Ralph Mowery wrote:
In article , says...

I also found out the 2nd 6au6 tube has been replaced by a 6AQ5 tube and
seems to be rewired to match.

That's also factory. Do you have the correct manual for the thing?
Get the one from:
http://www.radiomanual.info/schemi/S...ing-2_user.pdf

It is dated 1953 where the one I have is 1952 and it does show the 22
ohm resistors in the plates of the 807 tubes that is not shown on the
schematics I have.

I have 2 (now 3) schematics that are slightly different. However they
both show a 6AU6 tube as the second one in the audio amp driving the 807
tubes. The Viking 2 I have has a 6AQ5 tube in that place. Maybe it is
factory like you say and I need to look for another schematic. I know
for the short time I have looked on the internet there have been many
mods for the audio stages. The older schematic does not show it,but the
newer ones show a 6AQ5 for the screens of the 6146 tubes.

OH! You mean the second AUDIO tube was turned into a 6AQ5, not the second RF
tube!

Yeah, that wouldn't be factory, that would be a modification, and likely
a good one since the 807 could benefit from more drive.

The second RF tube is also a 6AQ5 in all but the first few units. It sags
a little from Miller effect on 10M but is generally a good plan.

I know there are many modifications to it. A ham gave me some old QST
and CQ magzines from the late 1940s up to the 1970s. I do remember
seeing a few mods for the Viking 2,but would never be able to find them.
I looked on the internet and it is also full of mods.

Yes, these were inexpensive and reliable radios that were in common use for
many years, so as technologies changed people adapted new stuff for them.

My guess is that the combination of the regulated bias and the 6AQ5 probably
improve the audio quality a good bit over the stock unit especially with high
duty cycle signals.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."