Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tmknight on November 14, 2021, 12:05:45 pm

Title: Yet another JCM 800 Mod: Good or bad design?
Post by: tmknight on November 14, 2021, 12:05:45 pm

OK, this is more of a question of "how" to implement rather than "should I".  I've already arrived at what I'm changing and what values will be applied.  My plan is where I'm looking for some constructive feedback.  My approach is to put it on a perf-board so I could completely switch-off the circuit(s) as desired. 

Update:
Implemented and safely working as designed.  You may wish to consider an electrolytic for the C2 (layout) bypass cap.

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: sluckey on November 14, 2021, 12:17:07 pm

A schematic would be much easier to understand.

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: shooter on November 14, 2021, 12:47:10 pm

Quote

but rather is it safe?

with a schematic it'll be easy to see if you're switching HighVolts DC and signal or just signal

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: tmknight on November 14, 2021, 02:22:49 pm

Thanks, gents.  From the "standard" 2204 schematic, splitting the "straight line" V2b cathode to tone stack and inserting the clipping circuit.  So, my thinking is that it is "pure" signal, albeit with quite a bit of DC.  This is a well-known/proven mod in and of itself, just haven't seen it switched in this same way...most leave in the res/cap and "eat" the signal loss.

Thanks, you've given me the pointer that helped me think through it...

Cheers!

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: thetragichero on November 14, 2021, 04:07:18 pm

a picture is worth a thousand words, even when it comes to a relatively common design. it's not so much pedantry but accuracy: we wanna make sure your thing works when you're done!

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: tmknight on November 25, 2021, 10:36:38 am

 :thumbs:

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: sluckey on November 26, 2021, 03:38:51 pm

 

Quote from: tmknight on November 25, 2021, 10:36:38 am

:thumbs:

:thumbsup:

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: 66Strat on November 27, 2021, 09:55:32 am

Are there posts missing from this thread? I seem to recall at least one post with the layout for this mod that appears to be missing.

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: sluckey on November 27, 2021, 10:47:25 am

The layout was in the original post but he removed it yesterday.

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: 66Strat on November 27, 2021, 11:01:56 am

So much for information sharing.

Title: Re: Yet another JCM 800 Mod: Good or bad design?
Post by: tmknight on November 27, 2021, 02:51:07 pm

Updated