[Hallicrafters] HT-44 Carrier balance drift

[Jeff]

Thought I'd post an update:

Bill, WA9MXQ posted in July 2003 to the list of a similar problem. There 
are four .01 mfd caps on the 12BH7s. It appears that one or more were 
leaky, which caused the carrier balance to shift as temperatures 
changed.  Replaced all four and the carrier balance is solid as a rock 
now from cold start to several hours on. Additionally, the 22K resistors 
are now operating at around 160 F, well within acceptable limits. I 
didn't shotgun the capacitors in this rig as they looked like "modern" 
film capacitors.

Spectrum analysis shows everything as per the manual.  Posting to the 
list to save somebody the research time if you've got an HT-44.



Jeff
WB3JIH



On 11/29/2015 5:03 PM, Jeff wrote:
> Input appreciated:
>
> Have a working HT-44 that's getting excellent audio reports and good 
> spectrum views on air.  I've aligned the audio phasing for a good 
> circle pattern at 1 KHz.
>
> In going through it, I found the 22K 2 watt resistors feeding the 
> balanced modulators to have different values.  I replaced both with 
> metal oxide resistors.  Voltages on the plates are 80 volts (manual 
> says 60, but also feeding it at 123 VAC.)  After a day or two, I 
> checked them and they have been clearly subjected to heat -- paint is 
> now hard to tell what color it was. When I removed the original carbon 
> comps, one of them was also quite toasted looking.  There's no 
> evidence of any other component stress however.  The 12BH7s are 
> closely matched and test good.
>
> Second, and maybe related, I am having difficulty maintaining carrier 
> suppression.  At first turn on, the carrier shows quite high- maybe 
> 5-10 watts out at full power (130 watts).  removing the cover and 
> adjusting the balance pots will quickly take it back to zero, but as 
> the rig heats, it goes off again.  Eventually, it stops "drifting" and 
> I'm able to set it so it stays suppressed.
>
> The 22K resistors appear to drop the full B+ to the stated voltages, 
> so I would expect for them to get warm. It bothers me to see them 
> thermally stressed like that though.  I suppose I could put in a 
> couple of 5 watt resistors, but that seems like it might just be 
> masking a problem.
>
> As I said, the rig is getting excellent reports.  I have it slaved to 
> a SX-117 and am successfully using it in transceive configuration, so 
> I don't want to overly tinker with something that's more or less 
> working.  It's just that the carrier balance controls are inconvenient 
> to have to tweak.
>
> If anybody out there has experience with this rig, let me know. 
> Perhaps it's just the nature of the beast?  I do know that my other 
> phasing rigs will hold carrier balance well enough, so I'd be 
> disappointed to hear that this one wont.
>
> Jeff
> WB3JIH
>
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