[Hallicrafters] 101a problem

[Mike Everette]

If you check for B plus voltage on the plate pin of
the audio output tube and find none, and then check
for B plus on the screen pin of the same tube, and
have it there, it'd be a good bet that the transformer
could be open.  But before jumping to that conclusion,
do a little more testing:

Measure the resistance of the primary.  The leads are
probably red (B plus side) and blue (to the plate
pin).  It should read at least 100 ohms, maybe more. 
If you get nothing, it's open.  You don't have to take
it out of the circuit to do this.  Just BE SURE the
power is off and that the filter caps are discharged. 
Or, you may be FILLED with the gLO-ry of the lord....

Also measure the resistance of the output side. 
Measure between ground and the 500 ohm terminal; you
should read somewhere between 30 and 60 ohms.  Then
measure the 3.2 ohm terminal, to ground.  You should
see maybe one or two ohms.  Do this with the speaker
disconnected, of course.  If you see no resistance,
the secondary may well be open (this does not often
happen).  

Have you tried plugging in a pair of headphones to see
if you hear anything?  It could be that the contacts
in the phone jack that "break" the speaker lead when
the plug is inserted, are not "making" when the jack
is open.

Off hand I cannot remember if the 101 series has a
bypass capacitor from the audio output tube plate to
ground.  If it does, this might be shorted and that
would kill the audio for sure.  It also will cause a
LOT of current to be drawn through the transformer
prinmary, and you need to fix the short PRONTO.  If
you measure a short to ground from the audio output
plate, that may well be the problem.

73

Mike
WA4DLF




		
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