I now have a pair of GM70s and a pair of bases for them, so I'm committed. Or perhaps I should be committed?
The plan is to use two cap coupled 6EM7 stages into the GM70. I have a 750V CT mains tx so should be able to get a 300V - 350V choke input supply for the 6EM7. Originally I had intended to use 6DN7 instead, but I couldn't find a good compromise of operating point and HT - the second triode needs more HT than I can muster and I don't have suitable anode chokes or ITs. So 6EM7 it is.
Which just leaves me to acquire a rather large mains tx for the GM70s. I guess something like (eventually) a 1000V 400mA lump is going to be big, heavy, and expensive.
I've got a spare 700-0-700 350ma with 5amp 10volt heater windings aswell as the obligatory 5v and 6.6v windings. If you want WELLY, this has potential!
pre65 wrote:What value of HT are you aiming for on GM70 ?
Well, nominally not over 1kV. Though that's pretty arbitrary - why not 900V or 1000V? Well, I guess the practical consideration is caps. But, from memory 900V to 1kV would give me 16W to 20W.
The PSU I use on mine gave 905V HT when used cap input with the 845 project, but on GM70 with choke input its about 600V. You don't need 16-20W do you ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Looking fwd to seeing it progress, seeing as how I've "retired" from amp building for now anyway.....
Mind you that big Haddon mains transformer on Michael's Emporium would easily power a pair of 13E1s and with our Ant's 500mA Haddon choke to go with it it would make a smashing PSU for those pretty little beauties.
STOP IT!
Sgt. Baker started talkin’ with a Bullhorn in his hand.