[Hammarlund] SP-600 audio term

[Roy Morgan]

On Jul 22, 2008, at 10:11 PM, telegrapher at att.net wrote:

> Put my SP-600 back on the bench ...replacing the audio tranny which  
> has gone south... a Collins Audio transformer with the same  
> impedances, well close anyway.

Close is good enough.  The actual impedance of any normal speaker  
varies a LOT over the audio range.  In a circuit with original tube,  
different transformer, and speaker load, the maximum power at a  
certain distortion will vary with frequency anyway.  If the  
transformer is not specified for just the right impedances, but is  
within 10 or 20 percent, all will be well.


> ... i'm not using the 600 ohm winding of the tranny.  Do i need to  
> put a 600 ohm resistor across it anyway?

Not if there is a speaker load.  If there sometimes might not be a  
speaker load, then having a moderate load on the 600  ohm winding is a  
good idea.  This can prevent breakdowns due to very high voltages  
developed with no or very little actual load on the transformer.


> ... i'll never use it at full output anyway, i don't think?

It's very enlightening to measure or estimate the actual power being  
used in a high fi or radio system.  I once measured the power in my  
home stereo.  The amp I had was modest - 20 watts per channel or some  
such. The measured power to the speakers with a symphony turned up  
quite loud peaked at a watt or less.  Normal listening levels were  on  
the order of 20 to 100 milliwatts.

Roy

Roy Morgan
13033 Downey Mill Rd
Lovettsville, VA 20180
k1lky at earthlink.net