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Old 11th July 2011, 01:12 AM   #11
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DavesNotHere,

Here are those specs you asked for:

Transformer 1 Transformer 2
DC resistance
Primary gr/br 2.32k 2.34k
Secondary y/bk 3.04k 3.07k
Secondary r/bl 2.37k 2.41k

100mv @1k
Primary gr/br .100v .100v
Secondary y/bk .120v .120v
Secondary r/bl .120v .120v

Amperage Primary 1ma 1ma

I noticed that I had to reverse the leads on the Y/bk secondary to get a clean sign wave out.

I hope I've measured these correctly I'm a bit of an amateur with the scope. Thanks for any help you could provide.

Kevin
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Old 11th July 2011, 02:39 AM   #12
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...sine wave...
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Old 11th July 2011, 03:38 AM   #13
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the dcr winding readings are a bit strange as they do not reflect the AC signal properties.

there should be two windings that are the same and one that will be different.

by using that logic, yel/blk would be the primary if I go with the dc resistance route, but the ac signal test makes it inconclusive.

do the test again, but use the yel/blk coil as the primary.




If I did my usual guesses, and just rely on the dc resistive data,

yel/blk is around 150k impedence

grn/brn is around 50k impedence

red/blue is around 50k impedence

but need to confirm voltage gain properties.
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Old 12th July 2011, 02:44 AM   #14
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DavesNotHere,

I ran the tests again. The DC resistance is correct. Also the primary is green/brown not the yellow/black. You can see this on the previous page schematic. Also, I removed the transformers from the chassis myself. The primaries had very short wires while the secondaries were about five inches long.

I used a high quality DVOM to measure the voltages again. With .100 volts AC at 1k on the primaries. I had .119 and .118 on the red/blue. And .133 and .138 on the yellow/black.

Kevin
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Old 13th July 2011, 04:44 AM   #15
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ok, now looking at everything, you have a 40k input with a 47k and a 50k secondary screened with a 10k resistor in series with the transformer.

make sure you use the 15pf cap to reduce interference.

you might want to play with the 100k resistors to tweak the sound stage (47k-470k has been used historically here) the feedback decoupling cap (.01 cap in series with 100k resitor on the grid circuit) can be high as 1 uf however if you go big, I would suggest it to be bypass with a .01 uf cap A .47 uf cap would be a starting choice for me.

Last edited by DavesNotHere; 13th July 2011 at 05:13 AM.
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Old 14th July 2011, 02:00 AM   #16
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Thanks Again Dave,
But can I trouble you with another question? I see that the 39k resistor and the 2.33k primary are a resistor in parallel to come to about 40k. But I am not sure how you derive the 47k and the 50k? If I could understand that calculation it would be very helpful.

And then, if I have a 40k input to what exactly does that match up to on the original 6J5 preamp tube? And the 6V6 output tube. If I could understand these calculations I could modify the circuit to use the tubes I would like to use. Namely the 6l6 output, and whatever preamp tube I decide to use?

Thanks again, Kevin
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Old 15th July 2011, 02:28 AM   #17
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Hello mr2racer,
You bring up an interesting topic, interstage transformers, and thank you. As I progress through DIYaudio I like to chunk of pieces to study in greater detail. It is like a puzzle I canít leave it alone.
At one level transformers are just a pair of inductors that interact on the same core. They are voltage adjustors and impedance matchers blah blah. Dig deeper and the complexity is over your head quickly. Prof. Leach, RIP, used an approach to understanding electronics that makes it easier for me to get a grasp. Dr Leach would break down the item; resistor, capacitor or whatever into an equivalent circuit that when plugged into SPICE or my brain it would make scene.
Interstage transformers match the output impedance and voltage of the preceding stage to the next. The transformer equivalent circuit is not just inductance; there is also resistance and capacitance. Many times a matching network of resistors and capacitors (think zobel possibly) is added to tune the circuit.
I bought one of these EDCOR Electronics Corporation. S2S10Kt/10Kt to play with on the bench. The test tools are a signal generator and Oíscope. I will start looking for square waves and then take a listen. It will be trial and error to start with.
DT
All just for fun!
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Old 15th July 2011, 03:15 AM   #18
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interesting IT http://livinginthepast-audioweb.co.u...99-leaflet.pdf
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Old 15th July 2011, 09:35 PM   #19
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Thanks Everyone,
When I saw a pair of these go for $150 dollars I figured they must be nice transformers. I was going to use them in a 6L6 amp I'm building. But I've decided trying to make them work correctly is beyond me at this point. So I'll stick to Hafler's original design.
Kevin
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Old 17th July 2011, 06:39 AM   #20
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Thank you Rod Elliot.
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