Ralph Mowery wrote:

From what I have read, there does seem to be lot of mods to the audio
stages. Ihave not spent too much time with this unit so far. Got a
couple of crystals from a friend this morning sowas able to load it on
40 meters into a dummy load. Cw seemed ok,but no audio. Driving it
with a audio signal generator I could get a slight ammount of audio
out,but it took about 5 volts into the mic. Way too much. Found the
plate and screen resistors open on the 1st audio amp. Replaced them and
getting over 100 % when using a D104 mic if I turn the audio all the way
open. I am showing about 10% hum on the Viking on my ifr 1200s and can
hear it somewhat on a receiver in the other room. It is that way in CW
or Phone. Most of the capacitors have been replaced, but could be bad.

If plate and screen resistors failed, I'd replace the tube and see what
happens, because likely it was the tube that caused them to fail.

Check the supplies with a scope. If you see hum, you have decoupling cap
issues. If you don't, then it's something else.

You can also try pulling the first audio tube. Got a hum? If so, pull
the second audio tube. Still a hum? Pull the finals from the audio deck.
Still humming? You can track it down stage by stage... and it may well be
in the RF stages and not the audio stages.

Maybe a HK leakage in one of the tubes. Ihave some 6AU6, but not any
6AQ5 tubes. That 6AQ5 was good for around 5 watts of audio and used in
many receivers as the output.

When the 6AQ5 develops a heater-cathode short, which they are prone to doing,
they usually hum SO LOUD that you won't have any usable audio. So I am not
going to put money on that... but you should have a spare handy since the
6AQ5 is a very common tube and you will encounter them in the future.

The Vikings were not that inexpensive when new. The book says $ 279 in
kit form. A friend that is much older than I am told me it was about $
100 more if factory built. It todays dollars, that is probably a 3 to 5
thousand dollar rig.

The Vikings saw commercial service all over the place, and even found
themselves in broadcast service. As late as the 1980s, both HCJB and
one of the C&W stations in the Caribbean were using them as shortwave
broadcast transmitters, continuous key down for days on end. New, they were
not cheap by ham standards, but they were very cheap by commercial standards
and because there were so many in commercial service they turned up surplus
at good prices a lot.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."