|[AMRadio] Hallicrafters HT-37 Alignment Question|
bpancake at mindspring.com
Sun Aug 22 21:16:29 EDT 2004
Now that my Hallicrafters HT-37 has undergone it's cosmetic restoration successfully, it's time to tackle the alignment.
It appears that someone before me has used the proverbial "golden screwdriver" to align it before. There is practically no output on any band except 15 meters (60 watts). The driver tube bias resistor R25 had been wired to ground instead of wired to the grid. Corrected that, but still no change in output.
All tubes check OK by substituting known good tubes. Power supply has been restored with new electrolytics. All the black beauty caps were replaced as well. HV and LV tubes have been replaced with Weber "Copper Cap" rectifiers to take the load off the power xfmr. Gave the bandswitch a good cleaning and treated it with DeOxit. No change.
Electrically, everything appears to be OK. HV, LV and bias supply voltages are good. PA bias in MOX/LSB position is -49vdc as recommended. In standby position, PA bias rises several volts as it should.
I started to align it using an HP 606A rf signal generator and HP 410b VTVM following the procedures in the factory manual. The driver and 2nd mixer stages aligned as per manual. The 1st mixer 40m coil (L23) will not cause a PA grid voltage peak on the VTVM as it is adjusted like it is supposed to. Now I'm dead-in-the-water. Since I can't align the 1st mixer, I can go no further.
>From those of you who have experience with HT-37 alignment, I'd almost sell my soul for a suggestion on what's wrong with the 1st mixer stage. L23 (40m coil) has good continuity and circuit wiring for that entire stage appears to be wired correctly.
If there are other "lessons learned" in aligning an HT-37, or if I've missed a key procedure, please pass them on. There's no question in my mind that I'll take your advice if it's offered.
I want to say many, many thanks to Al Parker, W8UT, who has already helped enormously with good advice, especially on the procedures for upgrading of the HT-37 power supply circuits. I've purchased another restorable HT-37 that hasn't been hacked-on from Al so I can do a side-by-side circuit wiring comparison.
Since the previous owner of my HT-37 got creative with parts replacement wiring, I'm hoping that looking at both chassis' at the same time will help find the wiring mistakes. Can't hurt to have another HT-37 anyway.
Thanks, Bill, ab0zz
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