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Old 24th December 2012, 05:10 PM   #21
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Quote:
Originally Posted by DUG View Post
1. Gost22 wants to regulate current. Placing a CCS in the plate circuit is for a different purpose. The load line would be almost horizontal. Perhaps something to look at. (If you can get a very low capacitance CCS)

2. Yes, you are correct in that a CCS without a bypass cap will get zero gain to the plate.

Gost22, you do need to put a bypass cap in the cathode cct. (parallel with the CCS)

3. The CCS I have suggested will go down to almost 1V...Well within what Gost22 asked for.

4. The bias point is specified at 7.5mA not 2V. Depending on the tube it might be 1.9V or 2.1V but the CCS will compensate for that. LED would not. LED's also have temperature characteristics that are rather bad for a voltage reference.
How about the LM337 ?

look at something like this Click the image to open in full size.

Cheers ,

Rens
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Old 24th December 2012, 07:44 PM   #22
EUVL is offline EUVL  Europe
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All the above suggestions are valid.

But IMHO the difficulty lies in that the voltage headroom is only 1.9V.
And we still want the current to remain constant to any small changes in that headroom voltage.

If one will go the the extra complication of a separate supply, either a positive one for the opamp solution,
or a negative one for similar solutions to tube cad, then the problem becomes much simpler to solve.

But if we only want to insert one module between the cathode and Gnd,
then the heavily degenerated JFET is one of the few solutions I know.


Patrick
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Old 24th December 2012, 11:18 PM   #23
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Originally Posted by kevinkr View Post
Take a look at SY's "His Master's Voice" article for a good example of the cascode CCS I am thinking of: His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Thanks for that recommendation. Not only did it answer my stated concerns, it addressed a few other issues that that I was pondering. Well written too.
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Old 25th December 2012, 03:19 AM   #24
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Quote:
Originally Posted by EUVL View Post
But IMHO the difficulty lies in that the voltage headroom is only 1.9V.
Only if one insists on using a CCS in the cathode, instead of (the better approach) using it in the plate.
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Old 25th December 2012, 06:03 AM   #25
djn is offline djn  United States
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Don't know what you bought or have already but you might want to look at Pete Millete low-mu pre design.
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Old 25th December 2012, 07:52 PM   #26
GoatGuy is offline GoatGuy  United States
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Maybe this is hopelessly simplistic, but wouldn't a gate-grounded common JFET in series with the cathode ... and a suitably sized source-to-ground resistor (to get the 7.5 ma) be the ticket? I mean... its trivial, it scales really well... and if a J201, J301 or J211 JFET is used ... the minimum voltage drop is very low.
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Old 25th December 2012, 11:04 PM   #27
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Quote:
Originally Posted by kevinkr View Post
Take a look at SY's "His Master's Voice" article for a good example of the cascode CCS I am thinking of: His Master's Noise: A Thoroughly Modern Tube Phono Preamp
A+

CCS on the ANODE and LED on the CATHODE.

Build a test board (i.e. with a battery and resistor...) to set each CCS circuit mA's and away you go....
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Old 25th December 2012, 11:23 PM   #28
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Quote:
Originally Posted by soulmerchant View Post
A+

CCS on the ANODE and LED on the CATHODE.

Build a test board (i.e. with a battery and resistor...) to set each CCS circuit mA's and away you go....
Yes, and if want stable working point add servo to anode load turning such a way CCS into gyrator.
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Old 26th December 2012, 04:05 AM   #29
Gost22 is offline Gost22  Bolivia
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Please be more specific your offer for circuit or schematic to solve the problem.
thank you!
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Old 26th December 2012, 04:57 AM   #30
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you still haven't defined the problem - apart from identifying the solution you want
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