Need help troubleshooting an HT-32A

Discussion in '"Boat Anchor" & Classic Equipment' started by N2TC, Jan 26, 2021.

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  1. N2TC

    N2TC Ham Member QRZ Page

    I currently have an HT-32A (my first) on the bench. I have already replaced the rectifiers with SS replacements and dropping resistors in the B+ and B++ lines. All paper and electrolytic capacitors have also been replaced (Hayseed Hamfest). Also added a grounded three-wire power cord. All tubes either tested good or were replaced with NOS. Brought everything up slowly with a variac without incident. Smoke test passed. Initial testing showed very low power output (5W) or so on all bands. Proceeded to alignment and all was well re: the 3rd mixer/driver. HOWEVER, when trying to align the 2nd mixer on 40, I get no VTVM reading at the 6146 grids at 12.5 MHz at ANY L23 setting (I WAS able to peak this at 7.2 Mhz with the driver tuning control). My signal generator is putting out 10V and still nothing. Resistances on V7 pins on or close to spec.

    Any ideas/suggestions/likely suspects?

    Tim N2TC
  2. KI4ZNV

    KI4ZNV Ham Member QRZ Page

    You mean you're getting no RF at the grids or no DC at the grids?

    What do you see on the plate of the 12BY7?

    If you have signal on the 12BY7 plate, but not on the grid of the final, check the coupling capacitor between them and
    the DC coupling inductor for the final grid bias.
  3. N2TC

    N2TC Ham Member QRZ Page

    Just saw this and am not at home where the HT-32A is. In answer to the first question, I'm not getting RF at the grids (using an RF probe and a VTVM) with an injected 12.5Mhz signal.

    Haven't checked the 12BY7 plate but I HAVE been able to read RF voltages on the 6146 grids during the 3rd mixer/driver alignment process, so that's not likely the issue.
  4. KP4SX

    KP4SX Premium Subscriber QRZ Page

    I don't understand. I don't think you should see 12.5 MHz at the 6146 grids.
  5. N2TC

    N2TC Ham Member QRZ Page

    You don't. But you DO get an RF voltage there that is the result of the mixing scheme on 40m. Check out the manual. The alignment process takes the band specific crystal oscillators out of the circuit. When they are functioning, the output of the 2nd mixer is 12.5Mhz on 40M. During alignment, the 2nd mixer just amplifies a 12.5 Mhz signal injected to it's grid. This part of the alignment peaks the tuned circuits between the 2nd and 3rd mixers, with the 3rd mixer and driver outputs having already been aligned.
  6. N2TC

    N2TC Ham Member QRZ Page

    I may have figured out at least part of the problem. The alignment instructions begin by having you remove the VFO tube (V9-6CB6), among other things, which seems fine for the 3rd mixer/driver process (injected signals are all in-band). However, when setting up the 2nd mixer (actually, the tuned circuits between the 2nd and 3rd mixer), if the VFO isn't running, the output from the 3rd mixer won't produce an in-band signal so it will get essentially blocked by the tuned circuits following the 3rd mixer. Also, when aligning for F2 (12.5 Mhz) for 40M, the instructions say to set the VFO to 7.2 Mhz. If the VFO isn't running, why would this matter? I suspect an omission in the alignment instructions and that V9 should be re-inserted prior to Step 7 in Section 7-4-4. I have looked several times to make sure that step is there and I just missed it, but it doesn't seem to be there.

    I would love it if someone could confirm my suspicions or tell me if my logic is flawed. Thanks!

    Tim N2TC

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