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Old 26th April 2012, 01:14 PM   #681
massimo is offline massimo  Italy
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Did anybody try (or even think) a choke loaded version of this preamp?
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Old 28th April 2012, 03:23 AM   #682
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No one I remember.
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Old 28th April 2012, 04:36 AM   #683
rongon is offline rongon  United States
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Oh jeez. I have all the necessary parts. Don't tell me I'm elected...
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Old 28th April 2012, 04:38 AM   #684
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Old 28th April 2012, 04:44 AM   #685
rongon is offline rongon  United States
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Well, the question is -- 6N30P unbalanced in/balanced out line amp for my push-pull 2A3 amp? Or plate-choke loaded 6V6 line amp (unbalanced in and out)?

But wait... Somebody here is going to have this great idea for how to take the 6V6 line amp and add a balanced out... Oh no....
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Old 28th April 2012, 05:24 AM   #686
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Like in post #17
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Old 28th April 2012, 12:55 PM   #687
rongon is offline rongon  United States
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I was afraid of that.

But no, I don't want to spend the money for a pair of OPT's. Tell you what...

I have a pair of old UTC CG51AX interstage transformers. The primary is 22H measured on my LC meter, DCR is 1050 ohms. I can commit these to the cause. I would use only their primaries as the plate loads.

I figure 22H and DCR = 1050R loading a triode with an rp of 2k ohms will give a -3dB point of about 7 Hz.

Can these IT transformers deliver their inductance under a 22mA load? Well I don't know. Is there a way to infer from the L and DCR what the current capacity is?

--
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Old 28th April 2012, 01:11 PM   #688
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if they're gapless , saturation (read- distortion) is inevitable

but you'll not fry them ......... so , you can try

go here : http://vt52.com/

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Old 28th April 2012, 01:32 PM   #689
rongon is offline rongon  United States
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Quote:
go here : VT52.com
Sorry, did not see any software tools. What am I looking for?
--

Since the primary was intended to be a plate load (the secondary is a push-pull winding), wouldn't that primary work as a plate choke? I have no idea if there is an air gap in the core. There just isn't much info available for UTC CG51AX.

Back in 2005 on another forum, someone wrote:

"I have a pair of UTC CG51AX ITs (sorry, no link) which according to UTC can adapt just about anything to a 2A3, 6L6, or similar. The catalog doesn't provide impedence specs but claime to "match single tubes like 6C5, 6C4, 12AU7, 2A3, 5814A" to tubes like "2A3 or 6L6". There are two primary connections and 5 (I believe) secondary connections, one is ct. Ratio is specified as 2.8:1 or 3.1:1 primary to 1/2 secondary. Also the IT is rated at 5W."

I don't know how 5W translates to max current capacity before core saturation. Just Ea times Ia?

What is the lowest plate current you'd use with a 6V6-triode in this circuit?

--
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Old 28th April 2012, 01:39 PM   #690
rongon is offline rongon  United States
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Info on the CG51AX from an ebay auction:

"The CG-51AX is a Single Plate to Push-Pull Grids Interstage Driver transformer. The Primary was designed for a single 6C5, 12AU7, 6A6, 6N7, 45, 2A3 or other tubes with a maximum of 5 Watts (!); to couple to the Grids of 45, 46, 2A3, 6L6 or other push-pull audio output tubes. The Secondary can be configured for a Ratio of 2.8:1 or 3:1 Primary to 1/2 Secondary, making these interstage driver transformers very versatile. Maximum Level is 5 Watts on the Primary. Frequency Response is actually impressive for a Single Plate to Push-Pull Grids transformer that can handle significant unbalanced DC in the primary, listed as 40-10KHz + or - 1 1/2 db. Each of these vintage UTC transformers is physically about 3 1/4"H with base width of 2 9/16" x 2 9/16" which have mounting center holes at 2 3/32" square. "
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