12-02-2020, 09:34 PM
Yesterday, I accidentally put a 130K resistor on the 50A5 Cathode, didn't work too well. That's one of those moments that describe experiential knowledge of cathode biasing as opposed to mere book or secondhand experience. It was sure quiet, an hour later I realized what I had done but I was out of resistors.
Amazing how the B+ voltage climbed to near 133V - I didn't run it very long at that level.
I put a new 150V in it today and it's back to making sound. Also added a 22uF cathode bypass capacitor in parallel.
At low volume it's fine. When the volume control reaches a certain threshold then the distortions shows up. Like a switch it kicks in. However you can touch pin 6 with the meter probe and the distortion goes away and it seems to work.
I have to agree that it seems that something is going on in the avc/agc. Maybe a I have another wrong resistor somewhere. Bad eyesight, I do almost everything under a lit up desk lens.
The DC voltages below reflect approx. 1/2 volume level and a local station is tuned in.
[Image: http://bingamon.com/Philco48-230/schemat...ltages.jpg]
Amazing how the B+ voltage climbed to near 133V - I didn't run it very long at that level.
I put a new 150V in it today and it's back to making sound. Also added a 22uF cathode bypass capacitor in parallel.
At low volume it's fine. When the volume control reaches a certain threshold then the distortions shows up. Like a switch it kicks in. However you can touch pin 6 with the meter probe and the distortion goes away and it seems to work.
I have to agree that it seems that something is going on in the avc/agc. Maybe a I have another wrong resistor somewhere. Bad eyesight, I do almost everything under a lit up desk lens.
The DC voltages below reflect approx. 1/2 volume level and a local station is tuned in.
[Image: http://bingamon.com/Philco48-230/schemat...ltages.jpg]
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