Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jhj on December 15, 2023, 05:15:02 pm
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I recently completed a Hoffman 50w Plexi. It works well but needs a bit more “bite”. I added a bright cap to channel 1 (47pf) after trying a 500pf.
What else can be done? Anything with the NFB? Move it to the 4ohm connection, perhaps?
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Hoffman Amplifiers Plexi50 – with Hot Switch Gain Mod
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Try a 56k for R16 if you're just looking for more high end.
I assume you've tried jumping the channels? If not, put a jumper wire between pins 2 and 7 on V1. This will activate both volume controls. Acts as a gain boost and an eq. People normally turn up channel 2 for dirt and bite and just turn channel 1 up enough to fill out the low end.
Failing that, there are entire companies formed based on the modification and perfecting of this circuit.
I think these two suggestions are a good start.
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As sluckey said, try using the Hot Switch mod. I wired it always on in the one I built.
And, what stratomaster described sounds worth trying, too. And, probably less trouble to add!
[edited to remove my PDF that has errors]
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Hoffman Amplifiers Plexi50 – with Hot Switch Gain Mod
https://el34world.com/schematics.htm#Mods%20and%20Projects%203
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I had considered the hot switch mod and may still decide on that direction. However, internally connecting the V1 inputs is a great suggestion that I’ll try first.
I’ll report back. Thanks.