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Old 24th September 2012, 09:24 PM   #1
pilovis is offline pilovis  Italy
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Default 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)?

Click the image to open in full size.

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

Last edited by pilovis; 24th September 2012 at 09:30 PM.
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Old 24th September 2012, 09:39 PM   #2
DF96 is offline DF96  England
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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.
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Old 24th September 2012, 09:42 PM   #3
pilovis is offline pilovis  Italy
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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.

Last edited by pilovis; 24th September 2012 at 09:48 PM.
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Old 24th September 2012, 09:48 PM   #4
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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 ?
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Old 24th September 2012, 09:49 PM   #5
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by flatheadmurre View Post
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!
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Old 24th September 2012, 09:56 PM   #6
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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?
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Old 24th September 2012, 10:00 PM   #7
DF96 is offline DF96  England
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Quote:
Originally Posted by pilovis
there is no DC for heaters, heaters are connected directly to the 6.3 Vac.
Sorry, my mistake.
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Old 24th September 2012, 10:11 PM   #8
pilovis is offline pilovis  Italy
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Is this correct?

Click the image to open in full size.

Last edited by pilovis; 24th September 2012 at 10:37 PM.
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Old 24th September 2012, 10:58 PM   #9
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by aardvarkash10 View Post
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 ?

Click the image to open in full size.
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Old 25th September 2012, 12:16 AM   #10
SY is offline SY  United States
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The gain seems mighty low...
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