|[AMRadio] Mobile RCVR converters|
John Coleman ARS WA5BXO
wa5bxo2005 at pctechref.com
Sun Jul 9 13:18:30 EDT 2006
K5SWK, Otis, had built several, band switched, 80, 40, 20 mtr
converters using 12 volt tubes. These were the tubes that you found in the
hybrid car radios. These car radios were all tube except for the solid
state output stage. I think they were used about 1960 to 1965 in GMC
vehicles. You historians may pin this down a little closer.
He built the first one for himself and then about five or six for
other mobile hams in the Houston area. These special tubes used 12 volt
heater supply and 12 for the plate supply, no vibrators or power converters.
The mixer/osc was one tube and a RF stage was another. He incorporated a
small amount of adjustable regeneration and adjustable gain in the RF stage.
The RF tune was extremely high Q and was able to reject very strong adjacent
channel signals. It would go into blocking while sitting in a drive way and
transmitting from the big rig in the house but all you had to do was tune
the RF tune off resonates and the blocking would quit. It was also very
sensitive probably due to the regeneration.
In the house, Otis ran a single 833 at a kilowatt input. The house
80 mtr antenna was up about 70-80 ft high and was near flat top. While the
big rig in the house was transmitting, he could burn out a #47 lamp
connected to mobile antenna yet not damage the RF stage in the converter
when it was connected.
It really was the best converter I had ever tuned and heard and you
could almost cover the face of the thing with your hand.
I can't recall all the people that had one but I know that Ronnie,
K5MKB, and Bill, WB5UMJ, did. He later built another for him self that had
an OSC running at about 1600KC for SSB/CW reception. With the old one he
had to engage the "SPOT" function of the XMTR to copy CW or SSB. When he
decided to build the new converter, he had not had a mobile rig for about 15
years. I think he gave the old one away. He said he was not going to build
a XMTR just for the "SPOT" function when all he wanted was to "read the
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