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Old 16th January 2003, 11:55 PM   #1
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Default DHT Triode Amp Project

Ever since I acquired a batch of Svetlana SV572-3 from a fellow board member (the ever-so-helpful Dhaen, aka John), I have been dreaming of building an all-triode amplifier. My general requirements are for reasonable power (~20W for my moderatly efficient speakers), and an all-triode single ended topology.

I plan to drive the 572 with a interstage transformer coupled 2A3, in a Loftin-White configuration. Now, I must admit, I never heard a L-W anp, so my decision is purely based on what I have read & heard.

Not being a tube design specialist, I am designing this using the 'cut and paste' philosophy. That is to say, I took existing L-W designs, and replaced the output transformer with an interstage xformer (whose primary is the same as the original output xformer's primary), and used that to drive the 572. It seems to make sense to me, at least.

For the PS, I plan to use individual PS's for the 2A3 and 572's, with a Pi (or double Pi) tube rectified configuration.

Perusing my collection of tube articles & magazines, I found 3 L-W 2A3 designs, so I cut & pasted 3 proposals, which I will post here. I would greatly appreciate any and all comments & suggestions!
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Old 17th January 2003, 12:00 AM   #2
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Default Triode Amp Version 2

Here is Version 2:
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Old 17th January 2003, 12:02 AM   #3
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Default Ver 3

And here is Version 3:
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Old 17th January 2003, 12:19 AM   #4
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Default SV 572-3

Hi,

Not a Loftin White but take a look anyway:

SEKIDO

And here:

ANDREA CIUFFOLI

The Loftin White circuit has been discussed in *L'Audiophile* many years ago.

Likewise it can be found in a summary book by Mr.J.Hiraga called:

*Initiation aux amplis a tubes* and *Selection de L'Audiophile,Tome 1*

Bonne chance,
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Old 17th January 2003, 12:28 AM   #5
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Default Loftin-White

Yes, I did read Hiraga's book. That was one of the reasons that I chose the L-W configuration. There is also the O. Asano 2A6 & 2A3 L-W design, on page 79 of the aforementioned book.

My dilemma is that I do not really want to build too many versions of the circuit - I want to select one layout, breadboard it, refine parts selections, and then build it.
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Old 17th January 2003, 07:27 AM   #6
dhaen is offline dhaen  Europe
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Default Here's mine so far

Hi Igor,

I don't know how much you know of how far I've got so far.
I've been using both channels breadboarded for a couple of months now, and am very pleased with the results.
The metalwork has taken much longer than expected, as I'm using a rather unconventional construction.
I'll post an early schematic of one channel:

Cheers,
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Old 17th January 2003, 07:37 AM   #7
dhaen is offline dhaen  Europe
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The 845 has turned out similar to drive to the 572-3.
As you know I was lucky to get a pair of VV32's (300B on steroids) as drivers. This turned out to be a mixed blessing.
It was more difficult to drive: With a maximimum grid value of 100K, the input stage had to have better drive current capability. This meant investigating mu stages. I'm glad I did. The linearity up to massive voltage swings is perfect. And, unlike some of it's detractors, I think it sounds "sweet".

Once everything is finalized, I'll put it on my web-site for "critisism".

Cheers,
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Old 17th January 2003, 11:00 AM   #8
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Default AH...A MU FOLLOWER AT LAST.

Hi John,

Seems like a good circuit you concocted.

Is the 300B really necessary?
How about a regulator valve (IHT,I know) such as a 6C41 or 6C33-C to drive the 845?

It's just that I feel it such a pity to waste a 300B like that.

Cheers,



P.S.You knew I had to say at least something,didn't you?
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Old 17th January 2003, 11:29 AM   #9
almarcy is offline almarcy  United States
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Default backwards progress!

Hi,

SV572-30 driving 2A3 SE works well.

I recently added jumper to create shared cathode bias networks under 2A3. Outstanding!

Happy Ears!
Al
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Old 17th January 2003, 11:30 AM   #10
dhaen is offline dhaen  Europe
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Default OnRyoku

Frank,
Quote:
Is the 300B really necessary?
Good question.
I can't answer that for sure without trying something else, such as a 2A3. It was the 2A3 that I was considering when I got the oportunity of the VV32B's (biggie 300B's). It's true that Rod Burman did take a second breath when I said I was going to use them as drivers...
Probably, if I'd kept with the 2A3 plan, I'd have been able to use AC heaters for the driver.


Quote:
How about a regulator valve (IHT,I know) such as a 6C41 or 6C33-C to drive the 845?
Yes, I considered this, but in the end decided on a DHT, partly because of the low distortion, and the fact that I could use a 1:1 transformer.

My deliberations and philosophy are here if you are interested:
http://www.dhaen.org.uk/vdocs/onryoku.htm
Like everything else, it's not finished yet. But it's a start.

Cheers,
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