[AMRadio] small power transformer needed

John King via AMRadio amradio at mailman.qth.net
Mon Jul 14 14:42:13 EDT 2014

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

More information about the AMRadio mailing list

This page last updated 21 Jan 2018.