[R-390] 6BJ6/6BH6 sub

[Dan Merz]

Hi,  sometimes luck is the right kind. After being on for a few hours, my
390 suddenly went dead,  no signals and little indication that it was still
on.  I just didn't feel like moving it and groaned a bit at the prospect.  I
pulled the top cover, and the tubes appeared lit and I fingered a few tubes
with high hopes that it would show some response.  The i.f. tubes seemed
warm but I could touch them.  I pulled a 6BJ6 i.f. tube out thinking I would
put a tube extender in and see if there was hv. Without the extender, I
measured the filament voltage on socket pins 3/4.... Nothing.  As I recall,
with the tube pulled it should have been 26 volts ac.  I pulled the tube
next to it and put one of the tubes back in the first socket I pulled.  The
voltage on pins 3/4 there was well over 20 volts ac.  I measured the
resistance between pins 3/4 on the pulled 6BJ6 and it was open,  a dead
tube.  I couldn't find a spare 6BJ6 so I stuck a 6BH6 in per my Rider's sub
book.  The set came to life and operated much as before.  My good luck was:
the first tube I pulled was a good one and the series filament string was
still affected by the bad one that was still in the radio.   And then by
dumb luck, the second tube I pulled out was the bad one.   And then of the
two tubes I had out,  I by chance put the good tube back in before I thought
to measure the pins on both tubes I had out.  This made my day.  In
hindsight,  I should have just measured  pins 3/4 on the tubes themselves as
I pulled them out since I had a pretty good idea one of them in that
filament string was dead.   

I surmise the radio will not operate with good response to strong signals if
6BH6's are sub'd for all the i.f. 6BJ6's,  since a 6BJ6 is remote cutoff and
the 6BH6 is sharp cutoff.  But will one replacement as I have done really
matter much?  I'll do one more search for a 6BJ6 today and can probably get
some at a hamfest in a couple of weeks.  I seem to recall depleting my
supply when I rejuvenated the 390 about a year ago and I seem to have a lot
of 6BH6's.  Dan.