Mesa Duets

[dmcguitar]

Why does mesa only sell their matched tubes in duets, when most of their amplifiers are quartets? I guess since they only take certain specs, they can all be "interchanged?"

 

[dodger916]

With the Marks, the quartets are really two pairs of duets, and as long as each pair of duets is matched, you should be alright. I believe the same holds true for Lone Stars and progressive linkage amps. Class A/B or "push/pull" amps use two tubes in the power circuit and should be matched, hence the duets.

 

[stokes]

With the Marks, the quartets are really two pairs of duets, and as long as each pair of duets is matched, you should be alright. I believe the same holds true for Lone Stars and progressive linkage amps. Class A/B or "push/pull" amps use two tubes in the power circuit and should be matched, hence the duets.

Not really.With a quartet,you have two tubes on one side and two tubes on the other side of the OT and the two sides have to match,so it is preferable to have a matched quartet.A quad or quartet is used in class A/B or push/pull the same as a duet or two tube output.Just as I described the quad having two tubes on each side of the OT,a duet has one tube on each side,for half the power.Mesa will sell you a matched quad,they just sell them as two seperate pairs.It is really just a matter of six of one/half a dozen...

 

[dmcguitar]

so if you just buy 2 duets off the shelf, it would be fine, so long as one pair goes in the middle, and one goes in the outer sockets?

 

[stokes]

If you are talking one of the simul-class amps with different bias settings as for 6L6/EL34 combos,Mesa intends for you to use El34's in the outer and 6L6's in the inner so each tube on one side of the OT will match current draw,even tho you have an EL34 and a 6L6 on one side of the OT.If you have,lets say a Marshall type where all four sockets match,you would buy two sets of matching pairs which is the same as a matched quad.And to just confuse things even more,the Mesa bias settings are pretty cold so even in a simul-class amp,which has the outer sockets biased a little hotter for the EL34's you can get away with using 4 matched 6L6's.The way it is biased you have one outer and one inner on one side of the OT,so even if one is slightly hotter,the two "mismatched" tubes are on one side of the OT so the total current will "match" the other "mismatched" side of the OT.Confusing,huh?So the short answer to your question is,yes if you buy 2 duets off the shelf you will be fine,but it doesnt matter inner or outer because if you buy two duets of 6L6's from Mesa they will be a matched quad.

 

[phyrexia]

just buy two of the same color-coded tube duets.

 

[dialectric]

I have an older Mesa, a 79 mark I or II? with the 60/100 option, and 4 power tube sockets. I'm wondering if I could use a vintage duet of 6v6s and a set of Groove Tubes 6L6s at the same time. If this works, would the 6v6s go in the outer sockets? is there a possibility of burning out the tubes / fuse /amp ?

Thanks,
Dialectric

 

[dodger916]

I don't know about the Mark I, but the Mark II manual makes no mention of running 6V6 tubes. Per the Mark IV manual, 6V6s will work in a Mark IV ONLY when 1) all four sockets have 6V6s; 2) run the amp in Tweed mode which greatly reduces the amps output (plate voltages?); and, 3) run in Simul-class only. Without the Tweed switch, I believe the high plate voltage would sentence those 6V6s to a quick death, assuming no catastrophy occured first.

I wouldn't do it, but I'm no expert.

 

[stokes]

The MKI from that era is not a simul-class amp.It uses 2 tubes in the 60watt mode and 4 tubes for 100watts.Dont try to put 6V6's in that amp,unless you do some mods to the bias circuit,even still the plate volts are too high for 6V6's.In any event,you need a matched quad,if you buy 2 matched pairs of the same grade,you will have a matched quad.