Output Transformer 1750 ohms

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gammelnalle
Junior tube assistant
Posts: 5
(2/11/04 4:31 pm)
 Output Transformer 1750 ohms
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 I found this old transformer in my junk yard !!! Its old, at least 30 years, Its heavy around 5Kg (10 pound I'd guess) and its marked: 70W Prim winding 1750 ohm sek: 4, 8. 16 an 100 ohm
Centertapped.
What could I use i for??? The prim Impedence is way too low for a pair of 6L6 or EL34 I guess????

I have no need for 70W !!
Any suggestion ??
 
ganzonimx
Hey get your own solder
Posts: 368
(2/11/04 5:33 pm)
 Re: Output Transformer 1750 ohms
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 A pair of 6L6 ore a quartet of EL84 like to see 4000 ohms, a pair of EL34 like to see 5000 ohm.

Hooking up a 8 ohm speaker to the 4 ohm tab would reflect 3500 ohm to the primary side, ok for 2x6L6 ore 4xEl84, may bee also 2xEL34.

Cris
 
Lucid Alice
Senior tube assistant
Posts: 156
(2/11/04 9:33 pm)
 Re: Output Transformer 1750 ohms
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 1750 ohms would be right for 4 - EL34's. The power rating is most likely with a frequency range out to 20,000 or 30,000 hertz so for a guitar amp it would probably be safe up to 140 watts (your mileage may vary seeing as it's old). You could build a 100 watt plexi with it.

I just noticed the 100 ohm tap. The HiWatts offered Partridge OT's with those.


Edited by: Lucid Alice at: 2/11/04 9:36 pm
 
gammelnalle
Junior tube assistant
Posts: 6
(2/12/04 2:30 am)
 Re: Output Transformer 1750 ohms
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 Thanks alot for answers.
Maybe I didnt express my self clearly (Im just a dumb swede so forgive my poor english)

I don't want 70 or MORE watts I want less.....

Less is more u know especially Les Paul....

thanks
 
6G6
Junior tube assistant
Posts: 77
(2/12/04 8:11 am)
 Re: Output Transformer 1750 ohms
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 Your English is fine.

It's just that a big tranny tends to work in a big amp.
You could still build a Hiwatt, Marshall or whatever and sell or trade it for something more in line with your needs.

One other ugly thought did occur to me.
Have you checked it to see that it doesn't have a shorted or open winding? There might have been a reason for it to be in the junk yard.
 
ganzonimx
Hey get your own solder
Posts: 369
(2/12/04 10:37 am)
 Re: Output Transformer 1750 ohms
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 Lucid Alice and G6G of course are right, that the OT you are talking about is designed for something big, like 4%%WORD15%4 oder 4x6L6, but that does't mean that you can't run less tubes through it. Just hock up`the right speaker to the right tab and the tubes will see what they want. You'll end up with less output and overkill OT but it'l sound great.

Cris
 
gammelnalle
Junior tube assistant
Posts: 8
(2/12/04 12:33 pm)
 Re: Output Transformer 1750 ohms
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 Thanx a lot guys !!
I´ll use it for my new "bassvox" a bassman end with a Vox preamp and no feedback !!!!

and YES I have mesaured it, but only resistans.... and they seem to be ok.
I was more worried to "overload" the output tubes when the impedence is so low....

björn
 
gammelnalle
Junior tube assistant
Posts: 16
(2/20/04 9:45 am)
 Re: Output Transformer 1750 ohms
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 Hi again!!
Now I've done some mesaurment and some math. Please correct me if Im in deep trouble...

Resistans primary: 45,8 ohm and 42,8
Secondary from "zero" to 4 ohm 0,1 ohm to 8 ohm 0,3 ohm
to 16 ohm 0,6 ohm 32 ohm 0,9 ohm and to 100ohm 3,3 ohm

By applying 1 volt (a filament trafo via a variac) to the sec:
I read the following results:
4 ohm 29,3 V gives a square of 858
8 ohm 21,4 V " 458
16 ohm 15,0 V
32 ohm 10,5 V

if my math is allright that would only be parts away from "exact" when counting on 2 6L6 thats wants 3800 ohm Plate to plate....Even thou my tranny is stamped 1750 ohm...


Please correct me if Im out of the ballpark!!!

 
ganzonimx
Hey get your own solder
Posts: 398
(2/20/04 11:08 am)
 Re: Output Transformer 1750 ohms
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 Are the secondaries marked 4 ohm to 32 ohm ore do you suppose these values? They might also be 2 ohm to 16 ohm, and then you would have 1750 primary impedance.

But actually this does not matter. If you hook up a 8 ohm speaker to the tap that gave you the 21.4V reading, the power tubes will see 3664 ohm an will be happy...

Cris
 
gammelnalle
Junior tube assistant
Posts: 17
(2/20/04 12:01 pm)
 Re: Output Transformer 1750 ohms
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 Thanx for the fast reply !!
Well than I'm back in the field again !!!
and my math seem to be , at least OK ...

and the tranny is actually stamped : Prim 1750 ohm
sec 4 8 16 32 100 ohm
70W



 
 
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