Grateful Dead Music Forum

Hey,

I'm looking into getting a JBL D130 8 ohm speaker with thoughts of using the power and preamp section of my pro with a 1x15 cab with the D130. The pro ('73) is rated at 4 ohms. But since it is running two speakers it's 8 ohms right? So will using just one 8ohm speaker through an extension cab work with this? I know it's been covered before, but not sure if I'm going in the right direction with my 4 ohm with two speakers is 8 ohms math.

Thanks!

yes, 2 in parellel = 4 ohms. 2 in series = 16 ohms
http://www.prestonelectronics.com/audio/Impedance.htm

thetumblerspdx wrote:... So will using just one 8ohm speaker through an extension cab work with this?..

It will work, but the max output will be approx 30% less than if it were an identicle 4ohm speaker.
If you want the Output section to want to see an 8ohm load, pull either the two inner or two outer power tubes.
So now your power section is cut in half, but your speaker load is matched.
I'd try it both ways and see how it sounds.
What is the rated power output of your Pro???
I see they were either 40w or 70w:
http://jazzatelier.wordpress.com/2008/0 ... ro-reverb/

It's 40 watts.