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Is my Output transformer good for the ZKit? (Read 3841 times)
Diego
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Is my Output transformer good for the ZKit?
05/27/16 at 21:34:59
 
Dear all,

I'm a newbie in this forum. So, please forgive me for any (too) basic question, and be free to link me to any existing posts concerning similar topics.

I have a pair of output transformer Hammond 1628SE, and would like to know whether I can use them into a ZKit1 instead of the EM406, and, if this is the case, whether I have to modify anything in the circuitry.

The characteristics of the transformers are:
- Primary impedance: 5000 Ohms
- Inductance 48 H
- Max DC bias: 120 ma
- Secondary Impedence: 4-8-16

My loudspeakers are full range Audio Nirvana Standard 8" into a 1.3 cabinet enclosure, with around 96db efficiency

I bought these OT almost 15 years ago for a different ampli project, for different (lower efficient) speakers, but I never had time to built it. Now, having these new speakers, I would much prefer to go for the Zen, and wonder whether I can use such OTs, which I think are of good quality (they costed to me pretty much, at least in my young memories...)

Thanks a lot for the answer!

Diego (from Madrid, Spain)
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Steve Deckert
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If the 1st watt
sucks why continue?

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Re: Is my Output transformer good for the ZKit?
Reply #1 - 05/28/16 at 04:55:43
 
The Zen Triode design used a 9800 ohm primary against a 6 ohm secondary giving it the ability to drive super low impedances.  

For example since impedance is reflected, hooking a 3 or 4 ohm speaker load to the amp would drop the primary impedance from 9800 to around 5K.  This pulls more power from the EL84 and 6P15P-EV output tubes the amp is designed around.

The amp is famous for it's ability to drive even 2 ohm loudspeakers without loosing it.

If you take your 5K transformer with the three output taps and use the 4 ohm tap with your 8 ohm speaker the reflected impedance will rather closely mimic the original 9800/6ohm results.  

Of course you would also have other taps to play with Wink

As a general observation, the higher the actual reflected primary impedance the less power the amp has, but the better the clipping characteristics become.  Higher primaries also sound better in the top end, with more shimmer and detail which I speculate is due to the smaller wire and higher winding count. It packs better and more solidly in the core gap leaving less air which improves efficiency which in turn improves speed which in turn improves detail and resolution, not to mention bandwidth and flatness in frequency response.  For this reason I find it's better sonically to have a higher primary than normal and then set up the secondary so that the reflected impedance is what you want the tube to actually see.  

-Steve  :)
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clowkoy
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Re: Is my Output transformer good for the ZKit?
Reply #2 - 05/28/16 at 04:57:36
 
Yes, you can use it. No changes in the circuit. You will be getting a little more power and more bass. Just use the blue and red wires for the primary. You can use either the 8 or 4 ohm tap with no problem.
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Diego
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Re: Is my Output transformer good for the ZKit?
Reply #3 - 05/28/16 at 20:05:49
 
Thanks for the very clear answers. That is very good news,
I think I can now proceed with building my own Zen.. Smiley
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holg
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Re: Is my Output transformer good for the ZKit?
Reply #4 - 02/23/23 at 23:14:29
 
Steve Deckert:
Quote:
(…) so that the reflected impedance is what you want the tube to actually see.


… but what is the reflected impedance in ohms that I do want the 6P15P-EV to see??

Over the past weeks I’ve done lots of forum searching here and there and data sheet interpreting to be able to put a number on what primary impedance would be the “best” one, but am still a far cry from a clear answer.

Here in this thread and elsewhere it’s mentioned that one great feature of this design is that even 2 ohm speakers can be driven, but with a reflected impedance that’s vastly different compared to having the same amp hooked up to an 8 ohm speaker must sound vastly different as well?
E.g. ca. 3.2kohm vs. ca. 13kohm on the original design (9.8kohm-6ohm OPT).

If I’ve deciphered the 6P15P-EV data sheet correctly, the plate load resistance is 10kohm at 300V.

The current (?) 10-2021 schematic for the ZKIT1 recommends anything between 3.3 and 9.8kohm as OTP primary impedance. Unclear is whether this is already reflected, or based on the secondary of 6ohms that’s in the schematic.


To come back to the beginning of this post: Assuming my 8ohm speakers are really 8ohm speakers and the amp will never have to drive any other speakers, what’s the impedance I want the 6P15P-EV tubes to see?
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