[Hallicrafters] help with SX-42

[Edward B Richards]

It's me again. I have done extensive work on this radio and now it is
numb. When I first got it, it worked on the BC band but when I changed
bands it smoked. I traced the smoke down to carbonization on the H wafer.
I soon discovered this is rather common for this radio. I removed 2 RF
transformers and 2 wafers from the band switch (a monumental task) and
repaired the wafers and re-installed them. As long as I was at it, I
replaced all of the paper caps and upgraded it according the
Hallicrafters Service Hint #21.  This requires work in various stages of
the radio. Now it doesn't receive anything. I can force a signal through
it with a signal generator but it is numb. I am sure that I screwed up
somewhere but I have not been successful in finding the sick stage. All
of the tubes voltages are right on. The band switch is very complex but I
traced out the circuit best I could and every thing checks out. I made
stage gain measurements but they don't tell me much because I don't know
the effect of using a 50 ohm insertion probe on high Z circuits. Below
are the microvolt levels required to maintain 1 VAC across the 500 ohm
speaker.

Signal gen: URM/25D modulated 30% with 400 cps tone at 455 kc, 50 ohm
injection probe (Motorola TEK 10, 50 ohm load with a .05 mfd cap to the
probe tip).
6SG7 plate = 100k
6SG7 grid = 1,000
6SK7 plate = 2,000
6SK7 grid = 30
mixer plate = 1,000
mixer grid = 90

Sig gen and radio at 600 kc:
mixer grid = 700
2nd RF plate = 1,000
2nd RF grid = 2,500
antenna term = 950

Does anyone please have the correct numbers for these tests or any other
way to find the bad stage? I suspect the 2nd RF stage as that is where I
did most of the work, but cannot find any thing wrong. Voltages are good
and the band switch rings out according to the schematic. Thank you very
much for reading this.

73, Ed Richards K6UUZ