"Bob in PHX" wrote in message
news:4kQZd.112804$bu.90490@fed1read06...
To All,
A recent ham fest has left me with two new toys. A Hallicrafters s-120 (4
tube wonder) and a heathkit QF-1 q multiplier. I would like to hook them
up
together, but need some very explicit help in doing so.. I will need
someone
to help me understand the s-120 schematic and help in me install the QF-1.
any takers....

bob in phx



Are you going to run them off an isolation transformer?

The S-120 has no power transformer. One of the power wires is soldered to
the radio's internal common wire.

The QF-1 takes power from the radio. The common wire of the QF-1's power
lead and the shield of the coax are connected to Q-multiplier's case, if I
recall.

The S-120 already has regeneration. The "BFO" puts the IF stage into
oscillation. The IF stage is still regenerative when adjusted just short of
oscillation.

I suppose it would be possible to rewire the heater circuit of the
Q-multiplier to operate on 150 ma and to interrupt the radio's series heater
string to power the Q-multiplier's heater. Heathkit recommends a minimum of
150 of B+ to operate the Q-multiplier and the highest voltage inside the
S-120 might almost be that high. Unfortunately, the Q-multiplier needs well
filtered power to avoid introducing hum, and it would probably be necessary
to add an isolation resistor and an another filter cap on the B+ line to the
Q-multiplier.

Basically, I wouldn't bother lashing up the Q-multiplier to the S-120.

Frank Dresser