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In Reply to: RE: dynaclone and triode not offering transformers posted by rage on September 05, 2021 at 16:54:57
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.
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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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