Is this risky?

[daz]

I have 2 bad winged C el34's that blew the mains fuse when used. I now have them mixed up with one good one. Would it be foolish to try all 3 to find the 2 that blow the fuse or is it risky to the tranny or anything else? I hate to throw away even one good one since they are going out of production, and a couple 50 cent fuses are worth the cost, a amp issue isn't.

[Enzo]

You can't always tell with a meter, but if the meter reads shorted, then the tube is bad for sure. Ohms scale, probe from pin 1 to pin 2,3,4,5,6,7,8. ANy shorts? Now from pin 2 to pin 3,4,5,6,7,8. It should show a low resistance to pin 7, the other end of the heater, but no others. Now pin 3 to pin 4,5,6,7,8. Pin 4 to pin5,6,7,8. Pin 5 to pin 6,7,8. Pin 6 to pin 7,8. And pin 7 to pin 8. It takes seconds to do this. ANy that are shorted, throw away immediately. But many only short under voltage or at heat. Got a tube tester?

[big_teee]

I have 2 bad winged C el34's that blew the mains fuse when used. I now have them mixed up with one good one. Would it be foolish to try all 3 to find the 2 that blow the fuse or is it risky to the tranny or anything else? I hate to throw away even one good one since they are going out of production, and a couple 50 cent fuses are worth the cost, a amp issue isn't.

That is the kind of thing the dim bulb tester is great at.
It saves your fuses, and if the light comes on and stays on bright, then that is the bad tube.
I had a KT77 that blew fuses, and I proved it with the dim bulb tester.
Dim bulb tester - Google Search

[Jazz P Bass]

In cases such as this I like to monitor the B+ voltage.
Turn off the power switch & insert the tube, while looking at the B+ voltage.
If the high voltage drops like a rock, that tube will most certainly blow a fuse.

[Enzo]

Knock out a real basic simple Champ-style amp. One 12AX7 and one octal power tube. Wire the octal socket so EL34 will work as well as 6L6/6V6. We don't care about tone, so it doesn;t even need a tone control if you want to leave that out. Leave the little chassis out so you can swap tubes into it in a heartbeat. Plug a bench speaker into it when you need it. Now you have the ultimate tube tester - an actual amp circuit. You will know right away if you have a screwed up power tube. And the small socket will work on 12AX7, 12AT7, or any of the others in that family. Not only will it tell you that the tube works, but you will also be able to hear if it is noisy or microphonic. Not worried about impedances and stuff, all we are doing is checking if the tube works or not. We are not looking for full power and super freq response. Just does the tube light up and work, does it amplify.

[daz]

Knock out a real basic simple Champ-style amp. One 12AX7 and one octal power tube. Wire the octal socket so EL34 will work as well as 6L6/6V6. We don't care about tone, so it doesn;t even need a tone control if you want to leave that out. Leave the little chassis out so you can swap tubes into it in a heartbeat. Plug a bench speaker into it when you need it. Now you have the ultimate tube tester - an actual amp circuit. You will know right away if you have a screwed up power tube. And the small socket will work on 12AX7, 12AT7, or any of the others in that family. Not only will it tell you that the tube works, but you will also be able to hear if it is noisy or microphonic. Not worried about impedances and stuff, all we are doing is checking if the tube works or not. We are not looking for full power and super freq response. Just does the tube light up and work, does it amplify.

Well, no shorts per Enzo's meter test, tho i know one of them has an intermittent short because t blew a fuse when i flicked it with my finger. Hard to do that holing probes tho so i need to try t with some clip leads which i don't have at the moment.

[leydenjar]

I built exactly what Enzo describes in the post above a couple years ago.

Build it with a beefy power transformer and leave the tube rectifier in the circuit that way you can test rectifier tubes as well.

Get a socket adaptor and you can test el84 too!

[daz]

Well, back to the original question......is it risky to test them by putting them in the amp and blowing fuses to see which are bad?

[Jazz P Bass]

Well yeah, it's risky.
You are stressing the circuits.
I think the worst case would be a plate to heater short.
You could try it with the lowest fuse value that the amp will start up on.
A 2 tube 6L6 amp should not draw more than 70 watts at idle (depending of coarse on how insane the bias is set).
Also, the initial cap draw has to be taken into consideration.
It may be best to try it with only one tube.
Now a 1/2 amp fuse should be sufficient.

[daz]

Well yeah, it's risky.
You are stressing the circuits.
I think the worst case would be a plate to heater short.
You could try it with the lowest fuse value that the amp will start up on.
A 2 tube 6L6 amp should not draw more than 70 watts at idle (depending of coarse on how insane the bias is set).
Also, the initial cap draw has to be taken into consideration.
It may be best to try it with only one tube.
Now a 1/2 amp fuse should be sufficient.

Thanks. Guess i'll just trash em and grab some new ones b4 they're all gone or start demanding $150/pair NOS status.

[Jazz P Bass]

Grab a 1/2 amp fuse & have at it.
All tubes run a 'risk' of going bad.