I've been trying to restore an SX-117 and HT-44 to use as
a vintage setup. Its been a challange! Seems that everything
that could go wrong has, and in ways that have driven me nuts.

One of the last issues is with the HT-44. The output stage
wants to break into oscillation at (about) twice the freq
its tuned to. I have been unable to neutralize the finals.
The tubes are good (and matched), band switching has been
checked (switches and coils), bypass caps, etc. Everything
looks OK. All of the obvious stuff has been checked (biasing,
power supplies, etc).

Hopefully there is someone out there that is familar with
the HT-44, and may have seen this problem and found a
solution. Nothing useful was found with a google search.

Steve

Steve wrote:
I've been trying to restore an SX-117 and HT-44 to use as
a vintage setup. Its been a challange! Seems that everything
that could go wrong has, and in ways that have driven me nuts.

One of the last issues is with the HT-44. The output stage
wants to break into oscillation at (about) twice the freq
its tuned to. I have been unable to neutralize the finals.
The tubes are good (and matched), band switching has been
checked (switches and coils), bypass caps, etc. Everything
looks OK. All of the obvious stuff has been checked (biasing,
power supplies, etc).

Hopefully there is someone out there that is familar with
the HT-44, and may have seen this problem and found a
solution. Nothing useful was found with a google search.

Steve Hello Steve, I have a HT-44 ,works good... If I can take some readings for You I will do so. Do you have a good scope? I know the T 44 is short on meter readings. I am guessing that you are low on drive..If I can help let me know . I am OK on QRZ..W4PQW Harold

Steve wrote:
I've been trying to restore an SX-117 and HT-44 to use as
a vintage setup. Its been a challange! Seems that everything
that could go wrong has, and in ways that have driven me nuts.

One of the last issues is with the HT-44. The output stage
wants to break into oscillation at (about) twice the freq
its tuned to. I have been unable to neutralize the finals.
The tubes are good (and matched), band switching has been
checked (switches and coils), bypass caps, etc. Everything
looks OK. All of the obvious stuff has been checked (biasing,
power supplies, etc).

Hopefully there is someone out there that is familar with
the HT-44, and may have seen this problem and found a
solution. Nothing useful was found with a google search.

Steve Hello Steve, I have a HT-44 ,works good... If I can take some readings for You I will do so. Do you have a good scope? I know the T 44 is short on meter readings. I am guessing that you are low on drive..If I can help let me know . I am OK on QRZ..W4PQW Harold

Harold,
That'd be great! I'll contact you via e-mail.

Steve
wrote in message
ups.com...

Steve wrote:
I've been trying to restore an SX-117 and HT-44 to use as
a vintage setup. Its been a challange! Seems that everything
that could go wrong has, and in ways that have driven me nuts.

One of the last issues is with the HT-44. The output stage
wants to break into oscillation at (about) twice the freq
its tuned to. I have been unable to neutralize the finals.
The tubes are good (and matched), band switching has been
checked (switches and coils), bypass caps, etc. Everything
looks OK. All of the obvious stuff has been checked (biasing,
power supplies, etc).

Hopefully there is someone out there that is familar with
the HT-44, and may have seen this problem and found a
solution. Nothing useful was found with a google search.

Steve Hello Steve, I have a HT-44
,works good... If I can take some readings for You I will do so. Do you
have a good scope? I know the T 44 is short on meter readings. I am
guessing that you are low on drive..If I can help let me know . I am OK
on QRZ..W4PQW Harold

Steve wrote:

One of the last issues is with the HT-44. The output stage
wants to break into oscillation at (about) twice the freq
its tuned to. I have been unable to neutralize the finals.
The tubes are good (and matched), band switching has been
checked (switches and coils), bypass caps, etc. Everything
looks OK. All of the obvious stuff has been checked (biasing,
power supplies, etc).

snip

You should check the brand of the final tubes.
GE 6DQ5's will neutralize quite differently than RCA's.
You can see the difference in the construction -
some 6DQ5's have a U-shaped clip at the top mica,
surrounding the plate lead, and some don't.
(I think the U-clip is connected internally
to the screen). If you mix the two types, you will
never get the final stage to neutralize.
Some rig manufacturers caught on to this problem,
and specified which brand of 6DQ5 to use in their rigs.

73,
Ed Knobloch

Ed,
Thanks for the tip. Both are GE, and they appear to be
closely matched. Yesterday I went though some of my
stash of tubes to see if I had another pair. No luck yet, but
I've got several more boxes to go through.

Frankly, I'm running out of things to try.

Steve

"Edward Knobloch" wrote in message
news:Tn2jh.67$175.41@trndny05...
Steve wrote:

One of the last issues is with the HT-44. The output stage
wants to break into oscillation at (about) twice the freq
its tuned to. I have been unable to neutralize the finals.
The tubes are good (and matched), band switching has been
checked (switches and coils), bypass caps, etc. Everything
looks OK. All of the obvious stuff has been checked (biasing,
power supplies, etc).

snip

You should check the brand of the final tubes.
GE 6DQ5's will neutralize quite differently than RCA's.
You can see the difference in the construction -
some 6DQ5's have a U-shaped clip at the top mica,
surrounding the plate lead, and some don't.
(I think the U-clip is connected internally
to the screen). If you mix the two types, you will
never get the final stage to neutralize.
Some rig manufacturers caught on to this problem,
and specified which brand of 6DQ5 to use in their rigs.

73,
Ed Knobloch