[Amps] Henry 3k Filament transformer taps

[Gerald Williamson via Amps]

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 at 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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