09-01-2009, 10:56 AM
I just finished rewiring and recapping my 42-355. I get nothing but some hum, so I'm starting the troubleshooting process by measuring voltages. The B+ seems to be low, compared to the schematic values.
The AC is about 121 volts, and the output of the rectifier (across the 1st filter cap) is 277 VDC instead of the 290 on the schematic. The B+ across the second filter is about 165 instead of 190, and I get 160 and 165 at the plate of the two 41 output tubes. Schematic values are 185 and 190. I didn't replace the candohm resistor because the resistances are close to spec, but I could try that next.
I'm not sure this is enough difference to matter, but I thought I'd ask some wiser heads here on the forum before I went any further. I'm concerned that the plate voltage on the oscillator XXL will not be enough if the B+ is 25 volts low.
I get audible clicking when I touch my soldering iron onto the plates of all the tubes except the oscillator, but I don't get anything when I inject a 455KHz modulated signal into the signal grids of any of the tubes, so I might have wired something wrong somewhere.
Any thoughts? I have another 42-355 chassis that I could pull the power transformer from if needed to get the proper B+ voltage (assuming that transformer is good.)
The AC is about 121 volts, and the output of the rectifier (across the 1st filter cap) is 277 VDC instead of the 290 on the schematic. The B+ across the second filter is about 165 instead of 190, and I get 160 and 165 at the plate of the two 41 output tubes. Schematic values are 185 and 190. I didn't replace the candohm resistor because the resistances are close to spec, but I could try that next.
I'm not sure this is enough difference to matter, but I thought I'd ask some wiser heads here on the forum before I went any further. I'm concerned that the plate voltage on the oscillator XXL will not be enough if the B+ is 25 volts low.
I get audible clicking when I touch my soldering iron onto the plates of all the tubes except the oscillator, but I don't get anything when I inject a 455KHz modulated signal into the signal grids of any of the tubes, so I might have wired something wrong somewhere.
Any thoughts? I have another 42-355 chassis that I could pull the power transformer from if needed to get the proper B+ voltage (assuming that transformer is good.)
John Honeycutt
