|This project came out of an old console piece that was once a fine piece of furniture. As with many electronics these days, there was a need to miniturize so we are rebuilding this for a smaller cabinet. Unfortunately, it was powered on before checking anything, and one of the output tubes was shorted, which in turn took out the output transformer along with a couple other components. To make a long story short, I located a replacement transformer from a chassis found on eBay. For info on why you shouldn't power up older equipment that hasn't been used for a long time, and what I do to prevent catastrophic failures, read this.
|Testing all the caps on my Sprague Capacitor Analyzer showed them all to be out of tolerance so I replaced them all. Including the power supply filters. (See further down)
|So after a new troop of push-pull valves...
...there was some reason why I couldn't get a good signal through them.
They began singing like angels
|After realizing the heaters on the phono input tubes I removed and rewired (this will never be used with a phonograph again) were in series as a common-cathode resistor for the finals...
...I added a reststor where they used to be, and...
|Frequency sweep of 1000 hz to 5000 hz
(I call this my 'Elephant' test.)
|As I was attempting to adjust the ratio detector, I noticed the secondary slug was difficult to turn. Upon further inspection the ferrite slug had cracked. I was reminded why I pilfer so much stuff from old radios...had one! It was much easier to align with a fresh slug.