"Chiswick"-ing the PRR varimu?..

If I increased the B+ to ~250Volt and played around with the anode resistors, is there any reason the PRR wouldnt work if I replaced the 12au7 with a ecc/pcc/ucc85?  http://www.cicognani.eu/pdf/Tubes/ecc85ph69.pdf
I do love my PRR varimu the way it is, but always looking for different flavors and have been thinking for some time about building a second unit.
the UCC85 (100mA/26Volt heater)is dirtcheap and easy to find (at least here in Sweden) and seems to be well liked in the Chiswick Reach comps(they use the 300mA/9volt heater version)
obviously, the tube sockets will have to be separate from the PCB that many people have used. (the copper tracks are a little close for 250volts, I believe)
will the sidechain be able to chut these tubes off?....I realize just changing a tube wont turn it into a Phoenix, but will it work?...
any thoughts?
johan

If you're worried about the pcb tracks being close together with 250v HT, you could just wire that part of the circuit point to point. There's hardly anything to the circuit so it should be easy to do.

> increased the B+ to ~250Volt

Why?

> played around with the anode resistors

Lower than 10K or 6K or so, the tubes will overheat; also the resistors will have to be 2W.

Note that while *CC85 can stand 250V, it will conduct a LOT of current and is liable to over-heat before it over-volts. Note that the suggested conditions run 100V and 170V supply. That's for a TV tuner, which is different yet much the same as half an audio VCA. It aint a guitar amp. Jacking up the voltage is not always best.

> the copper tracks are a little close for 250volts, I believe

If the tracks are cleanly etched, 300V is nothing.

> wire that part of the circuit point to point. There's hardly anything to the circuit

Agree, agree, agree!

I don't know why anybody (except a mass-producer) would PCB a single bottle.

*CC85 will "work". The higher Mu means the 15V sidechain can do the job. The very high Gm (S) means the input sensitivity will be very small (getting into hiss). You may even need some idle bias to avoid low-level distortion (grid current).

I'm not sure what advantage the *CC85 has over a 12AU7. Different, not better in any obvious way. The '85 is a "good amplifier", while a vary-Mu really wants a "poor amplifier". (Perhaps cost, but a vintage 12AU7 is 1/10th the total project cost.)

Different? EL84. We could skip the whole output buffer. And stay warm in winter.