Trouble Shooting and Alignment

Part Two

HALLICRAFTERS S20R COMMUNICATIONS RECEIVER


Now that the mechanical restoration of the S20R is complete; dials clean, new dial cords installed, tube sockets cleaned, cabinet finished, lettering decals applied, main tuning capacitor removed-cleaned and plates aligned,caps and resistors replaced along with rotten or questionable wiring fixed-according to schematic- its time to begin the trouble shooting and alignment phase of the project. At the close of Part I, at first power up I noticed the plates of the rectifier tube 80 were glowing red hot. Shutting down the power, I checked wiring against schematic- wiring was correct- The transformer was suspicious because of its physical condition- all leads were removed and winding resistances were checked in accordance with the Marcus and Levy Text -data noted near end of Part 1. A new transformer was ordered and the installation is as good a place as any to begin the Trouble Shooting segment of the project.

Note: I am documenting this project as an entry tech class operator with some Ham Radio experience, kits, home-brew etc. These notes are provided along with reminders to use safe practices during all restorations, use safety eye ware, employ proper grounding of receivers and test equipment and use extreme caution working around the high voltages in this and other so-called boat anchor receivers. Good luck in your projects and stay tuned to Antique Radio Forum.

Mike Malsbary
K4CWN-ticket expired 1969,
1965-N0EFD-Chu Lai S.Vietnam,
1965-W6IAB-Camp Pendelton California,
1964-KR6MB-Camp Schwabb Okinawa
1967-MARS Station Marine Corps Base Eltoro

mmwnj2@verizon.net

"Restore it before it's gone forever."

RESTORATION INFORMATION S20R

Hallicrafters Communication Receiver #126721-circa 1934

Information Source Location Data Type
A fresh new transformer was located and in time was installed onto the S20R chassis. Resistances of all windings comply with Marcus and Levy text. After re-installing the AC line through the on/off switch to the Primary and checking output voltages at all terminals, all leads, (5 VDC filament to the 80 rectifier, 6 VDC filaments/ panel lights, B-plus,will be connected) in that order. Check for filament glow in 80 and rest of the line up- the B-plus will once again be connected. Prior to the transformer problem the brief power up did generate a weak background noise in the speaker, the tone control worked, the RF Gain did raise and lower the weak noise level. The Audio Gain had no effect at all. During the down period, wiring in the Audio Amp section was double checked- as was the Audio Gain pot, all found to be correct per schematic. So once the transformer is fully connected - the restoration process will proceed and recorded here. MikeMalz www.antiqueradios.com/forum Trouble Shooting per Marcus and Levy Text
The effort here is to practice the fundamental trouble shooting instructions of Marcus and Levy on this receiver. To build a skill. Prior to the transformer problem, during the brief power up the first trouble shooting practice was applied. A AF signal, attenuator set for max output, Signal Generator ground to chassis ground and the "hot" lead through a .1uf 600VDC capacitor- (the condenser keeps plate voltage present in the 2nd AF tube from getting back into the Sig.Gen. circuits.) The 2nd AF tube was checked as follows:

Power on- using established variac/isolation transformer hookup- the 2nd audio tube 6F6 was located. On the schematic is it the last tube leading into the audio transformer and speaker. The "hot" probe was applied to the plate terminal (pin 3) and a faint signal should be heard in the speaker. This was done and a faint tone was heard. Next the "hot" lead was placed on the grid of the 6F6. (pin 5) A significantly stronger tone should be heard in the speaker. A stronger tone was heard. (the gain in volume is the gain of the tube) With the results noted, per Marcus and Levy "this stage is functioning."

MikeMalz www.antiqueradios.com/forum Trouble Shooting per Marcus and Levy Text
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