C3g:GM70:GM70 schematic advice

[Wavebourn]

gm70 se

Impressive!

 

[louischia]

Here you go: how GM-70 tubes were used in Russian amplifiers originally.

thanks Wavebourn!
atleast now I know that they are design for sound reproduction!

D3a driver...hmmmm a bit weak in my opinion, OK for voltage amplification but otherwise maybe a bit weak to drive the GM70 grid with it's 15mA or so current.
Personally I would choose something like 2A3, 300B or 6L6 to drive the GM70 through a 1:1 interstage transformer; this gives headroom into A2 territory.
With for instance 5687 or 6H30 as voltage amplifier you have a three stage amplifier with around 1 VRMS of input sensitivity.
Pieter

thanks pieter! nice to see you here!
i have quite a number of C3g lying around and besides, i love it's sounding!

One positive side of tubes designed to be driven with control grid currents is drivers that are required to drive their grids deal well with Miller capacitances. Otherwise people tend to neglect them.

Wavebourne might have some more (accurate) thoughts on the subject.

care to elaborate further?

 

[Wavebourn]

thanks Wavebourn!
atleast now I know that they are design for sound reproduction!


thanks pieter! nice to see you here!
i have quite a number of C3g lying around and besides, i love it's sounding!



care to elaborate further?

You already got LOT of information from this thread.

Including very high anode voltage that kills instantly.

 

[louischia]

im not too sure about my biasing calculations. will it b running pure class A1? or running too hot?
can anyone help me verify?

- louis

 

[kevinkr]

im not too sure about my biasing calculations. will it b running pure class A1? or running too hot?
can anyone help me verify?

- louis

You haven't posted your calculations so it is hard to know, and I don't have the characteristic curves in front of me either..

However the Pd of the graphite plate version is rated at 125W and many with long experience with this tube have told me it is not uncommon to run them at the rated dissipation. (This is in fact my plan, but I can back it off to 100W) Metal plate versions have lower dissipation ratings which should not be exceeded.

I suspect your dissipation as a swag is going to be less than 75W which IMHO is even a bit low. Depending on driver scheme you will either operate in class A1 or A1/A2 depending on power level.

I don't like the design you have posted.