Hi All, if there is room for a Variac it makes for a nice solution for
setting filament voltage. If space is limited a small value resistor can be
connected in series with the transformer primary to lower the secondary
voltage.
A surges limiter can also be added in series to soften the turn on shock
which is a good thing. The limiter will have a voltage drop of a few tenths
of a volt and that will lower the secondary voltage a bit as well.
This is even more important when using filament transformers capable of
supplying higher current than needed. A typical filament has a cold resistance
about 10% of the hot resistance and ohms law says the turn on current can
be 10X at turn on if the filament transformer is oversized enough to supply
the current.
Surge limiters are available from Mouser and other suppliers.
73,
Gerald K5GW
In a message dated 9/8/2014 8:13:27 A.M. Pacific Daylight Time,
robrk@nidhog.net writes:
Are you sure it's 240? I'm sitting watching my fancy UPS, on the TV stuff,
beep with 124(248) coming out of the wall.
Lots of stuff in the junk box says 115 if not 110. Bet your transformer is
from the 115 days.
You need a variac on the fils, anyway.
Isn't nice we pay by KWH. Don't have raise the price, just crank up the
volts....
On Sep 7, 2014, at 7:09 PM, glenn riccio wrote:
Hello all you henry radio amp owners. I just bought a Henry 3k filament
xfrmer off the internet. It is supposed to deliver 7.5 v @ 21 amps. There
are taps on the primary side to adjust output . I cannot get less than
8.75
volts out. My input voltage is 240vac. I tried all the taps on the primary
side using #1 as the common leg. It is a EC1216a transformer. I want to
use
it for my 4-1000a amp I'm building.
I suppose I could call or e-mail henry radio but they might be annoyed that
I'm not using it for one of there amps. Any help would be appreciated. 73
Glenn K7gfr
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