[morzh]

Ask her to overpack it.

[HowardWoodard]

Well, with the replacement tuning assembly, I have finally put the unit back together and aligned the dial.  The first station that came in was a local station and the dial was only 5 KHz off -- an easy adjustment.  Btw, the ones that did come in were very clear.

I have started the tuning process with the broadcast band.  I don't have an antenna and even the really local stations don't come in unless I am touching terminal #1 with my finger.  Even with that, it only picks up stations from 1250 KHz and up.  Looking at the audio out with an oscilloscope, the signal simply flat-lines when it gets down to 1250 and stays that way to the bottom of the band -- like it is being muted.  Makes me think of that little custom-made plastic strip that I didn't know where to put back in the tuner.

Trimmers 36A (gang 1 to RF Amp) and 36B (gang 2 to Det-Osc) look like someone thought they were mounting screws and are tightened all the way down.  When I adjusted the other trimmers, they seemed to be working correctly, and it was easy to find the peak.  I'll loosen 36A & B tomorrow and see how it effects things.

Tomorrow I'll start tracing the signal from my signal generator.  I saw a couple of articles/posts/YT vids on tuning.  I expected to hear the output and be able to tune it by sound but that didn't happen.  Also, none of the ones I reviewed said what the two input voltages (when injecting into the Det-Osc control grid and when injecting through the antenna terminal) from the signal generator should be -- my sig-gen can be set from .1V to 3V P-t-P.  So, if someone knows what they should be I'd appreciate hearing.

I'll post back tomorrow with my specific findings/results.

[RodB]

You may have to start further back with your signal injection at the IF signal grid, then tune the second IF transformer. When you're satisfied with that then move the signal generator to the front. Signals around 0.1 - 0.5 volts should make it through.

[HowardWoodard]

Thanks.  I'll try that.

[HowardWoodard]

Ok, I think I'm about done.  I've got one anomaly left but other than that, it is working great and picking up lots of stations, including on bands 2 & 3.

Here's the "anomaly"...

I kept getting stuck at the tuning stage where I was to tweak the two ganged trimmer capacitors, 36A for the RF stage and 36B for the Det-Osc stage.  36A seemed to have a little effect but 36B had none.  Both of them would occasionally spike to a much higher voltage but that was all, just a spike.  I took them off to clean them.  While they were off, I turned the radio back on and when I did, the signal amplitude jumped up to about what I was expecting to see.  It could receive lots of stations and they were all strong and clear.

That's when I took a closer look at the trimmer setup and realized that whenever they were installed, they were shorting the signal.  As you can see in the attached pictures, there is a thin plastic insulator that goes over the mounting post -- the mounting post is chassis ground -- then the trimmer goes over the post and is held in place with an insulator and cap nut.  Then a screw goes through the spring-tensioned end of the trimmer to adjust the trimmer up and down.  The problem is that unless you have carefully held everything in place such that the trimmer mounting hole, which is bigger than the mounting post, does not touch the post when you tighten the cap nut down onto the top insulator, then the moment you insert the adjusting screw you have a signal short to ground.  I got lucky once with 36A.

So, as far as this old beast is concerned, I can just leave these trimmers out and everything will appear to be working perfectly -- which I may end up doing.  But my curiosity makes me want to at least understand if this is the normal mounting components for these trimmers or if, like most everything else, has been jury-rigged over the 88 years it's been in operation.  Is there a different setup, or perhaps a little bushing for the trimmer than what I have?  Perhaps these insulators once had a ring/shoulder on one end that kept the trimmer centered?

Thanks for all the help I've received from you fellas, and it looks like I've managed to stumble through putting it to good use.  Just once more if you would...

[RodB]

Far as I know, that plastic insulator should be mica. I don't know if plastic is an equivalent insulator.

[morzh]

This looks like mica anyway.

[HowardWoodard]

I think my thinking is upside down but just flipping it raises another question. I think the gap that I was adjusting when turning the bottom screw is a red herring. I think that bottom screw is meant to be tight, securing the trimmer cap to one side of the variable cap. The top "cap nut" is probably the adjustment device. While that makes sense and agrees with the schematic, it raises the issue of how the mica is held in place. Right now, if I loosen the cap nut, the insulator and the mica become loose, allowing the mica to slide around and, in fact, allowing the copper to come into contact with ground.

Obviously, I can put a little adhesive under it, but I doubt that's what the factory would have done. Should there be a little dielectric grease on the back side of the mica to help hold it in place? Or something else?

Just about done...

[Vlad95]

The mica insulator serves only to prevent short circuits at maximum capacity. And to increase the maximum capacity due to the increased dielectric constant of the gasket. The plastic washer insulator isolates the hole in the elastic movable trimmer lining from the threaded axis due to the protruding rim, which can simply wear out. To prevent short circuits, it is necessary to precisely center the hole in the movable lining relative to the adjusting rod during assembly and install the plastic washer so that its rim fits completely into the hole in the plate.

[Vlad95]

The bottom screw must be FULLY tightened when assembling the trimmer. But before that, as I mentioned, you need to accurately center the plate. Only the top screw is used for adjustment. The mica can lie freely, it is guided by the hole and the cutout. That is why you shorted out, because you loosened the plate mount and knocked off the centering.

[HowardWoodard]

Thanks. I’ll be back home in a couple hours and will reassemble the trimmers, finish the alignment and start packing it up for it’s journey back to North Carolina.

I’ll report back…

[HowardWoodard]

That took care of those trimmers -- thank you, thank you.

All the rest of the tuning worked as expected except for the very last step which is the 53S trimmer (32-2376) for the discriminator (6H6G) at 1,000KHz in the broadcast band.  It seems to have a little effect but not really predictable.  It looks like one might hold the nut while turning the inside screw but without really honking on it -- which I haven't -- it doesn't do that.  The whole thing turns, giving that small "fuzzy" effect.

Does anyone know how this particular trimmer is supposed to work mechanically?

Thanks in advance...