Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ac427v on May 27, 2025, 08:22:17 am

Title: Dual 1MA pot for dwell-volume control?
Post by: ac427v on May 27, 2025, 08:22:17 am

I sometimes play my newly modified Deluxe Reverb build with the Volume control at maximum and the Master Volume on 3.
Internet lore says that this may result in damage to parts in the reverb driver circuit.
What would be the good/bad effects of reverse wiring the second half of 1 MA dual pot to reduce the dwell at high settings of the preamp volume?

Thanks in advance for your thoughts and experiences.

Title: Re: Dual 1MA pot for dwell-volume control?
Post by: stratomaster on May 27, 2025, 09:31:22 am

There's no damage to be had with that practice.  The biggest concern with master volume controls on AB763 type amps is the minimal headroom in the reverb driver being exposed, but you've already put in countermeasures for that by giving the reverb driver a dedicated HT node at ~350v and reducing the cathode resistor. 

You're absolutely fine to make no changes.  But if you want to add a dwell control, I'd be more inclined to replace the reverb control with a dual concentric pot at 250k/500k (500k as dwell, 250k as mix/"reverb") and scale the associated caps accordingly to keep the frequency response unaffected.

Title: Re: Dual 1MA pot for dwell-volume control?
Post by: ac427v on June 01, 2025, 06:38:11 am

Thanks Stratomaster, for taking a deep look at my schematic. Your analysis has me thinking that I have sufficiently reduced the risk of damaging the reverb components when setting the preamp volume at maximum. I will try playing this amp as built before trying to squeeze in a dwell pot. :worthy1: