audio-talk

I've been looking at the folded cascode design on jc's blog and I have drawn what I think is the thing from a conceptual perspective to bring out the nature of the folded cascode and show how it differs from a standard cascode... I hope I have it right :? In a standard cascode the bottom device curr...

Works for me too!

Wow! Many, many thanks, jc!!!

Brilliant post with so much info in it - it will take the weekend and more to process. I've been thinking about your Gm amp and how to use it best for a phono - must try it now you confirm again how nice it can sound...

James

I assume the input goes into the FETs gate not the drain/cathode junction?



James (being constructive) :0

Yippee!!!!

Fantastic stuff Mark - just fantastic!

and hats off to jc for sharing via his blog!

Hello Ian, It is a general rule for pentodes that screen current is 20-25% of anode current with beam plate tetrodes being closer to 25% and true pentodes being closer to 20% for normal operating conditions... Their are some exceptions like the EF86 (17%). C3g is a nice driver for DHTs but it is sta...

Normally g2 current is 20% to 25% of Ia so for 20mA anode current design for 4mA g2 current as C3m are at the 20% end of the spectrum... If you are using a potential divider to fix g2 voltage then you need some current for the bottom resistor and so the 10mA for the g2 chain is not unreasonable... N...

The point about the error amp for the shunt reg is that it acts to supplement the Gm for the shunt valve i.e. it makes it act as if it had much more Gm - typically the error amp gain times the Gm of the shunt valve so its easy to make your 6L6 act as if it had a Gm of 100mA/V or more... Pauls remark...

Not to put any pressure on you and just for interest here is a page from Tubecad about shunt regulators http://www.tubecad.com/2011/08/blog0209.htm and at the bottom he shows a tube shunt reg with error amp using 12DW7 with a performance curve. He also discusses the benefits and drawbacks of using a...

I've no more space on the top deck for another valve Well that's easy - replace the 6AU6 with a dual pentode! There are several see http://www.mif.pg.gda.pl/cgi-bin/vs4.pl Damn! Search doesn't work but a search on tubedata for double pentodes yields lots of the beasties! Honest!!! or take the easy ...

How about an error amp for the shunt reg?

Previously I designed the attached psu for Dave Dove's RIAA amp using a TV dual triode :D It would have been better with a VR ref in their somewhere on the shunt but not sure that a 75V VR tube would work at these B+ volts... and , following this discussion the BG should come out! This is a fantasti...

Nick,

Nice change-up

Looking at it makes me wonder about using a 6F12p - Pentode first stage with gain at 100 and triode CF to drive the IT... Both stages have a Gm of about 20mA/V so should do the job nicely...

Shout if you want to borrow a couple

J

If you find a copy of the RCA datasheet such as http://www.hifitubes.nl/weblog/index.php/rca-2a3-datasheet/ then the spec is 5250uohms for transconductance but really that is nothing more than a number on a spec sheet :lol: If you look at page 4 of the same pdf then you see the transconductance curv...

Hello Chris!

Quartz monofilament sounds a cut above most things!



Happy New year

James