Mis-matching tubes

[isolated1523]

Maybe this is a dumb question..but with the ability to individually bias each tube, is it then possible to mis-match a set of tubes in the same channel? For example, can I run a single 6L6 and a single EL34 in channel 1 of my RT2/50? The 6l6/EL34 mix was my favorite in my RM100s, so I was wondering if it was possible to mimic that with two tubes instead of 4.

-Adam

 

[tschrama]

Sure, why not. The EL34 will draw more current at the same bias setting, so THAT'S the tube to measure bias on. Tell us how it sounds!

 

[isolated1523]

Is there a preferred order to put the tubes, EL34 first/6L6 first?

 

[tschrama]

In a push-pull amplifier, the tubes work in pairs. You want to make a pair from dissimilar tubes. That's radical, but I guess it wont hurt the amp.

Why would it matter which tube goes as 1st or 2nd?

It certainly wont mimic a pair of similar tubes, combined with another pair of different, but similar, tubes.

Furthermore, in the RT2-50, you can bias each channel separately, but you can't bias each tubes separately.




:idea: Read some more

 

[isolated1523]

Yeah, I dont know why I was thinking each tube could be biased individually, but I went back and looked at it and realized they had to be biased in pairs. Not sure its worth the effort if I cant be pushing both tubes in the correct ranges. Oh well!

 

[tschrama]

It would be a fun and unique experiment!

 

[Jaded Faith]

DO NOT DO THIS!

You can not mix pairs of tubes in the same side of a class A/B circuit and you will have a VERY expensive repair bill. The amp wants to see two of the same tube working together, much like pistons firing in an engine. You can mix in the RM100 because each pair runs exclusive to each other.

If you give this a shot in the RT 2/50, expect to replace the OT, burn up the PCB and Screen resistors with near certainty.

 

[tschrama]

DO NOT DO THIS!

You can not mix pairs of tubes in the same side of a class A/B circuit and you will have a VERY expensive repair bill. The amp wants to see two of the same tube working together, much like pistons firing in an engine. You can mix in the RM100 because each pair runs exclusive to each other.

If you give this a shot in the RT 2/50, expect to replace the OT, burn up the PCB and Screen resistors with near certainty.

Sure you can, you can even run it with only one tube.

Why would the OT be damaged, why would the screen resistor burn up, or the PCB?

 

[Jaded Faith]

Absolutely not. A push-pull stage requires at least two tubes to operate, but can have more connected in parallel with each side, resulting in an amp with four, six, or even eight output tubes for higher-power amps. Note that you need to have at least two tubes to operate. This is why you can pull two tubes from a 4 tube amp, but you can not pull one from a 2 tube amp. The OT needs to see at least one tube feeding each side of the primary for the circuit to be in balance. You need one tube to "push" as the other "pulls".

As for mixing pairs in the 50W scenario with only two tubes, you are going to have a rather unhappy OT. It might work for a while, but it would never sound it's best. The output transformer would be struggling with one side doing a lot more of the work than the other due to the unbalanced PC and TC. When components are not happy for extended periods of time they tend to release the magic smoke, if you know what I mean. :lol:

 

[isolated1523]

Sounds like, even if it works for a bit, the juice isnt worth the squeeze! lol