Thank you for replying.
I have had some success. I found 2 bad tubes using a simple
EMISSIONS tube tester. The HF Osc. tube and one of the I.F. amp
I had a 6AH6 to replace the HF Osc. But I did not have a 6JB6 for
one of the I.F. amps. One of the two 6JB6 tubes used in the 2 I.F.
amps checked out GOOD, no Grid Leakage or Shorts. The other
6JB6 shows GOOD Emissions but BAD on Grid Leakage and SHORTS.
If I tap the tube it would show GOOD on Grid Leakage and no Shorts.
So I thought the tube might have dirty contacts and I cleaned them.
The things I found so far, The Accessory socket near the back of the Chassis
uses rivets to mount it to the chassis. I was probing around with a insulated
tool and when it hit the area I got a low level hum. The grounding of the socket
which has a couple wires connected was bad. So now I have low level hum
all the time. Continuing my probe I tapped around the 12AT7 and I noticed
a cap connected to pin 1 with the other side not connected but it look
like it was touching the chassis. I moved it and the audio can on really
loud. I moved the tube and the audio would come and go so I cleaned
the socket and now I have good audio all the time with no hum.
The receiver looks like it has a couple of coupling caps that have been
Where I am right now. I thought the receiver was working. In fact
on 160 80 and 40m it appears to be as sensitive as my IC-735.
Now for the strange part. After it warms up, if I change from 80m
to 160 or 80 to 40 then back to 80m the receiver is some what deaf.
I can hear stuff very low in the receiver and tuning the dial has
no effect on what I hear. If back on 80m, power the receiver off
for 2 or 3 seconds, power back up it works again on 80m
This I discovered yesterday and have not had a chance to do anything with
If the receiver has been off for a while, turned on it works fines. Its only
after it warms up do I loose 80m and I think 20m too. If I leave it
on 80m it continues to work fine. Its only if I change bands
and back to 80m does it go deaf. I am wondering if the HF Osc
circuit has a out of tolerance resistor and when I turn power
off and on it shocks it circuit into working???
Any thoughts? Would you like to take this off line for discussion?
Thats a pretty easy receiver to work on; I have 2 in the shop now.
Besides replacing electrolytics, paper caps and checking for out of tolerance resistors, its usually just cleaning tube pins & sockets by reseating several times, cleaning switches and pots if noisy and check alignment/performance. May need a few tubes.
National Radio 1963-69