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Old 16th February 2014, 02:18 PM   #1
kees52 is offline kees52  Netherlands
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Default 6H9c Idle Current.

Hi There

I have seen much people who says, low idle current give tube more detail, others say put it in class A to get better sound.

What are your experience with idle current, I have a cascode mosfet on plate so I have a horizontal loadline, because of this distortion is low make tube sound hars/hard buit with a lot detail and deepness.

I did use a 6H9C, I have heart this are hars sounding tubes.

A penthode 6J9N in triode mode last time did make warmer sound, what I do like, this 6H9C do not, the 6H8C will do sound warmer, more what I like.

regards

kees
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Old 16th February 2014, 03:16 PM   #2
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Idle current about 2 ma /more current - big sound, IMO/
But I prefer 6SN7 with 8 - 10 ma /Loftin-White two stages with adjustable gain from 20 to....max/.
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Old 16th February 2014, 03:33 PM   #3
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by azazello View Post
Idle current about 2 ma /more current - big sound, IMO/
But I prefer 6SN7 with 8 - 10 ma /Loftin-White two stages with adjustable gain from 20 to....max/.
Thanks

I have now put it on 0.5 mA and it do sound nice, don,t forget I have a horizontal loadline, not a resistor loadline, this change things.

2 mA put 0.4 watt dissipation on tube when 200 volt on plate. I go try out what sound it delivers.

I have to use a high mu triode because of it is a mosfet hybride amplifier, it do the full voltageswing needed.

regards

kees

Last edited by kees52; 16th February 2014 at 03:39 PM.
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Old 16th February 2014, 04:01 PM   #4
kees52 is offline kees52  Netherlands
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A 6H9C on 2 mA is not so good, cahtode resistor is to low make just 1.45 v negative, resistor 680 ohm is needed for 2 mA.

I let it on 0.5 mA for a while, looks like it has more detail and deepness.

Still a penthode do better.
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Old 22nd November 2014, 01:56 PM   #5
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by kees52 View Post
A 6H9C on 2 mA is not so good, cahtode resistor is to low make just 1.45 v negative, resistor 680 ohm is needed for 2 mA.

I let it on 0.5 mA for a while, looks like it has more detail and deepness.

Still a penthode do better.
After a longer time I did look again on the current who has to be 2.3 mA but I did say about the cathode resistor make not enough negative (negatief needs -2 volts, input signal 1 volts max).

Solution is higher voltage, this tube likes high voltage, make it sing.
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Old 22nd November 2014, 03:29 PM   #6
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From the plate curves it would appear that at Ip = 2mA you would have Ep = 160V and grid bias would be -16V. Your cathode resistor would have to be 8k ohms.
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Old 22nd November 2014, 07:52 PM   #7
kees52 is offline kees52  Netherlands
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Originally Posted by Palustris View Post
From the plate curves it would appear that at Ip = 2mA you would have Ep = 160V and grid bias would be -16V. Your cathode resistor would have to be 8k ohms.
When I do this I get not 2 mA with 8 k ohm, I have included a measurement with plate voltage 260 volts, and 1 K ohm cathode resistor I get 2.04 mA.

When I do in sim 8 K ohm and 160 volts then i get no more then 0.227 mA that is quite low??, I did read somewhere these tubes need high voltage to sing properly.

Do I miss something here, don,t forget I do use cascode fets so loadline is horizontal, things change..

Now the amp plays with 260 volts plate voltage and 1 K ohm cathode resistor and I get 2.04 mA max is 2.04 volts on 1k resistor.

Or do I have bad tubes, she are in original box.

regards

kees
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Old 22nd November 2014, 09:21 PM   #8
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R4 should be on the grid, not the grid leak resistor!
Valves are very tollerent and do not need special component values.
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Old 22nd November 2014, 09:36 PM   #9
kees52 is offline kees52  Netherlands
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Originally Posted by JonSnell Electronic View Post
R4 should be on the grid, not the grid leak resistor!
Valves are very tollerent and do not need special component values.
This is drawn there I have did in final schematic in eagle corrected I did see, also is now 1k ohm.

I still do not get on why cathode resistor 8 Kohm and 2 mA and 160 volts? I do not get more then 0.227mA?, I have now 260 volts (plus minus) en have with 1 K ohm resistors 2.04 mA.

So what is problem?

thanks.
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Last edited by kees52; 22nd November 2014 at 09:40 PM.
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Old 23rd November 2014, 05:32 PM   #10
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I would guess that you have a problem with the design of the CCS. Try breadboarding the circuit to test it.
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