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EL 34 Red Plating - What to do?

Not able to see clearly if pin 1 and 8 are connected on your pic. Please check to make sure.

Also check to make sure the pink (to pin 6) and the black (to pin 1) resistor legs are not touching or too close to each others.
 
Thanks! I have a matching quad of 1.2K's that I think are 1/4W but not sure??? And yeah, I agree that I need to dig deeper, but when the caps are wired to the wrong places, I'm thinking the .22 should all be connected to PIN 5 via junction at PIN 6???
 
Plugged it in, and it would seem like there is a ground problem as the amp “hums” with a steady tone... The signal is there, and is clear, but the hum coming through the speakers is rather loud. Ground problem?
 
1. Hum on both channels? Same hum?
2. Can you disconnect the inputs and connect cheap speakers to the amp. Turn the volume up and down to see if the hum noise changes.
3. Was there any hum before?
4. Was the output transformer buzzing?
5. Power transformer buzzing?
 
bbqjoe said:
I don't know, any number of things.
Voice coil shorting, crossover problems, speaker blown all together?
Click to expand...

so theoretical question, not a specific case of your speaker being busted.

The only thing tube amps really get unhappy about is being run with no load at all, and thats mostly only if you crank the volume up. The voltages can swing very wildly in the transformer and it can cause the insulation to fail and kill the transformer. Otherwise I doubt anything bad would happen to the tubes with a malfunctioning speaker that was still making some noise and presenting some amount of load.
 
There was no issue prior, this is something new altogether.



audio3000 said:
1. Hum on both channels? Same hum?
2. Can you disconnect the inputs and connect cheap speakers to the amp. Turn the volume up and down to see if the hum noise changes.
3. Was there any hum before?
4. Was the output transformer buzzing?
5. Power transformer buzzing?
Click to expand...

will pull some old speakers and see


audio3000 said:
Are you using 3 pin or 2 pin AC connector. According to the SLI-50 user guide:

View attachment 1795001
Click to expand...

3 pin... Think I have an adapter to get rid of the ground connection


audio3000 said:
Also potential loose ground on the RCA connector?

Is it still hum when the interconnects are unplugged?
Click to expand...


I’ll check when I attach new speakers. But this has never happened before.


audio3000 said:
Also, was the bias readjusted after EL34 changed...

View attachment 1795016
Click to expand...



I have the second version which does not have a bias adjustment. It is supposed to auto bias...


Will follow up in a bit


Thanks!
 
Ok. Plugged it in, no source. Removed the ground pin from the plug. Hum is there. It’s constant, and does not change with volume. There is some static that comes and goes as it powers up and drains when powered down. No physical noise from transformer(s). Checked everything that I touched when re-soldering, and nothing seems out of place. It has never made a noise like this before?
 
Was it playing music properly except the hum?

Do some tests to isolate the source of hum. No input connection to anywhere and using 2 pin AC plug:

1. Pull the 12AU7, test for hum
2. If still humming, pull 12 AU7 and 6SN9, test for hum
3. If still humming, pull all tube and test for hum.
 
1. Still hums when 12au7’s pulled
2. No hum when 6SN7’s pulled

Music plays clearly under hum, but it’s quiet.

Hum is in both channels...

thanks!
 
Can you take a very high resolution clear picture on how the components are connected and paste the pic here. I think it's time to trace the connections together.

Do you have a multi-meter to measure both DC and AC? I want to check the DC power and it's AC ripples?
 
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