Fender Reverb amp set up and build Tips

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aegert
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Fender Reverb amp set up and build Tips

Post by aegert » Sun Dec 23, 2012 7:58 am

Hey... was in another Thread on a BF fender Twin Reissue. The discussion had veered so here is a new thread for some Ideas... See accompanying diagram

Have you ever noticed how your reissue BF just doesn't have that old tone you really wanted. It sounds great but its just missing that little thing that makes that amp sound "THAT" way....

When dealing with Fender Amps for that issue any amps it is good to mind a couple of things:

1) Tone coupling caps foils should point up stream of signal flow. This means in most instances the foil goes to the high DC voltage side or from where the signal is coming from in the circuit, closer to the input. In a fender Black/silver face amp only the .01uf leading into the PI will be reversed facing from the other coupling caps. This is the 3rd from the left looking at the amp in standard Layout Diagram orientation.

2) Tone caps. If you have an older amp that doesn't have the old blue molded Coupling caps a change will make a big difference. I have bags of Moulded blue caps that I re lead regularly but for new builds for some pro's I have settled on the Zoso Blue caps. $'s for donuts they sound the best and almost in distinguishable from the originals. You need to break them in. Why the manufacture doesn't do this burn in I don't know but you will notice over a 10hr playing period that the get warmer , more open and will make your BF sound right

3) Heater circuit phase.. Taking notice of your heater circuit wiring is very important to make a very quiet amp with less chance for tone sucking interference. If you look at the diagram it is unimportant which leg starts out as phase A or B but keeping them lined up as in the diagram is. If your tubes are in and you heater wires are connected to the Power Transformer you will be unable to verify continuity with a tester so remove these obstacles. This will keep heater noise to the smallest possible sans going to DC heaters. The subsequent induced AC noise should cancel not add with this configuration. Note that the wires are still run as twisted pairs above the tubes.

4) Tubes: There is a place for Mojo and there is a place to just forget about it.. These are my observations and the confirmed observations of 2 of the best Amp techs I have ever seen. These are sort of the secrets for setting these amps up and this is the first time I have ever talked about it in a forum. I don't htink these other guys have either.. At least I have not seen.... so


For your First preamp tubes NOS RCA Grey plates 12AX7A's are the way to go if you never use the normal channel don't waist money on it .. Throw a EH 12ax7a in there...

Reverb Driver should be an RCA 12AT7 (Mill version RCA 6679 is the same thing maybe better). This tube is being driven like a power tube . Most every other tube will take a dump short term being driven that hard. This will last. They are not that expensive. If you put one in you will not change it for a very long time.

Reverb Recovery you can use any good tube. if you have a monophonic RCA 12AX7A go for it but a an EH, Ei, Groove tube all work here..

Phase inverter: GE12AX7 Grey... Most musical you will find. Makes a big difference.. For your tweeds the best thing you could ever do to the amp is to put a NOS Long Plate Black RCA 12AX7 as your PI Just magic

Vibrato tube: The cheapest most micro phonic piece of crap you have makes absolutely no difference.

power tubes.... I have a stash of older STR tubes Plenty of GE , Phillips and RCA 6l6's For 6v6 I happen to have a bunch of old Tungsols branded as IBM and older RCA Black plates but I put EH and the new New sensor Tungsols in most new builds. They are cheep and very musical.

Don't believe the rectifier nonsense in the GZ34 world.. Just get one that is on spec.. 5y3's are easy to come buy NOS cheep so buy them, 5u4's buy the eh don't spend big coin..


5) WIre and boards...if your amp has that shitty stranded wire from the early 70's swap it out! these amps have boards that look waxy too. Definatley lift all components off the board. They used some really crappy material that tends to take in moisture and develops a capacitance. . You can see voltage on many of these boards. even if you don't they sound like crap. Yes the boards sound horrible. The worst of them are found by using your DMM. Put the black lead to your ground point at the PT and with the red probe read the voltage around the eyelets with the power supply plate resistors. If you see any voltage on the board near the eyelet you should most definitely make sure no components are laying on the board... Better yet swap out the main board or sell the amp and get one without the problem... These older amps have had usually seen mods and Ahab and the blow torch have most likely had their way with the main board. Take out the crews holding the board to the chassis and slide the backer board out.. Blow out with air under the board in the chassis. Wipe down the backer board with deoxit and clean it good .. Scrub it with steel wool even. make sure if you do this that you wipe it very clean with a cloth so as not to leave any metal hairs on it. There is usually big time oxidation on these and the cleaning removes it and any stray partials that give your amp those ghost crackles and fizzes. Many of you mechanically/ vibration based problems are here

6) Tube sockets. Tighten them with a sharp pick. Loose tube pins cause a lot of havoc and can lead to arcing and ghost notes. use deoxit on them.


Image
Last edited by aegert on Mon Dec 24, 2012 12:23 pm, edited 1 time in total.

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Re: Fender Reverb amp set up and build Tips

Post by aegert » Mon Dec 24, 2012 12:04 pm

Just added a bunch more info to this as I was in a rush the other morning.. please re read

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Re: Fender Reverb amp set up and build Tips

Post by 46346 » Thu Jan 03, 2013 5:32 pm

great info - especially #3 and #5. can we move this to the amp technical forum for future reference?
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Re: Fender Reverb amp set up and build Tips

Post by sookwinder » Thu Jan 03, 2013 6:03 pm

done
relaxing alternative to doing actual work ...

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Re: Fender Reverb amp set up and build Tips

Post by øøøøøøø » Fri Jan 04, 2013 6:58 am

on record: I disagree with the tube stuff. It's all a matter of taste. I dislike the GE for PI in many/most Fender amps as compared to a good RCA. I think the grayplate RCA falls far short of a long black plate RCA in V1/V2 as well. A good old Amperex Bugle Boy is actually my favorite, except the 12AY7 in some tweeds in which I prefer an RCA.

Having tried every GZ34 ever made, I've found that (contrary to my expectations), the old Mullard GZ34 really does perform best and actually makes the amp sound better in 9 cases out of 10. However, the new Chinese GZ34 are getting better and are really the best value since the Mullards are so expensive.

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Re: Fender Reverb amp set up and build Tips

Post by aegert » Fri Jan 04, 2013 7:36 am

øøøøøøø wrote:on record: I disagree with the tube stuff. It's all a matter of taste. I dislike the GE for PI in many/most Fender amps as compared to a good RCA. I think the grayplate RCA falls far short of a long black plate RCA in V1/V2 as well. A good old Amperex Bugle Boy is actually my favorite, except the 12AY7 in some tweeds in which I prefer an RCA.

Having tried every GZ34 ever made, I've found that (contrary to my expectations), the old Mullard GZ34 really does perform best and actually makes the amp sound better in 9 cases out of 10. However, the new Chinese GZ34 are getting better and are really the best value since the Mullards are so expensive.
As from our previous thread ... TUBES ARE MOST DEFINITELY SUBJECTIVE AND STUFF OF OPINION I AGREE. I just have mine and they tend to fall to my tastes. I Have found it hard to get Long Black plate RCA's that are not somewhat micro phonic in v1 v2 of AA and AB circuits so I defer to the 12ax7a grey plates.. Tweed is a different story and we sit firmly on the same side of the fence there... Not having spent $x00's on a recto tube ever! LOL I can't refute or agree with the mullard GZ34 :-)

And from our other thread your point regarding LISTEN FIRST should be Put at the front of this thread.... Some times they just sound right. Better not to F with a great amp save normal maintenance. My original posts were born of the thought that It is very hard to find strait amps any more. Most of them have been messed with pretty hard so the thoughts I gave were relating to what a buyer of a fleabay or guitar store amp might see when opening up a 40+ year old amp that has had a 100 moders through it...

Thanks for the input "0000000"

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Re: Fender Reverb amp set up and build Tips

Post by øøøøøøø » Fri Jan 04, 2013 4:58 pm

Yeah, I wouldn't pay that kind of money for a rectifier tube, either!! I lucked into about 6 of them... one in my Deluxe, one in my brown Super, one in my HiFi amp, one actually died(!!!) which I've never seen happen before, and I think I sold or traded the rest away (probably a bad move).

I really was of the mind that "power supply, probably not a big deal." I really learned something when I took the Mullard out to use in another amp and put something else in instead. The difference when I went back to the Mullard was striking, and surprising. I have been a believer in the importance of power supplies ever since... tubes, caps, everything!!

You're right that the long blackplate RCAs tend to be a touch microphonic. As long as they don't squeal, this doesn't bother me. For my tastes, I've actually found that I prefer the overall tone of a slightly microphonic tube to one that's completely free from microphony. I actually feel the same about pickups, as well, and don't generally like what wax potting a guitar pickup does to the sound.

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Re: Fender Reverb amp set up and build Tips

Post by andy_tchp » Sat Jan 05, 2013 12:30 am

FWIW, the cheap (usually $10-$12) and readily available NOS JAN Philips 12AT7 also serves very well in the reverb driver slot.
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Re: Fender Reverb amp set up and build Tips

Post by aegert » Sat Jan 05, 2013 5:52 am

andy_tchp wrote:FWIW, the cheap (usually $10-$12) and readily available NOS JAN Philips 12AT7 also serves very well in the reverb driver slot.
It serves for sure :-) but serving isn't the thing about teh RCA.. The RCA lasts and lasts and lasts. The way that thing is driven it saves big time in the long run...

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Re: Fender Reverb amp set up and build Tips

Post by øøøøøøø » Sat Jan 05, 2013 7:59 am

aegert wrote:
andy_tchp wrote:FWIW, the cheap (usually $10-$12) and readily available NOS JAN Philips 12AT7 also serves very well in the reverb driver slot.
It serves for sure :-) but serving isn't the thing about teh RCA.. The RCA lasts and lasts and lasts. The way that thing is driven it saves big time in the long run...
Agreed. The way the reverb driver is run is quite demanding on 12AT7s.

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Re: Fender Reverb amp set up and build Tips

Post by 46346 » Sat Jan 05, 2013 2:11 pm

re: the 12at7 in reverb ckt - i'm figuring one triode is working a lot harder than the other, yes? i'm starting to think with all my tube swapping and experimenting, i might want to keep my well-balanced 12at7's aside for PI work (BF Bassman, SR, etc.) and not dog them in reverb circuits.

agreed that the GZ34 game is weird. there seem to be so many NOS available, yet $100 and up. but i've had great luck with used pulls - Mullards and Amperex. sometimes i've found them in junked gear, or i'll pay no more than $45 for a tested/guaranteed one on ebay when i get lucky.
indeed, Brad - that's the first Mullard GZ34 failure i've heard of! many times in a band setting, i don't notice the difference all that much from JJ and others. other times, the Mullard or Amperex just *feels* better. also, i've burned through three modern-made GZ's in the last two years on three different amps.

you guys are rad for typing up your experiences for us all to consider!
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Re: Fender Reverb amp set up and build Tips

Post by jimboyogi » Sat Jan 05, 2013 2:59 pm

In the reverb driver, the 12AT7 is connected in parallel, so both triodes are working together. Theoretically then this would be a better spot for a poorly matched 12AT7, keeping better matched ones for PI duties.

I bet that some people prefer poorly matched tubes in the PI spot though, as it will give more 2nd harmonic distortion this way!

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Re: Fender Reverb amp set up and build Tips

Post by aegert » Sat Jan 05, 2013 4:22 pm

really the reverb driver tube discussion for my set ups is always about reliability. don't want a tube taking a shit on stage. on stage I use plenty of cheaper tubes in all spots. Plenty of the EH 12ax7's. I set up with best stuff for smaller gig settings or studio. when playing through a PA the subtitles of this whole discussion start to wane for me. but the rca12at7 is in every build and set up regardless of setting... OPINION

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Re: Fender Reverb amp set up and build Tips

Post by andy_tchp » Sat Jan 05, 2013 5:02 pm

aegert wrote:
andy_tchp wrote:FWIW, the cheap (usually $10-$12) and readily available NOS JAN Philips 12AT7 also serves very well in the reverb driver slot.
It serves for sure :-) but serving isn't the thing about teh RCA.. The RCA lasts and lasts and lasts.
So does the NOS JAN Philips - perhaps I wasn't clear but that's what I meant by 'serves very well'. I wouldn't have bothered mentioning it otherwise.
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Re: Fender Reverb amp set up and build Tips

Post by øøøøøøø » Sat Jan 05, 2013 5:23 pm

aegert wrote:really the reverb driver tube discussion for my set ups is always about reliability. don't want a tube taking a shit on stage. on stage I use plenty of cheaper tubes in all spots. Plenty of the EH 12ax7's. I set up with best stuff for smaller gig settings or studio. when playing through a PA the subtitles of this whole discussion start to wane for me. but the rca12at7 is in every build and set up regardless of setting... OPINION
I find that how much I care in any situation is directly proportional not to how audible the difference is, but rather to how busy I am. If I'm swamped, I tend to just use any old thing that works and is available, almost no matter what. I still have a Chinese Groove Tubes preamp tube in my main gigging amp's V1 spot for this very reason... it was replaced in an emergency and I still haven't gotten around to putting something better in there (even though I have about 6 NOS Mullards in the next room!)

If I'm more in a down period, I start to get fussier. As always, though, busy or not, the best amp is one I don't have to bring myself. Important-ish recording sessions are perhaps a lone exception to this rule, but even that is best when there's budget to just have a cartage service come pick your shit up and drop it off at the session!! But this is a luxury that isn't often afforded, at least not anymore.

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