Need help evaluating 2A3 transformer coupled designs - diyAudio
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Old 11th September 2003, 08:27 PM   #1
Eric is offline Eric  United States
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Question Need help evaluating 2A3 transformer coupled designs

Hi Everyone,

I'm rather new to tube circuits and for some reason seem to be drawn to 2A3 based designs that feature interstage transformers for coupling. I suppose it is their simplicity that attract me...

I mainly listen to classical, pop, and jazz music at low volume levels, so I'm not concerned with low power output and cost is not really an issue.

Anyhow, I really have no idea how to evaluate the design itself and was wondering if a few of you who have more experience can help me. I found a nice looking design posted on the web by Ralph Powers that I find interesting:

Click the image to open in full size.

I was wondering if anyone has any comments about or critique of this design or a reason why I should not build it.

thanks!
Eric
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Old 11th September 2003, 08:39 PM   #2
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I built it about 4 years using I.T's from Jack at Electraprint and also hisOPT's. Works great. Just take care with the 417A and oscillation. I cut off the unused grid socket pins.

BB
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Old 12th September 2003, 02:35 AM   #3
G is offline G  United States
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Actually a better approach is to tie a 200 ohm resistor to each of the grid pins and twist them all together at the other end. Then connect your signal in at the junction of the resistors.

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Old 12th September 2003, 02:37 AM   #4
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The 1000uF cap on the cathode of the 5842 seems a bit excessive. I would think that 100uF would work fine.

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Old 12th September 2003, 03:57 PM   #5
Eric is offline Eric  United States
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Thanks for the tips! G, I'm not sure what you mean by tying the grid resistors together - could you please provide me with a little more detail?

Also, does anyone know of any other transformer coupled design available on the web? I've spent a great deal of time searching, and found relatively little.

Eric
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Old 12th September 2003, 04:06 PM   #6
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the 417A has I think 4 grid connections or pins on each tube so what "G" means is to solder one 200R resistor to each of the grid connections (on the tube socket of course :-) and then twist together the 4 leads on the unsoldered side of the resistors and then you connect your input here.

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Old 12th September 2003, 04:13 PM   #7
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A few I.T. designs here, mostly 300B though.
I have a lovely looking one using a 6V6 at home in my files. Never built it but I am a fan of the 6V6. I'll take a look unless you only are interested in DHT's.

http://www.diyparadiso.com/sedesign1.htm
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Old 12th September 2003, 04:18 PM   #8
Eric is offline Eric  United States
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BB: Thanks for the explanation and the links. I think for now I am primarily interested in DHT. I was also wondering about using AC or DC on the heaters, but see that topic has been addressed in another thread recently.

Eric
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Old 9th October 2003, 04:59 PM   #9
Eric is offline Eric  United States
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Andrewbee, What kind of speakers are you using with this amp?? I've been contemplating a set of Hammer Dynamics Super 12's for a little while now. ..

Thanks, Eric
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Old 9th October 2003, 06:21 PM   #10
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None

The has been pulled apart for awhile because I wanted to redo the chassis plate. I was using a 1/8" thick piece of steel and originally 6B4G's. Then I changed to 2A3's and of course had to open up the holes so I used a dremel tool and file and it did not look as good as the originally machine shop punched holes

Anyway, at the time I was using a pair of "Afterburners" which are Thorstens idea, which are for lack of a better expression a
"Super 12 clone" and also Jerico horns. Both speakers worked very well but I prefered the Jericos'.

BTW I prefered the 6B4G's to the 2A3's, both are Sovtek.

Everyday at home when I go into my office / workshop I see the transformers for the amp on a box next to the doorway and say I should get busy with the chassis but I have been listening to a gainclone for the last couple months and .....

Andrew
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