[Hallicrafters] SX42 restoration notes

[Joe]

After changing all the wax coated paper capacitors and all the out of tolerance resistors the radio still lacked gain even though all the IF and RF coils peaked.  All the tube voltages measured nominal so I tried replacing the mica capacitors in IF can T3 which seemed to be most deficient.  The improvement was a surprising 10 dB at 455 kHz and 6 dB at 10.7 MHz.  After changing capacitors in the other two IF cans, the receiver become "alive" and a real performer, even though I didn't pick up as much gain with T2 and T1.  The mica caps that were removed didn't measure any leakage on a 20 Meg scale so I can only assume that the ESR was the problem.  Apparently the ESR was't bad enough to show up as inability to peak the tuned circuits.  The 455 kHz coils are very delicate and made up of very fine litz wire, don't break any of the leads as I did.  I used CM05 mica capacitors for the replacement. 

Now I'm close to the specification of 60 uv for S9 at 14MHz.  I say close because the S meter which is speced at 5 ma FS actually is almost 7 ma FS.  Does it need a magnetic jolt? 

The receiver is a delight to use on both AM and FM especially with the sweet audio from the P-P 6V6's and R42 speaker.   

Now I need to do the same on my SX62 which has low FM gain. 

Joe Hanulec