Mixing tubes in a 50/50

[backyardburial]

A while back I bought a set of unopened Mesa branded 6l6's, just because they were cheap and I did have a Roadster head. I ended up putting EL34's in that tho anyway, but Now I have gone back to a 50/50 power amp, with 6L6's. Can I use this pair of mesa tubes and another pair of...say JJ's, if they aren't a matched quad? Or should I really buy more Mesa tubes? I'm wondering about matching plate voltage...or something along those lines. My other thinking is that because this is a stereo amp, do I really only need 2 sets of matched pairs? I don't really understand the whole 50 watts per side...

 

[crane]

Right, there are 2 amps in the 50/50, each with a 6L6 pair. So you need 2 matched pair.
But The JJ you are speaking must be in a Mesa's bias range (ask the vendor for that).

 

[backyardburial]

Thank you Crane, that's what I thought. I didn't mention JJ for any reason there, I was just naming any other brand tho.... Cheers again.

 

[crane]

JJ or any other brand, ask the seller for a Mesa bias range :wink:

 

[backyardburial]

Have not replaced all the tubes in this yet and just deleted another thread I started because it was very similar to this one....whoops. Anyway, Im getting a huge difference in volume between the 2 channels now...I still have my unused pair of 6l6's, I guess from what Crane said I can just replace one side at a time, assuming that this loss of volume is a possible tube issue? Also what side of the amp uses which tubes? I would assume that the right side of amp will use right hand tubes? But I don't like to assume anything!

What else could cause this volume loss on one side of the amp if not the tubes? Thanks for suggestions if you have any!

 

[bluestometal]

Also what side of the amp uses which tubes? I would assume that the right side of amp will use right hand tubes?

As I remember: looking at the back of the amp the 2 right hand side tubes drive channel A wile the 2 on the left hand side drive channel B.

 

[backyardburial]

Thanks Blues...but can someone confirm that it is ok to change one pair at a time?

 

[bluestometal]

Thanks Blues...but can someone confirm that it is ok to change one pair at a time?

Lat year I asked to Dough from Eurotubes if it was possible, for me, to swap just one channel tubes with a different matched pair (JJ's while I had Sovtek's) so to have 2 JJ's on channel A and 2 Sovtek's on channel B. That's what he said:

"Yes, if you only use one channel then you can swap the tubes out in that channel independently of the other channel."

You're welcome.

 

[crane]

Even if you use the two channels with different pairs it will work. It may be a slight different volume and sound between channels.

If you put in a pair of tubes that are out of Mesa's bias range, and that it require a bias adjustment then it could cause problem finding a bias that could be fine or match the two different pairs. One pair could run very cold ans the other one very hot.

So just put a Mesa's matched pair inside (ask the vendor for that) and everything will run fine on the two channels.

 

[backyardburial]

Thanks again Blues...but I'm not using just one channel. But I guess I see what you mean. Looks like Crane has come thru again....the tubes I have are actually mesa ones so I would assume they are within the bias range! Thanks again mate!

 

[backyardburial]

Ok...so I just replaced two tubes, facing the amp, it's the two right hand tubes....now the right side volume (again, facing the amp) has almost no sound. The two I replaced were, as mentioned above, a brand new pair ( according to the guy who sold them to me anyway, beginning to wonder now) of mesa branded 6l6gc, and these are 440, while the existing tubes were 430's. From what I gather this doesn't matter tho. Anyway, next step is to swap the two pairs around, at least I figure that way I will know if its the amp or the tubes. Any ideas? By the way, my last jam I ended up using one side of the amp because the volume on the same side was low, i thought it was old tubes. The new tubes however, have made it even quieter!

 

[bluestometal]

Swap tubes around to check if the newer ones works.

 

[backyardburial]

Swapped the tubes and same deal....practically no volume on the same channel.....not good at all! Somehow by swapping tubes I have managed to make it even worse! Is it possible that I have damaged the tube sockets doing the swap? I cant see where anything has come loose, but I do notice that the sockets wobble around quite a bit?

 

[bluestometal]

The socketcs wobble a little bit but not too much, just to soften the tube movement. Probably, to say, something was a bit loose and, swapping tube, has gone out of place. Do the tubes glow as usual, if not could be the sockets (or something in that field), if not could also be the output to the cabs.

 

[backyardburial]

Thanks Blues. Looks like socket pin things were loose, a friend tightened them up for me and now sounds like everything is sweet! Thanks for the replies guys!

 

[bluestometal]

Thanks Blues. Looks like socket pin things were loose, a friend tightened them up for me and now sounds like everything is sweet! Thanks for the replies guys!

Good to hear that

 

[backyardburial]

Ok, so I thought I could avoid starting a new thread by posting in here...I have the same 50/50 still, but am now getting volume sweel much the same as before, but less dodgy...basically fading in and out. I guess these "unused" tubes I got were not so unused...
For the sake of band practice tonight, I have 2 questions...

1. If this swell continues, is it ok to keep using the amp on both channels? TBH, the band I'm in is noisy as hell, so I don't even notice half the time in the middle of a song, its only when I get a chance to play by myself that I notice it even happens. Is it safe to continue using the amp for another jam or two? One channel still seems fine so I can get through the jam fine.

2. Can I just plug into the mono out put of my mesa recto cab, and use it this way. I know I should have a load on the power amp, but I read somewhere that if I turn volume to 0 and presence to full it makes not having a load ok? Also will doing this actually drive the whole quad as opposed to half? If someone can help me out it would be much appreciated!

 

[backyardburial]

OK just saw the bit in the manual that says I can do this....don't know how I missed that! Not sure where i got this idea but having to turn the presence on to full though....anyone shed any light on that idea?

 

[bluestometal]

OK just saw the bit in the manual that says I can do this....don't know how I missed that! Not sure where i got this idea but having to turn the presence on to full though....anyone shed any light on that idea?

The "volume on 0 presence on full" thing's from the 2:90 poweramp manual, I don't know why you've to do that but it's not required with the 50/50.

 

[crane]

Used mine for 10 years on one channel, the other one with volume and presence turned to 0.
It still works perfectly !