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Old 03-04-2015, 09:35 AM
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dtvmcdonald dtvmcdonald is offline
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Rca u-10

Yesterday I got an RC U-10 radio-phono, ostensibly to use
as amplifier chassis for a TRK12. But in any case I want
to get it working properly.

I looked at the chassis and a couple of paper caps had
late 60s Mylar replacements. The people I got it from said
it worked, though how the phono could have with no insulation
on the leads to the pickup and the motor loose and flopping around,
I don't know.

I tried the radio only on a dim bulb, Variac and B+ meter, and
it works fine. A recap is pending.

But two questions: the pickup is a crystal one, It runs into the
volume control of a standard AA-5 style 2 stage audio setup (it does
have a power transformer). Its probably bad, though does generate
up to 0.1 volt (into 1 megohm) if the needle is thumped. Do replacements
for these exist?

Second question is how the phono-radio-TV switch works. It has three
positions and the radio signal appears at high volume in two of them
and low volume in the other. The description of the switch on the
schematic is opaque. Does anybody know how this works? I don't
relish the task of tracing it out.

I have zero experience with old phonos. Mine is with radios and TVs.

Doug McDonald
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Old 03-04-2015, 11:24 AM
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Electronic M Electronic M is offline
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Odds are the phono and TV inputs are connected together, and the switch is just a radio-input switch with extra positions to act as a tone control.

It is rare to find a 78 rpm era crystal cart that still works worth a damn. There are two options get it rebuilt (IIRC west-tech services is a rebuilder), or replace it with a modern cart with a larger 78RPM appropriate stylus, and possibly add a stage of preamplification to compensate for the possibly lower output of the new cartridge.

The TRK 12 never had a built in phono so you don't really need to keep the phono that came with the radio chassis.
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Old 03-04-2015, 12:06 PM
Olorin67 Olorin67 is offline
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78 rpm era crystal carts are a restoration problem for sure, unless you can get it rebuilt. The crystal material goes bad from heat or humidity. Most 78 rpm era phonographs and changers track too heavy to use a more modern cartridge, and would need to be modified to lighten the tracking to go that route. The VM website should have rubber motor mounts that fit most units.
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