[Boatanchors] small power transformer needed

[Robert Moses]

One solution might be to do away with the transformer altogether: From
the '120' V line feed run it through a full wave bridge, then a current
limiting resistor, and finally a large electrolytic capacitor. This will
tend to charge the capacitor to the RMS voltage of about 165V. If you
are dropping the DC voltage down to 95 to 125 volts this should give you
enough to feed your dropping circuit. (BTW a 1 - 10 meg bleed off
resistor across the capacitor is not a bad idea.)

On 07/14/2014 12:39 PM, John King via Boatanchors wrote:
> I need a physically small power transformer to build a small bias supply for my Hallicrafters HT 33A  amplifier with Eimac 8295  which is a direct replacement for the original Penta PL-172. The original filament transformer had a bias winding that would produce -200 vdc from the rectifiers. The original filament/bias transformer COOKED and was replaced with a filament transformer without a bias winding.  
>
> The bias variable circuit varies the bias between -95 vdc and -125 vdc. I am looking for a PHYSICALLY SMALL power transformer that will supply the AC voltage to give me a rectified -200 vdc from a bridge rectifier. Low current rating is not a problem because the tube runs in class AB1 or AB2 depending on user's choice.
>
> If I can't find  such a physically small transformer that produces rectified -200 vdc with a bridge rectifier, I might be required to locate two small filament transformers and run the (secondaries) in parallel off of 6.3 vac ( now becoming primaries) and series the 120 vac  primaries  they becoming a secondary to transform 6.3 vac to approximately  -220 or so vac. which can then be rectified with a bridge rectifier to provide the required negative voltage to the circuit that makes the bias variable. 
>
> Does anyone have the  physically small transformer that would perform the aforementioned chore or a pair of identical small filament   transformers that would do the job? Please email me and let me know. Thanks and 73, John, K5PGW
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