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Darius Loftin White explained
Darius Loftin White explained
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Old 1st June 2008, 03:19 AM   #21
Sheldon is online now Sheldon  United States
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Default L F Version 2

Or one I suspect you will prefer:
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Old 1st June 2008, 03:23 AM   #22
Sheldon is online now Sheldon  United States
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Default And the Power Supply

This conversion re-uses most of the components from the initial version, amp and power supply. The one exception is that I will need to wind some transformers to for regular SE duty. I can use the same chassis too. If I had to change that, I might not do it.

Sheldon
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Old 1st June 2008, 04:08 AM   #23
kenpeter is offline kenpeter  United States
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RE: Version1 (With Bootstrap)

Current set by 625R source of lower LND150 = 1ma???

If so, then 1ma thru 10R at that drain is a 0.01V drop.
Never changing, never doing anything too interesting.
Even the bootstrap end tied here won't conduct any
variance thru the lower 10R due to the CCS.

Quite probably the other 10R above the top LND150
is equally inert. It might see some slight activity due
to the bootstrap capacitor... I am not sure it has any
other significant effect. Is it necessary?

I often throw in overzealous optional parts, and later
remove them... I had one thing in mind when I drew
them there, but then a crazy new idea evolves.
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Old 1st June 2008, 05:15 AM   #24
Sheldon is online now Sheldon  United States
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Quote:
Originally posted by kenpeter
RE: Version1 (With Bootstrap)

Current set by 625R source of lower LND150 = 1ma???

If so, then 1ma thru 10R at that drain is a 0.01V drop.
Never changing, never doing anything too interesting.
Even the bootstrap end tied here won't conduct any
variance thru the lower 10R due to the CCS.

Quite probably the other 10R above the top LND150
is equally inert. It might see some slight activity due
to the bootstrap capacitor... I am not sure it has any
other significant effect. Is it necessary?

I often throw in overzealous optional parts, and later
remove them... I had one thing in mind when I drew
them there, but then a crazy new idea evolves.
I copied that from a different version that uses DN2540 at higher currents. Just left the drain "stoppers" in. They were originally suggested by someone here, as I was having some issues that could have been oscillation related. They may well do nothing.

Sheldon

Sheldon
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Old 1st June 2008, 03:16 PM   #25
oldeurope is offline oldeurope  Germany
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Default #21

Hello Sheldon,

Quote:
Originally posted by Sheldon
Or one I suspect you will prefer:
Yes, this is the way I like it.
And I like the tubes you are going to use.
I think you'll have something between 90VDC to 100VDC at the cathode?
Did you calculate the expected output resistance of the driver and it's
"characteristic factor"?

Kind regards,
Darius
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Old 1st June 2008, 04:29 PM   #26
Sheldon is online now Sheldon  United States
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Default Re: #21

Quote:
Originally posted by oldeurope
Yes, this is the way I like it.
And I like the tubes you are going to use.
I think you'll have something between 90VDC to 100VDC at the cathode?
Did you calculate the expected output resistance of the driver and it's
"characteristic factor"?
I didn't have to guess at your preference.

With these values, the voltage at the output tube cathode will be about 135V, at a little under 30mA. With a bias offset of -26V, the grid will be at about 110V.

Using 60k for the ra, and a u of 70, I get about 90k for the output impedance. With an estimated 50pF input capacitance for the 801, that gives me a roll off at about 35kHz - maybe borderline. I like your bootstrap approach with tubes, but I want to avoid having to redo my chassis http://www.diyaudio.com/forums/showt...61#post883561. I've made a number of changes to the power supply of that amp, so that thread is not the current version, but the rest is the same. I might consider redoing the top plate, as a last resort. That's why I posted the bootstrapped fet follower. I could also simply use the follower after the SL7 without the bootstrap.

I'm not sure about the "characteristic factor". I have seen reference to it on on your blogs, so I'll have to find it and see if I can understand it.

Sheldon
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Old 1st June 2008, 05:19 PM   #27
Sheldon is online now Sheldon  United States
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For the characteristic factor I calculate: 420000/(((800)+(1/0.0014))*70) = 0.01.

That's with transconductance expressed as Mhos.

Don't know what it means yet, though.

Sheldon
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Old 1st June 2008, 05:23 PM   #28
oldeurope is offline oldeurope  Germany
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Default #26

Thanks for your reply.

Quote:
Originally posted by Sheldon


I didn't have to guess at your preference.

With these values, the voltage at the output tube cathode will be about 135V, at a little under 30mA. With a bias offset of -26V, the grid will be at about 110V.

...

Sheldon
Hi Sheldon,
I'd like to see ≈95VDC ≈20mA in your application.

Quote:
Originally posted by Sheldon



Using 60k for the ra, and a u of 70, I get about 90k for the output impedance. With an estimated 50pF input capacitance for the 801, that gives me a roll off at about 35kHz - maybe borderline. I like your bootstrap approach with tubes, but I want to avoid having to redo my chassis http://www.diyaudio.com/forums/showt...61#post883561.


Sheldon
Yes, I agree.
At this current will be lower and maybe you can take
a lower cathode resistor?
If not you can increase the cathode resistor of the output triode
to get 20mA.
What is the roll off of the output transformer?
The amp looks good. .

Quote:
Originally posted by Sheldon


I'm not sure about the "characteristic factor". I have seen reference to it on on your blogs, so I'll have to find it and see if I can understand it.

Sheldon
This is important to understand for a good triode circuit design.


Kind regards,
Darius
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Old 1st June 2008, 09:07 PM   #29
Sheldon is online now Sheldon  United States
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Default Re: #26

Thanks Darius,

Quote:
Originally posted by oldeurope
I'd like to see about 95VDC & about 20mA in your application.
Do you mean 95V at the cathode or at the grid? At 95V on the grid, the operating point for the driver becomes harder.

Quote:
Originally posted by oldeurope
.At this current will be lower and maybe you can take
a lower cathode resistor?
If not you can increase the cathode resistor of the output triode
to get 20mA.
What is the roll off of the output transformer?
The amp looks good. .
I can increase the current in the driver a bit and that will lower the plate and cathode resistors some.

Haven't got an OPT yet. Might use this program to design one: http://www.dissident-audio.com/OPT_da/Page.html

Sheldon
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Old 1st June 2008, 09:22 PM   #30
agent.5 is offline agent.5  United States
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Sheldon,

Have you considered AC heating the 801A?
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