07-05-2013, 07:36 PM
The 41-280 I am restoring has a bad audio transformer. Both ends of the input side are open relative to the center tap, and to each other.
I had a post on the Wanted forum, looking for a replacement transformer (Philco part number32-8120) without success. Having exhausted my other sources I am now thinking about a generic replacement. If anyone does have a good 32-8120 transformer I would definitely be interested in buying it.
For a generic replacement, below is my analysis of what's needed, and would appreciate critique if I've got it wrong:
The speaker measures a 5 ohm dc resistance, so I'm considering it 6 ohm impedance (1.25 multiplier suggested by a reference on radioremembered.org). The Philco 41-280 uses two type 41 output tubes in a push-pull circuit. The Type 41 tube spec I googled (Tung-Sol Lamp Works Inc, 1950) has a Typical Operating Conditions and Characteristics table for both Class A and push-pull circuits, and lists plate-to-plate load resistance as 12K ohms. So 12000/6 = 2K impendance ratio, and a 45:1 turns ratio. The Philco 41-280 specification lists audio output of 2 watts, so I'm thinking a 5 watt rated transformer should be OK.
This seem about right?
I had a post on the Wanted forum, looking for a replacement transformer (Philco part number32-8120) without success. Having exhausted my other sources I am now thinking about a generic replacement. If anyone does have a good 32-8120 transformer I would definitely be interested in buying it.
For a generic replacement, below is my analysis of what's needed, and would appreciate critique if I've got it wrong:
The speaker measures a 5 ohm dc resistance, so I'm considering it 6 ohm impedance (1.25 multiplier suggested by a reference on radioremembered.org). The Philco 41-280 uses two type 41 output tubes in a push-pull circuit. The Type 41 tube spec I googled (Tung-Sol Lamp Works Inc, 1950) has a Typical Operating Conditions and Characteristics table for both Class A and push-pull circuits, and lists plate-to-plate load resistance as 12K ohms. So 12000/6 = 2K impendance ratio, and a 45:1 turns ratio. The Philco 41-280 specification lists audio output of 2 watts, so I'm thinking a 5 watt rated transformer should be OK.
This seem about right?
