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Old 7th May 2013, 09:17 PM   #721
Abszero is offline Abszero  United States
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Quote:
Originally Posted by merlin el mago View Post
I have questions for fixed bias for 4P1L is -21V:

-How much current.
-Any suggested schematic will welcome.

TIA
Felipe
Hi Felipe,
35 mA sounds quite right. And you need about 240V Uak. There is slight difference between tubes. You are looking good with +300V before the CCS.
Instead of having fixed bias and add the capacitor to separate the input, I would use quasifixed bias through filament bias. You will lose a little amplification, but get rid of Cin and Ck. The only disadvantage is that you will need a raw supply at about 27-28V and 685mA(650+35) and Rod's regulator.
Best,
Radu
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Old 8th May 2013, 09:40 AM   #722
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Hi Radu,
-21V also 35mA?
Could you draw a schematic or elaborate more because I don't follow you.
Cheers
Felipe
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Old 11th May 2013, 08:53 AM   #723
mogliaa is offline mogliaa  United Kingdom
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Hi Felipe,
I will run the 4P1L driver at 210V/20mA with filament resistor of 25 ohms. Both 4P1L filaments sections in parallel so filament current is 650mA. Set Coleman regulator to 650mA.
Ale
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Old 11th May 2013, 08:55 AM   #724
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Thanks Ale, Coleman set to 1.8V? or 1,62V starved?
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Old 11th May 2013, 01:29 PM   #725
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Quote:
Originally Posted by mogliaa View Post
Hi Felipe,
I will run the 4P1L driver at 210V/20mA with filament resistor of 25 ohms. Both 4P1L filaments sections in parallel so filament current is 650mA. Set Coleman regulator to 650mA.
Ale
I have two Coleman's filament regs for 4P1L, I set each one to 325mA?
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Old 11th May 2013, 02:08 PM   #726
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Ale that's the schematic that I want to use.
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Old 12th May 2013, 07:33 AM   #727
mogliaa is offline mogliaa  United Kingdom
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No starved filaments. Run them at 2.1v. You need minimum ra and current drive in that configuration. If microphonics is an issue as a driver you can deal with that later and adjust.
Schematic is ok.
Ale
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Old 12th May 2013, 07:34 AM   #728
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by merlin el mago View Post
I have two Coleman's filament regs for 4P1L, I set each one to 325mA?
No, each regulator at 650mA.
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Old 12th May 2013, 11:19 AM   #729
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Updated schematic, are correct the filament voltages?
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Old 12th May 2013, 01:02 PM   #730
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Quote:
Originally Posted by merlin el mago View Post
Updated schematic, are correct the filament voltages?
Please see the triode curves for 4P1L.


If you want to run 210V and 20mA then the effective bias must be more like 20V.

This means that at 650mA the filament bias resistor is about 30 ohms, and burns > 20W

This is really a bit too much power burn, considering the requirement of the stage.

I see no reason to run the 4P1L at high voltage in this position. Instead, I would suggest 140V 30mA for the 4P1L, so that you can use the 9V bias (650mA and ~14 ohm resistor). You will still get plenty of output swing with a CCS.


This will burn about 6W in the filament bias resistor - much more manageable!
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