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Old 4th Oct 2019, 12:18 pm   #12
Silicon
Nonode
 
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
Default Re: Hallicrafters S27

If I have understood the schematic correctly, headphones plugged into the 'phone jack' are connected to the grid of one of the 6V6 output valves. High impedance headphones only need a few milliwatts to power them. Low impedance headphones were also used by the military.

The switching in the phone jack puts a 4k resistor across the 5k winding of the output transformer.
This puts a load on the output transformer which protects it from 'flashover' damage and impedance mismatch if a speaker is not connected.

Check that the phone jack contacts actually work.

The instruction manual does not give the power rating of the 500 and 5,000 Ohm windings of the output transformer. It suggests that speakers can be connected to both. I would like more proof.

On receivers such as the RCA AR88, some of the output windings are only rated at 10 milliwatts.
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