Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: gloriousfrance on October 30, 2024, 12:05:45 pm

Title: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: gloriousfrance on October 30, 2024, 12:05:45 pm: Hi all! I recently completed a AA1164 build. It's my first amp build with reverb. When I increase the reverb pot, the volume increases but, no reverb is mixed into the signal, just volume. I've read that this could be a ground issue. I've checked grounds and everything seems to be correct. It behaves this way with or without the reverb pan plugged in so I'm assuming it's an issue with the amp. I've also verified the 470k resistor in the reverb attenuation. There is continuity between the the reverb filter and reverb mix. All voltages are present where they should be and within reason across the board. Any other ideas what could be causing this issue? Thank you!!!

Notes on build:
NFB switch on ground switch
5U4GB Rectifier
Used Robrobinette mod layout
Title: Re: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: shooter on October 30, 2024, 12:14:30 pm: without the actual build schematic, i'm using this to start with
https://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf

does yours have a foot switch?
did you verify it's working?
do you get a "splash" sound when thumping on the tank?
Title: Re: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: Willabe on October 30, 2024, 12:16:45 pm: What shooter said.

Then, this works great to find a wiring mistake.

https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630
Title: Re: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: SEL49 on October 30, 2024, 12:27:01 pm: Looks like the 3.3M mix resistor is NOT really 3.3M. Probably something much lower, perhaps 330Ω. That 470K looks like a wrong value also. You can check both resistors in circuit.
Title: Re: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: mresistor on October 30, 2024, 05:05:10 pm: This looks like a regular Princeton Reverb AA1164 circuit. What "mods" did you incorporate into it?
Title: Re: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: gloriousfrance on October 30, 2024, 06:30:04 pm: Thank you all for the quick comments. I can't believe I missed that 3.3M. It was a 3.3k. I had checked it so many times my mind must have tricked me. So I now have reverb but it's still doing the same thing with the volume. With the reverb at 0 and the volume at 10, it's really quiet. The minute I turn up the reverb even a little bit there is a big boost of volume and a ton of reverb. I quadruple checked the 470k resistor, it reads 460k. I forgot to mention in my original post that if I knocked the reverb tank I would get a splash. I'll go through it again, thanks for the link Willabe!.

Shooter, the only mods I added were the bias pot, NFB switch and 470k PI grid stop on V4.
Title: Re: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: Willabe on October 30, 2024, 07:01:34 pm: Somethings wired up wrong, or wrong value part, or both.

That's a fairly simple amp circuit. Not real simple, but it's not very complex. You can fix this. :icon_biggrin:
Title: Re: Reverb control increases volume (no reverb) in a AA1164 Princeton Reverb Build
Post by: SEL49 on October 31, 2024, 05:59:07 am: Quote from: gloriousfrance on October 30, 2024, 06:30:04 pm
I quadruple checked the 470k resistor, it reads 460k.
What I see in the pic sure looks like a 47Ω or 470Ω. NOT 470K. 470K would be yellow-violet-yellow. That's not what your pic shows. Double check that value and watch your meter closely. This resistor looks just like that 47Ω resistor just to the left in your pic. A low value resistor in that position would cause the Reverb pot to also act like a volume control.