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I believe there are at least three different versions of the Fifty/ Fifty. My version has the blue pilot light, four larg filter caps and no choke. Are there any schematics for this particular version? I think that way back I managed to locate some for this version but I don't now when I need...

I'm amidst of trying to sort out this converted american model Fifty/ Fifty. The PT seems to be the export version, so that checks out. But it doesn't have a varistor and the voltage is much higher than expected, unhealthily high if you're the screen grid of a 6L6GC. As it were it didn't look...

Just how the heck was the PT in the Fifty/ Fifty fitted? Those four threaded studs at the bottom I understand. But then those other two holding it in place at the front? With basically no wiggle room those front-side two effectively see to that the PT effectively isn't going anywhere. It just...

I'm about to re-cap my 50/50, a bias pot fitted and possibly even looking into having the OTs replaced. However I just don't get the wiring of the OT secondaries. The 8 ohm outs appear to have twin leads, orange and yellow. If I got it right the OTs were designed for 8 ohms, be it 2 x 4 ohms...

I do love the basic sound and operation of the Fifty/ Fifty I have. I just wish it had some more headroom. Do you think the TS 7581A would work in my favour here? Could the amp even handle those, you think? The PT looks rather sturdy, I think. If not then I suppose I'll just have to fit a...

I have not been using my 50/50 for quite a while, since it had some issues that could have had something to do with it having been submitted to force to one of the presence knobs. Ah well, I did have it replaced and fired it up yesterday. Sounded good and strong and I felt I was back-in-busines...

I've heard about some guys that use this valve instead of the 6L6GC for which the Fifty was designed. Would it be safe to run a pair in one channel, do you think, and if so: how do I modify the amp? I read somewhere that the KT77 would be a direct replacement for the 6L6 in that the output...

I read somewhere a guy who ran EL34s in a 50/50. Knowing british style valves have a higher current draw and have a different bias point I thought I'd stay with beam tetrodes to avoid modification. Then I read the KT77 is basically an EL34 sounding beam pentode, the diff being the increased...

I know Mesa wouldn't recommend this due to the higher heater current draw, but I read somewhere about a guy who ran EL34s in his Fifty/Fifty. Do you thinks it's advisable to do this at all? Would it help if I only ran one channel of the amp and hence lessen the total current draw? Cheers!

I'm trying to get the full picture of what makes a valve/ tube into what it is but sometimes I get a bit confused over it. For example: people tend to use hot and cold rather arbitrary depending on how they see things. I was told Mesas were biased cold, in this case meaning the bias current is...

I'm curious as I'm about to re-valve/ tube my 50/50 and I don't want it too cold or too hot, just slightly on the chilly side ;)

One plus as well as a minus to me is the fixed bias of Mesa gear. I'm in the process of replacing the powervalves of my Fifty/Fifty and I had some Groove Tube valves in mind. As I'm to ask for a specific rating to go well with my Fifty/Fifty which rating should I go with (Mesa or GT rating)? I...

One plus as well as a minus to me is the fixed bias of Mesa gear. I'm in the process of replacing the powervalves of my Fifty/Fifty and I had some Groove Tube valves in mind. As I'm to ask for a specific rating to go well with my Fifty/Fifty which rating should I go with (Mesa or GT rating)? I...

I was considering the 5881 for my 50/50 but then I read the oldstyle 5881s shouldn't operate at more than 400V to the plates. Would be a pity and a costy lesson to learn to blow my poweramp for a different flavour of tone, wouldn't you say? Cheers!

In which end should I begin... I just replaced the Celestion G12T75s in my 112 and 212 cabs with Webers (Alnico Cali and SB+1230-55). Just prior to that I had found the sweeetspot with the Celestions where the crystaline vibe of the strings sound almost like a piano. The Webers being rated...

I think my Fifty/Fifty is truely a great piece of gear. I really like the dynamics the 6L6s has to my Plexi pre-amp with the exception of being really heavy on the lows and rolling off any highs. Since I can't set the bias manually at all I guess I can't just put any valve in there with an...

I got a used fifty/fifty that I just love, but I find it a bit dark at times. Do you think it has been modified or is it supposed to sound like this? I do like the tone of it, but I'm kind of curious. Cheers!