Hsu wrote:
> You are correct. But a problem ,AD's true RMS chip is not a inexpensive
> device.
> I have an idea, using a inexpensive CdS photoresistor-LED or micro-bulb
> photocoupler( like N110 in ICOM PS-35 power supply) because bulb and CdS
> photoresistor with very bad frequency response
> so the sampling voltage will associate with true RMS volt (I guess)
> ...
> If the noise is not a problem and the tube's cathode is oxide-coated ,
> the switching regulator is the best. but monolithic IC maximal out put
> current
> only 10A (ST's L4970) others need external power MOS FET.
Hsu said his idea is to use the CdS photo-resistor and a micro-bulb to
create a home made
photo-coupler to get a "slow response" version of a
"opto-isolator" to measure a tube's heater Voltage, but that will result more
in an
averaged value.
The best idea is to use a true RMS Volt meter such as almost every Fluke DVM
ever
made to SET the RMS Voltage "at the tube," then use THE CURRENT Amperage
reading to maintain
that Voltage. The advantage is if a connection becomes lose and develops an IR
drop, the current
will drop and you will turn up the Voltage control for the current that gets you
the correct current which is the correct "at the tube Voltage" until you can no
more make that
current, then you will look for a bad connection, find and fix it. (as you
tighten connections
the current will rise) A lot of commercial equipment works this way.
--
Ron KA4INM - Mistakes are often the stepping stones to utter failure.
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