Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: spunko on July 16, 2023, 10:57:15 pm

Title: Fender Twin Reverb RI - What would happen if lower the capacitors value?
Post by: spunko on July 16, 2023, 10:57:15 pm

Hello good people, I came across this picture of a Twin Reverb RI where the caps have been replaced with Sprage Atoms, but the main issue here are the two 80uF, these should be 220uF each. Does this mean it will induce more AC ripple or hum?

(https://i.imgur.com/tD8SdjU.jpg)

Title: Re: Fender Twin Reverb RI - What would happen if lower the capacitors value?
Post by: PRR on July 17, 2023, 12:51:24 am

Isn't the factory spec two 220uFd @ 285V in series?

So like 110uFd @ 500V?

I can't see how those Atoms are really wired. If really giving 40uFd @ 800V, that's an odd thing to do.

Title: Re: Fender Twin Reverb RI - What would happen if lower the capacitors value?
Post by: Latole on July 17, 2023, 03:09:09 am

65 Twin Reverb RI


In my opinion, it was a mistake to set these small capacitor values.
If it doesn't generate more noise, the amplifier will lack "punch", especially at medium and high power, and no doubt bass.
All things that require a lot of reserve current that only the right value of capacitors can provide.

Really, there's a lot of nonsense on the web when it comes to DIY.

Title: Re: Fender Twin Reverb RI - What would happen if lower the capacitors value?
Post by: Latole on July 17, 2023, 03:19:17 am

Quote from: spunko on July 16, 2023, 10:57:15 pm

Hello good people, I came across this picture of a Twin Reverb RI where the caps have been replaced with Sprage Atoms, but the main issue here are the two 80uF, these should be 220uF each. Does this mean it will induce more AC ripple or hum?

(https://i.imgur.com/tD8SdjU.jpg)

Picture from Telecaster forum

https://www.tdpri.com/threads/fender-twin-reverb-65-reissue-cap-job.785148/

Title: Re: Fender Twin Reverb RI - What would happen if lower the capacitors value?
Post by: sluckey on July 17, 2023, 04:50:12 am

Quote from: spunko on July 16, 2023, 10:57:15 pm

Hello good people, I came across this picture of a Twin Reverb RI where the caps have been replaced with Sprage Atoms, but the main issue here are the two 80uF, these should be 220uF each. Does this mean it will induce more AC ripple or hum?

There will be more AC ripple at the first filter node but the common mode rejection of the push/pull output stage will take care of that. And the choke and other filter caps will reduce the ripple to hum free levels for the rest of the amp. Leo thought two series connected 70µF caps were sufficient in the AB763 TR (https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_ab763.pdf).

Title: Re: Fender Twin Reverb RI - What would happen if lower the capacitors value?
Post by: tubeswell on July 17, 2023, 09:25:40 am

Quote

65 Twin Reverb RI…


there’s a lot of nonsense on the web.

RI = ‘Re Imagined’ LoL