[Hallicrafters] HT-37 -- No SSB

[ss409ss at aol.com]

the only Halli I know is the Hurricane and still learning I might add. The carrier balance I am familiar with though and I am sure it is similar if it has two pots, mine has two adjustments also. You center the large one first, very carefully since a hair off is no good. Then you use the little adjustment to finish it. it's tricky and very sensitive but with some practice you can do it in under a minute. Big first for the best null, then the small. When I mean a fraction, I mean a fraction or it's a no go..!!! As far as the balance goes, null it out (carrier) first since this was
my problem a couple of times. once it's clean you will prob solve the other issue. Or adjust it easily with the null squared away. Regards, Richy N2ZD



-----Original Message-----
From: 9artus at gmail.com
To: hallicrafters <hallicrafters at mailman.qth.net>
Sent: Tue, Dec 13, 2011 2:38 pm
Subject: [Hallicrafters] HT-37 -- No SSB



Folks,

I've been fiddling with a HT37 and have run into an issue. I have CW and DSB
output but no SSB either at the output nor the generator unit. I have replaced
v3, v4, and v5 with supposedly matched tubes and replaced the bias supply and
the generator caps, awaiting new caps for the rest. I believe the problem may
be with phasing; but, for the life of me I can't isolate it. I have a decent
150 MHz 4 channel scope and have probed the 9 MHz carrier and its phase shift
network -- I see clean signals adjusted to 90 degrees and the same voltage
coming from the phase shifter.

For the audio side, I see 4 signals 90 degrees apart and of the same magnitude
as measured just before the RFCs going to the balanced modulators. I tried
various audio phase control settings to see if I could find a setting that would
give me output-- nothing. In DSB mode, with a -20dbm 1000 Hz signal in, I can
drive the modulation to 100 percent. In SSB mode, I have put the scope on the 4
grids of the balanced modulators and see the audio signals superimposed on the 9
MHz signal. Again, I can get good modulation of the carrier. Because the unit
appears to be working in DSB, I suspect the phase relationships between V4 and
V5 are screwed up but I cannot seem to resolve the issue.

Also, I see both carrier balance controls appear to work, however there is
still quite a bit of residual carrier. The carrier controls seem to me to be
somewhat strange -- starting at either ends of the ranges, the output is high as
expected, there is a sudden drop in output when turning the control toward the
center, but there is no further drop in carrier, continue turning and the the
carrier jumps back at the other end of the control range. Both controls act
this way.

Any thoughts on how I might proceed to resolve this problem? Thanks.

Jack (W0FNQ)
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