Zenith blonde wood console

[Firedome]

sorry for the double pic...

the 6V6GT PP amp:

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The site is loading 1.4 Mb pics now without re-sizing... go figure!

[Motorola minion]

This chassis is a close cousin of a slightly newer one (12A20?) I restored last summer. This one has fewer problems than the one I did already. Both had broken dial strings (3 on each one!) and the infamous multi-tap power resistor, otherwise known as a "cand-ohm", was partly open and shorted to metal case! Someone attempted partial repairs with equally unsuitable resistors of the wrong values.

Looking at the pictures below, you would assume correctly all those yellowed wax caps are suspects but the two 2-section electrolytics tested fine for power factor and max voltage of 450v with spot-on values of capacitance and ESR.

Mallory is EIA 232 and type FP caps are usually OK. The same does not hold true for original capacitors being reformed in television sets, which need to bypass frequencies much higher than a half-wave or full-wave power supply 60/120 Hz. When I powered up, all 3 supply voltages were within a few volts of schematic.

This chassis actually played fine on both AM and FM, despite broken dial string and all those wax caps . This just after replacing the 4-section resistor with individual wire-wound types of double wattage called out on the factory schematic I am using. I was also able to reattach the 3rd IF transformer which I accidentally pulled off, along with the coil and four tiny wires. Again, darn glad to have that Zenith schematic from a 1957 issue of "circuit digest", because I do not have the Photofact for this model.

Next is to replace all those wax caps and perform a decent alignment. The multiple-option record equalization switch and a "piggy back" 6J5 phono preamp are ideal for a bluetooth input, even if the cobramatic is connected as well. There are tuner-style feed-thru caps from each end of the output transformer to the two electrostatic tweeters.

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12Z20 chassis c.jpg (42.63 KiB) Viewed 1123 times

12Z20 chassis b.jpg (32.75 KiB) Viewed 1123 times

[TC Chris]

Remember that what Zenith calls a "preamp" is really an oscillator/demodulator for the Cobra system. The cartridge is a vane that modulates an AM RF signal and then is demodulated ti get audio. That's what's in my Wurlitzer 1100 jukebox.

Chris Campbell

[Firedome]

That's a fairly crowded looking chassis for a mono unit...good that someone who really knows what he's doing is in there doing the troubleshooting!