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Old 24th August 2012, 03:27 AM   #21
diyAudio Member
Join Date: Feb 2011
Originally Posted by palmas View Post
Best solution:
remove both srpp (I'm not a big fan), use the 6SN7 ground cathode single triode with 400V plate voltage, 22kOhm plate resistor and the 1,5k cathode resistor bypassed with a film cap of 8 to 10uF.
This has much lower gain (14x) than the product of both srpp, can take high signal at input and can provide all swing needed to drive the 300B, and will sound much better than the origínal project.

If you can make it simpler why make it worst?
Thanks and really a good idea. I will do the trial tonight.
Just to clarifiy your direction is make both stages with a single triode. The input valve with 15k plate resistor / 1.5k cathode (8uF bypass); the driver stage with 22k plate resistor / 1.5k cathode (8uF bypass). Is that correct?

Thanks again!
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Old 24th August 2012, 09:32 AM   #22
palmas is offline palmas  Portugal
diyAudio Member
Join Date: Jun 2007
Nop, from the two stages you make only one with a single 6SN7, using the cathode resistor from the 1st stage (1,5kOhm) and a plate resistor of 22kOhm ( minimum 5W).
I'll draw it for you if I get the time today.
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Old 24th August 2012, 09:47 AM   #23
palmas is offline palmas  Portugal
diyAudio Member
Join Date: Jun 2007
The 300B part you can use as it is on your schematic
Attached Files
File Type: pdf 6SN7 300B.pdf (8.2 KB, 35 views)
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Old 24th August 2012, 04:31 PM   #24
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Join Date: Feb 2011
I did an initial trail tonight.

Instead of remove all the SRPP but I keep it at the driver stage as of. I just changed the input stage to one triode with

- 15k ohm Rplate (310Vdc) and keep the 1.5K ohm at cathode (11Vdc), for some reason it does not work at all. No signal go to the driver stage.

- I have then changed the Rplate to 74K ohm (154Vdc) and keep the 1.5K ohm cathode (5.4Vdc).. the same problem of no signal at all.

I just not sure what is the problem or may be the connection error... I have to check it again tomorrow.
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