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I recently picked up a nice 46/132 Farm radio in a good condition cabinet - but when I pulled the chassis out, it looks to me like someone has removed 6 of the moving plates and the associated fixed plates from the oscillator section of the variable capacitor.
If you take a look at the picture below, you can see the empty slots where I think these would have fitted.
But it seems like such a bizarre thing for someone to do - and not all that easy either - that I have my doubts. Maybe this is actually how the factory supplied them ?
I'm certainly having issues getting it to tune in to stations - I can get 3 or 4 strong stations but nothing is in the right place on the dial; everything is pushed up into the higher end of the dial scale.
Also I cannot get it to work when the B+ voltage is at 90V - I made a simple dc power supply but I actually have to reduce the supply to about 70V to make he 1LA6 tube go into oscillation - I feel this is connected with the first issue but again I'm not sure. When I do get it tuned in, it sounds great.
The radio has been recapped (not much to do really) and a couple of borderline resistors were replaced.
I guess I might have to hunt for a new variable cap. but I'd appreciate any information or ideas.
Here is the the schematic diagram and a picture of the tuner :
http://www.nostalgiaair.org/Resources/590/M0013590.htm
http://www.hightail.com/download/OGhmYUlqSEJrWS9MYnNUQw
Thanks !
Chris
(This post was last modified: 11-13-2013, 04:42 PM by
Chris Cusick.)
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The tuning condenser looks ok to me. You may want to listen to the LO in another receiver. Should tune from 995kc to 2055kc.
Terry
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OK - Thanks - I have a little digital AM radio, and using this to pick up the frequency of the LO, I am only getting a small range which coincides with the stations that I can pick up - so nothing at the low end below about 670 kHz (1125 kHz from the LO). I can pick it up for frequencies as high as my digital set will go which equates to 1245 kHz on the Philco, being 1700 kHz in the digital set. Practically I can pick up actual stations between 720 and 1050 kHz although everything is too far up the dial.
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Is the needle in the correct position? IF on frequency? Tuner in need of alignment?
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Honestly Chris, that variable cap doesn't look right to me. In general, the osc section needs less capacitance than the ant section, but in your case it looks extreme. No only are the plates smaller, but there are much less of them. The fact that you can't tune the LO below 1125 kHz seems to confirm there is too little resonating capacity available.
The only reason I can think of to remove the osc plates would be to bandspread the tuning so that the dial would cover a smaller tuning range. But this would also cause the tracking with the ant tuned circuit to be way off, which seems to also be what you are experiencing.
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The thing is, he's picking stuff up too far up the dial. This would indicate too much capacitance in the LO, not too little.
In the pic, I see no signs that any plates were actually removed. If they had been, there would be telltale signs like nubs of metal on the mounting points of the stator, and damage to the phenolic holder on the rotor. But there don't seem to be even any scratches on the outside rotor plates, which certainly there would be if adjacent plates had been removed.
Just my observations.
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It would sure be easier to tell if that tube were removed.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
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I wonder if the previous owner did some mods and added an additional cap across the oscillator coil to compensate for the reduced capacity of the plates? That would explain why the stations appear further up the dial.
Chris, do you see an extra mica or ceramic cap soldered across the oscillator coil, which does not appear on the schematic?
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Thanks so much for the feedback and ideas. I took out the tube and took another picture. If you look at the phenolic spacer strip in the middle of the moving fins, you can see that they actually over hang on either side. I did not notice any other capacitors related to the oscillator coil - but I will double check. Maybe I should add some !
The dial does track normally from fully closed to fully open, so it is not a case of the needle just being mis-aligned.
http://www.hightail.com/download/OGhjY05tcWYwMEdVbDhUQw
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Thanks for the new pic. I still see no evidence that the tuner has been modified.
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OK - in that case, I think I'll go 'back to basics' and make sure that I'm not missing something simpler by fixating on the tuner then.
Thanks !
Chris
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