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Old 7th February 2011, 07:21 PM   #1
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Default current production pentode, I_a ~ 8mA

Hi there,

does anyone know about a current production signal pentode capable of delivering 8mA in a CCS without getting red?

Currently I am thinking about using EF184, but as all other tubes of the planned amplifier (EL34, ECC88, 5AR4, EZ81) are still produced, I would like to have also a current production pentode for the CCS...

Any ideas?

Greetings,
Andreas
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Old 7th February 2011, 08:15 PM   #2
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Have u concidered a 6550 yet? Or maybe a 813?
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Old 7th February 2011, 08:21 PM   #3
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Both tubes are rated for higher dissipation than my output tubes! Not quite what one wants to use for a CCS in the driver stage. I think its hardly possible to turn them "off" enough to give just 8mA...

I hoped for something like a EF86, just with a current capability of 8-10mA in continuous operation...

Last edited by Rundmaus; 7th February 2011 at 08:23 PM. Reason: clarification, added last sentence.
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Old 7th February 2011, 09:01 PM   #4
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You haven't quite said what you want to do with them yet, so I'll just assume you want to use a pentode CCS for an LTP?

Trying to remember the table from Morgan Jones, I think it goes something like 6AU6 up to 5 mA, EF184 up to 10 mA, EF86 up to 15 or 20mA?
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Last edited by leadbelly; 7th February 2011 at 09:07 PM.
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Old 7th February 2011, 09:09 PM   #5
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Hi leadbelly,

the Morgan Jones table you mentioned lies here in front of me^^ Unfortunately no current production tubes in that table...

EF184 is good for the task up to 15mA, but also not current production...

EF86 would be good and is still produced, but will deliver hardly 4mA, definitely not 8.
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Old 7th February 2011, 09:25 PM   #6
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Maybe use the pentode section of a 6BM8?

Although I have to be my normally blunt self and ask why are you so fixated on new production? I doubt you will run out of NOS supply on these in your DIY lifetime! New production is only necessary for commercial amps, and if you were in a position to be designing a commercial amp you would probably have known better than to just say "CCS" without describing the intended use and think that people would have known what you were talking about
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Old 7th February 2011, 09:29 PM   #7
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Not really fixated on new production, just thought it would be nice as all other tubes in the amp are still manufactured...

No, I am not building or designing amps commercially, but I thought that in the "tubes" forum of DIYaudio most readers can extract enough information from pentode, CCS=constant current source/sink and 8mA. What more simple information is there to describe a current source that the intended current?
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Old 7th February 2011, 09:30 PM   #8
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EL84.
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Old 7th February 2011, 09:34 PM   #9
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Hi SY,

Quote:
Originally Posted by SY View Post
EL84.
Thought about that, yes. Operating point is on the lower edge of the curve sheet then, but might work. First amplifier testing will be with the FET current sink proposed by the designer anyway. Enough time then to take an old EL84 (have lots of them around from tube radios), set it up as CCS and see what happens...

Greetings,
Andreas
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Old 8th February 2011, 02:08 PM   #10
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Prefer the NOS EF184. It's screened, cheap & plentiful. No reason for going to new.
The EL84, the greedy heater current for a few mA CCS operation... is it justifyable ?

richy
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