It is more than possible, it is very likely. Get well soon!

It says so here (from Deleeh's link): "Man kann die Octal- V-Serie als französische Version oder Gegenentwurf zu den amerikanischen GT- Röhren ansehen". "Der Suffix V steht höchstwahrscheinlich für „verre“ = französisch für Glas".

I am also very fond of 6C5 but this is a very special version of 6C5, 6C5V, that causes hum. They don't do it in every amp, probably, and not with every power tube.

If you try the aluminum foil experiment you will know if these tubes will need to be 'screened' in some way. It will also tell you if they are any good. Proper 'shielding/screening' makes them sound so much better if this is something that causes problems. But they need to be 'burnt in' too, to...

Some of these tubes with metal paint have a very thin wire connected to one of the pins to let the metal paint act as a screen. Can you see such a wire on your 6C5V? If so, is the connection intact?

With some tubes you need to remove material to get a proper contact. Not often but sometimes. Some use a metal brush with a Dremel type tool, others sand paper /emery board. @mordy usually uses a small pen knife. This is good practise. You don't want dirt to enter your sockets.

Have you mechanically cleaned the pins? Does the hum go away if you wrap aluminum foil around tubes and top of adapters? If this doesn't help, you can connect the foil to the upper screw on one of the output transformers, just as an experiment. Someone suggested that this is a problem in just...

You don't eat the same food all the time, do you? There are several combinations that is good and we like variation. You don't listen to the exact same music all the time even if it is very good. Tube combinations can be good in different ways and suit different tasks. So we do it for different...

Just contact @Deyan

How high? And STC was a subsidiary of ITT, their British operation.

If so, you will have to change something else in the design :fearful:

Flat head and dome nut wins any beauty contest... But how do they sound?

Why don't you give him one as a small gesture? :wink:

And I like dome nuts, not donuts. :wink:

They are clearly different with a brighter tone that some might call clarity. At least this is my experience.