Halli HT-32 Carrier Level Circuit Problem

[AJ1G]

I recently put an original HT-32 (not an A or B) back on the air.  It was given to me by a now retired ham co-worker who is shedding load, and figured I would appreciate it for what it is.  All 85 pounds of it!

It originally powered up fine and after giving the VFO tuning cap a few shots of Deoxit to cure a case of the jumps,  and a re-cal reset of the VFO, it operated nicely.  However, after a few days of operation, the carrier level control (used only on AM and CW modes), became at first flaky, and then failed to full throttle.  Per the manual, this is a 1 megohm pot that adjusts the grid bias on the 9 MHz exciter output stage to change its output level.  I am hoping that I can clear this up with some deoxit into the pot, but therein lies the rub....

The 9 MHz exciter, including all of its control pots and switches, is completely enclosed in a subchassis box.  Poking around to get the lay of the land, it looks like it is designed to removed in one piece after disconnecting all of the associated cables, which are (thankfully) all terminated with plugs, and there are slots in the front panel for all associated control shafts to allow tilting the box to it lift off and out of the main chassis.  Looks like you have to remove four sheet metal screws from brackets that hold the box to the top of main chassis.  Looks  fairly straightforward, anyone been there and done that, any gotchas?

Several people, including Tron, have advised me about the high failure rate of the power transformer in these sets.  While I was looking around under the chassis, it appeared that there might already a replacement transformer in there, as evidenced by fresh(er) looking plastic transformer wiring.  Sure enough, on the rear side of the core topside, there was a paper label stating that it had been rewound by Jess Price, W4CLJ, Orlando, FL in 1976.  Anyone know of his work and how it holds up?  Googling him came up with a few hits, including a post on the Gonset forum about his rewinding service, apparently he was doing a lot of work in the mid-70s.  

And while I am in the 9  MHz box, any tweaks that can be made to the audio stages?

[k3msb]

Hi Chris

Here's a pix of what you need to do:  http://www.k3msb.com/ht32mk1/ht32_4.JPG

You will need to remove the front panel before you remove the subchassis.    As you'll see, you can not simply slide the subchassis backwards.  You need to rotate the rear upwards.   However, the round holes in the front panel will not let you do this.

When you remove the front panel you'll see the main chasis has rectangular openings through which the subchassis shafts pass.   Those rectangular holes allow the room for the shafts to rotate downwards as you rotate the subchassis upwards and out of the main chassis.

I think you'll need to disconnect the two wires to the meter as the front panel can be removed.

Remove the two Jones connectors on the subchassis rear, and the connectors from the top of the unit.

It's been many moons since I worked on the 32, but I think that's it.

[AJ1G]

Thanks for the picture Mark.  Definitely worth more than a 1000 words.  I saw the slots for clearance of the lower row of controls and was hoping that there was enough wiggle room, perhaps if I took the square sheet metal cover off of the power transformer, to swing the 9 Mhz generator box up and out without pulling the front panel.

Is the panel held on by just the middle two of the 4 vertically  stacked screws on the left and right side on the panel?

Doesn't look too difficult.  I just hope that all of the hex head set screws in all of the knobs loosen up without any damage.  That has been a problem on at least one of my E.H. Scott receivers when I have tried to do a front panel-ectomy.

Also looking for info on any differences between the original HT-32 and the HT-32A circuitry.  My set is a 32, but the manual supplied with it is for the 32A.  One difference I  seem to have come across is that the 32A manual mentions a line-level audio input RCA phono jack for use with a phone patch on the 9 MHz generator box, but I do not see it on mine.  I see there is a 32MK1 schematic on the BAMA site, but it is in djvu format which I do not appear to have an app for.

[Pete, WA2CWA]

HT-32A adds push to talk, RTTY, and phone patch input. There were also several component value change differences.

[k3msb]

>>Is the panel held on by just the middle two of the 4 vertically  stacked screws on the left and right side on the panel?

Yes.  The middle two hold the front panel on,  and the top and bottom secure the chassis to the cabinet.

Unless the square tranny sheet metal cover covers the rear part of the square chassis hole for the subchassis,  removal of it won't help as the subchassis needs to clear the rear part of the square hole.

Really, the "front panel-ectomy"  isn't all that hard.   Remove the connections for the meter, the lights string, slide the front panel out a bit and rotate it down.  If you want to remove it completely you'll need to unsolder the connector to the mic jack.

The knobs can be cantankerous -- are they hex or bristol spline?   The ones on the HT-37 are Briston spline,  but I can't recall on the HT-32. I do recall using a drop of penetrating oil on a few knobs.  Aside from that, they weren't much problem.

While you're in the subchassis, I think there are a few electrolytics in there that are very easy to replace, and I'd adivse taking care of them while the beastie is open and splayed open like a fish on your workbench.  "Lubing" the pot for scratchy operation is striaghtforward.

I think I still have a pretty complete subchassis in the parts pile if you need parts.  How I came across it I don't know;  why I keep things like that for radios I no longer have my wife doesn't know......

[Chris P.]

If its the same as a 32B, the box can be opened without removing it from the chassis.

[AJ1G]

Does not look possible on the original  HT 32 to remove the 3 sided wrap around cover..  I  got most of the knobs off without any trouble iths afternoon before having to get going to get the grass cut before dark.  I don't think the set screws are Bristols.  Coming out nicely with Allen wrenches.  The one on the carrier level pot was a little balky but eventually broke free.

It looks like the leads for the pilot bulbs and the meter are long enough so that I won't have to remove them from the front panel to move it enough to get the 9 MHz generator  control shafts clear of the panel.

[AJ1G]

Well, as typically happens, I got all of the knobs off without any problem except the band switch knob.  Seems like one of the two setscrews is frozen and the head looks stripped out from the get go.  Looks like I may have to drill it out and hopefully re-tap the knob collar and replace it, or at worst go with just one setscrew in there.  Also have to pull the knob on the tuning knob drag adjustment, that looks like it has very small square drive headed setscrews.

You can indeed pull off the one piece bottom and side shield "C" section with the sideband generator box in place.  Tedious process involving many screws but it did come out.  Unfortunately, the carrier level pot is really buried up in the top of the box and not really accessible without pulling the box.  Back to trying to get the tuning knob off so the front panel can come off so the generator box can come out.

[AJ1G]

Finally got some time to work on the HT-32 this weekend.  Got the recalcitrant band switch knob off using a fresh long length hex key.  Never did get the small knurled knob off the VFO  main tuning knob dial drag shaft, but with only that knob installed, was able to pull out the front panel enough on the left side of the chassis mto extract the sideband generator chassis.

Deoxit applied to all the pots in the box and on the mode switch and function switch contacts completely cleared up the lack of adjustment of the carrier level  on AM and CW.  Glad I didn't have to change the pot, it's really shoehorned in there!

Set it up for a some quick on air checks on 75. Seems to have plenty of output, at least 100 watts key down on CW, but when looking at the RF envelopes on  a scope, there appears to be a notable sag following key down and then a subsequent recovery in output level when keying  on CW that is evident on individual dashes and, and I think the same thing is happening during SSB voice peaks.  Have never seen such a sag/recovery on the various other transmitters I have on the air here.  Wondering if this has anything to do with the relatively low amount of filter capacity in the HV B plus circuit, only a single 10 uF oil cap following a choke in a choke input filter arrangement.  May try adding some additional capacity and see if that helps reduce the sag.  Like I said, the period of the sag and recovery is such that both the sag and recovery is evident within a single dash on CW at about 18 WPM.  Opinions?

[AJ1G]

Got rid of the sag described above simply by powering the 32 directly from a wall outlet vs a daisy chain pf a light duty 2 wire extension cord plugged into an outlet strip plugged into another light duty extension cord.  Should have gone for the oxygen free copper No. 16 2 wire cords!

Just had a number of QSOs on 40 with it, getting at least 100 watts PEP out, received several good audio comments on it.  Now  need to find a nice early SX-101 to match up with it.