Another tube needed

Glen Zook gzook at YAHOO.COM
Thu Dec 22 17:35:39 EST 2005

I have done something to anger the boat anchor gods! 
Obviously I am not supposed to get the 2-meter Gonset
Communicator IV AM station going!

Actually, I have some 6BQ5 tubes on the way for the
modulator in the Communicator IV and that will finish
it off.  But, now my National VFO-62 that I want to
use with the Gonset has problems.  First of all, it
was highly modified, but fortunately no additional
holes drilled and the modifications could be reversed.
 After doing that I have a "hum" problem.  Now the VFO
can also act as a crystal oscillator (has a crystal
socket right on the front panel) and that part works
fine.  At least no "hum" on the carrier out from the
Communicator IV when using crystal control.  When
operating as a VFO that is a whole new ballgame.

Replaced the electrolytics and the paper capacitors
that were in the unit (total of 2 electrolytics and 3
paper capacitors).  Didn't help at all.  Soldered all
of the ground lugs and grounding rings on the 2 tube
sockets to the steel chassis (they are rivited, not
attached by machine screws, so couldn't tighten them).
 Didn't help at all.  Relocated all of the AC carrying
wires away from all the rest of the wiring (AC input,
unrectified B+, and heater wires).  That did help a
little, but not that much.  Also installed a 3-wire
cord and a fuse holder while I was at it (originally
had a 2-wire, non-polarized, cord with no fuse).

Finally discovered that the dual purpose tube (triode
/ pentode) is microphonic.  Doesn't happen when used
as a crystal oscillator but definitely when used as a
tunable oscillator.  The tube is well shielded but is
still being affected by the power transformer.  The
tube is a 6BH8.

So I went to my tube stock (both new and used) and,
guess what, not a 6BH8 to be found.  I have plenty of
tubes that could substitute except that they have
different base connections.  The 6BH8 uses 9DX.  Went
to my trusty RCA Receiving Tube Manual looking for
tubes that have 9DX as their base.  Right, not a
single one of these in stock (did have an 8 volt
heater equivalent of one and tried it "just in case" -
didn't work).

So, I am in dire need of a 6BH8 tube.  Have other
tubes, parts, and, if all else fails, a little cash
(money, that is) that can be exchanged for a genuine 6BH8.

Glen, K9STH

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