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Old 26th May 2005, 12:42 PM   #1
arex is offline arex  France
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Default help on ul transformer please

Hello,

I am on the point to finish my first all-tube amplifier: 6L6 SE ultralinear, bout 5-6 watt, 2 x 12ax7 as voltage amplifier.

Now I am looking for output transformers. (they must be cheap). I found this one: http://store.triodestore.com/tf65wscta48o.html

But it is a GUITAR amplifier transformer (I think, made for replacing a fender one) with 50-20KHz at 20W, 80 mA.

The alternative is Hammond 125ESE, but I must change my final stage, it has no the 43% winding..etc. It has a 150-15000Hz bandwith, 80mA too. but I found somewhere on the internet some test where it makes better than this. (20-20000).

Could somebody more experimented give me an idea, please? Or maybe you know where to buy some other cheap ultralinear otp?

many thanks.
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Old 26th May 2005, 02:17 PM   #2
Giaime is offline Giaime  Italy
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I think you're in the wrong direction. That Fender replacement OT is a push pull one. Yes, you can use push pull OTs in a SE amp, but you must use an extremely big one to avoid DC saturation. Better to try some SE OT... try the Hammonds, they're cheap... maybe you can get one, try... if it sounds good, but the other one: if it doesn't, well... keep it for old tube replacement!

Btw where did you found tests on the Hammond Universal Series trannyes? I was looking for a PP one for a guitar amp, but that "150Hz" scared me... that OT has no bass I thought...
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Old 26th May 2005, 02:39 PM   #3
arex is offline arex  France
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Test of the Hammond transformer here:
http://members.myactv.net/~je2a3/OPTtestbench-1.htm

You think I can use this transformer. Can I use it as ultralinear?
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Old 26th May 2005, 03:11 PM   #4
Giaime is offline Giaime  Italy
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What tranny? The Fender replacement one? Yes you could but it will sound awful... since it is a PP, you can connect the center tap of the primary like it was an ultralinear tap, so tie it to the screen.
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Old 26th May 2005, 03:40 PM   #5
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Quote:
Originally posted by arex
You think I can use this transformer. Can I use it as ultralinear?
No, not in the conventional way via a screen tap on the OPT, since this OPT does not have a screen tap.
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Old 26th May 2005, 04:43 PM   #6
arex is offline arex  France
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Thank you audiousername!

The schematic I used until now is this.
What must I change in the final stage to make it with Hammond 125ESE?
(I didn't make the variable feedback, and C2B and C8 are 280 and 165 uF. Any other changes until now)
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Old 26th May 2005, 04:46 PM   #7
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I'm sorry, I can't see the schematic. Did you attach it to the post?
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Old 26th May 2005, 04:46 PM   #8
arex is offline arex  France
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sorry; schematic:
Attached Images
File Type: jpg aceschem.jpg (84.7 KB, 302 views)
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Old 26th May 2005, 04:54 PM   #9
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You can't modify that circuit to use the 125ESE since the 125ESE does not have a tap for the screen (aka "ultralinear" tap). The possible alternatives would be to operate the valve in fixed screen mode (screen at fixed voltage, as the name implies), or triode mode (screen tied to anode).

The 125ESE has a primary inductance of only around 9.5H or so, therefore it may be useful to drive it with a low-ish impedance source, either a triode, or pentode with local feedback applied - possibly from the anode to grid.

Is this a hi-fi amp or guitar amp?
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Old 26th May 2005, 05:00 PM   #10
SHiFTY is offline SHiFTY  New Zealand
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I think there is now also a hammond 125FSE you could try...

Simplest solution is just connect each G2 to the B+ with a 1K 2W resistor...
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