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-   -   need help for my new amp: 6G6G driver & 807 SE (http://www.diyaudio.com/forums/tubes-valves/220317-need-help-my-new-amp-6g6g-driver-807-se.html)

pilovis 24th September 2012 09:24 PM

need help for my new amp: 6G6G driver & 807 SE
 
I've just started designing my new 807 SE amplifier with 6G6G driver and need some help from experts.

What do you think about my schematic (local feedback and fixed bias for 807)?

http://i34.servimg.com/u/f34/17/14/70/27/807-6g14.jpg

Note: R should be greater than 180k-200k to avoid lowering too much the R-input of the 807

DF96 24th September 2012 09:39 PM

The 807 bias needs a few changes:
1. bias resistor should go to bias supply, not ground.
2. bias supply needs some smoothing.

The first stage looks wrong. Should the cathode voltage be 3.0V rather than 30V?

Why use DC heaters? Better to learn how to wire AC heaters.

pilovis 24th September 2012 09:42 PM

there is no DC for heaters, heaters are connected directly to the 6.3 Vac.

Right, I made a mistake: 6G6V cathode voltage is 3.0V

I should just remove the 330K resistor, I suppose.

flatheadmurre 24th September 2012 09:48 PM

Taking the bias from the heater winding will give you a hotter dissipation during startup if you have SS HT rectification and no delay.

Small PCB transformer for the bias instead ?

pilovis 24th September 2012 09:49 PM

Quote:

Originally Posted by flatheadmurre (Post 3177456)
Taking the bias from the heater winding will give you a hotter dissipation during startup if you have SS HT rectification and no delay.

Small PCB transformer for the bias instead ?

Good idea! :)

aardvarkash10 24th September 2012 09:56 PM

No, the 330k resistor needs to be in the bias supply line to grid 1.

You sure abut that 220uF cap bypassing the cathode resistor on the 6G6C?

DF96 24th September 2012 10:00 PM

Quote:

Originally Posted by pilovis
there is no DC for heaters, heaters are connected directly to the 6.3 Vac.

Sorry, my mistake.

pilovis 24th September 2012 10:11 PM

Is this correct?

http://i34.servimg.com/u/f34/17/14/70/27/807-6g19.jpg

pilovis 24th September 2012 10:58 PM

Quote:

Originally Posted by aardvarkash10 (Post 3177464)
No, the 330k resistor needs to be in the bias supply line to grid 1.

You sure abut that 220uF cap bypassing the cathode resistor on the 6G6C?

Would be better something like this for biasing the 6G6G ?

http://i34.servimg.com/u/f34/17/14/70/27/807-6g20.jpg

SY 25th September 2012 12:16 AM

The gain seems mighty low...


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