[Hallicrafters] S-27 Help Needed (Again)

[Joe Connor]

I need your help again because the intermittent problem with my S-27 has come back.

The receiver plays well. After being on for about an hour, it sometimes goes dead. With a signal injected on the plate of the 1st RF (956), I get reception. With a signal injected on the grid of the 956, however, I get nothing. After the set cools off for an hour or so, reception is normal. 

I've cleaned the pins on the 956, as well as the socket, and substituted several NOS 956s. This does not bring reception back. Voltages and resistances on the 956 socket are normal.

I have a couple of suspects: (1) C-4, a .002 cathode bypass cap on the 956; and (2) C-5, a 330 pf screen bypass on the 956.

Do you think leakage in either of those two caps could cause my symptoms? Is it possible that one of these caps develops leakage only when the set has been on for a while? Can I use a regular film cap for the cathode bypass?

As always, thank you for your guidance.

                                   Joe Connor