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Old 1st July 2004, 04:27 PM   #1
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Default recommend operating point for EL84?

I am going to build a pre-amp from a triode connected EL84...

What is a good Va and Ia to run it at?

Probably use a CCS or mu-follower configuration with either pentode or SS.

low voltage 100-150v ?

Thanks!!!

maybe 120v 10mA 4v bias..

?
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Old 1st July 2004, 04:45 PM   #2
benny is offline benny  Australia
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just curious to know why you want to use a triode conected el84 in a preamp?
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Old 1st July 2004, 08:52 PM   #3
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Default because....

well because i want to.



I want to use current production tubes mainly.

any other ideas?

besides the 6H30 which sucks.
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Old 1st July 2004, 09:57 PM   #4
316a is offline 316a  England
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Default Re: because....

Quote:
Originally posted by AudioGeek
well because i want to.



I want to use current production tubes mainly.

any other ideas?

besides the 6H30 which sucks.
Hello ,
How about the 12B4A ? Pro's : Look nice , cheap , plentiful , good sounding . Cons : can be microphonic but saying that , at $2 a throw on Ebay.... Plenty of other candidates along the same lines : 6S19 , 2C50 , 6BX7 , CV1884 , A2293

cheers

316a
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Old 1st July 2004, 10:09 PM   #5
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In current production triodes, JJ's ECC99 is definitely worth trying.

BTW, what sort of source and what sort of power amp are you going to mate with the line stage? Be alert for a possible "hair trigger" volume control.
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Old 1st July 2004, 11:59 PM   #6
G is offline G  United States
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Default Re: recommend operating point for EL84?

Quote:
Originally posted by AudioGeek
I am going to build a pre-amp from a triode connected EL84...

What is a good Va and Ia to run it at?

Probably use a CCS or mu-follower configuration with either pentode or SS.

low voltage 100-150v ?

Thanks!!!

maybe 120v 10mA 4v bias..

?

I'm thinking about 125v on the plate with a -4 bias on the grid @20mA. You would need a 200 ohm cathode resistor. the problem is you would need to use a CCS on the plate or you would need to use a plate choke because a plate resistor ain't gonna get the job done. With a CCS or a choke it may end up being a killer linestage. Here is a link to a alternative plate load that is dirt cheap at digikey. It will take some tweaking but it's definately doable. :

http://www.pmillett.addr.com/current_source.htm

You will need to use a heatsink with the IXYS current source. Also you have to understand that when using a solid state CCS you have to bias the tube with the plate to ground voltage drop in mind. It looks like you would need a 150 ohm resistor on the current source for 20mA. You might try a 500 ohm 5 watt resistor in parallel with a 500 ohm 2 watt pot so you can just dial in the current. If you build a supply that will provide 40mA at 250 volts all you would need to do is adjust the pot until you got a 125v drop from plate to ground across each tube and viola, you have a EL84 linestage. Strange but interesting . Cheers.
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Old 2nd July 2004, 02:39 PM   #7
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Default hehehe

I threw together a linestage with some 6BQ5's...

120v on anode, 20K plate resistor, 4v bias.

gain is good.

FLAT response to about 35Khz...

smokes my 6H30 pre-amp.

no noise really.

VERY low distortion.

I am going to convert this to a mu stage with SS CCS and a regulated power supply.

Any thoughts on the power supply???

Thanks!
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