When is it OK to sub power tube types?

[Randy]

Are there any hard and fast rules? If I want to try 6550's in a Bogner XTC or EL-34's in a SLO or 6L6's in a Marshall, am I safe as long as they bias in range?

[Structo]

Depends on the power transformer (enough current supplied) and the output transformer (impedance matching).
Don't know anything about that Bogner but some research into the build should answer those questions.

[cochese]

You are always best contacting the manufacturer. It saves time and is pretty easy to talk to the designer with smaller companies.

[rockon1]

Its my understanding an amp that uses EL34's can use 6L6's or even 6V6's. The heater draw less current in both cases and as long as you bias it for them they will work. I just tried both in my EL34 based Rivera Chubster with no problems. The bias pot has a lot of range in it.

You shouldnt try the reverse(EL34's in a 6L6 based amp) though as an EL34 draws more heater current than an 6L6 (might strain the PT) and theres a possible wiring/component issue's too.

Thats all I got and hopefully some one more knowledgable will be along. Bob

[jay42]

Its my understanding an amp that uses EL34's can use 6L6's or even 6V6's.At the lowest level, the sockets have to be wired to accept all the different Octal parts. Traditional Fender 6L6 wiring does not work with EL-34s. The next level would be adequate screen resistors. Again, Fender part selection is marginal for EL-34s. If that's all taken care of, you still have to rebias which requires an adjustable bias circuit with an adequate range. If you're thinking about cathode biased output stages, then it would be difficult to choose a safe value for a range of tubes. I don't know, but I suppose that the Univalve must have a switch for different cathode resistors, labeled with the tube names.

[rockon1]

At the lowest level, the sockets have to be wired to accept all the different Octal parts. Traditional Fender 6L6 wiring does not work with EL-34s. The next level would be adequate screen resistors. Again, Fender part selection is marginal for EL-34s. If that's all taken care of, you still have to rebias which requires an adjustable bias circuit with an adequate range. If you're thinking about cathode biased output stages, then it would be difficult to choose a safe value for a range of tubes. I don't know, but I suppose that the Univalve must have a switch for different cathode resistors, labeled with the tube names.

Like I said an amp that uses EL34's can use 6L6's . Not the other way around. Bob

[Blue Strat]

Are there any hard and fast rules? If I want to try 6550's in a Bogner XTC or EL-34's in a SLO or 6L6's in a Marshall, am I safe as long as they bias in range?

The final word. THERE ARE NO HARD AND FAST RULES.

Variables which must be considered in all cases are plate voltage, heater current demand, output impedance, power output and bias setting.

[cochese]

Its my understanding an amp that uses EL34's can use 6L6's or even 6V6's. The heater draw less current in both cases and as long as you bias it for them they will work. I just tried both in my EL34 based Rivera Chubster with no problems. The bias pot has a lot of range in it.

You shouldnt try the reverse(EL34's in a 6L6 based amp) though as an EL34 draws more heater current than an 6L6 (might strain the PT) and theres a possible wiring/component issue's too.

Thats all I got and hopefully some one more knowledgable will be along. Bob

This is why I think it's best to contact the amp designer. I thought of trying 6V6's in my Rivera M100 ( with EL34's) a number of years ago and was told by Paul Rivera that the impedance of the output transformer was wrong for those tubes. It seems to me it's just as easy to contact an amp company as it is to write a thread on the Gear Page and you will probably get more accurate information.

[rockon1]

This is why I think it's best to contact the amp designer. I thought of trying 6V6's in my Rivera M100 ( with EL34's) a number of years ago and was told by Paul Rivera that the impedance of the output transformer was wrong for those tubes. It seems to me it's just as easy to contact an amp company as it is to write a thread on the Gear Page and you will probably get more accurate information.

Yes thats probably best. I have to say I cranked them up for about a bit and they sounded pretty good- fat and warm. I did feel safer running the 6L6's in place of the stock EL34's though. Ran those for a few days until I decided I liked the EL34's better. Bob

[Wakarusa]

The final word. THERE ARE NO HARD AND FAST RULES.

Sure there are... basing and pinout. Problem is that matched basing and pinout are just the first two questions to be answered re: tube substitutions and not conclusive :)

[Blue Strat]

Sure there are... basing and pinout.

Yes, but that's not what the question was;)



Problem is that matched basing and pinout are just the first two questions to be answered re: tube substitutions and not conclusive :)


My point exactly.