[Amps] AC filament voltage regulator

[Ron Youvan]

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.