Single Ended 50's... be very scared of the rabbit hole...  

I seem to keep building with the 50... I used to think it was too warm, even a touch slow... and then I began to work on other projects, other tubes, extremely linear drivers, nickel output transformers, direct coupled circuits, and my favorite variation on fixed bias... and now this tube does everything I want.  I see right through my horns to my sources.... the amp just passing music to my mind... everything is there... not pushed, just waiting for you to look... pitch black background... soft, floating sounds... and then a startling whack... horns and direct coupled amplifiers have the leading and trailing edge dynamics that I love... and the big, bold, loud pieces they handle like *nothing* else can.... 

a request on this amplifier was to use my filament circuit that allows the use of several medium power output tubes - engraved base WE300b's and VT52's, along with 50's, were the tubes of choice... driver is the VT51, also known as the 841... alternately, with the flip of a switch, the type 10 can be used...

I was able to use the best parts in the rest of this circuit - all mercury rectifiers, including some engraved base WE323 thyratrons..... nickel output transformers... nickel plate chokes... even nickel filter chokes!  Caps are oil in the power supply... occasionally bypassed by film where my ears liked that combination... 

VT51 -> VT52....

and of course 50's and 300b's....

mercury rectified choke input power supply

directly heated triode driver.. 10, VT25, 841, VT51

300b, VT52, 50, AVVT AV5 output tubes

direct coupled circuit

nickel transformers and chokes

two walnut chassis

IEC powercord input

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some steps along the way: