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38-690 Missing amp and 14" woofer
#11

I acquired a NOS 6B8 and 6R7. The diode sections on the new tubes tested much higher (read about 40 on tube tester, VS 11-15 for old tubes). It would not surprise me if the old tubes would work in the circuit. I have now finished fabricating the 2 sockets that duplicate the sockets on the missing amp that the receiver chassis plugs into. 1.5" Dia nylon rod was used to fabricate the shells, the 10 pin female contacts are the same as what are used for a PATA computer hard drive power connector. Receptacle pins for the other socket came from 3-4 pin sockets that would fit a 2A3 tube. All items were found on Ebay. The 4 pin socket pins were held into the original shell by a nut. Remove the nut, and the pins come out, and can be inserted into the new shell after wire leads are soldered on. I have fabricated a voltage divider resistor board that will power the receiver chassis from the jukebox amplifier. I have re-capped the amp, and removed all components that were used in the jukebox control circuitry. 2 Hammond 6.3 V 4A filament transformers were added to provide the separate F1 and F2 filament feeds as on the original amplifier. I don't know that is necessary to have 2 separate feeds, but the designers must have had a reason for doing this. Perhaps it was just the ratings of the transformers they used, or perhaps it was an attempt to avoid feedback through the heater circuits. I didn't use the jukebox filament source because I wanted to avoid the possibility of overloading the amplifier filament transformer.


Messages In This Thread
38-690 Missing amp and 14" woofer - by peteivan - 10-31-2012, 02:01 PM
RE: 38-690 Missing amp and 14" woofer - by Arran - 10-31-2012, 10:27 PM
RE: 38-690 Missing amp and 14" woofer - by peteivan - 11-29-2012, 03:03 PM



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