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Author Topic: Hallicters HT-44 Transmit problem  (Read 1391 times)
K7TPD
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Posts: 4




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« on: February 27, 2013, 07:59:41 PM »

Hello everyone, I have the Hallicrafters HT-44 and SX-117 twins. The HT-44 has a problem, when using SSB, after about 30 minutes or so, when the PTT is pressed it puts out full power, 100 watts, almost acts like CW mode. Turning the MIC Gain down all the way does nothing, turning down RF all the way does nothing. If I turn off the HT-44 and let it cool for 10 minutes or so, the problem goes away for a while, but comes back after it heats up again.

Any help is appreciated! Thank you! Tom K7TPD
« Last Edit: February 27, 2013, 08:04:55 PM by K7TPD » Logged
KE3WD
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Posts: 5689




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« Reply #1 on: February 28, 2013, 01:08:00 PM »

I'd start by looking at all electrolytic capacitors.  AC ripple can modulate the SSB transmitter...
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K7TPD
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« Reply #2 on: February 28, 2013, 01:56:19 PM »

Yeah, gonna start with ceramic caps in the final amp area, resistors in the final screen voltage area as well, then on to the electrolytics in the PS. Was hoping someone has battled this and could save me time Smiley Thanks for the reply and suggestion!! Tom K7TPD
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K7TPD
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« Reply #3 on: February 28, 2013, 04:38:25 PM »

Found it, you were right, it was an electrolytic causing modulation problems, it was C10/C11 of V3 (12bh7a) the balanced modulator. I used a can of Super Cold to help narrow it down. As soon as I blasted C10 with coldness, the problem went away, then after a few minutes problem came back, blasted it again, went away again. Thanks for the input! I shall be re-capping this dude! Tom K7TPD
« Last Edit: February 28, 2013, 04:40:47 PM by K7TPD » Logged
AC5UP
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« Reply #4 on: February 28, 2013, 04:49:42 PM »

Good Catch!

One other rare but completely frustrating issue that masquerades as a bad AC ripple condenser is the ol' heater to cathode short in the 1st audio tube or phase inverter. B+ looks clean, yet there's a hummmmmmmmmmm that just won't quit. Sometimes a tap of the tube will blip the hummmmmmmmmm and that's a clue, other times the set plays fine until it warms up for five minutes or so. Then the hummmmmmmmmmmm starts to sneak into the audio.

Freeze spray can be a useful diagnostic tool but never, ever let it splash on the glass of a hot tube....... Instant stress fracture followed by extreme gassiness.

Yuck.   Angry
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KA3BVJ
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« Reply #5 on: March 27, 2013, 05:57:42 PM »

Well I have been working on my twins also I finnally got them on cw the other night.How ever some problems .I did find out no go with audio bad hum but the cw note seems to clean.. Also I seem have problem with the preselector control very touchy when tuning up.Also I found out the HT 44 likes to see very close tune Ant to make load right.I hope to get up on AM/SSB but for now CW is ok!!! Roll Eyes
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