Upgrading my 300B Fi Primer

[Pedro]

Hi,
I've built a few tube amps over the last 5 or 6 years with help from very generous people ( some of whom I see are here on this forum regularly )
My main amp is currently a 300B SET based on the Fi Primer with a slightly improved power supply, but basically a 6SN7/300B set up. It drives DIY folded TQWT with Fostex FE167E's in them. Occasionally I use an OTL pre amp to drive the main amp ( just for a slightly different character )

Now then , to my question.....

I recently asked on the SET Forum what good upgrades to my DIY 300B Fi Primer would be, and had lots of great feedback - partic on using the type 76 tube. I cant get availability of 76 triodes to try yet and have been reading round on other circuits. The C3m as a 300B driver gets lots of good coverage. So although I know i will have to set up 20V heater supply etc I wondered how easy a conversion this would be ? I want the simplest ( purest ) C3m / 300B circuit I can find. any ideas ?
I can get hold of some NOS siemens C3m's so looks like a quick project.
The 6sn7/300b can be driven Ok direct from CD source but I also have an OTL headphone/line stage designed by Kurt Strain that I built some years ago which drives the existing 300B amp really nicely - so I'm guessing I could use that to drive the C3m/300B set up given the lowish gain of the C3m's.
Does all that make sense ?

Although I can get my mind around the datasheets, and basic maths, I like to build direct from a well-liked schem and then check and tweak operating points once the amp is up and running.

Any views very much welcomed. In meantime still looking for the 76's as well here in the UK.

Stop Press - being an impatient soul I just went and ordered some C3M and C3g on ebay too !!

Rgds
Pete