catastrophe !

[hebaton]

What sort of damage will occur if a power tube is inserted wrong into the socket and B+ aapplyed ?

[sluckey]

What sort of damage will occur if a power tube is inserted wrong into the socket and B+ aapplyed ?

I'm guessing you're asking about an octal socket? If so, there are 8 possible scenarios and only one will give happy results. The other seven possibilities range from nothing will happen to burn the house down.

[Colossal]

There is a key on an octal tube that doesnt even allow the tube to be inserted into the socket incorrectly, unless the key is broken off the bottom.

[martin manning]

The key isn’t fool proof. Tolerances can be sloppy enough that the tube can be inserted 180 degrees from the correct orientation

[Stevem]

I have found out more then twice when retubing my champ in a hurry that you can swap the 5y3 and the 6V6 and only have the repercussion of no sound.

[sluckey]

There is a key on an octal tube that doesnt even allow the tube to be inserted into the socket incorrectly, unless the key is broken off the bottom.

I have several 6L6s with broken keys. Thankfully there's a readily available fix...

https://www.amplifiedparts.com/products ... ctal-tubes

[hebaton]

IT is entirely possible and one has tp be carefill which I wasn't, here. THe keys on modern tubes are often very small and the tube will fit wrong if in ahurry.
turn's out the screen grid resistor burned, all I had on hand was a 1 watt carbon comp, hope it will hold a while !

[Roe]

some new sockets are so bad and loose that you can insert a tube wrongly even if the key is not broken.

[jabguit]

The key isn’t fool proof. Tolerances can be sloppy enough that the tube can be inserted 180 degrees from the correct orientation

agreed - particularly with some overseas made ceramic sockets with less than acceptable tolerances....


cheers,

[R.G.]

Just thinking and riffing on the seven ways to get it wrong thought.

Exactly as noted earlier, there is one way to get it right and seven ways to get it wrong. I have not done this experiment with pencil and paper yet, but a tube with no heater power can not conduct from cathode to any other electrode - no electrons to move.

So any possible effect would come from the low resistance from the heater or from internal pin-to-pin connections. This can get sneaky. The 6L6-7027a combined datasheet shows the internal bridging that the 7027 has that a 6L6 does not. Beyond that, the socket in the amp may have no lugs at the "unused" positions for its intended output tube, or might have all eight lugs and the wiring could use a nominally unused lug on the socket as a solder tie point for something else entirely.

A quick session with a printed schematic, and a clear overlay drawn to show the internal bridging in the expected tubes would let you turn up the possible ill effects.

[martin manning]

Taking a look at the possibilities, it seems there is only one position, 180 degrees out, that has a low risk of damage for 6L6/EL34 tubes. This assumes socket lugs 1 and 8 are grounded, and lugs 2, 7, and 5 have a path to ground. That is also probably the most likely failure mode, since the pin on the tube can rest in the socket's keyway, which allows a bit more room on the opposite side for the key (on the tube pin) to fit into the hole in the socket.

[Fischerman]

The key breaking off is the main reason I don't ship amps with the power tubes installed. I've received amps with the key broken off, rattling around inside.

At the other extreme I have a pair of Mazda 6V6s that have extra fat pins that won't go into some octal sockets. I damn near broke something trying to get them into my Deluxe clone (either Tweed or Brown, maybe both). But they just would not go in.