Mis-matched valves in a 50/50?

[ZiggY!!]

Has anyone running a pair of 6L6's on one side and a pair of EL34's on the other in a 50/50? I assume it would have to be modified for individual bias for the respective sides... is there any reason this couldn't be done?

 

[fatboy135]

:lol:
what is the reason to do that???

 

[disassembled]

Yes you could. This would be similar to a road king setup where one set of outputs is EL34 and the other is 6L6. You have to worry about the different electronical characteristics of each tube and may require slight modifications to the amp. Call Bob at eurotubes and ask if this would be ok to do this with his integrated quad. As long as the current draw is the same and you rebias the amp to where it should be stock or where it will sound good to you it should be fine. I think the EL34 needs a pin grounded that the 6L6 doesn't use, you may need to replace the screen resistors for the EL34's, and you need to check the plate voltage. If any of this doesn't make sense do not attempt to do it by yourself and employ someone that is qualified to do the work.

 

[ZiggY!!]

I understand what you are saying... but I'll still be getting my tech to do it. There is something about the work of a life-long professional that gives me some piece of mind when I'm in the studio. :wink: :lol:

The reason? Egnater M4. To further add to the versatility of the thing. I am planning on using an Axess electronics HS2 to switch between the two sides of the 50/50 and a CAA 1x12.

 

[disassembled]

Sounds good. You could even do 1 side into a opened back 2X12 (6L6) and the other into a closed back 412 or 212 for broader tonal options. If you are only running a 112 cab then you might want to see if you can do some 6V6's in one side rather than 6L6's. A lot of recto guys are using these instead of 6L6's and claim the clean channel is much better now.

 

[fatboy135]

Egnater M4

:lol:
but an egnater is a very special amp

 

[Paul Secondino]

Has anyone running a pair of 6L6's on one side and a pair of EL34's on the other in a 50/50? I assume it would have to be modified for individual bias for the respective sides... is there any reason this couldn't be done?

The 50/50 bias is set very cold .So without lowering the B- voltage (raising the bias) the EL34's will sound really harsh

The basic idea here as mentioned is to get a quad of tubes that draw about the same which is becoming referred to as an integrated quad. Once you have that, your tech needs to set the bias in a good range.

I put a hot quad of SED 6l6's in my Mesa 50/50 and they were only drawing 19 to 20 mA which is pretty cold. So EL34's would draw even less.

 

[disassembled]

Has anyone running a pair of 6L6's on one side and a pair of EL34's on the other in a 50/50? I assume it would have to be modified for individual bias for the respective sides... is there any reason this couldn't be done?

The 50/50 bias is set very cold .So without lowering the B- voltage (raising the bias) the EL34's will sound really harsh

The basic idea here as mentioned is to get a quad of tubes that draw about the same which is becoming referred to as an integrated quad. Once you have that, your tech needs to set the bias in a good range.

I put a hot quad of SED 6l6's in my Mesa 50/50 and they were only drawing 19 to 20 mA which is pretty cold. So EL34's would draw even less.

"Cold" is a relative term. Basically what you are trying to avoid is any crossover distortion. Raising the bias higher will just be preference. If your tech is biasing the amp properly he will be using a scope to look at the waveform. Otherwise, the tech is just guessing.

 

[ZiggY!!]

Sounds good. You could even do 1 side into a opened back 2X12 (6L6) and the other into a closed back 412 or 212 for broader tonal options. If you are only running a 112 cab then you might want to see if you can do some 6V6's in one side rather than 6L6's. A lot of recto guys are using these instead of 6L6's and claim the clean channel is much better now.

I've been thinking about this, and its probably a better Idea. I could put 6v6's in one side, and even EL84's in the other via THD yellowjackets. I use the amp mostly for blues and jazz so flat out volume isn't a necessity.

 

[Blueracer]

One question I would have for the 50/50 is that an EL34 is somewhat taller than a 6L6. Is there sufficient depth in the 50/50 so that an EL34 wouldn't stick out the back of the amp. I was thinking of getting a 50/50 and possibly setting up a channel for EL34s. Any help on this is appreciated.

 

[Paul Secondino]

Has anyone running a pair of 6L6's on one side and a pair of EL34's on the other in a 50/50? I assume it would have to be modified for individual bias for the respective sides... is there any reason this couldn't be done?

This isn't hard to do but the main effort will be towards getting the proper selection of tubes. All you really need to do this is to tbuy the tubes from someone that will supply with 2 sets that draw the same amount of vurrent.

Bob at eurotubes does this alot so you could buy a integrated quad from him and simply pop them in.

But as mentioned, the amp is biased cold and the EL34's will sound harsh. So my suggestion is to buy the integrated quad, then have a respectable tech modify the bias from there and set it for "that" quad of tubes

While he's at it, ask him to install a trim pot so that you don't have to deal with changing resistors. I had thsi done to my mark 3 head . My tech is good so he set it in a range where I can use the tubes I like and be able to raise or lower the bias as I need to. It's not a big deal for a good tech. The idea is to install the trim pot and or replaced the fixed resistor that sets the negative bias voltage.