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Dim bulb Help needed

S

shay1510

New Member
Hey guys,
I'm trying to restore a vintage PA tube amp (2 el34, 4 ecc84)
and I've built a dim bulb tester in order to test it.

Let me say in advance that my knowledge in electronics is far from being good. However I'm making sure to use saftey measures for my own safety.

the tubes are out. I've connected the dim bulb and the amp to the socket, both "standby" and "power" are on "0". I've switched "power" on and the amp starts making "working" sound (hum) but the bulb won't light. then I switch the "standby", and the bulb light bright and dim quickly (like it should I guess)

My question is, Why won't it light when using the "power" switch, and does it mean I have a problem?

Thanks everyone.

*I use a 75w light bulb for a 50w amp, and I've connected it to a 4ohm speaker rated 30w (I know that it's far from being great but I've read that It's possible just for the test)
 
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Since you don't have the tubes in, there's practically no current being drawn by the amp. Remember, the power switch is for tube heaters and everything else in general, and the standby switch is for the B+. So that sounds perfectly normal. If you really want to "see" the power the amp is consuming, you're going to have to use a much smaller bulb.
 
ok

Thanks for the answer.
actually I'm doing my first steps going from guitar pedals to amps.
If everything goes right, I'm going to change part of the circuit in order to turn it into a guitar amp.
 
Use caution with the high Voltages!

I am assuming you have a solid state rectifier circuit, and with all the tubes out of there sockets, the power supply capacitors will charge up and then (with nothing to drain the charge) hold their charge for some time.

The charging is what you "see" on the dim bulb tester.

Please use your multimeter to test for high Voltages (and drain them off) before working on the wiring of the amp.:thmbsp:

Leaving the standby switch ON, while the power is turned off (with the tubes installed) is a good way to drain the charge on the caps (double check with your meter!):yes:

Mark T.:music:
 
Thanks for the advice

Will try to do that.
If I understand correctly, I'll set my meter on DC voltage and put the two probes across the two lugs of each of the big filter caps to see if any voltage is still there.
 
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