I have a pair of Mk3's that I bought in 2001. They were slightly upgraded with tube sockets, some new wiring, jacks, etc. But pretty much stock. Up until about 2008 I was just listening to them with the stock driver board. I mean the stock phenolic water sponge of a board. I finally decided to upgrade the boards to glass epoxy and while I was at it, use new matched high tolerance parts. But still the same stock circuit. It did sound way better. I won't go into details. I knew there were other driver board options but it wasn't easy to figure out which was the best way to go. so i put that on hold until recently.
About a month ago I decided it was time for a driver upgrade. After reading what I could and emailing some of the vendors I settled on Roy's octal boards for the Mk3. Tung-sol tubes came from tube depot. This week I set out to build the boards and do the install. It went reasonably well except for a small hiccup that Roy helped me diagnose. Basically even though my Mk3's are wired to stock, I had to switch the outputs of the driver boards to the driver tubes to eliminate the feedback through the output xformer. after that i had working octal drivers. I basically completed this last night.
My initially listening (using well worn in svetlana flying C 6550's) was a bit of concern as there was a lot of grain and grit especially on the mid range. but after about 2 hours the sound started to mellow and smooth out. i attribute this to burn in. both the driver board and the tubes were new. but after a few hours it was really starting to reveal itself.
Here is what I wrote to Roy as my initial impressions. First some context about me and audio. I have been an audio enthusiast for 27 years and a bit of an electronics hobbiest. I listen to a wide range of music. My current system is a pair of Martin Logan SL3's, Martin Logan Dyano sub, Audio Innovations L1 pre-amp, Dynaco Mk3's and on the front end I use a Mac/Fidelia into a dBx Quantum II DAC or Benchmark DAC1 and also an Oracle Delphi Mk2/Linn Ittok LV4/Benz Ruby 2/heavily upgraded Parasound phono stage. I prefer a minimalist audio path. I buy into quality electronic components and balancing but I don't buy into anything more decent copper cables and regular power cables. My preference is for vinyl.
Its after 3am and i am still up listening. but time for bed. here are some initial impressions. much more controlled bass without giving up warmth. controlled and smoother extension more so than stock. the mid range confused me at first. i didn't like what i heard. very shrill and grainy. i was thinking maybe just because i have only been listening to stock for so long. but then after a couple hours it started to come together. i attribute this to burn in? its still getting better and better as i listen. so where its now, about 2 hours in, fairly loud volume. the midrange is definitely different - more forward and real. if i thought stock was real, your boards are even more natural. this is where the (burn in?) changes are happening most. at first shrill and now blending in more. there is just more detail like a veil blocking sound was lifted. better transient response on things like the snap of the vocal cords when singing. i can hear things i couldnt head before, in the quieter ambiances. i mean really! i've heard things in the silence with your boards more than stock, like real things in the audio. case in point, at the end of Radiohead "Everything in its right place" there is a what sounds like a lamb stick in very very quiet just at the end of the song. i've never head that before even listening only days ago on Stax Lambda 407/1T2 system. the high end is more precise than stock. the changes are less in the high end but still part of the over-all enhancement. depth of field is deeper too, as heard on my reference tracks for that quality which makes sense since more quiet detail is getting through. you can "hear" silence now (silence being not entirely silence - ambiance). over-all its a pretty dramatic step up. not subtle. really, like a new higher quality amp. after shipping and everything, with the tubes (quad matched), the cost was $110 canadian each - welllll worth the price. wow.
it blows my mind that c1950's amps would sound so good. i know your board is a big part of it bur even stock they sound amazing. a great platform to improve on. but still they are vintage, wow like 60 years old now. crazy that i am listening to them today.
i figure after about 10-15 hours they should be totally broken in and sounding great.