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HT-44 Common Problem?

 

This is the second HT-44 where I've run into this problem.? I use the HT-44 heavily on CW and my current one has logged hundreds of QSOs in contests.? The other day it suddenly had no output on any band, same symptom observed on another HT-44 I owned.? In digging into the problem, I found the cause to be the same as on the other HT-44.? Resistors R16 and R17 (22K , 2 watt) were cooked and V3, a 12BH7 associated with those resistors tested weak.? I replaced the resistors and the 12BH7 and now all is well again.? Had to adjust the pots to null the carrier for SSB.? I wonder if others have experienced that problem?? Not sure if the cause of the failure was the tube, or maybe the two resistors are undersized for the current?
?
73, Floyd - K8AC
 
Edited

I had to replace those resistors in a HT44 also. I recall measuring the current and it was exceeding the dissipation of the 2 watt resistors.

Unable to get my hands on 5 watt resistors, I put 10 watt 25k resistors in there.






On Mon, Dec 9, 2024, 9:32 AM Floyd - K8AC via <floydsense=[email protected]> wrote:
This is the second HT-44 where I've run into this problem.? I use the HT-44 heavily on CW and my current one has logged hundreds of QSOs in contests.? The other day it suddenly had no output on any band, same symptom observed on another HT-44 I owned.? In digging into the problem, I found the cause to be the same as on the other HT-44.? Resistors R16 and R17 (22K , 2 watt) were cooked and V3, a 12BH7 associated with those resistors tested weak.? I replaced the resistors and the 12BH7 and now all is well again.? Had to adjust the pots to null the carrier for SSB.? I wonder if others have experienced that problem?? Not sure if the cause of the failure was the tube, or maybe the two resistors are undersized for the current?
?
73, Floyd - K8AC
 

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Floyd,

I have seen that a couple of times over the years. It boils down to the balance of all triodes in V3 and V4.? The triodes in each tube need to be matched and V3 and V4 need to be matched. If either of the tubes suffers an intermittent short, large loss of gain or becomes gassy you can lose R16 and 17.?

(You probably already know this, but I thump the tubes in the tube tester while doing the shorts test to check for intermittent shorts.)

If you find it difficult to balance the system, look for drifted resistors or leaky capacitors. The respective components in the V3 circuit need to be very close to equal to those in the V4 circuit.

?


Walt Cates, WD0GOF
?
A majority of acceptance is not proof of correctness.


From: [email protected] <[email protected]> on behalf of Floyd - K8AC via groups.io <floydsense@...>
Sent: Monday, December 9, 2024 9:32 AM
To: [email protected] <[email protected]>
Subject: [HallicraftersRadios] HT-44 Common Problem?
?
This is the second HT-44 where I've run into this problem.? I use the HT-44 heavily on CW and my current one has logged hundreds of QSOs in contests.? The other day it suddenly had no output on any band, same symptom observed on another HT-44 I owned.? In digging into the problem, I found the cause to be the same as on the other HT-44.? Resistors R16 and R17 (22K , 2 watt) were cooked and V3, a 12BH7 associated with those resistors tested weak.? I replaced the resistors and the 12BH7 and now all is well again.? Had to adjust the pots to null the carrier for SSB.? I wonder if others have experienced that problem?? Not sure if the cause of the failure was the tube, or maybe the two resistors are undersized for the current?
?
73, Floyd - K8AC
 

I got some 3 watt 22k resistors from Amazon.? Slightly smaller than the original carbon 2 watt.? Will use them if the problem occurs again.
 

Hi Floyd,
Yep, my HT-44 also had a failed 22k resistor in that circuit.? It measured 568 ohms.? I replaced it and the others which weren't so far off.? At least one 1k and one 220 ohm resistor were also out of spec.? I replaced a lot of resistors in that circuit.? A prior owner had replaced the carrier balance potentiometer.? One of the 12BH7s had a bad section; replaced that too.? And a 12AX7 was bad...replaced.
One difference is that it didn't fail on my watch; I got it that way.
Cheers,
Halden VE7UTS
 

Yep - I read your document on the issues you ran across before starting any work on my receiver.? Oddly, all other resistors in my receiver were well within tolerance.? The guy I bought it from told me that he didn't think the SX-117 or HT-44 had ever been used.??
?
73, Floyd

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