[Hallicrafters] Output transformers

[Rich Oliver]

> Hi Folks... I have the good fortune to have a multi-tapped transformer 

with 0 > 4, 0 > 8, and 0 >16 ohm taps; with the following taps on the other side:
> 
> All are referenced to "0":
> 
> 30W = 165 ohm
> 25W = 200 ohm
> 20W = 250 ohm
> 10W = 500 ohm
>   5W = 1000 ohm
> 2.5W= 2000 ohm
> 
> There is also a 45 ohm tap that is not marked with a 'wattage'. 

> I suspect this is a 70V transformer, but do not know for sure.


Ed,

 From those numbers 45 Ohms corresponds to 110 Watts, probably the 
maximum rating of the transformer.

Here is some food for thought.  A 6.3 Volt CT filament transformer with 
a 115 Volt primary gives an impedance ratio suitable to transform 5000 
Ohms to 16 Ohms.  If you use the center tap to one side of the low 
voltage winding you get 5K Ohms to 4 Ohms.  Half of a 9 Volt winding 
gives you 8 Ohms.  Obviously filament transformers are not optimized for 
such service (core saturation can be an issue) but I have used this 
trick successfully several times.  The impedance ratio is the square of 
the Voltage ratio, and the transformer must be big enough to handle the 
power.  Bigger is better for decent bass response, and you want a unit 
rated at not much less than 10 Watts in any case.  Note also that a dual 
primary type transformer can be used for push-pull operation and that 
such connection gets around the saturation issue.

Cheers, Rich, KC9GQ