Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: WimWalther on January 31, 2024, 12:29:00 am
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Very good, longtime neighbor asked me to fix his amp. Neither of us know the model beyond what it says on the panel.
So is this the AA1164 PR?
Anyway, this amp survived a fire that destroyed the house. Still worked thereafter, but now it's several years on and the reverb is so noisy it's unusable. Is that a known issue with the model, by chance? He also said that the "reverb" noise sometimes crops up even when the reverb isn't in use.. whatever that might be.
The reverb cables look rough to me, so that will be the first thing to eliminate. Beyond that, it's a matter of tracking down the noise.
ETA: Gah, what a sight.. does anyone have a correct knob for this?
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I think the best thing to do is to post some high resolution pics of the guts, transformers and tubes. Try to describe the issues, like static/hum/crackles and so on. Hopefully the masters will chime in and help you.
/Max
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I think the best thing to do is to post some high resolution pics of the guts, transformers and tubes. Try to describe the issues, like static/hum/crackles and so on. Hopefully the masters will chime in and help you.
/Max
Hi Max. I don't have the amp in front of me right now. Was just hoping to properly ID it so I know which docs to work from.
Don't really need any t-shooting help atm, but it would be good to know if noisy reverb circuit is a common thing with this model.
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So is this the AA1164 PR?
Yes, AA1164 Princeton Reverb. It should say so on the tube chart in the cabinet.
You will use this schematic (https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_aa1164.pdf) or this schematic (https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_rev_gz34_aa1164.pdf), depending on the rectifier indicated on the tube chart. The difference between them is a 22kΩ to ground (5U4GB) or 27kΩ to ground (GZ34) on the bias board.
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So is this the AA1164 PR?
Yes, AA1164 Princeton Reverb. It should say so on the tube chart in the cabinet.
You will use this schematic (https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_aa1164.pdf) or this schematic (https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_rev_gz34_aa1164.pdf), depending on the rectifier indicated on the tube chart. The difference between them is a 22kΩ to ground (5U4GB) or 27kΩ to ground (GZ34) on the bias board.
Perfect, thanks.
27K on the GZ34 model, for more negative bias voltage to compensate the higher B+ furnished by the rectifier..?
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27K on the GZ34 model, for more negative bias voltage to compensate the higher B+ furnished by the rectifier..?
In theory, yes.
In practice, doesn't matter so much. Shoot for something like 20-21mA which is around 60% of 14 watts.
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would be good to know if noisy reverb circuit is a common thing with this model.
Reverb circuit is the same as all the other blackface reverbs. Not ‘noisy’ - just bucketloads of reverb. After cables, for noise, suspect the reverb tubes. The 12AT7 driver tube runs at a high voltage (just like in all the other blackface amps) and so tends to wear out faster. The recovery tube stage could also be bad
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ETA: Gah, what a sight.. does anyone have a correct knob for this?
I'm sure many of us have some that are damaged in one way or another.. I do and they wouldn't look good on that amp. Instead opt for a new replacement or alternatively procure a whole new set.
https://www.tubesandmore.com/products/knob-witch-hat-black-1-10-skirted-set-screw-thin-numbers (https://www.tubesandmore.com/products/knob-witch-hat-black-1-10-skirted-set-screw-thin-numbers)
https://www.tubesandmore.com/products/knob-fender-witch-hat-black-skirted-blackface-amps (https://www.tubesandmore.com/products/knob-fender-witch-hat-black-skirted-blackface-amps)
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Wait, hang on.. is there supposed to be one on the back??
Shouldn't that be a 1/4" TS jack, or maybe an RCA?
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Shouldn't that be a 1/4" TS jack, or maybe an RCA?
Yes, it should. That amp's been modded, so bets are off until you open it up.
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Well I'll be... there's your knob for the front .. LOL
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Well I'll be... there's your knob for the front .. LOL
Like NS, right? What the.. =/
Somebody must have modified it. Assuming there's a pot behind that knob, I wonder what it does? Guess I'll find out..
Question - does "Production 66" indicate it was built in 1966?
ETA: Looks like a GZ34 model.
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The serial number stamped on the right rear of the chassis, the date codes on the transformers and pots, stampings inside the chassis, should tell us what year this amp was made. It is from 1965 to 1967 - that we already know.
HBP would probably know what the production number meant. I don't.
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Question - does "Production 66" indicate it was built in 1966?
ETA: Looks like a GZ34 model.
Possibly, but probably not.
My '65 has "#2" in that position. It is also a GZ34 version & has the AA764 chart, supposedly a typo. That is one theory anyway.
As MrResistor points out, there are several things to check to zero in on the date. Most 60s Fender I have worked on usually have ink-stamped dates inside the chassis in a few places.
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I see, so the Production code is something else, maybe a shift or batch code, that sort of thing.
You'll have to forgive me, I don't know much of the lore surrounding this guitar equipment. As I might have mentioned, the bulk of my experience is with hifi and a particular line of hi-end gear.
So what should that reverb jack be - 1/4" or RCA? It's neighbor, tremolo, looks like RCA in my photo. I also used an RCA on my Hammond / Princeton project.
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So what should that reverb jack be - 1/4" or RCA? It's neighbor, tremolo, looks like RCA in my photo. I also used an RCA on my Hammond / Princeton project.
RCA jack
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RCA jack
Thank you!
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My '65 has "#2" in that position.
That "NL" stamp on your tube chart is the date code. N is 1964, L is December.
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My '65 has "#2" in that position.
That "NL" stamp on your tube chart is the date code. N is 1964, L is December.
That is extra early '65 then.. :icon_biggrin:
Good to know, thank you.
I seem to remember a '65 rubber stamp date but no pics, & amp is all put together.
I knew it was an early model as it is "Fender Electric Instrument" & also does not have a grille badge or the wood behind the grille cloth to mount one.
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If you really need a knob, I have some from my Twin. I’d jus tput it back to normal and use th eone on the back.
I’d love to see gut shots and see what someone has done.
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If you really need a knob, I have some from my Twin. I’d jus tput it back to normal and use th eone on the back.
I’d love to see gut shots and see what someone has done.
The owner says that the mod is a Master Volume control, added many years ago..