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 Very poor performance from crappy 5 tube Motorola clock radio

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MikeBrown

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Posts : 3
Join date : 2010-10-17

PostSubject: Very poor performance from crappy 5 tube Motorola clock radio   Sun Oct 17, 2010 3:15 pm

I have a Motorola 52CW3 clock radio. The set has been recapped, with the exception of several caps that are located in a couplate.

The radio works, but very poorly. I can just barely hear two stations at max volume. The set has a ferrite rod antenna. Reception is slightly improved when I touch rod. I suspect I am a better antenna than the ferrite rod....

Tube lineup is 35W4, 12BE6, 12BD6, 12AT6, 50C5. (I do not have a 12BD6 and have used a 12BA6 as a sub).

I measure 106V on the plate of the 50C5 and 95V on the plate of the 12BE6.

Any ideas?
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Chas

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Join date : 2010-10-12
Age : 70
Location : S. Dartmouth MA 02748-1225 ------------ Avatar: Uncle Tony's Shack

PostSubject: Re: Very poor performance from crappy 5 tube Motorola clock radio   Sun Oct 17, 2010 3:23 pm

Tune-up the rf front end and the IF. If it won't peak and track properly there is a component problem. Replace or discrete the couplate. Hand sensitivity is usually an out of resonance condition, unless the radio is in the cellar or a metal sided building.

I recently dumped three Motorola portables because of all the couplates and cordwood modules. Not that they did or didn't work, why bother going nuts over a a known problem that gets worse as time goes by Neutral
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Johnnysan



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Join date : 2010-10-12

PostSubject: Re: Very poor performance from crappy 5 tube Motorola clock radio   Sun Oct 17, 2010 3:36 pm

That couplet is only 4 capacitors. As a test, remove the ground lead of the couplet and connect a .005uf cap from pin 7 of the 12AT6 to pin 5 of the 50C5. If audio improves or is normal, the couplet is bad. If you need the Sams I can email it to you.
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MikeBrown

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PostSubject: Re: Very poor performance from crappy 5 tube Motorola clock radio   Sun Oct 17, 2010 4:12 pm

I disconnected the .002uF cap in the couplate and replaced it with a .002uF 620V film cap. The radio works really well now!

Is it worthwhile replacing the rest of the caps in the couplate? The schematic claims they are ceramic, should they not be pretty durable?
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jack shirley



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Join date : 2010-10-12
Location : SE USA

PostSubject: Re: Very poor performance from crappy 5 tube Motorola clock radio   Sun Oct 17, 2010 5:01 pm

The construction and internal connections of the couplate may be at fault even if the actual cap inside is good.

I don't often have to deal with them but I'm a pessimist when it comes to goofy radio manufacturing ideas that didn't last.
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