I have working valve I took out of a good working set and put it in a set that had issues.
The Valve is a 6cm5 and it works fine in both sets , but I noticed the glass has a defect in it like a indentation that causes the connection ontop of the valve to sit crooked and I wanted to ask is this a manufacturing fault or something else that can cause the glass to change shape slightly.
The Valve does work fine though.
Off set is probably a better term to use,the connection is off set due to a bend in the glass
Pete

I have quite a few of them. The only thing that usually goes wrong up top is the top cap breaking free.

If it works, no stress. I assume you know TC is the plate.

Hi marcc,
Yeah the cap is fine, not loose and so is the valve,just a bend in the glass .must be from the manufacturer

Pete

I once found a 6DQ6 line output valve that had gotten so hot that the glass had melted into a cocoon around the valve elements. The vacuum still appeared intact, but I had no way of testing it at the time.

This one is only slightly dinged Robbert,but as I said it works fine ,just I've never seen that before.

Pete

I have seen valves that were misshapen after red plating for an extended time.
It seems the glass gets so hot that the vacuum sucks it in slightly.
A 6CM5 will red plate if the Hor drive is removed but usually are dead after this happens.

Yes a 6CM5 won't tolerate that kind of abuse for very long.
A 6CM5 was designed to work as a switch, which is why they make very bad audio amplifiers and why, deprived of drive and bias, they turn on so hard they destroy themselves quite quickly.

Pete your Pedigree has a little delay fuse in the screen circuit to protect against this. It's a half-watt resistor with a spring around it. Overload heats the spring, melts the solder and it pops open. Protects against loss of drive as well as damage to the screen grid if the 6AL3 fails, which they did, often. Also protects the hor OP transformer.

One of the things that can happen is a failure in a power supply that is feeding the grid bias. Then we have diodes & things get seriously hot.

Ian, this 6CM5 is not out of the Pye set,it's in one of my old 50s sets ,but the set runs/

What brand is the 6CM5?
I'll bet it's not a Trigon.