It was then suggested to recap the phono board. all caps were replaced with hi end ones of the same value. At that time, we installed new issue matched Mullards in the phono stage. The next test produced a TON of hiss, and what I think was the documented impedance issue I had read about. Replacing with the old tubes took away the hiss, but issues started developing with the left and right outputs, with one louder than the other..
It was then suggested to replace the selenium rectifier. A rectifier board was sourced from dynacodesigns.com At that time, a new RCA board was sourced from Dynakit. To resolve the impedance issue, a matching impedance board was purchased from dynacodesigns. Those parts were installed and the phono stage tested. hiss was gone, but a new hum was introduced. All wiring instructions were followed by a qualified tech to the letter. After the impedance matching board was installed, there was a single ground line left from point 1 on the line board that was originally terminated at the RCA board. None of the supplied instructions for either the filament heater, or the impedance board mentioned reattaching this wire. It was attached to the original ground spot on the rca board. testing again, we had no sound at all thru t he phono section. the tube in that board closest to the rca board glowed extremely bright and was too hot to touch after we powered it down. the other tube, did not appear to glow much or at all.
We attached a line source and it appeared to play fine. we shut down the dynaco, and it still passed sound. i think we may have been on the tape out. all tubes were removed and it still passed signal when powered off. Is that tape out just a pass thru for the various inputs?
Anyway, my tech is at loss where to go from here. I am awaiting a reply from the gentleman at dynacodesigns dot com to see if he has any ideas since the filament board and impedance board were sourced there.
Any ideas on what may have caused the original hum? Im inclined to have my guy remove the impedance board and retest things. I'd like to use the tone controls if possible so bypassing them isn't an option unless all else fails. Any advice would be appreciated. Thanks
Sorry for a lengthy first post