[Amps] Re: Transformer in GLA 1000 B : OK for 2xGI 7 ?

[craxd]

David,

Actually they have that transformer de-rated some by calling it a 1150 
VA. It actually is about 1495 watts or VA for single phase. This leads 
me to believe they probably wound this for CCS duty (100%). Doesn't this 
transformers primary have the capability of 120 or 240 Vac? Running it 
at 240 Vac will only draw 1/2 the current of a 120 circuit. To get the 
3000 Vdc you need, it will have to put out at least 2100 Vac. that is 
open circuit voltage though. It will have a drop of anywhere between 
5%-10% is my guess. This is determined by the plate current, OCV, 
frequency, and capacitance of the filters. To get 3000 Vdc under load, 
you'll probably need around 2300 Vac. Now, if that 4600 Vac has a center 
tap, you can use a full wave rectifier with C.T. ground and get the 
required voltage. This will also double the current. You will have 2300 
Vac on either side of ground, then rectified with two diode strings. 
Actually, this is the most efficient circuit where there is 100% current 
transfer from the transformer to the rectifiers. You would then have 
about 3,250 Vdc at 650 mA to play with. The wattage or VA rating will 
stay the same. If the 4600 Vac doesn't have a center tap for 2300, it 
would have to be re-wound to do it. You might get by on the current 
rating at ICAS for the 750 mA if you have the C.T. circuit above. Just 
don't hammer down for long periods of time and let it cool. If you could 
find out the wire size of the secondary, I can tell how much it will do 
and what duty cycle they have it set at. Also, see if you can get a 
measurement of the tongue width in the center and the depth of the core 
from front to back. I can tell from this the actual power in watts its' 
capable of.

Will Matney

David C. Hallam wrote:

>Will,
>
>Maybe you can give me some insight.  I am building a 2 KW power supply and
>have an old Collins plate transformer and have no idea of its original use.
>It carries the Collins P/N 672N137.  It is rated 1150 VA and 4600 V CT @ 325
>mA and has a multitapped primary.  I am using the 112 V tap.  With a 122 V
>line supply; I get 3725 VDC with a 15 mA bleeder load.  I am installing a
>line side triac regulator to set the voltage at 3000 VDC regardless of the
>load.  I have a 2:1 transformer so I can use a 220 V line and just drop to
>110 V at the power supply input.
>
>I don't know how much the transformer weighs.  I used to be able to pick it
>up, but that use 30 years ago when I first bought it.  It's been in my junk
>box that long.  Now I just scoot it and slide it.  It's mounted in the power
>supply cabinet, and I don't intend to take it out again.
>
>I want to get at least 670 mA and would like to get 750 mA @ 3000 VDC out of
>it.  My bleeder resistor is 250K so I will have a 12 mA constant bleeder
>load.  The tube is a tetrode in AB1 biased past cut off during standby.
>
>Am I just dreaming or is this possible?
>
>73
>David
>
>
>
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