05-25-2016, 08:21 AM
So after tearing my hair out trying to figure this filament string out I found the problem. I only had .5v across the 1LH5 tube and the two IF amp tubes where low too. Now the confusing thing is that these three tubes are in the middle of the string. The three tubes (osc and mixer at one end/ 1LB4 at the other) all show about 1.5v as they should. Also to confuse things a little since the filament act as the cathode there is resistors and caps in the filament circuit which can seem like it's the problem but it's a red herring.
The actual problem ended up being a bad connection at the 117Z6 supplying the hv to the dropping resistor (56). As for #56 there is a service bulletin stating that the original part is prone to fail (dropping in resistance then going open) and damaging the tubes filament. Philco did recommenced a replacement with a larger wattage resistor. Found a 25w unit that should do nicely.
Sam if your resistor looks like the one in my second pic you may replace yours. The philco replacement is a long candohm that is mounted upright on the top of the chassis behind the second IF transformer.
http://www.ebay.com/itm/LOT-OF-1800-OHM-...-RESISTORS
Onward to injecting some signals to hear what is working.
Terry
The actual problem ended up being a bad connection at the 117Z6 supplying the hv to the dropping resistor (56). As for #56 there is a service bulletin stating that the original part is prone to fail (dropping in resistance then going open) and damaging the tubes filament. Philco did recommenced a replacement with a larger wattage resistor. Found a 25w unit that should do nicely.
Sam if your resistor looks like the one in my second pic you may replace yours. The philco replacement is a long candohm that is mounted upright on the top of the chassis behind the second IF transformer.
http://www.ebay.com/itm/LOT-OF-1800-OHM-...-RESISTORS
Onward to injecting some signals to hear what is working.
Terry
