Stereo 100w Valve Amp

[pwdrive]

Hi Rob t, Googling seems to suggest it's rated at 75/100watts which suprised me. That function of the -ve voltage switch to the screens in the diagram was just an assumption by me, I am still not entirely sure of the function of that switch, if anyone can contribute I would be interested to know, I have tried looking for a full manual for an explanation but no luck so far.

Lawrence.

[pwdrive]

A bit of progress, the switch positions are labeled on the diagram as "funz" and "rip" According to the Google translator I have just used: Function = Funz..ione and Rest = Rip..oso

Lawrence.

[tiv48]

yes its clever better than removing ht to the anodes of the output stage to get standby .
not shore about that quoted output must be heavely baised to class b . which woudl surgest it was not for hifi use.
rob t

[pwdrive]

Yes I agree, a PA design primarily, I think that standby arrangement was used to avoid various cathode emission/degridation issues. I found a reference to a similar Geloso amp and the manufactures recomended proceedure at intiall switch on was to go standby 'till the valves heaters/cathoder had warmed up to the correct temperature. Historically it seams to stem from the days when directly heated cathode rectifiers were used when the full HT was availble to the O/P valves before those valves cathodes had attained their working temperature, this situation can arise in the circuit posted in this thread as it uses solid state rectifiers, all interesting stuff, and gives an insight to circuit techniques used in vintage stuff we come across.

Lawrence.

[Mr Clock]

Thanks for replys. 75-100 w ? AFAIK the 807 wasnt designed as a audio valve,more for use in transmitters. Unlike the KT66/88. In the data sheets I have it says triode connection,G2 connected to Anode/Class AB/2 anode dissipation is 30/50 watts. (see attached PDF)

[boiss]

Just a thought, have you built anything before with bottles and got it to work?
807s wouldn't seem to me to be the best choice for 100W RMS Hifi. Having them already would probably still cost more overall to build than other alternatives.
From the safety point of view 807s have top caps which means casing to be sure that people or animals cannot receive shocks for whatever reason.
Good luck
Mike