[Boatanchors] Speech Amp

[WA5CAB at cs.com]

The difference between 600 and 500 is probably more administrative than 
actual.  For practical cases, the two can be treated interchangeably.

The audio line between the BC-614 (and HT-5) and the BC-610 (and HT-4) is 500 
ohms nominal.  It is unbalanced with pin 7 in the octal plugs being connected 
to ground, and there are no centertaps employed.  

If you run the same calculations on 500 ohms and use 70.7 volts instead of 
just 70 volts you will see that the calculations for a 10 watt plate to 70.7 
volt transformer result in near enough 10 watts across 500 ohms.  So the Bogan 
amp with a 70.7 volt line output should work fine into the HT-4 or BC-610.

In a message dated 11/17/2008 3:49:41 PM Central Standard Time, jfor at quik.com 
writes: 
> AFAIK, 600 ohms is used for inputs, not outputs, and is typically balanced. 
> 
> 
> A 70 V line means that the amp output is 70 V RMS at the amp's rated output. 
> The 70 V is usually stepped down at each speaker to voice coil impedance. 
> Typical transformers have taps for the desired wattage to the speaker, so you 
> can hook up a number of transformer/speaker combos. So on a 10 W amp, you can 
> hook up four 1 W and three 2 W speakers. The amp looks a lot like a voltage 
> source. 
> 
> Since Power = V * V /R, if R=600 ohms and V=70 volts, there is only one 
> possible power output from the amp. (4900/600 = 8.1 W) 
> 
> Nope, 600 ohm and 70 V are NOT the same. 
> 
> 
> 
> 

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.qth.net/pipermail/boatanchors/attachments/20081117/52526cee/attachment.htm