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Discussion in 'Shock Brother's DIY Amps' started by choosebronze, Jul 28, 2020.
And the smaller may also have soldering damage.
I replaced the .1uf cap you spotted D'tar. I inspected the .022uf cap up close and luckily that was just a drop of flux that splattered onto it. Was able to just push it off with my finger. Phew. I also shortened all the leads @Paul-T.
I would say with the resistors at the sockets, shielded wire, replaced components, shortened leads, elevated heater CT, etc... the static noise is much quieter and really only occurs now at Vol 11-12 with no instrument connected. I don't have a real Deluxe to compare it to, but that's sort of what I'd expect. So, thank you all! I've done so many things over the last week that I'm not sure which combination of things finally worked. I'll see if I can move the resistors back to the board when I get around to it, but if I have to leave them on the socket it's no big deal.
But V1 is still microphonic with several tubes tested. I'd say most of the time it has no audible effect. But I'd like to get whatever's causing it fixed so I know the amp's running properly. At this point I've rewired the input jacks several times and I just rewired V1 when I shortened all the leads. I apologize if my information isn't always clear but I've stood over this amp for hours now and I've tapped this tube with a pencil like 9,000 times... I think at this point, V1 is only microphonic on the Normal (V1A) side. With Normal Volume at 0 and Bright maxed, I can only lightly hear a tap on the tube. No microphonic singing or metallic noises. If I reverse those and max the Normal volume but turn Bright to 0, that's when I get full-on microphonics.
I can rule out the V1A coupling cap since I just replaced the melted one. I suppose that leaves the jacks, the volume pot itself, the tube socket, and the V1A load resistor? I have another 9 pin socket and more shorting jacks in the mail. Fingers crossed.
I had a similar issue: https://www.tdpri.com/threads/5e3-shhhhh-sound-diagnosis.322461/ for me I think fixing the input (removing the brass plate) made a difference but the hiss remains if I dime everything. (which I normally do not). There is a youtube link there if you want to compare.
Good for you on all your successful fixes. I lost track of this, but you say V1 is microphonic even when you switch in multiple 'known good' tubes? And it seems mostly or all on the 'Normal' triode? I think you're right to suspect the socket (if we're sure it's not the wiring/soldering to the socket).
You're getting a new socket? A trick Doug Hoffman suggests: solder it up with a used 12AX7 in place. This can even be a non-working one, *but* the pins should be straight. Theory is to put the springs in neutral alignment in case the soldering happens to fix them slightly in place. I try to keep my solder just at the lug eyelet, of course, but it can be hard in a crowded corner of the amp.
Well... I think this is all solved now. WOOO!! I really can't thank you all enough for all the help. Great tip @King Fan, Unfortunately I didn't see it until after I installed the new socket that came in today's mail. Luckily it seems like I got away with it. The amp is up and running. It sounds great! Nothing like a high quality amp to remind you that you really need to practice playing.
If I tap V1 now there's nothing microphonic. No ringing, no metallic sound. I do hear a dull thud through the amp. I vaguely remember experiencing that in the past with a different amp. So I fired up my Princeton Reverb, tapping the preamp tubes there makes no sound through the speaker. I guess now I've gone from troubleshooter to student. Is that ever normal behavior? Is something still wrong with my build? Does anyone have an explanation as to why that happens in some amps and not others?