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Hoffman Amps Forum image Author Topic: plexi 50 modification question.  (Read 1949 times)

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Offline Curranm

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plexi 50 modification question.
« on: February 25, 2020, 03:29:02 pm »
I am going to build a hoffman 50 with the hot switch on a relay. At the 470K/470K voltage divider going into the next tube stage after the relay I w9ould like to put in another Volume/gain control. So I was going to replace the 470K to ground with a 500kA or 1MA pot. is the right spot for something like that? Everything else about the schematic will stay the same. just curious! thanks in advance for your help!

Offline PRR

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Re: plexi 50 modification question.
« Reply #1 on: February 25, 2020, 04:17:24 pm »
Sounds like a good plan.

Offline shooter

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Re: plexi 50 modification question.
« Reply #2 on: February 25, 2020, 05:10:17 pm »
Quote
I am going to build a hoffman 50 with the hot switch

I attached Dougs version, He re-purposes the 2nd input so there isn't any 470k voltage divider. 
Are you doing something different than His intent?
Went Class C for efficiency

Offline shooter

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Re: plexi 50 modification question.
« Reply #3 on: February 25, 2020, 05:55:14 pm »
 :think1:
missed 12b
Went Class C for efficiency

Offline Curranm

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Re: plexi 50 modification question.
« Reply #4 on: February 27, 2020, 08:50:16 am »
I am not really trying to break away from the 50 hotswitch plexi, BUT I have built one of these before AND I want to make the switched in stage a bit more fun and controllable with the added gain control. that is really where my noodle is at.

Offline sluckey

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Re: plexi 50 modification question.
« Reply #5 on: February 27, 2020, 10:03:25 am »
Just replace R12b with a 500K pot. One leg to ground, one leg to C3, and the wiper to the switch.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

 


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