Danelectro Cadet 122 problems

[edge59]

Hi, I am trying to get this amp to work, it does not come on, everything looks ok, tested all the tubes in my Tube tester and the 50C5, 12au6 and the 35w4 rectifier shows good, but non light up in the amp. I replaced the mains fuse. This amp does not use a power transformer and is about a 1949 or there abouts build. I cannot find the problem, does anyone have an idea where to start? I am getting ac past the power switch....
thanks
Ed

[Ebtronics]

Re Danelectro Cadet 122 problems

WOW you got a good old one there!!! Start checking checking wires, your looking for an open or high resistance in one or more of the wires. If the amp is as old as you think it is, it is very likely that one of the wires in the amp has opened internally where you can't see it. Get your ohm meter out. NO POWER to the amp for, Oh 20 - 30 mins!!! This allows for the cap's to discharge, DON'T wana get SHOCKED!!! Start checking the resistance of the wires individually. Move the wires around a bit if you can. You might find one the opens up. Check the resistance of a wire when your moving it around or bending it. If you see the resistance go up when your moving a wire around. That is a sing of high resistance in a wire, on it's way to becoming open. All wires sould have very low resistance to none. Some wires are disinged to have resistance. These kind of wires are different looking than most other wires & are somtimes marked that it is a resister wire. Your mainly looking for an open or VERY HIGH resistance. Hope this helps !!! Eb the vet teck

[edge59]

Hi Eb. thank you for the tips, I hope to resume testing tomorrow
Hopefully I will find it, it is a very simple amp, class-A.

thanks again!
Ed

[Enzo]

Not so sure I'd expect a wire to be open, but I bet a resistor is. All those tube heaters are wired in series. You have a 50, 35 and 12 volt heaters. In series they add up to only 97 volts. A series resistor would have been added to soak up the remaining 20 volts. That resistor opens and the tubes stay dark.

SInce those are 0.15 amp heaters in series, the resistor with that current dropping 20 volts would be around 130-135 ohms. And it would dissipate about 3 watts. SO I would use a 7 to 10 watt resistor. See any power resistors in the 100-200 ohm range? Open?

Of course the wiring could also be open, so it does bear checking, and tubne socket pins could be loose.