01-14-2011, 11:30 PM
I recently bought a 50-922 set. This is the model with the "sun dial" on top. I've re-capped it, new electorlytics, X1Y2 bypass cap, CL-90 thermister for gentle tube warmup.
The good news it it plays with good volume and the cabinet is in good shape with a fair finish and no chips or missing parts.
The bad is poor sensitivity, especially mid band (1MHz) and distortion on local stations. I suspect silver mica desease.
AVC voltage is very low - 0.7V on strong stations, 0.3V on weak. Resistors checked out in tolerance. The set uses a dual diode - triode (14B6. I rewired it to use one diode for the AGC (33pf to the plate of the IF stage and 470K diode load resistor.) Great AVC action, voltage jumped to 7V on strong stations. The IF distortion is gone. I do notice some distortion on very weak stations (volume control up most the way). On most stations it sounds great, but overall sensitivity is lower than it should be.
I aligned the set, the IF cans do peak, but broadly - about 1/3 turn to see a change. The RF stage is not tracking right. It aligns well at 580 and 1600, but is rather deaf at 1000. Re-peaking the RF trimmer at 1000 restores the sensitivity, but it is then increasingly deaf above 1200.
Any suggestions? My thought is to remove the IF cans and replace the silver mica caps - but what values to use? Anything else I should check?
Thank you
The good news it it plays with good volume and the cabinet is in good shape with a fair finish and no chips or missing parts.
The bad is poor sensitivity, especially mid band (1MHz) and distortion on local stations. I suspect silver mica desease.
AVC voltage is very low - 0.7V on strong stations, 0.3V on weak. Resistors checked out in tolerance. The set uses a dual diode - triode (14B6. I rewired it to use one diode for the AGC (33pf to the plate of the IF stage and 470K diode load resistor.) Great AVC action, voltage jumped to 7V on strong stations. The IF distortion is gone. I do notice some distortion on very weak stations (volume control up most the way). On most stations it sounds great, but overall sensitivity is lower than it should be.
I aligned the set, the IF cans do peak, but broadly - about 1/3 turn to see a change. The RF stage is not tracking right. It aligns well at 580 and 1600, but is rather deaf at 1000. Re-peaking the RF trimmer at 1000 restores the sensitivity, but it is then increasingly deaf above 1200.
Any suggestions? My thought is to remove the IF cans and replace the silver mica caps - but what values to use? Anything else I should check?
Thank you
