This is a Howard 436-A communications receiver.
Restoration has been a challenge. The local oscillator dies on the Highest short wave band when going from the Highest frequency to the lower dial scale frequency. Usually an oscillator will die when going up in frequency.
The 436-a operates just fine on the next lower SW band at the same frequency as on the low end of the top SW band. I have replaced every cap associated with this band. Removed, cleaned and heat treated the oscillator coil (there is not much to it. Only three turns of number 20, 18 or 16 solid bare wire tapped at one turn). And rewound the secondary of the RF/IF coil (about three and a half turns of 26 magnetic wire that lost its insulation and shorted).
The Oscillator now works. After many attempts to change all associated components, washing the wafer switch with denatured alcohol (sometimes pulls out the moisture), baking the wafer switch did the trick. It now oscillates up and down the highest short-wave band. I held a heat gun (a hair drier would have worked, perhaps better, eliminating the high heat risk) near the wafer switch. I carefully monitored the other components for the affects of heat (melting wax and bowing wire insulation. I repeated the procedure once I detected an improvement in the low end range of the oscillator. It took about five cycles with the heat gun. It is winter here and rather cold and damp. A hot dry sunny summer day can also bake out the moisture. Now to run it for hours on end and "Burn in" all of the circuitry.
The other curios thing is the first RF tube is a 7H7 Loctail and not the documented 6SD7. The tube specs appear to be a close match in the Sylvania and RCA tube manuals. There was no publicly available schematic on BAMA or Nostalgia Air web sites. I relied on the schematic glued to the bottom of the chassis. I had to interpolate/calculate the max B+ from the tube specs and installed resistors.
The Electro Dynamic speaker has been retrofitted with a PM speaker and a separate choke of lesser DC resistance. This retrofit was accomplished by a previous owner. A series dropping power resistor was needed to set the B+.
I took the cabinet to my favorite Auto Body shop. The shop boss color matched the paint and added a crinkle finish. It looks FANTASTIC. www.RadioDaze.com created a custom decal set form my photos and font measurements. I believe they added this Howard series to their inventory. I can't say enough good things about the people at RadioDaze!
I restrung all three dial cords, removed the dial shafts that drive the cords to sand de-glaze and lubricate the shafts. I used high temperature lithium grease. The type used on automotive disk breaks bearing. It gives the shafts a smooth feeling when tuning around. Just DO NOT over lube the shafts or the grease will get on the cords.
Below are some pictures:
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