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Parasitic oscillation?

@ocdecio
Just wondering how your 1200 project ended. I just got mine back on the bench after a few years and move. I'd like to do some of the updates you mention above and have a short BOM at Mouser compiled. Not ready to power on yet. I want to test some of the transistors first.
Thanks,
John
 
nerdorama said:
@ocdecio
Just wondering how your 1200 project ended. I just got mine back on the bench after a few years and move. I'd like to do some of the updates you mention above and have a short BOM at Mouser compiled. Not ready to power on yet. I want to test some of the transistors first.
Thanks,
John
Click to expand...
My son uses it every day. The updates may or may not be necessary depending on what run is yours. You are wise not to power it on - first pull the drivers and pre drivers and make sure they are inside the gain range from the service manual. Check the resistors (there aren't too many) for any open or short. Look for physical damage. Check if your model uses the germanium diode or not. Many things really.
 
Mine is a very early serial number, 1208. Serveral years ago before I moved, I got to the point of having replaced every electolytic cap, all new output transistors, cleaned the pots, and that's about it. I turned it on once and didn't get any audio. Can't remember if the relay pulled in so now I'm starting again. I'll install new matched pairs for the differential amp, and check the drivers and predrivers. Not very excited to have to pull transistors to check them but I guess that's what it takes.
 
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