Is anyone using EL34's in there Bluesmaster or HRM? If so what mA are you setting the bias for? I'm using Winged C (SED) 6CA7's.

Sorry, your power transformer is made for 6L6 not EL34 and will not handle the additional current needed for those filaments......

In my correspondence with Nik during the ordering of my amp I asked about using el34's, and he replied that the amp was wired in the output tube sockets to take them, it's part of the regular design on the 50w HRM I own.  There is more than enough capacity in the PT to handle the increased heater current from a pair of el34's.  One guy on our forum is running a pair of 6550's in his 50 watter biased at 50mv, running at very loud volumes for long periods and he reports that the PT  still runs cool and has been reliable for several months.  The PT in mine runs cooler than nearly all the other guitar amps in my stable.  I am running vintage el34 RFT's at 39 and 42mv.  They are slightly mismatched, and the tones/sustain are wonderful with them at that setting.  Dropping the bias down 3-4mv yields a slightly brighter tone, and a bit less bloom on the long sustained notes.  I have also run a pair of very tightly matched vintage Sylvania 6l6gc's at around 35mv, fat, warm and huge tones gush out of that amp with those.

If you find out the specs on that PT you will know fo sho on the heater current thang.   EL34's draw around 1.4 amps apiece for their heaters.  Impedance on the primary side of the OT will be slightly off running el34's, but that probably won't be a serious problem. 

I have replaced power transformers in more than a few Twins over the years for folks who tried running EL34s in them. From what I've seen it's a crap shoot, sometimes you can be OK and sometimes they just get too warm and fry themselves. And as Greg already mentioned, he is not using Mercury stuff. He also plays very loud so since I built his amp I advise against it. But of course you can try it if you like!
I'm building a #183 for someone now using those same new tubes, using a TXFR rated for that current. I'm expecting good sounds!!

who says you cant use EL34s? I used SED and Shugaung in my 50 watt. 42mA was my prefered setting.

For all the nay sayers im currently running KT88's at 50mA now without any mods. Been 6 months nothing has blown up..