More info on the 6P1 tubes:
(in response to a Q are the 6P1 equivalent to EL84):
OK, Done some research and it appears that they are NOT the same/equivalent.
To make matters worse, the 6P1 (often seen in ebay tube amps) is usually advertised as 6AQ5. The problem is that the 6P1 is 9 pin while the 6AQ5/EL90 is 7 pin! It does seem that the 6P1 is the same as a russian 6P1P.
It really doesn't help matters that sellers of the 6P1P tube on ebay almost universally advertise it as 6P1P/6AQ5/EL90!!!!
I gather that electrically they are very similar, so could anyone shed any light on this? Is there such a thing as a 9 pin to 7 pin adapter that would allow one to use the EL90?
And a subsequent reply to that again:
Unfortunate, but I have seen these mixed up for years... electrically close, but physically different. But if you have an amp that uses 6P1s, they're cheap enough, likewise so are 6AQ5s. EL84s have higher gain and will require reduction of the bias voltage or cathode resistor if you rewire sockets for them. 6973, 6CZ5, 6CM6, 6061, 6BW6 will work in place of 6P1 without circuit changes, but are different 9-pin pinouts.
So theres the answers to your questions! I've posted another Q to ask is there a good way to aviod confusion in buying the wrong tubes off ebay, ie what to look for in pics of tubes on auctions otehr than the pins.
Fran