Starting a 2204 build

glpg80 said:
This is progress. This tells me it’s something coupling in or around the first gain stage.

Back to the coax, do you use regular wire from the 68k grid stopper to the first stage?

If you clip a cap across the 68k grid stopper, does the frequency change?
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I have coax from the input jack to the 68k at pin 2. And coax from pin 7 to the gain wiper. I have the 68k heatshrinked, so I can't really clip a cap across it. Could I clip the cap from pin 2 to where the coax is connected to the input jack?
 
glpg80 said:
Yeah you can clip the cap that way, I want to see if it shifts the frequency at all.

Do you measure 68k from the Jack to pin 2?

Check the grounds for the very last filter cap and make sure the filter caps aren’t floating at B+.
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I think I may have found an issue with the heater wiring at v2. Moving the wires around makes the buzz go away, then it slowly comes back.
 
Is that heater wire solid core or stranded?

Loose tube pins making poor contact?

You’ve narrowed it down to heater wiring hum. I’ll give you a tip - make sure the 68k resistor is parallel to the chassis and not standing up like that. Not only is if close to the heater wiring, it can still pick up noise sticking in the air. Think of the chassis as guarding one side of the 68k resistor.
 
glpg80 said:
Is that heater wire solid core or stranded?

Loose tube pins making poor contact?

You’ve narrowed it down to heater wiring hum. I’ll give you a tip - make sure the 68k resistor is parallel to the chassis and not standing up like that. Not only is if close to the heater wiring, it can still pick up noise sticking in the air. Think of the chassis as guarding one side of the 68k resistor.
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It's stranded wire. I guess I'll try reflowing the heater wires on v2.
 
ledvedder said:
It's stranded wire. I guess I'll try reflowing the heater wires on v2.
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It’s potentially a layout issue as much as a solder issue. I think you need to also make sure you mess with plate, cathode, and grid wires to make sure moving those also doesn’t silence the buzzing. That will tell you it’s wire routing as much as heater solder quality.

Glad I can help you narrow it down.
 
glpg80 said:
It’s potentially a layout issue as much as a solder issue. I think you need to also make sure you mess with plate, cathode, and grid wires to make sure moving those also doesn’t silence the buzzing. That will tell you it’s wire routing as much as heater solder quality.

Glad I can help you narrow it down.
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I did move around the other wires, but it made no difference. It's only when I move around those heaters wires on v2.

Yes! Thanks for putting up with my novice experience.

I'll redo those heater wires and provide an update.
 
Now you know why random wires leftover had to be removed lol. It literally doesn’t take much to make these amps go unstable.
 
ledvedder said:
I did move around the other wires, but it made no difference. It's only when I move around those heaters wires on v2.

Yes! Thanks for putting up with my novice experience.

I'll redo those heater wires and provide an update.
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Also tighten the tube pins for the heaters.
 
ledvedder said:
Wait... Are you saying it's all these things? Or just steps of troubleshooting?
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He’s just saying all the things that touch the first stage that could cause this symptom or multiples of things that cause symptoms. That doesn’t mean they are the cause, you found the cause for you to be Heater related and the buzz sounds like 60Hz as well which makes me think it’s the cause.
 
ledvedder said:
How do I do that?
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Drain caps pull all preamp tubes and take a mini screw driver. Look into the tube socket (right side up) and you’ll see the tube sockets are C shaped. Using the mini screwdriver, make them more O shaped by wiggling/working around the edge of the socket to the pin. A little goes a long way - don’t go crazy otherwise the preamp tubes will be too hard to push back in.
 
Well, I got the buzzing sorted out. I rewired the heaters for v1 through v3. That didn't kill the buzz. So then I swapped around the wiring for v1a and v1b like Ceriatone's layout, and now the buzz is gone. I'm not exactly sure why that mattered, but it works. The low input seems a bit lower in volume than it did before, compared to the high input. But maybe it's just that the high input in louder now? Who knows... I just know that it works now!

I also added the 100pF cap on v1b that's in the Ceriatone layout, but that was after the buzz was gone. I'm not sure if that cap makes any audible difference or not, but I know it has something to do with taming oscillation.
JCM800_2204Ceriatone.jpg
 
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