[John L Stewart]

Here is another alternative to the output section of the unity coupled cct. This one used a pair of 8005 triodes. Covered by Norman Crowhurst in an article reproduced in Audio Anthology, Volume 5.

Cheers, John

[Stephie Bench]

Hi John,
The unity coupled circuit and its variants has always intrigued me. Over the years, I have probably concocted a half dozen or so of them. Generally work out well, but I always came to the same conclusion: the performance was always tied to the characteristics of that complex transformer, and you could always get equivalent performance more conventionally.

Nice implementation using the 8005. Thanks for the Crowhurst revisit. He was one of my early heroes. I always anxiously awaited my Radio Electronics subscription in the hopes of finding a Crowhurst article.

Stephie

[John L Stewart]

Originally Posted by Stephie Bench

Hi John,
The unity coupled circuit and its variants has always intrigued me. Over the years, I have probably concocted a half dozen or so of them. Generally work out well, but I always came to the same conclusion: the performance was always tied to the characteristics of that complex transformer, and you could always get equivalent performance more conventionally.

Nice implementation using the 8005. Thanks for the Crowhurst revisit. He was one of my early heroes. I always anxiously awaited my Radio Electronics subscription in the hopes of finding a Crowhurst article.

Stephie

Back about 10-15 years ago I built two of the unity coupled ccts using the Crowhurst approach, that being a pair of tightly couped OPTs. Both ccts used off the shelf parts. I thought for the cost at the time the performance results to be a lot more than passable. Could have been better with purpose built OPTs as Crowhurst had done. An interesting experiment, anyway!

Both were published in AudioXpress magazine. Unlike a lot of published stuff I included lots of performance data, such as THD & IMD at various power levels. Tried various output tubes. The output cct used was basically unity coupled but UL as well. The plates & screens were about 100 volts apart.

That one had a FET reg PS. With a pair of 6LU8s it managed 37 watts at clipping. The other lower cost scheme used PP 6V6GTs & managed 15 watts.

Real watts, I used a prescion wattmeter to get the numbers. And a digital Scope, 16 bit SA.

Not much electronics going on here these daze. Still cleaning up from last Decembers ice storm. And had to do repairs on a couple of tractors. Everything wears out. At 81 think I am too!

Cheers, John