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Hello all,
Thought since the first 66 went so well,I'd try another one with all I learned. Radio works -- all caps replaced, out of specs resistors changed.
Two minor problems- tone control goes into a high pitched squeal when put in left hand position (less bass). Tone control was rebuilt. The volume control is very touchy- I cleaned it well but get very irregular control. I actually had this out of the radio and separated the on/off section and cleaned internal controls very well- they seemed to move as expected.
Any thoughts on either problem?
http://www.nostalgiaair.org/PagesByModel...013827.pdf
These problems are hopefully minor compared to the last one.
Thanks,
Joe
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Joe, are all the tube sheilds in place and grounded to their brackets? Also make sure the grid wire to the type 75 tube is routed inside the tube sheild.
Steve
M R Radios C M Tubes
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After following Steve's suggestions I would change the .002 in the tone control to .005 or so. That should take care of the squeal problem. It's sounds like the volume control is bad I'd replace it.
Terry
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Here's something I don't understand. I fully expected a capacitor after the field coil to the Chassis. There is none. There should be....
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There should be a 6mFd and an 8 mFd cap on either side of the filter coil, one side of the field coil is connected to the same side of the 8mFd cap the filter coil is connected to. There is no electrolytic connected to the other side of the field coil.
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Agree, wire the replacement caps exactly as originals. Schematics sometimes have dots missing, which can get very confusing.
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Thanks guys.
Steve- checked shields and grid wire== all good.
Terry- will change .002 to .005.
Any thoughts on where to track down a 350,000 ohm vol. control? I have 250,000 and 500,000 ohm vol. controls in stock. Will either of these help?
Joe
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Either one should work fine.
Terry
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I believe we had the same case of missing dot here in this forum, from exact same cap, a couple of months ago.
There SHOULD be a tiedot between the wire from the right #50 8uF cap to #28 resistor, and the crossing wire from the top side of the field coil and left bottom pin of the output xfmr.
If you did not wire the cap after recapping back when it was, this can be the reason of your squealing, you have a positive feedback and ocillation using xfmr and the tone control caps as resonant tank, turning the output stage into an oscillator. Actually this is why I asked about this cap after your question about squealing. So I would check this before changing value of that 0.002uF cap.
If the cap is there, then it is something else.
(This post was last modified: 07-06-2012, 06:51 PM by
morzh.)
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Dot was missing on schematic. You guys figured that out on the first 66 I did. That one was worked on in the past and left largely undone. The 2nd 66 was virtually untouched.
There is a connection at the point you question. Squeal is still there on left click on tone control. Hopefully will have some time this week to get back to it.
Thanks,
Joe
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Finally had a chance to work on 66.
Replaced volume control and radio sounds great! The squeal on tone control also stopped.
Two birds with one stone.
Will take some photos and post.
Thanks to all again!!
Joe
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Joe, so glad you got another one working!
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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A few photos of both 66s.
Thanks again for the great advice.
Joe
[Image:
http://i1079.photobucket.com/albums/w511...lco66B.jpg]
[I[Image:
http://i1079.photobucket.com/albums/w511...oth66s.jpg]MG]http://i1079.photobucket.com/albums/w511/jph141/66B3.jpg[/IMG]
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Two very nice sets!!!!
Terry
