Motorola 56x14ba

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Motorola 56x14ba

Post by regent on Tue Nov 03, 2009 9:58 am

Have a Motorola 56x14ba that has some audio from the speaker, but no stations are received. All the electrolytic and paper caps have been replaced and 5 of the six tubes have been swapped with known good ones. The IF, oscillator, and antenna test ok. It has the old dog bone style resistors and some are out of tolerance (over 20%). Some restorers automatically replace all of these because they drift, others only replace the out of tolerance resistors. These need to be replaced before voltage measurements can be made. Is it best to replace all of them upfront?

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Re: Motorola 56x14ba

Post by Bill Cahill on Tue Nov 03, 2009 2:06 pm

I'd start with checking voltages. But, if you must replace resistors start with audio section.
Do you have a schematic? You might also have accidentally mis-wired something. We all make mistakes.
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Re: Motorola 56x14ba

Post by regent on Tue Nov 03, 2009 5:41 pm

I have a schematic and checked all the wiring after the caps were replaced. Will also check the voltage measurements. I only have a DVM not a VTVM, how much will it affect the readings?

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Re: Motorola 56x14ba

Post by Bill Cahill on Tue Nov 03, 2009 9:07 pm

Shouldn't very much.
Are I F transformers large, or, miniature?
Miniature ones go bad.
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Re: Motorola 56x14ba

Post by regent on Wed Nov 04, 2009 12:05 am

IF transformers are large and show some resistance

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Re: Motorola 56x14ba

Post by Resistance is Futile on Mon Nov 16, 2009 9:59 pm

1. Why only 5 of 6 tubes?
2. why wasn't the 6th tube replaced?
You can use a probe to see if the volume control is working Touch the center tab and see if it causes a hum in the speaker, if not the the audio section is suspect.

If you get a sound then do the same thing in the previous stage. (in other words trace the circuit backwards for a signal).

If you have a pair (or single) high impedance headphone you could use it with a small signal diode and a capacitor for safety as a signal tracer. Trace the signal back that way. Keep one hand in your pocket to prevent shock.
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Re: Motorola 56x14ba

Post by Bill Cahill on Tue Nov 17, 2009 12:07 am

Very good idea. You should post that idea in our tutoring section. It's a great way to check for signals.
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Re: Motorola 56x14ba

Post by Resistance is Futile on Tue Nov 17, 2009 3:02 pm

OK will do. thanks bill.
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