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June 27, 2022, 04:46:40 PM

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Sears/Silvertone 40XL solid state amp schematic

Started by galaxiex, October 10, 2016, 12:37:47 AM

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BBailey

I did monitor V+ and A voltages and they held steady when the fault occurred. V+ at 26 VDC and A at 22
I have changed both C10 and C20

galaxiex

Do you have a scope to check the oscillator waveform?

If it ain't broke I'll fix it until it is.

BBailey


Jazz P Bass

You do not 'have' to have a scope.
You can see the waveform with your meter set to read Volts Ac.
In your case the tremelo is stopping.
So if you monitor the transistors you can see it.
I would start with Q10.
Base & or the emitter.

galaxiex

Its been quite some time....
....but I think I replaced both Q9 and Q10 on my 40XL.

Old guy memory here, but I also think I had a similar issue with the tremolo fading out.

Just went and looked, and I did indeed replace them with generic 2N3904 transistors.

If it ain't broke I'll fix it until it is.

BBailey

Thank you for the tip. I'll look for that in the morning.
cheers

gstang

galaxiex, I have printed out your schematic and layout from post #19. Thanks, I think its the only one on the planet! I'm not sure about the schematic yet but the layout is somewhat different from the 40XL that I'm working on. From the pot date codes this one looks like a 1971. (Sears 257.142220002). Not a good sine wave @ the output on the scope when on channel 2, channel 1 is okay though.