Screen grid driver for PL519?

Fuling · 6th November 2005, 06:46 PM

Hi,

Inspired by this ( http://www.geocities.com/bobdanielak/technoteNo33.html )
article I decided to give screen grid drive a try a while ago.
I made a prototype similar to circuit 1 in my drawing:

The amp worked quite well (except for some PSU issues that doesn´t belong here), actually good enough to be built properly.
Since the amp is DC-coupled it is sensitive to bias drift, that´s why I used a mu follower input stage.

Long after I made the proto the idea came that perhaps I can get rid of the 12B4 cathode follower if the top half of the input stage already is a cathode follower?

Half a 6SN7 wouldn´t be enough to feed the PL519 (10mA static current and 20mA peaks), but maybe a Mosfet or a high mu, high gm triode would? See drawings 2 and 3.

So, what do you think?

SY · 7th November 2005, 01:34 PM

I use an IRF820 as a source follower to drive the screens in my power amp. It works like a charm.

Fuling · 8th November 2005, 05:35 PM

Thanks for the reple SY.

I´ve pretty much decided to go for the hybrid version with IRF840 (or 820, whatever I find first) and a triode wired E280F.

Fuling · 13th November 2005, 10:52 PM

And off we go:

Bandersnatch · 13th November 2005, 11:42 PM

I'd recommend the IRF820. Acutal in-circuit gm is 100 mA/V which is absolutely nuts compared to valve's.

you could also run a straight triode amplifier, and then CF with a cascoded pair of MOSFET's. The input capacitance of the cascode is quite even and unlike the variable and funky single-gate capacitance. The input gate will be a higher Z load than the DCR of the reference voltage divider you'd use for the bias-ing function.
cheers,
Douglas

Fuling · 15th November 2005, 10:19 PM

Some progress since yesterday, you just gotta love the big red coupling cap. 0,27uF 1600V Jensen PiO.

Miniwatt · 24th November 2010, 02:36 AM

-just curious what happened..

7th November 2005, 01:34 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	I use an IRF820 as a source follower to drive the screens in my power amp. It works like a charm. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

13th November 2005, 11:42 PM	#5
Bandersnatch diyAudio Member Join Date: Jul 2003 Location: Ann Arbor, MI	I'd recommend the IRF820. Acutal in-circuit gm is 100 mA/V which is absolutely nuts compared to valve's. you could also run a straight triode amplifier, and then CF with a cascoded pair of MOSFET's. The input capacitance of the cascode is quite even and unlike the variable and funky single-gate capacitance. The input gate will be a higher Z load than the DCR of the reference voltage divider you'd use for the bias-ing function. cheers, Douglas __________________ the Tnuctipun will return

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8th November 2005, 05:35 PM	#3
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Thanks for the reple SY. I´ve pretty much decided to go for the hybrid version with IRF840 (or 820, whatever I find first) and a triode wired E280F.

24th November 2010, 02:36 AM	#7
Miniwatt diyAudio Member Join Date: Nov 2004 Location: Den Haag	-just curious what happened..

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