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previous: Marc Hi!I am looking for any inf... -- 2/25/2000 1:38 AM View Thread

Re: geloso schematic & EL503tubes?

2/25/2000 8:26 PM
Re: geloso schematic & EL503tubes?
Hi Marc:  
According to the GE book, the US equivalent for EL503 is the 8278 tube. When the book was printed in 1973, 8278 was not indicated as available from GE at the time.  
Looks like it would need about half the load impedance in the output transformer compared to an EL34. If it was my amp and I couldn't get replacement power tubes, I would probably replace the sockets and rewire for EL34s and their biasing requirements, then connect half the speaker load that the original amp was using, for instance a 4ohm speaker cab to the 8ohm output, that should do it. Then watch for any overheating of the filament transformer since the EL34 supposedly will draw 0.3A more current each than the 8278 was specified at.  
Hope this helps,  

Marc MB:I was thinking along tho... -- 2/26/2000 2:16 AM