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Model 50A rebuild
#21

The model 50 is a tuned RF receiver, two tubes progressively amplify the radio signal. To do that effectively each stage with one tube has one section of the tuning condenser connected mechanically with a common shaft called the rotor. The rotor is at "ground" potential, the fixed set of plates are called the stator, these are insulated and each section is connected to its respective tube. The third section is for tuning the detector. It was difficult to make a precise tuning condenser with multiple sections, so attached to the stator is a trimmer capacitor consisting of a blade of metal, a wafer of mica for an insulator an insulated washer and a nut or screw to compress the package to change the capacity.

What may have happened is that one or more of the trimmers was mal-adjusted or damaged during the cleaning process.  By disconnecting the wire to the stator to each section of the tuning condenser an ohmmeter can determine if the trimmer has shorted. If the mica has been damaged it must be replaced. Mica can come from a salvaged tuning condenser, but if no mica can be found. A poor but workable substitute is a piece of PEET plastic taken from a water bottle, the thinnest and flattest as possible.

Plastic changes with temperature and moisture so it is not ideal but the radio will work at least until correct mica can be found.

With the tuning condenser now out of adjustment, if a station can be found around 1000khz, adjust the three trimmers to bring that station in the loudest. Any more precise adjust is possible, helpful is using an RF generator or a pocket transistor radio using its oscillator as a signal by local coupling. Follow any alignment instruction published by Philco. If a trimmer is tight and still not peaked (loudest signal the plastic is too thick...

Above assumes problem began with tuning condenser cleaning, but a short created during re-installation of the tuning condenser may have occurred too. Trace the schematic to the radio and do the measurements.

Chas

Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”


Messages In This Thread
Model 50A rebuild - by Mtmattking - 04-08-2024, 06:19 PM
RE: Model 50A rebuild - by GarySP - 04-08-2024, 07:43 PM
RE: Model 50A rebuild - by morzh - 04-08-2024, 08:30 PM
RE: Model 50A rebuild - by Mtmattking - 04-08-2024, 08:35 PM
RE: Model 50A rebuild - by Mtmattking - 04-08-2024, 08:37 PM
RE: Model 50A rebuild - by klondike98 - 04-08-2024, 08:51 PM
RE: Model 50A rebuild - by Mtmattking - 04-08-2024, 08:57 PM
RE: Model 50A rebuild - by klondike98 - 04-09-2024, 02:20 AM
RE: Model 50A rebuild - by Mtmattking - 04-09-2024, 09:56 PM
RE: Model 50A rebuild - by morzh - 04-11-2024, 07:01 AM
RE: Model 50A rebuild - by Mtmattking - 06-29-2024, 08:58 PM
RE: Model 50A rebuild - by morzh - 06-30-2024, 10:07 AM
RE: Model 50A rebuild - by Mtmattking - 06-30-2024, 11:41 AM
RE: Model 50A rebuild - by morzh - 06-30-2024, 12:16 PM
RE: Model 50A rebuild - by GarySP - 06-30-2024, 03:25 PM
RE: Model 50A rebuild - by Mtmattking - 07-06-2024, 07:26 PM
RE: Model 50A rebuild - by morzh - 07-06-2024, 09:20 PM
RE: Model 50A rebuild - by Mtmattking - 07-07-2024, 12:00 AM
RE: Model 50A rebuild - by RodB - 07-07-2024, 08:24 AM
RE: Model 50A rebuild - by Chas - 07-07-2024, 08:50 AM
RE: Model 50A rebuild - by Paul Philco322 - 07-07-2024, 12:19 PM
RE: Model 50A rebuild - by GarySP - 07-07-2024, 02:19 PM
RE: Model 50A rebuild - by morzh - 07-07-2024, 06:33 PM
RE: Model 50 Capacitor values - by Mtmattking - 04-08-2024, 09:39 PM



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