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1962 Motorola no audio

S

stephenp

New Member
I am new to the forum and this is my first post. I have a 1962 motorola console that I am trying to get running. Have tested all tubes, amp,preamp and tuner all tested good (the tubes are all original). There is no audio from any source, not sure what to test next?. The only test gear I have besides tube tester is volt ohm meter. Any help would be great. Steve P
 
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I'd start by looking for the B+ (also called high tension) voltage at the rectifier. Give us some more info as far as tube numbers and such. Oh, and welcome to AK.:thmbsp:
 
Motorola amp no audio

Thanks for your reply.

Tubes in the preamp use 3 12AX7A. Tubes in the amp are 12AX7A, 6V6GTA, and rectifier tube is 3DG4.

When I tested the 12AX7A tubes on the amp, they were in the question mark zone on my tester -- not sure that would make a difference. The rectifier tube was in the low end of good range.

Still feeling my way around tube amps after more than 40 years of being away from building tube products.

Thanks, Steve
 
Looks like the filament on that rectifier is 1 and 3, so you should read ~3 volts across those two pins.......................then, one of them will have a wire going to the first cap in the filter. Reading from that wire (or pin) to ground (chassis) should show you your B+ voltage (I'd guess around 300+). Are you comfortable working with the voltages described? Make sure to be very careful, and it's a real good idea to keep one hand in your pocket so you won't get voltage across your heart if you do get on it somehow. I like to just use a clip lead or meter lead with built in clips. Clip the leads to what you want to measure "Then" power it up. Also be aware that the big can cap can hold a good deal of juice for a long time if it doesn't have a bleeder resistor to ground (many old units don't). So, whatcha think, feel like doing some troubleshooting?
 
Here's your rectifier pinout looking from underneath. Some sockets even have tiny numbers next to the pins, but it's easy to count them too. 1 or 3 should show you high DC voltage when warmed up (from there to chassis/ground). Five and seven is where the high AC voltage from the transformer hooks up and you should see voltage across them.


http://www.nj7p.org/Tube4.php?tube=3DG4
 
No audio

Greetings from Colorado. Yes I am ok with working with the stated current. I have a complete repair manual for this unit. It shows pin1-3 340v from source, pin 5-7 290vac from T1. I do have long covered clips for my meter.Should I perform test with all tubes out of chassis?

Steve
 
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