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In Reply to: RE: dynaclone and triode not offering transformers posted by Tre' on September 03, 2021 at 12:19:01
What is presently in that amp Tre? Z565 have a very good reputation. I believe they're 7200 with 23% UL taps but most claim 8K.
Follow Ups:
Eico HF-87 output transformers. I think they are 3400 ohms. Too low for the 6b4gs. Back when I was using them I probably hooked to the 4 ohm tap.
John Atwood tested the Z565 at 9.5K.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
re "John Atwood tested the Z565 at 9.5K."
According to the usual sources, it's 8K. I see that he also says the A470 is 5.6K ohms; the usual sources say 4.3K. I have some doubts about these measurements...
I've measured most of the Dynaco transformers with a Wayne-Kerr impedance analyzer- impedance varies with secondary used, I used 8 Ohms. At 1 KHz:
A410: 9400
A420: 7200
A430: 4700
A470: 5150
Z565: 8300
Z565-48 Clone: 8250
These include winding resistance as they're measured loaded. All will be lower if measured by voltage ratio (unloaded).
I have a pair of "A470"s, bought from Triode more than 20 years ago; I just now measured the turns ratios and got:
4 ohm tap: 4190 ohms anode-anode
8 ohm tap: 4676 --- " ---
16 ohm tap: 4306 --- " ---
Primary end-end DC resistance about 200 ohms, so a reasonable guess is to add 400 ohms for a loaded transformer (the secondary DCR is more difficult to measure so I didn't). That gives 5076 ohms on the 8-ohm tap, consistent with your 5150 measurement.
So it looks like the 4300 ohm spec is for the turns ratio, not the actual tube load impedance. And the 8 ohm tap is slightly different from the others.
People often refer to this body of work as though it were some sort of Bible for transformers. I have always suspected it to be seriously flawed.
--------------------------
Buy Chinese. Bury freedom.
Yep. Dave Gillespie, author of the EFB mod for the SCA-35 and ST-35 (which both use the Z-565) wrote, "The Z-565 is an 8K primary transformer..."
As I recall Atwood said the Z565 had response to 40khz and the square wave response was excellent. I was surprised about the 9.5Khz part.
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