10-20-2022, 05:53 PM
In another pix of the trimmer assembly, it appears there is either staining or an accumulation of wax on the metal leaves of the compression trimmer. Both mica and the wax are not mechanically compressible, therefore, the wax "layer" is preventing a minimum compression of the trimmer, thus limiting reaching a lower point of resonance. However, that does not seem to agree with the fact that the tuned circuit is resonating so low.
I would suspect a scenario where the tuned circuit is too high from this lack of compression. I do think there is a problem in the trimmer that careful cleaning will resolve, but I don't think that will fix it...Most "radio" wax will move when bathed with 91% alcohol.
You will need a steady hand to disassemble a compression trimmer. I did but I was a teenager 50 years ago.
I also suspect there is a problem in the coil itself. FWIR if the DC resistance is around 20 ohms or so. (OH! Use an analog ohmmeter that uses a bit of current like a Simpson 260.) I would consider it O.K. but where this resonance issue exists, I think that one or more strands of litz have either gone open internally or at the connection point, start or finish of the winding.
I have seen this on magnetically tuned RCA coils. One slug was "dead". I was unable to fix but it was a popular radio so I got a parts chassis
Another tedious chore is to de-solder the finish end of the winding, separate the litz into individual strands and measure back to the start of the winding each strand. Each strand is insulated by enamel and should be all connected at the other end. One or more strands are open they will constitute a capacitance that should effect the inductance/resonance relationship. Generally, the break is external, if not then the winding is "toast". The only hope is finding a used IF transformer from the same model. Or, muster all your skills and rewind. The most important factoids on rewind is closely replicate the wire type/size/position, the number of turns and direction most exactly. In still another pix I see the coil(s) they are universal wound. If you have the time and up to the challenge I will lend you a Morris coil winder with a cam that can throw 1/4" or wider if need be. I may have usable litz too. I have not looked at the details. I have some potting bees wax to finish the job if need be and a hot plate for melting. I also have a bankers box full of used and new IF's but it is slim I'll have the right one, FWIR, this is the detector transformer. ...
BTW I did look up your call, saw your saltmarsh experiments. I am not on the marsh but .6 miles from Apponagansett bay, S. Dartmouth.. About 25 miles East of Succotash Marsh as the Buzzard flies...
Life has kept the power off my rigs for many years.
Powered a 1940 National RAS this past Sunday, first time in more than 50 years. Works, trying too, tunes but very hissy (electron noise) will need caps, BFO dead, hope its not a coil, probably needs caps all around at a later date.
GL
Bill...
Chas
WA1JFD
I would suspect a scenario where the tuned circuit is too high from this lack of compression. I do think there is a problem in the trimmer that careful cleaning will resolve, but I don't think that will fix it...Most "radio" wax will move when bathed with 91% alcohol.
You will need a steady hand to disassemble a compression trimmer. I did but I was a teenager 50 years ago.
I also suspect there is a problem in the coil itself. FWIR if the DC resistance is around 20 ohms or so. (OH! Use an analog ohmmeter that uses a bit of current like a Simpson 260.) I would consider it O.K. but where this resonance issue exists, I think that one or more strands of litz have either gone open internally or at the connection point, start or finish of the winding.
I have seen this on magnetically tuned RCA coils. One slug was "dead". I was unable to fix but it was a popular radio so I got a parts chassis
Another tedious chore is to de-solder the finish end of the winding, separate the litz into individual strands and measure back to the start of the winding each strand. Each strand is insulated by enamel and should be all connected at the other end. One or more strands are open they will constitute a capacitance that should effect the inductance/resonance relationship. Generally, the break is external, if not then the winding is "toast". The only hope is finding a used IF transformer from the same model. Or, muster all your skills and rewind. The most important factoids on rewind is closely replicate the wire type/size/position, the number of turns and direction most exactly. In still another pix I see the coil(s) they are universal wound. If you have the time and up to the challenge I will lend you a Morris coil winder with a cam that can throw 1/4" or wider if need be. I may have usable litz too. I have not looked at the details. I have some potting bees wax to finish the job if need be and a hot plate for melting. I also have a bankers box full of used and new IF's but it is slim I'll have the right one, FWIR, this is the detector transformer. ...
BTW I did look up your call, saw your saltmarsh experiments. I am not on the marsh but .6 miles from Apponagansett bay, S. Dartmouth.. About 25 miles East of Succotash Marsh as the Buzzard flies...
Quote:...decoupling the generator's internal capacitanceIt's the generators low output impedance, 50 Ω that is the problem.
Quote:for I am an old man.My Elmer was W1ZE...
Life has kept the power off my rigs for many years.
Powered a 1940 National RAS this past Sunday, first time in more than 50 years. Works, trying too, tunes but very hissy (electron noise) will need caps, BFO dead, hope its not a coil, probably needs caps all around at a later date.
GL
Bill...
Chas
WA1JFD
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
