03-04-2023, 02:44 PM
Hi Group -
Working on my Philco model 212 (early) had have done the normal things - tested transformer windings for continuity, tested tubes, replaced capacitors and resistors with modern ones. When I powered up, I have tunable hum from the speaker. Measuring voltages, all the power transformer voltages are in spec as noted in Service Bulletin #54.
For the tubes all filament voltages are normal. However for the tube plates voltage several are too high and some too low. Rectifier # 80 tube plates are 750 vac as they should be. But for all the # 24 tubes (1st RF, 1st Dect., 1st I.F., 2nd I.F., ) the plate voltages are all about 223vdc. when they should be ranging from 180-190 vdc. For the # 27 tube Osc. I have -1 vdc for the plate voltage when it should have 45 vdc. for the # 27 Detector Amp and # 27 1st A.F. plate voltages I am generally within spec. for the two 2nd A.F. #45 tubes, plate voltage are high too 321 vdc when they should be 255 vdc.
Ideas are what could be affecting the plate voltages like this? -- Andy
Working on my Philco model 212 (early) had have done the normal things - tested transformer windings for continuity, tested tubes, replaced capacitors and resistors with modern ones. When I powered up, I have tunable hum from the speaker. Measuring voltages, all the power transformer voltages are in spec as noted in Service Bulletin #54.
For the tubes all filament voltages are normal. However for the tube plates voltage several are too high and some too low. Rectifier # 80 tube plates are 750 vac as they should be. But for all the # 24 tubes (1st RF, 1st Dect., 1st I.F., 2nd I.F., ) the plate voltages are all about 223vdc. when they should be ranging from 180-190 vdc. For the # 27 tube Osc. I have -1 vdc for the plate voltage when it should have 45 vdc. for the # 27 Detector Amp and # 27 1st A.F. plate voltages I am generally within spec. for the two 2nd A.F. #45 tubes, plate voltage are high too 321 vdc when they should be 255 vdc.
Ideas are what could be affecting the plate voltages like this? -- Andy
Andy Sorrell
Palmyra, Virginia
