I recall a commercial amp and patent that combines such a variable cathode resistor in the LTP with a type 4 master volume, using a dual track pot. The track values might not be the same.
It wasn’t one of the big brands.
That idea was bounced around on Hoffman's forum about 15 years ago. There was a pot version and this switch version. The switch became more popular. All was short lived and I haven't heard about it again until just now.
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