Output transformer ? - Printable Version

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Output transformer ? - Eric - 12-05-2014

I have a Crosley 20-AP link here:
http://www.nostalgiaair.org/PagesByModel/313/M0003313.pdf

The Output transformer is open on the primary side. The output tube is a 6K6 I have a transformer from Antique supply P-T291 that I've had it looks like it will work just want to make sure.
I've found that the resistance on the primary should be 700 ohms the new one reads 500 ohms, if I use C&1 on the sec I get .7 ohms which is close to the original.
thanks
Ericl

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RE: Output transformer ? - codefox1 - 12-05-2014

Tube radios aren't all that fussy about output transformers. Use whatever secondary combination that pleases you. There has to be a really large disparity to cause loss of volume or other problems.

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RE: Output transformer ? - Arran - 12-06-2014

 With most output tubes, 42, 6F6, 6V6, 6L6, 6BQ5, you can use a transformer suitable for one of the other types and it will work fine. For the 6K6 you could use one suitable for use with a 41 or a 6AQ5, as there are basically variations on the same tube, not sure about Loctals. Edcore has a good selection of replacements, some of the universal ones will work too but cost more more for including the extra taps to very the primary to secondary ratio.
Regards
Arran

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RE: Output transformer ? - morzh - 12-06-2014

Eric

Fom the sch it is not clear what your voce coil impedance is.
But the simple way to measure it (not exact but more or less) is disconnect your transformer alogether (it is bad anyway) and simply measure the resistance with an ohmmeter.
Then you may if you choose to multiply it by maybe the factor of say 1.2 for a good measure.

For demonstration let us have voice coil impedance equal 8 Ohms.

Then you go here
http://www.radiomuseum.org/tubes/tube_6k6.html
or to any place that lists the tube's parameters and see what your load is.
In this case your load impedance is 7.6kOhms.


Then you go here

http://www.hammondmfg.com/125SE.htm

And see the matching combination for 125Cse series.
The closest you get is BLK-GRN (10kOhms to 8 Ohms).

And when you know your output power (say 3.4W for 6K6) you go here
http://www.radiodaze.com/category/570.aspx

and buy 125Bse.

You will have to run your measurements but still 125BSE is I think a decent match.

Now those are expensive so you might give it a search to see what else is out there.

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RE: Output transformer ? - Eric - 12-07-2014

The voice coil is 3.1 ohms, I soldered the new one in and used the 4 ohm C&1 tap for 4 ohms and a 6k6 per the data sheet and powered it up works great and have good volume range.
Thanks everyone
Eric

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