Postby Vemmy » 12 Feb 2010, 10:14
I replaced first my 6100's EL34's with JJ tubes, but they were somehow faulty, so I had a quartet of TAD tubes, and have been very happy with them. I biased the amp quite hot, works best for me. It isn't the easiest thing to bias, there are no bias points like the VM, and the chassis is full of PCBs and loads of cable...
I believe (someone will probably correct me if I'm wrong) that the 6100's came with EL34's like all the other amps in the early 90's, but Marshall changed to use 5881's in mid-90's in JCM900's and 6100's (probably at the time the LM version was introduced?) for supply problems of 34's at the time, at least that's what I've heard.
So if you don't know exactly what you're doing, leave the biasing to an amp tech. Hot/cold bias is just a matter of personal taste, in my opinion. The real old school dudes plug in and adjust the bias according to their ears, without any meters, and I know a couple that have done this since the sixties... But I've never heard they would have broke a tube...
EDIT: By the way, I don't think the bias trimmer's range is enough to use 6550's, at least all the other Marshalls I've seen to use 6550's have had bias mods for this reason. Dunno if SteveD knows about these? I heard a rumour that Bjorn Juhl would have been working for Marshall in the 90's, and my 6100 is full of 'BJ'-stamps, should ask Mad Professor about this...
Marshall 2266 Vintage Modern
Marshall 6100 30th Anniversary
Marshall 1982
Marshall 6960
Fender American Standard Stratocaster (SD APS-1 x3)
Lector Mosrite
Epiphone Les Paul LQ (MIJ, SD SH-14)