[R-390] Role of the 3TF7 in PTO frequency changes

[2002tii]

Kurt wrote:

>I can document that the current regulator 3TF7 is the main cause for
>the observed PTO frequency changes.

That statement appears to make an assertion that I do not believe you 
intended, namely that the 3TF7 causes a greater PTO frequency change 
in response to a given change in line voltage than would occur in the 
absence of any "regulation" (i.e., than would occur if the oscillator 
heater were run straight off an appropriate transformer tap so that 
the heater voltage varied directly with line voltage).

While the 3TF7 clearly does not fully eliminate PTO frequency changes 
in response to changing line voltage, I do not believe it makes 
things worse than running the heater from an unregulated supply.

I agree with your basic proposition -- that regulating the heater 
voltage is a good way to regulate the PTO frequency against changes 
caused by line voltage variations.  Presumably, regulating the 
current would work just as well if it were done as precisely as the 
voltage regulation -- it's just that the 3TF7 is not a very good 
current regulator.

Best regards,

Don