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Ping: Fenderlover re early 70s Princeton Reverb

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dean_martin

A

I've had my Fender Princeton Reverb guitar amp since the early 90s. I had it serviced including tube swaps several times when I lived in cities with good amp techs.

Now, I live in the sticks and the amp needs help. I've changed out all tubes except the EL34 power tubes, but I'm still getting crackling sounds. I've held off replacing the power tubes myself because of concerns about biasing. I have a back-up pair of EL34s for my Jolida integrated. I'm wondering whether I can just drop'em in the guitar amp, or whether I need to take the amp to a tech for that. Any suggestions would be appreciated. Thanks!

Follow Ups:

Thanks for the info, guys . . . - dean_martin 14:10:17 04/26/12 (1)
Even though I'm not confident in doing this myself, at least I'm armed with some knowledge of what needs to be done.
- RE: Thanks for the info, guys . . . - FenderLover 03:56:27 04/27/12 (0)
  You're welcome! Good luck. This is one of the best little practice amps to come from Fender. Ever. IMHO.
  
  Very worthy of a nice restoration.
RE: Ping: Fenderlover re early 70s Princeton Reverb - jarebjr 10:54:46 04/25/12 (1)
Not sure where you are in Alabama but try these guys if you want to drive the amp in and wait: http://www.grangeramp.com/.
- Granger Amps - dean_martin 13:52:59 04/25/12 (0)
  Thanks! That's about 4 1/2 hrs north of me but I do go to B'ham and other northern parts like Huntsville for work. Might take a little creative scheduling to drop off and pick up, but it can be done.
  
  I don't think I want to ship it.
RE: Ping: Fenderlover re early 70s Princeton Reverb - FenderLover 15:10:59 04/24/12 (6)
OK... What circuit model do you have? Because all silverface era (late 1960's-early 1980's) Princeton Reverbs came with 6V6GT(A) output tubes. No Fender amp I know of, came with EL34 as OEM output stage tubes.
Unless, extensive modification was done to the amp (new PT and output stage).
- model B1270 (Open in New Window)
Edits: 04/24/12 04/24/12
- Yep. You're right . . . - dean_martin 16:00:24 04/24/12 (5)
  I'm not sure what I was thinking. This is a project I've had on the back burner for too long. In fact, I did some internet research on it last fall, but haven't looked at it in a while. I couldn't find anything that said you must do this or that when replacing the power tubes. I think the amp is probably from '72 (or maybe '73?). I guess since I replaced the rectifier and smaller tubes myself, I was thinking I had the power tubes to do it myself, too. I don't. Oh well, enough about my confusion. If I ordered a pair of 6V6GT(A)s, could I just drop'em in? I'd love to keep this thing going. I don't get to the big city for personal stuff very often and it's capable of awesome tone.
  - I'd check the anode plate voltage and idle bias - FenderLover 17:22:30 04/24/12 (4)
    The PR doesn't have an adjustable bias pot. You can add a 10-k ohm pot to the bias supply or juggle the C- to ground resistance to get the tubes into range. For the B1270 circuit, it's the 22k-ohm directly next to the 50mfd/70VDC 'lytic on the separate bias power supply board. For my last AB1164 job, this resistor ended up being around 34k-ohms... to get an idle output of about 7-9 watts per tube.
    Around 17-19mA at 415VDC plate voltage.
    Good luck! Tell us your results.
    - Clearer schemo with layout (Open in New Window)
    Edits: 04/24/12
    - RE: I'd check the anode plate voltage and idle bias - dean_martin 09:01:14 04/25/12 (3)
      Thank you for the info. Unfortunately, I wouldn't know where to begin so I will find a tech. I'm about an hour away from an independent guitar shop that might have someone who can help. The closest Guitar Center to me doesn't service amps.
      
      I'll keep your info and I believe a schematic is still inside the amp frame. BTW, do you have recommendations for replacement power tubes? Most of my tube swapping has been done on my stereo equipment.
      - Any good NOS US made 6V6GTA will be good - FenderLover 14:17:52 04/25/12 (2)
        
        In Reply to: RE: I'd check the anode plate voltage and idle bias posted by dean_martin on April 25, 2012 at 09:01:14
        
        The best of these (thus, one of the most costly) are the black plate 1960's made, TungSol 6V6GTA. RCA, Sylvania, or GE labeled 6V6GTA are fine, too. Max watts of dissipation, at idle is 14 watts (versus 12 watts for most GT's).
        Try not to run them too much over 70% max dissipation (~ 10 watts per tube).
        http://www.tubemonger.com/Origl_Tung_Sol_6V6GTA_MP_NOS_NIB_1 (Open in New Window)
        
        Edits: 04/25/12
        
        One other note... - FenderLover 19:36:21 04/25/12 (1)
        
        In Reply to: RE: Any good NOS US made 6V6GTA will be good posted by FenderLover on April 25, 2012 at 14:17:52
        
        Deano, when was the last time the cap can was changed-out? For the PR, I've been using the taller FP made 30/20/20/20 at 525VDC rated cap (available at AES) with a little better luck, than the 20/20/20/20 at 475VDC rated ones.
        Parts number:
        20/20/20/20 at 475VDC = C-EC20X4-475
        30/20/20/20 at 525VDC = C-EC30-20X3-525
        http://tubesandmore.com/ (Open in New Window)
        
        Edits: 04/25/12
        
        RE: One other note... - Jareb 03:55:02 04/26/12 (0)
        
        In Reply to: RE: One other note... posted by FenderLover on April 25, 2012 at 19:36:21
        
        Good suggestion from Fenderlover on having the cap changed. If its more than 15 y.o. I would change it while you have the amp in for bias etc. Spend the money and have the thing "gone through" so you will have a stable amp for many years to come.
        My .02
        John
        
        Edits: 04/26/12

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