A2 experiments.

We all start somewhere
Post Reply
User avatar
Dave the bass
Amstrad Tower of Power
Posts: 12276
Joined: Tue May 22, 2007 4:36 pm
Location: NW Kent, Darn Sarf innit.

#91

Post by Dave the bass »

Aaah right, got it. Ta.

I remember from a chat before that toggling around the 0V grid line can be a very non-linear area of operation too so if we 'can' keep the grid in (say) A2 for all its swing the driver has an easier/more consistent life.

Taking it a step further, IF we drive a +ve biased grid from the cathode of the preceding stage we need a fair amount of gain from the stage/s before the CF because we're not going to get any gain from the CF, unity (at best) but more commonly <1.

CF driver stage could be quite handy though in that the cathode is raised at a DC level so maybe that DC level could be the same DC bias that raises the Grid of the o/p valve to get the valve into A2 operation.

Ooooerrr. I have a feeling my next breadboard project is going to be much bigger and complicated that I thought....whahey! :)

DTB
"The fat bourgeois and his doppelganger"
Top
User avatar
pre65
Amstrad Tower of Power
Posts: 21400
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#92

Post by pre65 »

Dave, you might like to add this to your bedtime read list.

http://www.jrossmacdonald.com/jrmpubs/0 ... llower.pdf
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Top
User avatar
Dave the bass
Amstrad Tower of Power
Posts: 12276
Joined: Tue May 22, 2007 4:36 pm
Location: NW Kent, Darn Sarf innit.

#93

Post by Dave the bass »

Cheers Phil, if I get stuck can you help me with some of the calculus? :)

DTB
"The fat bourgeois and his doppelganger"
Top
User avatar
pre65
Amstrad Tower of Power
Posts: 21400
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#94

Post by pre65 »

Dave the bass wrote:Cheers Phil, if I get stuck can you help me with some of the calculus? :)

DTB
TBH Dave, I've not actually read this article in detail, but am doing so at this very moment. :)

I have got a GCE in maths, so I'll help if I can. :lol:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Top
User avatar
Dave the bass
Amstrad Tower of Power
Posts: 12276
Joined: Tue May 22, 2007 4:36 pm
Location: NW Kent, Darn Sarf innit.

#95

Post by Dave the bass »

Nick wrote:
One way is to drive the cathode. Its still low impedance, but its a more consistent low impedance.
Backtracking, just noticed that in your reply Nick, 'drive the cathode'. Oooeeerrrr, OK, so I take it the grid is still held +ve but the driver signal is introduced between the 0V rail and the top of the cathode resistor?

As anaside, Found a great page about A2 here. http://diyaudioprojects.com/mirror/memb ... part1.html

DTB
"The fat bourgeois and his doppelganger"
Top
User avatar
Nick
Site Admin
Posts: 15752
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#96

Post by Nick »

Dave the bass wrote:
Nick wrote:
One way is to drive the cathode. Its still low impedance, but its a more consistent low impedance.
Backtracking, just noticed that in your reply Nick, 'drive the cathode'. Oooeeerrrr, OK, so I take it the grid is still held +ve but the driver signal is introduced between the 0V rail and the top of the cathode resistor?

As anaside, Found a great page about A2 here. http://diyaudioprojects.com/mirror/memb ... part1.html

DTB
Yep, or you put the secondary of a interstage in the cathode. The big plus is there is no transition from A1 to A2
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Top
User avatar
pre65
Amstrad Tower of Power
Posts: 21400
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#97

Post by pre65 »

Nick wrote:
Yep, or you put the secondary of a interstage in the cathode. The big plus is there is no transition from A1 to A2
That IS interesting. :)

More reading matter.

http://mikea.ath.cx/eimac/eimac08.pdf

And there is a bit about it on here.

http://www.tubelab.com/SEoutput.htm
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Top
User avatar
Dave the bass
Amstrad Tower of Power
Posts: 12276
Joined: Tue May 22, 2007 4:36 pm
Location: NW Kent, Darn Sarf innit.

#98

Post by Dave the bass »

Ta Phil, the interstage would need to be fairly beefy to pass that standing sort of DC current flowing through the o/p stage though yeah? EDIT. Just thought, it might not be as bad as I thought as some of the cathode current flows out the grid and the rest to the anode, no, hang on ... its still ALL flows from the cathode though. Thats the trouble with typing while I'm still thinking. As you were!

Clever ccts though, when I'm braverand understand more I'll try that (with someone-elses IT's!) :)

DTB
"The fat bourgeois and his doppelganger"
Top
User avatar
Nick
Site Admin
Posts: 15752
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#99

Post by Nick »

Dave the bass wrote:Ta Phil, the interstage would need to be fairly beefy to pass that standing sort of DC current flowing through the o/p stage though yeah? EDIT. Just thought, it might not be as bad as I thought as some of the cathode current flows out the grid and the rest to the anode, no, hang on ... its still ALL flows from the cathode though. Thats the trouble with typing while I'm still thinking. As you were!

Clever ccts though, when I'm braverand understand more I'll try that (with someone-elses IT's!) :)

DTB
Yes, thats the point, because it all flows through the cathode there is no A2 change. But remember as long as its not a bifilar interstage, you can offset the secondary DC current by the primary current.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Top
User avatar
Mike H
Amstrad Tower of Power
Posts: 20189
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:
Contact Mike H

#100

Post by Mike H »

That's a point, grounded grid cathode input mode is low impedance. For a power valve very low impedance!
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Top
User avatar
pre65
Amstrad Tower of Power
Posts: 21400
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#101

Post by pre65 »

Looks like the 811a is purpose built for 360 degree A2 use at 500v. (A3 :wink: )

So, does the driver valve have to supply all the cathode current, about 80ma ?
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Top
User avatar
pre65
Amstrad Tower of Power
Posts: 21400
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#102

Post by pre65 »

Would an interstage rated for 100ma and a ratio of 8.3:1 (5K - 600) be a useful thing to have for cathode drive on an 811a ?
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Top
User avatar
Mike H
Amstrad Tower of Power
Posts: 20189
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:
Contact Mike H

#103

Post by Mike H »

I would think yes, and, quite likely.

Note Nick's mention about having the DC direction for the IT secondary reversed relative to primary, to reduce or cancel the standing DC magnetizing current.
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Top
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#104

Post by IslandPink »

Then you can claim you're mates with Nobu Shishido of 'Wavac' fame .
"Once you find out ... the Circumstances ; then you can go out"
Top
User avatar
Mike H
Amstrad Tower of Power
Posts: 20189
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:
Contact Mike H

#105

Post by Mike H »

I'll take your word for it. :D
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Top
Post Reply

Return to “Beginners”