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SUPPORT FORUMS FOR ZKITS >> ZKIT 1 Support forum >> ZKit Output Transformer Choice?
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Message started by GDSellman on 07/18/13 at 00:16:27

Title: ZKit Output Transformer Choice?
Post by GDSellman on 07/18/13 at 00:16:27

I've just ordered all of the parts to put together my first ZKit1, which will also be my first tube amp. Question on the output transformer. As I look at the schematic and recommendation for an Edcor transformer I see mention of a 6 ohm output impedance. Now, if I know for sure that my speakers will be either 8 ohm, why not choose one of the other Edcor transformers specified for 8 ohm speaker impedance? What is the advantage of or reason for the 6 ohm recommendation?

Title: Re: ZKit Output Transformer Choice?
Post by mboxler on 07/18/13 at 18:59:00

Hi

As far as I'm concerned, the real question is...

What is the best load (impedance) for the output tube used?

From what I've learned (and probably misunderstood) is this...

An output transformer has no impendance. The impedance the output tube "sees" is equal to the turns ration of the OT times the impedance of the speaker. An 8k->6 ohm OT has a ratio of 8000/6, or 1333. With a 6 ohm speaker, the tube would see 6 x 1333, or 8k. An 8 ohm speaker will increase the load to 1333 x 8, or 10.6k.

If I'm right, a 5.5k->4 ohm OT driving a 6 ohm speaker would work out the same, because the ratio is about the same.

The schematic has a 9.6k->6 OT, so perhaps a higher load works out better. I'm driving 8 ohm speakers with the 6 ohm OT. I believe Edcor will build the OT with more that one output tap. Perhaps both a 6 and 8 ohm would be nice, then see (or should I say hear) which sounds best.

I welcome any corrections to my rambling.

Best,

Mike