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In Reply to: RE: P2SE high bias posted by Chip647 on November 08, 2014 at 07:54:58
Above 20V to 21V.With this value plate current is above 80mA.Plate dissipation for 6S3P-E is above 21W and for 6L6GAY is 19W.With this plate current dissipation is much over limits.Regards
Follow Ups:
I've set up amps to run 6S3P-Es at 21 watts dissipation, and the tubes have lasted for years. When you say above 21 watts exactly how much above 21 watts do you mean? These tubes can take a beating, IIRC Michael Samra has run them at around 25-26 watts and reported they sounded very good at that dissipation. Of course it would take a couple years to know exactly how that dissipation affects tube life, so the jury is out on that one.
twystd
The issue with tubes being not exactly the same can best be solved by using CCS arrangements under the cathode of each tube. A simple LM317 with current setting resistor should do the trick. Any tube with the same socket pinout can be inserted and it must conduct the set current. With tubes that are going to have less than 35V of cathode bias voltage, like the 6L6, the arrangement is very simple and reliable. As for the resulting sound, in my view the improvement is huge.
It can be done with 7805 as well - for details please check out my RH84-PPE (Parallel Pentode Edition) design as published on my blog, basically an RH84 with paralleled output tubes and small signal pentode used as driver (thus the "Pentode" in the name).
If you like the result, you can easily further modify your "Audio Note" further along the line of RH amps... it's difficult to imagine the improvement you could get.
******
http://rh-amps.blogspot.com/
hi Alex thank you for sharing your experience and knowledge
I have an audionote p2 se and I had replace 6l6 by 6p3se
on the cathode resistor I read 32V across a 750 ohm one with 365v B+
for me the sound is good with its parameters
I would like to make the change you'd suggested
could you'll please tell me resistance value that is between the output and the adjustment of 7805 110 OHM as in RH84
does the voltage of the zener diode is always 22 V or higher
the screen voltage on the 6p3se is maximum 250v
does I must reduce my 355V by an input resistance on the input of the output transformer
I have already replied by e-mail (confusing forum messages, every time someone replies I get the impression it was a personal message).
750 ohm is far from 300 (600 in parallel with 600). That is the reason why you get 30+V at the cathode: current very low. I guess the original schematics requires 60-66mA of cathode current per tube (probably 50-58mA anode current when you deduct g2 current).
To set 66mA cathode per tube you need to provide an LM317 CCS under each cathode, and a current setting resistor of 18.9 ohm. In practice you can go with anything between 18 and 21, choosing some standard value. Use 1% tolerance metal film resistors.
As for a practical implementation, check out my RH84 PPE (on my blog).
Keep in mind that Russian 6P3S tubes have lower anode dissipation ratings, 18W if I am correct. This means they can't be used as replacement for 6L6GB, unless current is reduced. 27 ohm resistors are probably going to be the best option for you in that case.
******
http://rh-amps.blogspot.com/
Hi Alex
many thanks for your reply
I have change the transformer to supply 6p3se I have now 365V at B+ and understand to keep 250 V on G2
please could you'll take the schematic wich was sent on the first message and modify and transform it for ccs cathode biais as same as RH 84 as you'd suggest it on your reply message
This is a problem when designs are made with cathode bias trying to run very high Class A. Line voltage, tube variability and parts variability.
From what you describe you have an effective cathode resistor of 270 ohms on each tube. 600 + 600 + 2700. Replace one of the 600s in each stack with an 800 to 1000 ohm resistor, you will raise the cathode resistor to 304 or 330 which will cut your current down.
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