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arnoldc 8th July 2007 02:46 PM

Help with this transformer please...
So where does one use this?
By arnoldc, shot with K750i at 2007-07-08

I was given two pairs, the other pair is TRW UTC W-786 with the same winding specs...

richwalters 8th July 2007 04:39 PM

Not a hybrid telecom tranny but high quality made. Restricted LF resp implies speechband response i.e telecom isolated line apps. hermetically sealed against moisture- typ in telecom.
15dbm into 600 ohm is around 4 volts rms. Try using it at lower levels for better audio response v.s thd. The give-away is relatively low proof voltage but for telecom was an over generous spec. Obviously if it reaches 10Khz then leakage inductance must be quite low. Give it a whirl....


kevinkr 8th July 2007 07:02 PM

Try driving it with significantly lower source impedances than the rated 150/600 ohms and you'll probably find that the LF extension improves considerably.

Keep levels low to avoid saturation and linearity issues in the core. (say 1Vrms)

Hopefully leakage inductance is low enough that it may get you significantly beyond 10kHz - note that the lower source impedance may worsen HF response if leakage inductance is the dominant loss factor at high frequencies, but will improve it if the losses are mainly capacitive.

arnoldc 9th July 2007 12:05 AM

Thanks guys, and I must confess I'm not that smart as you have thought...

So do your recommendations mean-

a) preamp output transformer
b) interstage transformer


TonyTecson 9th July 2007 02:58 AM

input transformer can series connect 3 windings for an input step-up transformer,1:3 or 150ohms to 1350ohms......maybe a mike preamp...:D

jlsem 9th July 2007 03:35 AM

The 300hz - 10,000hz bandwidth is most likely what was called for in the Mil. Spec. written for this type of transformer. You will probably find that it is in fact wider in bandwidth, especially since it was made by Freed. I have some Freed output transformers (10K - 250ohms) that were military surplus with a similar specification that actually measured 5hz to 50khz +or- 3dB.


arnoldc 27th July 2007 10:22 AM

I was thinking if I can use this transformer to drive a 45...

That is, no driver tube, just the transformer and 45.

Do I connect 3 & 2 together, so my input is 4 (+) and 1 (-) then I connect 6 to the grid of the 45 and 5 to ground?


Input is 2 (+) and 1 (-), then short 6 & 7 and 8 goes to the 45 grid and 5 to ground?


kevinkr 27th July 2007 01:14 PM

Hi Arnold,
Sorry to burst your bubble, it won't work as a driver for the 45 as you need about 80Vpp with a plate voltage of 250V to drive one to full output. This transformer configured as 150:600 will give you a paltry 6dB of gain, not to mention that at 40Vpp on the input transformer (14Vrms) the transformer itself will not be linear..

You could use a 600:20K transformer and this would necessitate about 5V rms on the input to do the job, again not a very good fit. Cmiller would be multiplied by 33 presenting the driver circuit with a significant capacitive load as well.

Colt45 27th July 2007 01:18 PM

Telephone line trafo on a B-52?

kevinkr 27th July 2007 04:02 PM

IMO these transformers are useful for things like breaking groundloops between hifi and video component audio grounds, and possibly in a transformer coupled pre out with a low source impedance driver parafeed coupled.

I'd trade them for something more useful..

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