A 548

[boater sam]

I think its an A 548.Supposed to have an EL3 output valve but its got an octal socket.

Sam

[boater sam]

It would seem that the equivalent for EL3 is an EL33 which is an octal base, I will try this checking the connections first.
However the rectifier, supposedly an EZ33, has no equivalent that I or AI can find so I will have to rewire the base for a 6X5GT as it needs to be an octal with a 6.3v heater.
Sorry if others are finding this boring but I like a challenge.

Sam.

[boater sam]

It would seem that the equivalent for EL3 is an EL33 which is an octal base, I will try this checking the connections first.
However the rectifier, supposedly an EZ33, has no equivalent that I or AI can find so I will have to rewire the base for a 6X5GT as it needs to be an octal with a 6.3v heater.
Sorry if others are finding this boring but I like a challenge.

Sam.

[Paul_RK]

I'm very suspicious of that EL3, I don't think I've ever met one in a thoroughly British post-WWII radio, and even the set photographed at RM.org sports an octal output valve. So I've just been up to the attic to dig out my own A548 - I repolished its cabinet about 30 years ago, fairly sure it was working at the time - and its current output valve is a KT61, rectifier a U50, for whatever that may be worth.

Paul

[boater sam]

Thanks Paul, that is interesting. I will have to remember that when I get round to restoring it. 
KT61 is very probable but the U50 confuses me as its a 5v heater of course and the EZ33 was 6.3v which is why I thought of using a 6X5G. I will have to check the transformer for a 5v winding.

Incidentally, why were most of the rectifiers of the period 5v?   And why 6.3v and 12.6v, is there some magic reason?

Sam.