Tweed champ build blowing power tubes

[JoshBernstein]

Hello everyone
I just completed a tweed champ build. I put in a jj 6v6, and when i turned the amp on, it immediately blew. It appears to be an internal short. The tube was brand new, so i dont think it was shorted before i put it in.
Ive checked all of my connections and they are in the proper places.
My b+ voltage is about 425, using a jj 5y3 and a 330-0-330 transformer. Is this voltage too high, and could it have caused the tube to immediately blow?
Thanks,
josh.

[jjman]

The 425 will go lower when there is a 6v6 running. Check the cathode resistor and temporarily remove the cathode cap.

[JoshBernstein]

The resistor is reading at the correct value...
What is the purpose of removing the cathode cap?

[Stevem]

I have used those JJ tubes at 520 volts so your voltage is not a issue.
You likely just had a defective tube that was bad when you pulled it out of the box, or was just due to go south!

If you set your voltmeter to ohms you can test for shorts on that tube( likely pin 3 or 4 to pins 2 or 7) the only pins that should read to one another will be the heater, pins 2 to 7.
This is assuming that you do indeed have the socket wired up right!
If that cathode cap is shorted, than the tube burns itself up by red plating.
Is that the case, did the tube get very hot?
The question for me is that with a short like that then within 5 seconds the amps fuse should have blown!
Until you get things worked out I would derate that main fuse by 25 % to keep the PT from seeing too many over loads!

[JoshBernstein]

The tube didnt red plate, but it looked exactly like this: https://youtu.be/mBym83g78NY
According to the meter, only pins 2 and 7 are connected.
The fuse did not blow, which i thought was pretty odd as well.
I am 99% sure the socket is wired correctly, but i will check again and report back.

[JoshBernstein]

Just double checked the socket wiring and everything is in the proper place, and none of the pins are shorted.

[Firestorm]

The tube didnt red plate, but it looked exactly like this: https://youtu.be/mBym83g78NY
According to the meter, only pins 2 and 7 are connected.
The fuse did not blow, which i thought was pretty odd as well.
I am 99% sure the socket is wired correctly, but i will check again and report back.

Are you sure you were seeing arcing and not just the blue glow?

[JoshBernstein]

Yes, it was very bright and i could hear it arcing within the tube. It also smelled burned.

[M Fowler]

I wouldn't be wiring the AC neutral white wire to the AC on/off switch like that.

[Phil_S]

Wire the AC power like this:
Wall supply hot/black > fuse > switch > PT
Wall supply neutral/white > PT (nothing between)
Wall supply ground/green > direct to chassis bolt.

If in the Eurozone, I believe both legs need to be switched, in which case, use a double throw switch and wire the "white" to the other half of the switch. I'm not sure if you are required to fuse both legs, as well. Of course, "white" is in quotes because the Euro standard colors are different, probably blue instead of white: http://www.sherline.com/powrcord.htm

There is a reason for wiring this way. When you plug the amp into the wall, the fuse is hot immediately. If there is a fault, it is supposed to blow. The purpose of that is to protect the house, not your amp, though it may do that, too.

I hope your other problem gets solved.

NB: edited for a spelling error

[jjman]

Arcing is often just a bad tube. Temporarily removing the cathode cap will remove it as a possible cause (could be shorted.) Having it off will not change the idle performance. Only the potential volume output will be reduced somewhat.

[stretch2011]

Bad output transformer can blow power tubes.
But when my power tube blew in my deluxe it was because the tube socket was cracked on the plate pin.

[JoshBernstein]

How can i test for a bad output transformer?
I tested the resistance between the primaries, and im getting 340 ohms. This seems low to me. Is that indicative of a bad transformer?

[sluckey]

Have you put another 6V6 in it yet?

[Stevem]

A bad OT can only pop a output tube if your playing thru the amp and letting it red plate, not by just taking it off standby like he did!