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I bought an old Webster Chicago (Webcor) Amp. It was originally setup with a mic and phono input (even had the original mic with it!!). It worked when I got it but was really setup very low gain. All the components were perfect for a Tweed Harvard (5F10) circuit...
6AT6, 12AX7, 2 X 6V6'S, 5Y3, VOL, VOL TONE
However, there is no HV bias tap on the power transformer.
OK, so I wired the whole circuit with some physical conversions to the small chassis. I also wired in the bias network by just tapping off of the Rectifier Plate. I also subbed a 1N4007 for the selenium rectifier.
THE AMP WORKS!! Surprise Surprise. But the bias is off. I used a 10k resistor from the tap instead of 6800 (cause I didn't have one) and my bias read -150 instead of -27. I read something about a 100K 1W resistor in that spot. I don't know how to figure out if that is correct. Can someone help me with the math?
P.S. I will post some photos when I'm all done cause it's really cute.
Thanks,
Doug
6AT6, 12AX7, 2 X 6V6'S, 5Y3, VOL, VOL TONE
However, there is no HV bias tap on the power transformer.
OK, so I wired the whole circuit with some physical conversions to the small chassis. I also wired in the bias network by just tapping off of the Rectifier Plate. I also subbed a 1N4007 for the selenium rectifier.
THE AMP WORKS!! Surprise Surprise. But the bias is off. I used a 10k resistor from the tap instead of 6800 (cause I didn't have one) and my bias read -150 instead of -27. I read something about a 100K 1W resistor in that spot. I don't know how to figure out if that is correct. Can someone help me with the math?
P.S. I will post some photos when I'm all done cause it's really cute.
Thanks,
Doug
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