[Hallicrafters] ht32b

[Patrick A. Thompson Sr.]

I have just recently restored an old GE BCB radio.  One puzzling thing was
that after 10 minutes or so the audio would distort and slowly diminish
until all that was left was sputters and pops. But for the first 10 minutes
it would play quite well.

This tuned out to be a 35L6 that did not show any leakage until the tube was
hot.  I diagnosed this by watching the drop increase across the cathode bias
resistor.  Later I saw the same effect on a tube tester.  Each time it took
10 minutes or so for the problem to occur. A replacement tube fixed the
problem.

I've heard that similar problems occur from leaky bypass caps changing grid
bias.

The trouble-shooting procedure is to find a place in the circuit where the
problem can be noticed and go backward one stage at a time until you isolate
the problem stage. At that point you begin looking for the component that is
changing value.

If you have a tube tester that will read leakage and a spare afternoon you
could test each tube in the signal path for an extended time.

I almost always start a repair by first checking the power supplies.

You didn't say but another good starting point would be to determine if you
have an RF problem or an audio (microphone amp and modulator) problem.

Pat
wa4tuk

> -----Original Message-----
> From: hallicrafters-admin at mailman.qth.net
> [mailto:hallicrafters-admin at mailman.qth.net]On Behalf Of Jack Schrader
> Sent: Sunday, June 08, 2003 9:17 PM
> To: hallicrafters
> Subject: [Hallicrafters] ht32b
>
>
> When I was on the net today and talking to Duane he mentioned
> that I should ask the net about what causes my 32b to lose its
> modulation after the rig has been on for awhile. I check into the
> net ok but if i want to check back in later on there seems to be
> no modulation but if I turn it off and later on turn it on again
> all is ok . I don't have a clue as to what might be breaking
> down. Any idea's ?
> 73 Jack
>
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