Search found 599 matches

by RhythMick
Mon Jun 08, 2020 7:53 am
Forum: Everyones Projects
Topic: Loftin Shushido 2a3
Replies: 13
Views: 348

Re: Loftin Shushido 2a3

andrew Ivimey wrote:
Sun Jun 07, 2020 10:53 am

The speakers ( in the shed) are the superb Scott designed six feet tall, five inch wide monsters with FE126s. Lovely.

Speakers in the shed is impressive
by RhythMick
Sun Jun 07, 2020 10:34 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

Ok thanks Nick. As usual I'm not explaining myself. I need to go experiment, Spice first.
by RhythMick
Sun Jun 07, 2020 9:07 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

Without being factious. Maybe you need to understand voltage first. Once you have that it all becomes simple. Trying to think why you thought I didn't understand voltage. Please reassure me I'm right that the current through the source load will change as the signal varies the voltage on the 300B g...
by RhythMick
Fri Jun 05, 2020 10:41 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

Actually Nick you did it with the phrase "source follows gate". Obvious, but for some reason I was looking for curves to show me an amplification effect. Nonsense, I was just not looking at it right.

Sorry
by RhythMick
Fri Jun 05, 2020 10:26 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

OK so let's go to an easier question (perhaps).

How do you choose the Source Load resistor for a particular FET and circuit requirement ?
by RhythMick
Fri Jun 05, 2020 10:19 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

Sorry Nick no that's not it. It's not the "where you reference zero" either. Something in my head just hasn't properly got the behaviour of solid state components. For a valve cathode follower I can draw a load line and see how current relates to grid voltage. For some reason I can't picture how a v...
by RhythMick
Fri Jun 05, 2020 8:44 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

You need the drain of the fet to be > 0v or you won;t be able to swing to source up to 0v. OK thanks - let's say that I make the FET supply +200/-200. See again, something I'm struggling with here. If the source is at 0v and the supply is +200V, so Vds is 200V ? Vds will swing to 374v - Is that rig...
by RhythMick
Fri Jun 05, 2020 8:21 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

izzy wizzy wrote:
Fri Jun 05, 2020 8:10 pm
And http://www.bartola.co.uk/valves/for-sal ... lower-pcb/

Down a bit are links to further reading/homework ;)
Looking forward to it - many thanks
by RhythMick
Fri Jun 05, 2020 8:20 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

Nick wrote:
Fri Jun 05, 2020 8:13 pm
You need the drain of the fet to be > 0v or you won;t be able to swing to source up to 0v.
OK thanks - let's say that I make the FET supply +200/-200.
by RhythMick
Fri Jun 05, 2020 8:08 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Re: Request for design guidance with FET source follower driver

pre65 wrote:
Fri Jun 05, 2020 7:44 pm
The type I first found was named "power-drive".

http://tubelab.com/articles/circuits/power-drive/
Ha - thanks, you posted that as I was typing my brain-dump of where I think I'm up to.
by RhythMick
Fri Jun 05, 2020 7:34 pm
Forum: Everyones Projects
Topic: Request for design guidance with FET source follower driver
Replies: 14
Views: 302

Request for design guidance with FET source follower driver

Inspired by Nick, I'm trying to get my head around the design of a FET source follower so I can give it a try. I kept coming back to Tubelab's Powerdrive SE page : http://tubelab.com/articles/circuits/power-drive/ I want to get the real basics right in my head first. The way George Broksie draws tha...
by RhythMick
Fri Jun 05, 2020 7:33 pm
Forum: Everyones Projects
Topic: Request for design guidance with Fixed Bias Output Tube
Replies: 41
Views: 645

Re: Request for design guidance with Fixed Bias Output Tube

Nick has inspired me to go learn about FET-based source followers. My brain hurts !

I'll start a separate thread for it as I have LOTS of (probably dumb) questions about that !
viewtopic.php?f=11&t=7863
by RhythMick
Thu Jun 04, 2020 4:16 pm
Forum: Everyones Projects
Topic: Request for design guidance with Fixed Bias Output Tube
Replies: 41
Views: 645

Re: Request for design guidance with Fixed Bias Output Tube

I'd be concerned about injecting noise into the more sensitive parts of the amp by going fixed bias on the first 2 stages. Seems like more hassle than it could be worth. Nothaving done any sums, I think I'd want more HT + and - for a driver of that type. Not sure of the swing you need to drive the ...
by RhythMick
Thu Jun 04, 2020 3:55 pm
Forum: Everyones Projects
Topic: Request for design guidance with Fixed Bias Output Tube
Replies: 41
Views: 645

Re: Request for design guidance with Fixed Bias Output Tube

Paul Barker wrote:
Thu Jun 04, 2020 3:23 pm
Did anyone read the article on the Andy Grove parallel 300b? First stage; I can’t figure why he’s shunting the cathode resistor and cap instead of bypassing.
Do you have the link to the article ? I saw the diagram Nick pasted but can't find the link in Google
by RhythMick
Thu Jun 04, 2020 3:52 pm
Forum: Everyones Projects
Topic: Request for design guidance with Fixed Bias Output Tube
Replies: 41
Views: 645

Re: Request for design guidance with Fixed Bias Output Tube

So - here's my current thinking. As always very happy to be guided ... I have an unused secondary winding on the mains transformer which is 150-0-150 @ 20mA which seems to me ripe for providing bias +/- rails. Solid state rectification and filtered not regulated (as the valve B+ supplies aren't regu...