Strange things afoot at the combo amp motel

[WRC34]

https://youtu.be/QVxM1BWDXLM?si=IIqi4BNjH4tgs6uX

Here it is

[Colossal]

Very good sounding amp! Did you go with 500k or 1M pots for Volume and Tone? Also, your Tone cap says 333k. That is 0.033uF. Did you choose that value to roll off some serious brightness? The amp does not sound overly bright in your video.

Also, it may be nothing, but check this out. It looks like the tone control ground conductor is touching the pot but not soldered to it. I can see that it is grounded on the terminal strip ground, where it should be.

Tone Control.png

[WRC34]

Hi Colossal - thanks and good eye there!

I believe the pots are 1M.

The tone cap probably snuck its way into my little drawer labeled “.01 uf” and I must have just grabbed it without looking closely when getting all the parts together. Once a build gets going I start to chuck along at a pretty good pace as I am relegated to working at night once my kids are asleep

I felt like the amp was actually less bright than anticipated when I first completed it, and the .033 in place of an intended .01 would certainly explain why. That being said in hopes of cutting a little bass when I swapped out what I thought was the problematic coupling cap I went with a .015 in place of the .022. I’m happy with the general tone and once I get this issue resolved probably will leave the .033 in there!

If the ground tab on the tone pot is touching the back of the pot that would be unintentional. I haven’t connected that tab to the pot in any build so far. Should it be that way??

I won’t have a chance to get back in there and root around until I get home in late March. Til then keep the theories coming & thx again!

[Colossal]

Hi Colossal - thanks and good eye there!
I believe the pots are 1M.

Thanks.

The tone cap probably snuck its way into my little drawer labeled “.01 uf” and I must have just grabbed it without looking closely when getting all the parts together. Once a build gets going I start to chuck along at a pretty good pace as I am relegated to working at night once my kids are asleep

I felt like the amp was actually less bright than anticipated when I first completed it, and the .033 in place of an intended .01 would certainly explain why. That being said in hopes of cutting a little bass when I swapped out what I thought was the problematic coupling cap I went with a .015 in place of the .022. I’m happy with the general tone and once I get this issue resolved probably will leave the .033 in there!

If that 33n cap is working and there is a good sweep to the pot without it getting dark and muddy immediately, hey, why not?

If the ground tab on the tone pot is touching the back of the pot that would be unintentional. I haven’t connected that tab to the pot in any build so far. Should it be that way??

I don't like to ground the tabs to the pots in any build. There should be dedicated local grounds for each B+ node. I might trim that excess lead short just to ensure it is not touching the body of the pot in any way. The ground for that tone circuit should be at the B+3 node, on the terminal strip, as you have it. No other connections which might cause ground loop issues.

I won’t have a chance to get back in there and root around until I get home in late March. Til then keep the theories coming & thx again!

[WRC34]

Guys! I have been home for a few days but just got a chance to get back to the amp.

Colossal, the wire you spotted - I snipped it late last night but only this afternoon got a chance to give it a go. I think that was it!! I played the amp for 10 mins straight, cranked, 5AR4 rectifier, hottest it could get and it held together beautifully without a trace of the problem. I owe you a beer…or four! Where do you live? I’m coming over to celebrate!!

Made a quick video of the amp being run with me playing some slop through it to showcase Colossal’s genius

https://youtu.be/50o9kczLhxA?si=yMHdRQ5__DLZcg80

Thanks again everyone!!