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Transformer Interaction - Fact or Fiction?

Posted by Triode_Kingdom (A) on April 2, 2021 at 12:30:13

My apologies for banging this drum again. It's holding up my project, because the entire layout depends on the positioning of the power and output transformers. I've been studying this topic in more detail and searching everywhere for commercial examples that might point to an orientation known to work well. But in terms of the relationship between the transformers, as well as between the transformers and the output tubes, there seems to be no correlation whatsoever. The output transformers appear to be oriented every which way relative to output tubes, including beam power tubes, and there's absolutely no observable pattern to the positioning of the power transformer.

This issue is probably exemplified best by the Dynaco SCA-35, shown below. The two output transformers are positioned in what must be both the best and worst locations relative to the power transformer. The same is true of the relationship between the OPTs and the output tubes (although the latter in this case are pentodes, not beam power). The point is that when I search Scott, Fisher, Dynaco, HK and others, the orientations appear to be totally random. Cores pointing toward the output tubes and away. Power transformers both aligned with and 90 to the OPTs. And none of this seems to create noticeable differences in the specifications. The SCA-35 - as only one example - does not indicate any unusual numbers regarding either hum/noise or distortion.

I guess this leads to a critical question. Has anyone here seen a PP AB1 amplifier with hum that was induced between the power transformer and an OPT, or issues that could be traced to interaction between an OPT and output tubes? As time goes by, I'm becoming more and more skeptical about the real-world likelihood of this occurring, due primarily to the huge variety of layouts and orientations used by well-respected commercial manufacturers. Nevertheless, I'm putting out the call to anyone who has seen this issue in practice. I just want to explore all the available resources before committing to a layout and cutting the chassis.

Thanks for everyone's patience with my obsessiveness on this topic.

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