with a resistor in parallel positive side of cap and both leads to pin 8- then to ground on the other side... this correct?

What would be some good values to make the normal channel a bit more "lead" like? along with maybe a slope resistor change or plates? any suggestions there?

Also was wondering, if I do this... is it still possible to share the reverb channel coupling cap and get reverb on both channels?

ANDDDDD.... haha sorry... I'm wondering if anyone has any good uses for the bright switches? I definitely dont need those damn things! I'm going to be adding a mids knob and a negative feedback control pot. (can anyone send me to a good site that shows exactly what to do for negative feedback mod) so maybe a switchable boost or something- couldnt I just sub the 120pf bright switch cap with a larger cap value and get a big boost?

ANDDDD... I'm basically trying to make the normal channel useful- but I know I do not like fender preamp gain for the most part... I dont know if it could be made better with circuit mods... i'm gonna try I guess. anyways, I've heard that you can convert the normal channel and it's two inputs into an FX loop! Can anyone point me in the direction to some more info on a fender fx loop mod? I take it that it would be using the tube as a buffer or else it wouldnt be a good loop.

ANy ideas are appreciated! I'm thinking once I get the right tube (or transformer for the current tube) This amp will be on the bad ass track!!!
Thanks so much for all your help here! Couldnt have done it without you!

Man, you have got it bad.

Here's the thing. I was once where you are now. You have a good early silverface amp w/ blackface specs. You have it sounding good. But your urge to mod the amp is overpowering.

Leave the SF alone, and get parts together for a new build with enough space & sockets in it to experiment with mods. It's the only way to get it out of your system.

Close up the Pro Reverb chassis, and play some guitar.

I really just want an all in one amp thoughhhhhhhh! haha I know, i've been playing the **** out of it, actually. Now that i've got the gain soudning good, i'm like well **** I need an effects loop, and well this bright switch is pointless. and now that I have it sounding fantastic I'm thinking the nnormal channel is completely useless as is and with just some tone cap mods still pointless.

You really think a negative feedback loop and making the bright switch useful wouldnt be a good idea?

I dont know about the effects loop- i've read it can be done well using the normal channel, but I dont know. that would be the creme de la creme

I agree with firemedic

so you both think it's pointless to decouple the shared cathode bypass cap? id have to disagree based on my limited knowledge of tube amps, but i'm pretty positive that can only have a positive affect

You really think a negative feedback loop and making the bright switch useful wouldnt be a good idea?



Didn't say that.

The issue is not how your amp sounds, at this point. Because it sounds good & you like playing through it.

You need to address the fact that you're at a point where there's always another mod you want to do. A lot of us here know exactly what that's like. We've been there. It's a great road to go down, you're going to learn a lot.

A stock BF/SF Pro Reverb is a classic amp that lots of guitar players would love to own. Tone to die for. One day you may get a guitar with darker pickups, or a Telecaster that loves this amp. My point is: take it from me & whoever wants to back me up on this- Don't do anything to the amp you may someday regret.

To answer the question:

1- buffered effects loops color the tone. It's unavoidable. You may or may not like how it sounds. You seem pretty hell-bent on doing something with the normal channel so if I had to modify the normal channel I would make it a high-gain Marshall-esque channel. Having never tried to make a Normal channel into an effects loop, my opinion here is not worth much. My 2 cents.

2- What's wrong with the bright switches, too bright or harsh? If your pickups are in series that's not a big surprise. To make them less brassy consider using 47pF bright caps instead of 120pF.

so you both think it's pointless to decouple the shared cathode bypass cap? id have to disagree based on my limited knowledge of tube amps, but i'm pretty positive that can only have a positive affect

Not pointless. It's a good idea.

Clay....as I read this thread, I am fearful that this amp is headed down a road that will dead end at a point where this amp is not original AND it won't be working properly. The non-orignal thing is done, right? So, the deal now is to get the amp to do what you want it to do. This is where I am wondering...but I suppose you will come to understand the things that I have doubts about.
Here are my 'points of interest' that I found in this thread.
1) I may have misread, but it seems to me that you are of the mind that V1 is operative as part of the Vib Ch. IF I am mistaken here, my apologies. V1 = Norm Ch pream. V2 = Vib Ch preamp.
2)SEparating those cathodes on V1 and V2.... You can simply 'cut' that wire out and build a new bypass circuit for pin 8 on V1. You do need to understand that if you proceed this way, the gain in the Vib ch will increase because you will have changed the bias on V2 by leaving that 820 ohm bypass resist6or there. You may like that. I tend to want gain in that channel to remain the same since it already is the hotter of the two channels, and that means agoing to a 1.5K resistor in that bypass. I use the 820ohm resistor in the new bypass for P8, V1....along with another 25mfd/25 cap there.
3)IF you really want things to get interesting, then as firemedic notes, you can change the tone stack in the Norm ch to go toward the tweed thing....smaller bass and mid caps....and a change in the slop resistor if you want to go that far. This wil give you a totally different sound out of the Norm ch.
4)NEg Feedback loop.....that amp has one.... in the stock format, anyway.
I like to install an adjustment pots in series with that 820 ohm resistor....50K Audio gives you a wide range of sonics available. 820 ohms of resistance there will be 'stock' clean while things get hotter and richer as you increase the resistance.

As for the problems with the sonics, imho, that should be resolved before any further mods are considered. The idea to check out some different speakers is of definite value. Also, IIRC< you never say whether the bad sonics are common to both channels or if the problem exists only in one channel. IF I missed this info, again....apologies.....but knowing this piece of info makes a big difference in how one goes about trying to find the problem. IF the problem exists only in one channel, have you tried subbing in the other channel's preamp tube to see if that helps? V1 for V2 or vice-a-versa?

Also, I have neard trash that is caused by a slightly bad ground on a reverb jack...whether or not the reverb was in circuit.

i dont know why you guys think this amp has any value at all stock... it's a silverface pro reverb- definitely my favorite fender amps besides princetons and twin's, but in its class the pro is the best bar non. 2x12 35watt tube rectifier with reverb and tremolo, cmon...

But yeh, it's a silverface, it had the blue turds in it, it had components changed out to a hodge podge of stuff. I've replaced every component in it with quality stuff and the amp is sounding awesome now!

Wally- I'll check out the reverb jack. I know that v1 is normal and v2 is vibrato... but they leak into each other... because of the shared cathode right? the amp sounds fantastic now that i've gotten the plate voltages closer to being correct. The voltages are still a bit high on v1 and v2 IF i use a 12ax7 (probably why i'm liking the 5751 and 12at7 in those positions so much) The guys over at amp garage have helped me quite a bit with this amp. But I still am having the snap crackle pop on the vibrato channel only- meaning when I unplug v1 the crackle pop is still there... when i unplug every preamp tube BUT v1 and the PI- the crackle is gone. I've been told the standby switch could cause this... could this be true even though v1 isnt crackling? maybe the arcing isnt affecting the v1 tube all the way down there on the other side of the amp?

The power cord is a 3 prong now... but the death cap and auxiallary power socket and ground switch are still installed... could those be causing the background rice krispies?

I'll try the reverb jack grounds... pretty sure i've checked every ground in the amp, but 3rd time can be the charm right? could a pot be the cause of all this? even if none of my pots are scratchy when twisted? I cannot find a single component that makes any noise with the tap and push test- going in the amp while running and tapping components looking for loose connections. I cant find nothin! Except I touched the death cap and the crackle stopped for a while... but started up a few minutes later (This is normal though, and probably just happened to happen when i touched that cap- no other sound was made that would lead me to believe it's loose or poorly grounded) I disconnected the bright switches trying to rule those out.

I'm crossing my fingers its the standby switch- should I even bother since I dont get any snap crackle pop on the normal channel when the vibrato channel tubes are pulled?


I definitely would not agree that changing caps and slope resistors alone in the preamp will change the tone of these amps drastically.

And sorry I mentioned those mods because That day i played the amp for like 10 minutes and it was perfect (with new 5u4 rectifier tube and no krispies) But yeh I just need to get these damn rice krispies fixed and the amp will be so freaking money. If it didnt have this background noise it would be one of the best fender blackface 6l6's I've heard. I mean it is DEAD quiet in terms of hum and hiss... There seriously isnt a noise difference between hum cancelling and single pickup positions on my strat unless I'm really close to the amp or it's above 7 on the dial. (D allen pickups are damn quiet for some reason too)

Please tell me the standby switch is the problem... then we can think about mods :)

I just did a 2 to 3 prong conversion on my BFDR. I wired around the ground switch per the instructions.
Afterwards I had some rice krispy noises. I checked my work and it was all good, solders were fine. Still the rice krispy sounds. The ground switch should be out of the mix, but I flipped it the other way and the noise was gone.
Who knows? Maybe yours would do the same.

Clay...I love a PRo REverb when it is working properly.

Sanp crackle pop! For the rest of thismessage, I will call this SCP, okay? The test for this is not to remove all of the tubes except V1 and the PI, imho. When you do that, you have nothing excpet the PI and the power tubes online. So, that 'test' proves very little. V1 and V2's signals both have to travel through one triode of V4 on their way to the PI. IF the SCP occurs only in the Vibrato ch, then you can stop worrying about V1 and the NOrm Ch. IF the SCP occurs in either channel, that tells you something.....I would think that your problem lies downstream from those two preamp tubes in this case. In other words, the problem is common to both channels, and the possibilities are numerous. IF the SCP occurs only in one of those channels, you can concentrate your search in that channel.
I am not going to tell you that the stand by switch is definitely the problem....especially if the SCP! occurs only in the Vib channel. (;^)

Yeah...get it working properly and then we'll talk about mods. IF you think that tone cap changes don't make much difference, that will be an eye opener for you when you get the amp working properly. And.....the day I can't hear a single coil hum is the day I'll stop working on guitars and amps. Nothing does away with that. Nothing.

I just did a 2 to 3 prong conversion on my BFDR. I wired around the ground switch per the instructions.
Afterwards I had some rice krispy noises. I checked my work and it was all good, solders were fine. Still the rice krispy sounds. The ground switch should be out of the mix, but I flipped it the other way and the noise was gone.
Who knows? Maybe yours would do the same.

IF you truly 'wired around' that switch (got pics?) and IF a noise went away when you switched the switch after the rewiring bypassed that switch, then imho the cessation of noise when you switched from one position to another on that switch was purely coincidental. OR....you have a loose connection or nut or something that made better contact when you jostled that switch....but that bad connection or loose nut has nothing to do with the switch position itself...IF the switch has no wiring connecting it to the AC circuit.

Wow, there is a lot of ideas and info in one thread. My advice as a designer and sometime repair guy is to get the thing operating in the stock fashion before modding anything. Fender designed a great amp so you need to start with getting it working well that way. Another thing to remember on the higher than expected voltages is that the AC line voltage is higher in most areas than when this amp was built. I remember 110 volts in the late 60s. Now my house is at 123VAC. My 64 yellow Bassman head (6G6-B circuit)has a plate voltage on the 6L6s of about 510 volts! The thing works great but worries me. It has a solid state rectifier According to the Fender schematic, the plate voltage is supposed to be about 435 Volts. My builds of a somewhat original circuit is at 440 volts on the plates of 6L6s (I've built three so far) The voltages on Electrolytic caps is the Working Voltage in DC. The older caps used to be labeled WVDC. They are OK up to the listed voltage. 900 volts in a filter cap is fine but not necessary. 500 should be fine.

hepcat, I haven't seen it all, but I have never seen over 510VDC for a B+ on an amp like that. What is the current draw? What is the plate dissipation? A 9% increase in wall votlage would not be the reason for 510V to the plate in that BAssman, ime. ORiginal PT?

Listen to Wally.

Then Listen to Wally.

Then - if you're really reaching for what I'm reading into your description of the sound you want (and BTW, it's 40 watts into 2x12's, not 35.), once you have solved your "SCP" problems through conventional means there is one mod you can do that will turn it into a monster of an amp - change the output transformer. You want to do it (preferably) without drilling any holes, so try to find one that fits the existing mount OR install some brackets and mount it a little off the chassis.

The one weak point in the Pro Reverb - ALL BF/SF models (we'll exclude the 70 watt ones as being total anomalies); they had weak OT's. In both these and Banbdmasters a common mod is installing a Bassman-spec output transformer, which has more iron and far more punch. With that change you can play with rectifiers and it won't over-sag on you.

I mentioned it in another thread as there's a transformer in the classifieds (I can't vouch for the particular model, but it seems right). But I have run both the original and a Bassman in my '69 (BF circuit) and it's unbelievable. Turns it ino a mid/high power desert island amp.

Listen to Wally.

Then Listen to Wally.

Then - if you're really reaching for what I'm reading into your description of the sound you want (and BTW, it's 40 watts into 2x12's, not 35.), once you have solved your "SCP" problems through conventional means there is one mod you can do that will turn it into a monster of an amp - change the output transformer. You want to do it (preferably) without drilling any holes, so try to find one that fits the existing mount OR install some brackets and mount it a little off the chassis.

The one weak point in the Pro Reverb - ALL BF/SF models (we'll exclude the 70 watt ones as being total anomalies); they had weak OT's. In both these and Banbdmasters a common mod is installing a Bassman-spec output transformer, which has more iron and far more punch. With that change you can play with rectifiers and it won't over-sag on you.

I mentioned it in another thread as there's a transformer in the classifieds (I can't vouch for the particular model, but it seems right). But I have run both the original and a Bassman in my '69 (BF circuit) and it's unbelievable. Turns it ino a mid/high power desert island amp.

actually, it's labeled as 45 watts. but it really isnt.

now i'm having problems with the amp- I have lost my clean headroom. I have been working on the problem over at the amp garage forum. But I'm not getting far. The amp used to have TONS of clean headroom, and recently it's been slowly degrading (during the process of writing this thread) and really even before- it's become more and more progressiive and now i'm at the point that I get dirt at 3 on the amp. It used to be unbearable volume levels before I could get breakup.

the funny thing is- the breakup isnt amazing sounding, but it sounds a lot better than it used to when i had clean headroom for days

Clay...I love a PRo REverb when it is working properly.

Sanp crackle pop! For the rest of thismessage, I will call this SCP, okay? The test for this is not to remove all of the tubes except V1 and the PI, imho. When you do that, you have nothing excpet the PI and the power tubes online. So, that 'test' proves very little. V1 and V2's signals both have to travel through one triode of V4 on their way to the PI. IF the SCP occurs only in the Vibrato ch, then you can stop worrying about V1 and the NOrm Ch. IF the SCP occurs in either channel, that tells you something.....I would think that your problem lies downstream from those two preamp tubes in this case. In other words, the problem is common to both channels, and the possibilities are numerous. IF the SCP occurs only in one of those channels, you can concentrate your search in that channel.
I am not going to tell you that the stand by switch is definitely the problem....especially if the SCP! occurs only in the Vib channel. (;^)

Yeah...get it working properly and then we'll talk about mods. IF you think that tone cap changes don't make much difference, that will be an eye opener for you when you get the amp working properly. And.....the day I can't hear a single coil hum is the day I'll stop working on guitars and amps. Nothing does away with that. Nothing.

and the SCP is fixed- yeh taking out all tubes besides v1 and PI helped a lot, because it removed the Standby switch as a possibility obviously.

and about hum- my amp was dead quiet before all these problems- when the amp was working properly after I changed out all my resistors and caps to modern metal films and whatnot... if i was standing more than 10 feet away from the amp (even with the amp cranked) there was VERY little difference between hum cancelling positions and regular positions. D allen pickups have a lot to do with this. combined with high grade metal film resistors. I also never said that tone caps dont change the sound- I believe I said increased plate resistors didnt change the gain much. maybe i did, dont have time to read.

try d allen pickups and PRP metal film resistors. Amazingly quiet strat there... I have his voodoo 69's... I dont know how but his pickups are just amazinglly more quiet than fender's cs 69's (and not just because his middle is RP- i'm talking about single pickups) The PRP metal films and F&T higher voltage filter caps (they had a bit to do with it, not too much though) And I am talking, i replaced every resistor in the amp but like 5 that I didnt have the values for.
Although the SCP was coming from the plate resistors of the reverb section (i guess plates- between the .0033uf and .1uf coupling caps) I probably overheated them with experiments in tone caps (if I said that tone caps dont change sound then I was meaning to write something else) I definitely could have overheated the one that went snap crackle pop though. I'm not even using 1 watts- just 1/2watt PRP metal films- they arent even overpriced

So yeah, SCP fixed... now we have a new problem- my headroom is just going down the drain. I'm thinking its a transformer- just my instinct- I've done some tests to determine some things from advice at the amp garage forum, but that didnt work. If only I had a good shop and a spare OT or PT.

I love my pro stock- I am just looking for mods to make the normal channel more useful for me. an ab switch with different volume and tones isnt that useful for my purposes. an FX loop or a preamp out so I could run one preamp out into an external power amp would be what i'm into.

Clay, this will be my last post...I think. I hope you take this with teh spirit in which I post.
Imho, that amp needs a tech. IF not, then you are on a long path of discovery. IT seems that you have over time taken an amp that used to sound great and reduced it to a PRo Reverb that doesn't yield good cleans...adn I suspect that he breakup sonics are not 'useful' either.
You have an amp that has few original parts on the board, right? Nothing you have done has gotten the thing to work for you. You say that you are working with the guys over at amp garage. Do you post voltages and such over there??? Without some sort of guidelines like that, it is hard to know what is going on in that amp. Now you supect that the OT has gone bad. Frankly, imho and ime, that is a pluasbile possibility IF you have been doing this and doing that with that amp and not taken note of voltages,etc.

AND.....you still insist on thinking about mods. I applaud anyone who is curious and wants to learn. IF you want tolearn, you have to start dealing with the basics first....get an amp working properly as designed. Then, if one has some understanding of what is going on and what the changes will do, the amp would be ready for 'mods'. Repalcing every component on the board of a vintage fEnder is, imho, not the way to go about making such an amp work properly. IT is a way to occupy time and obscure the reality of what is there and how it is working. IT is also a way to quickly devalue an amp. I have a csometically dead mint March '67 BFTR sitting here. Every component on the board is new. EVery pot except the bias pot is new. The ampsounded like trash when it came in. One resitor and a set of tubes changed all of that. NOw the amp soudns great....but it still isn't worth what it would have been wroth from now on IF the roiginal board components had not been removed----for no reason at all....except it seems that those blue molded caps and the pots are worth soem money. ?????
I hope you get the amp going to your satisfaction. IF that amp had been in the hands of a good tech before all ofhtis unnecessary work was done, that amp would still have its vintage value, and it could have exactly what you want coming out of the speakers. That is, two very different channels...one clean BF sonics and one a hotter more big tweed-like sonic. IN less time than I have spent typing mu posts in this thread, agood tech would have that amp singing sweetly or breathing fire. You would also know...if the tech was any good at all...what all of your voltages are, what the current draw is and what the plate dissipation is. That way, the OT would not be at any greater risk than it should be. IF the amp has been biased too hot, there is a possiblity that something has gone amiss with a major component. But....we don't see the voltages so we don't know much about this amp. Maybe the guys at Amp Garage know more about it than we do. I hope so since you have been taking their advice, it seems.
Good luck with it.