Lot's of good information here gents.
@rayma thanks for the reminder that this IS an autotransformer, which
is not isolated from the mains.
Funny, when ever I switch mine on, I can always hear it "engergize" with that
energize noise for lack of a better description, but those of you that have heard
it you know what I mean, it like a weird springy vibration that only happens once
and with it the lights also dim briefly until the variac is fully energized.
I'll try and link to my wiki of my rebuild/clean up of mine.
Now, why am I posting here?
I was just using mine as I was bringing up a Dynaco ST-70 slowly, after
I did a dim bulb test (DBT) after undoing a screw up prior repair to it. Some how
it wouldn't bias up and lost bias diode, which seemed strange to me as it was
an FR157 in a bias circuit that I first tested at -60VDC. Then after replacing
leaky caps on the aftermarket SDS Labs capacitor board kit (some of the caps
were leaky)...Trying to bring it up first w/o tubes measuring then finding there would
be no bias, so checked diode and it tested okay in circuit.
But, I pulled it anyway and replaced it with one of those fancy ones that
Mark Johnson wrote about in Linear Audio, then check again w/o tubes
and had Source -80 VDC bias voltage w/o tubes, then in stages brought
it up with DBTer glowing as 4 EL34s, two 7199s and rectifier try to pull
about 1.2 amps through a 100 watt bulb.
Plugged it in the Variac and brought it up slowly, to 120v, Then started carefully
setting the bias of the tubes cool at 80mA per pair, which resulted in about 1.8 amps
being pulled at idle.
Let it rest there for a bit, and shut it down.
Then I was going to do another round of fine tuning bias adjustments and actually
measure the current drawn for each EL34 with my HP428B. Low and behold
the amp wouldn't power up...
The variac died without a sound.
Both output fuses were good, that is the 2A and 10A fuses on the output.
So, the only thing I can think of ( haven't looked yet) is that the On/OFF switch
much broken or one of the line wires split of broke off the the on/off switch.
When I get to looking I show what I find.
And getting to an earlier question, what IS the term used to describe
that "energize" sound?
Going to the wiki and searching for "variac" brought no results.
Searching google outside our site brought up the following:
LINK
It's the link I was the link for which I was looking, for the variac, surprise
After editing and reading the post after PRRs, (Vovk Z) Maybe I should wire in one of those
fancy CL60 (varistor) in series with the on/off switch, which would "slow start" ease the inrush
current of the variac?
Would I want just one? On the Line in only?
or would I want two? One on the Line in AND one on the Neutral?
Thinking out loud here.
Isn't that smaller transformer above the OP 110, on the top of my linked variac and isolation
transformer built into the variac? Pics 2, 3 from the link. Pic 3
is enlargeable.
Cheers,