Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Esquirefreak on June 08, 2024, 03:51:30 am
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Anyone here tried driving a reverb tank with a dual triode tube in push pull - rather than parallel SE like in Fender amps? Thinking that hum rejection would probably be better? Any direct down sides?
Just thinking out loud here.
/Max
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You’ll need to think about how you achieve phase inversion - self-split vs another stage for PI etc. And the PP xformer. Go for your life.
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The Silvertone 1484 (https://el34world.com/charts/Schematics/files/Silvertone/Silvertone1484.pdf) used a twin triode push/pull cap coupled reverb driver in it's cheesy circuit.
Not exactly what you asked for but probably worth a look/see. The Ampeg Echo Twin (https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_et1_echotwin.pdf) used a foldback reverb circuit. The reverb tank was driven from the push/pull output transformer.
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Kevin O’Connor has a push/pull reverb kit on his London Power web site.
I don’t know if this is covered in any of his TUT books
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Maybe a solid state phase inverter would do the trick? Like a cathodyne mosfet? To clarify, I'm not aiming to build anything (yet). Just thinking about alternative ideas. Might be unnecessesarily complicated, though.
Thanks everyone!
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Kevin O’Connor has a push/pull reverb kit on his London Power web site.
I don’t know if this is covered in any of his TUT books
Yes, it's in his books.
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... Thinking that hum rejection would probably be better? ...
Most people don't turn their Reverb control full-up. That implies there is plenty (too much?) reverb available if wanted.
"Hum Rejection" would only be hum present in the power supply when thinking SE vs PP.
- We could simply feed the reverb transformer from a different, more-filtered point in the power supply.
- We would reduce total supply-voltage available at the reverb transformer, which could limit how hard the tank is driven.
- However, the observation earlier suggests we don't need as much reverb-drive as we have, so some reduction would be acceptable.
The challenge of a push-pull reverb transformer is that London Power seems to be the one source (though I suppose one could buy over-capable transformers from other places).
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I was thinking maybe the Hammond 125B would be a good choice? 5w push pull with a multiple primary impedance alternatives. 22,5ΚΩ for one.
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Maybe steal some ideas from the Firefly...
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Cool! Thanks!
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Yes you can use a push-pull driver, and yes it is more immune to PSU hum and magnetic hum from the PT. The Vox AC30TBR used a push-pull driver for a 600 ohm tank.
Note that KOC's push-pull driver seems to have a drawing error in it; the tail resistor is way too small.
Here's a push-pull driver I have used, the OT is a small power transformer. An SRPP (http://valvewizard.co.uk/reverbdriver.html) is also a push-pull driver, technically speaking!
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That looks awesome, thank you!
/Max