Hi John:

The 6BA7 might be a poor choice. It will have the highest noise figure of
all the tubes you mentioned. I have never seen the 6BA7 used above 50 MHz,
and that was only with an rf amplifier.

On the other hand, a triode or pentode would be acceptable, though it would
hot have good weak signal performance.

The easy approach for a circuit is to look at the K4XL/ BAMA website and
steal the mixer - oscillator circuit from one of the many receiver
schematics available. There are some crystal controlled converters and you
can steal the electronics from them. Ignore the rf amplifier if you are not
going to use one. Tecraft made good converters, as did Filter King. Ameco
also made converters and National had a series to go with the NC-300.

After awhile, you can build stuff like converters without a schematic - you
just start picking up parts and start soldering. The triode has a bit lower
noise operating as a converter. Decades ago, there was a 6J6 converter
known as a ZL converter. That was simple and worked well.

You could also look around for an old tubed vhf mobile rig that would be
available for hauling away. Steal the converter out of one of those. I
have one here in Western Oregon you can haul away.

73, Colin K7FM

73, Colin K7FM