1П24Б 1p24b

[Amie]

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The traditional point to inject NFB is generally a cathode. Here, with DH filamentary cathodes, it is not quite so trivial to squirt a signal in, without compromising the LT heating current. However, a pair of low-resistance windings on the output transformer can introduce the same feedback signal into both sides of the filament. With this configuration, capacitive coupling from other windings in the OPT is irrelevant because one end of the feedback winding is grounded.

The result is approx. 6db of feedback, with a 2-turn winding. Circuit is as shown.

Clever idea.

Thanks for sharing Peter.

So, would a good description for how the NFB works now, be that the NFB signal is common mode and unipotenially "modulates" the whole filament within the circuit, leaving the heater power unaltered?

Thanks,
Amie.