Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tdvt on May 02, 2024, 12:18:04 pm
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Sometime ago, while researching mitigating noise in Fender reverb circuits, it was mentioned in one thread that some noise might be reduced if Fender had not typically put the reverb transformer on the same B+ node as the screens, but used something more filtered.
I am wondering why the reverb B+ ended up where it did as far as the classic Fender reverb circuit? Higher voltage requirements? Or just not a friendly neighbor to the LTPI? (or even further down the B+ rail)
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That parallel triode 12AT7 is a small single ended power amp. You can even plug a speaker into the reverb out jack and use it as a small guitar amp. The circuit was designed to produce a LOTTT of reverb. That's probably why Leo used the screen node. I've always thought the reverb driver should have it's own more filtered B+ node. But look how many of those reverb circuits are out there. Those numbers say a lot too!
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If the screen supply node is following a choke filter, it will be as good a filter as you can get. And likely to be as high-voltage as you can get, allowing the plate of the reverb driver as much clean headroom as you can get. Will the driver still ‘work’ on a lower B+ node? Of course it will. Try it and see.
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Thank you both for your replies.
In one instance (my vintage PR), I DID move the reverb B+ to the unused node after adjusting rail Rs to keep the preamp voltages close to stock. Seemed to help.
I am wrapping up new build PR-ish project, which is what got me wondering about that again, but I have used a choke on this one, so it sounds like I am ahead of the game for now.