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Old 17th June 2012, 04:17 PM   #1
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Lightbulb Re: Buffer with tube PCC88

Hello all!
I need schematic a stereo buffer with Tube/Valve PCC88, where the input resistance will be 1Mohm, and with an output <1Kohm
Thank you for your cooperation.
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Old 17th June 2012, 04:33 PM   #2
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How many tubes may be used ?
With one PCC88 it is most likely impossible.
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Old 17th June 2012, 04:49 PM   #3
SY is offline SY  United States
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Quote:
Originally Posted by artosalo View Post
With one PCC88 it is most likely impossible.
Why? gm is likely 8mA/V, so source impedance of a cathode follower will be ~125R plus perhaps another 100R for a cathode stopper.
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Old 17th June 2012, 05:27 PM   #4
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True, if no gain is required.
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Old 17th June 2012, 05:35 PM   #5
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Quote:
Originally Posted by artosalo View Post
How many tubes may be used ?
With one PCC88 it is most likely impossible.
Why not? percent of it is double triode.
Here's how I conceived the schematic. I'd say that the values ​​that are components of the input = 1Mohm and output <1Kohm ( for frequency 30Hz ...20kHz to + / -0,5dB), with a gain of about 0,95 dB!
thanks
Attached Files
File Type: pdf Buffer with PCC88.pdf (23.5 KB, 255 views)

Last edited by formula 22; 17th June 2012 at 05:53 PM.
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Old 17th June 2012, 05:51 PM   #6
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Your circuit is fully OK if gain just below 1 is sufficient.
The following component values will give good operation: R1 = 1 M, R2 = 1k, R3 = 470, R4 = 10 k, R5 = 1k, C3 = 100 uF, C4 = 10 uF, R5 = 100 k, C1 = 22nF.
But what will be your load impedance and required output voltage ?

Last edited by artosalo; 17th June 2012 at 06:03 PM.
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Old 17th June 2012, 06:11 PM   #7
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artosalo thank you for your prompt response. After this comes the buffer Po=60W/8R audio amplifier with an input voltage Uin(max) = 1V; Rin = 47k.
If someone has something else to add some of this buffer is welcome, ...
thanks and cheers!
P.S.
Sam should now look like this:
Now please offer some quality power supply for the buffer ..
Attached Files
File Type: pdf Buffer with PCC88 (complet).pdf (28.4 KB, 180 views)

Last edited by formula 22; 17th June 2012 at 06:28 PM.
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Old 18th June 2012, 12:53 AM   #8
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Do you only have +90V available for the B+ supply? That's not much for this type of tube (or any tube, for that matter).

I'd aim for +90V between the PCC88's plate and cathode. The 10k cathode load resistor would drop 90V across it if you have 9mA current through the tube, which is not excessive at all for a 6DJ8/ECC88 class of tube. Gm goes up with increased current through the tube, which is good for a cathode follower (reduces output Z). PCC88 has max plate dissipation of 1.8W. Ua of 90V * Ia of .009A = 0.81W, so you would still be well within that limit.

You might want to consider using something like a +180V supply.

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Old 18th June 2012, 05:16 AM   #9
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[QUOTE=rongon;3063443]Do you only have +90V available for the B+ supply? That's not much for this type of tube (or any tube, for that matter).

I'd aim for +90V between the PCC88's plate and cathode. The 10k cathode load resistor would drop 90V across it if you have 9mA current through the tube, which is not excessive at all for a 6DJ8/ECC88 class of tube. Gm goes up with increased current through the tube, which is good for a cathode follower (reduces output Z). PCC88 has max plate dissipation of 1.8W. Ua of 90V * Ia of .009A = 0.81W, so you would still be well within that limit.
You might want to consider using something like a +180V supply.

OK, if I go with the power supply B+(+Ua)=+180V, which should have value resistors in the schematic (P1, R1, R2, R3, R4, R5, R6)?
thank you!
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Old 18th June 2012, 05:53 AM   #10
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You do not need to change anything. With 180 V supply voltage the performance is just better.
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