[Hammarlund] BAND change DIAL - SP-200 / BC-794 Oscillator mod, PURPLE FLASH!

[Rodney Bunt]

I need the band chang knob or even the band change plate that shows the band you are on for the
Super Pro 200

Bands are 1.2-2.5MHz 2.5-5MHz 5-10MHz 10-20MHz 20-40MHz

I am trying to do an alignment on this beast and just cant get the tuning right for band spread.

If I get the top of the band right I cant get the bottom of the band. In the manual TM-866 for the
military variants IE the BC-794 it mentions on the top band the dont Super Hetrodyne but sub
hetrodyne on the 20-40MHz band, do they do this on all bands on the earlier models ????? Set the
oscillator 465kHz LOWER than the RF ??? I will try this at home tonight.

Another strang thing about this rig is there is a "factory looking" Modification for the local
oscillator which uses a 6C4 tube, there is also a gas regulator tube to stabilise the plate volts.

The Octal tube socket has been punched out, and a rectangular hole punched in the chassis, not an
easy thing to do, but quite neatly done. Then two 7 pin tube sockets fitted, the "tube cap" grid
connection, is fed via coax, to the tube socket for the 6C4 except for a 47k resistor instead of
the 50M (50k) on the circuit.

BUT it looks like a wiring error, as the gas VR tube is on the input side of the +270v power
supply IE: PIN 5 of the POWER supply connector, I MEAN BIG PURPLE FLASH HERE !!!!! Moving the wire
for the VR tube to the plate of the 6C4 IE placing a 12k resistor in series with the VR gives the
desire 150V and no purpler flash. I received this radio with the VR tube socket empty, NO WONDER
!!!

All seems to be ok except the band spread issue. Maybe I have too much capacitance on the grid
connection to earth, as this would be in parallel with the Main tuning and the band spread
capacitors. If O cant figure this out soon I am going to put in a real 6J7 (wred as a triode) and
go back to factory!!!! Maybee there was problems getting this old 6J7 to oscillate at 40 MHz
inthis old girl. Any thoughts would be apreciated.

Regards,

Rodney
VK2KTZ



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