Silverface Champ mods?

[Bruce / Mission Amps]

Hmmm... not really... I have used larger values like 100nF and then run a 220K resistor to ground using the other side of the DPDT... that would be inbetween the and before the volume pot end of the cap so it acts like a voltage divider when engaged. It can get pretty wild with the many extra dB of signal bypassing the tone controls.
I think those pots have the on off switch at the begining of the pot rotation as view clockwise turning the volume up.
They work good as an on-off switch volume control like and Old Champ would have with no seperate on-off toggle.

[Tim Hall]

Bruce,

Do you think subbing the 12AX7 for a 5751 would help tame it, or does the drop in gain defeat the purpose? Also (referring back to my earlier question in this thread), could you replace the fixed resistor in your mod with a no-load pot to have variable gain? Sorry if these are dumb questions - like I said, I'm new to this.

[Bruce / Mission Amps]

Bruce,

Do you think subbing the 12AX7 for a 5751 would help tame it, or does the drop in gain defeat the purpose? Also (referring back to my earlier question in this thread), could you replace the fixed resistor in your mod with a no-load pot to have variable gain? Sorry if these are dumb questions - like I said, I'm new to this.

Sure you could use a pot but that is what the volume control is already doing.
The resistor I mention is to create a filter, to cut some of the harshness and the other resistor, (which would be grounded) will form an AC voltage divider, stearing some of the raw audio off to ground to reduce signal level.

I'd experiment with a 12AY7 and a 5751.

[Tim Hall]

Bruce,

Thanks for the reply. I understand all this better now. I suppose what I’m aiming at is being able to shape the tone somewhat while mixing in a little bit of the raw signal.

I‘m imagining (with my non-technical imagination) something like a 1Meg pot effectively acting as a kill switch (for the bypass) if turned all the way up, preserving 100% of the signal path through the tone stack. When turned down I imagine it dialing out your ability to shape the tone as it dials in more raw signal.

Maybe the ability to do this isn’t worth the effort or extra parts.

[Alex R]

Champ neg feedback

...as some of the links in the posts have mentioned, removing or reducing the negative feedback around the OT makes a big difference to these amps - seems to bring them alive, and delivers a nice gain increase. Generally there are no problems if you completely remove the resistor (the 2K7 wired from the speaker jack). Simpler.

A.

[bob p]

I think those pots have the on off switch at the begining of the pot rotation as view clockwise turning the volume up.
They work good as an on-off switch volume control like and Old Champ would have with no seperate on-off toggle.

I thought the Log Taper/SPST pot/switches were rotary on/off switches, like those you described for the champ.

What threw me for a loop is the Linear Taper/SPDT pot/switches. I can't understand the reason for an SPDT switch if its a rotary on/off type. To me, it would make sense if those were push-pull, so I just thought I'd ask if anyone was familiar with them.