Scenario:
I have a Fluke 77 DVM (not RMS-reading, AFAIK). I show 243.5 VAC on my
dedicated 20A, 240V line in the shack, amp unplugged, no other load on this
branch. Run is about 45 feet of 10/3 copper Romex to the breaker panel,
adjacent to the meter.
I have 400 amp service at my home, with no other home sharing the service
transformer. I split the feed to two separate 200A panels, and run about
1/2 the house off each one. The local power substation is 1/2 mile away.
Pretty stiff supply, doesn't budge much.
After I send this message, I am going downstairs to measure the filament
voltage on my L7 amp. I haven't done this before; I probably will
tack-solder leads onto the fil pins so I can meter the voltage from outside
the amp, with the amp sitting level, and covers on. Safety first, you know.
(Why don't amplifiers have filament volt-and/or-ammeters built in, or at
least test points for this? Tubes ain't cheap anymore.)
I intend to look at the voltage on the tube side of the choke, to account
for any I2R loss in that component.
So, there's the situation. Here are the questions:
1. I assume the Fluke measures P-P voltage, and is this an issue? I can't
think of a reason why it would be, but... perhaps the 3-500Z 5-volt
filament spec is in RMS volts?
2. Suppose that the filament voltage is a bit high. What are some good
ways to cut it down? I was thinking a small resistor in series with the
primary, as the L7 has a separate fils transformer, and the primary wires
are easy to get to.
3. What if it's too low? ;-)
TIA
Steve KZ1X/4
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