Name:    Steve Kennedy
Email:   steve@pacair.com  
Subject: speaker wiring question
Thread:  246
Time:    Thu, 8 Nov 2001 20:42:48 UTC

Did the previous owner replace the speakers with 4-ohm drivers and wire them in series to GET 8-ohms?


If not (and you have 2 8-ohm drivers in series for 16-ohms total), this would only be a problem IF you used an external cabinet. Most tube amps can handle a 100% mismatch with no problem (with a few caveats).


You typically don't want to go any higher than 16 ohms on the 8-ohm setting. The amp will start to get "squirrely" without some sort of a load and can actually oscillate if the speaker impedance approaches an open circuit, especially with crummy or long speaker cables. This is because the output stage feedback comes from the secondary (speaker) side of the output transformer and it gets more sensitive to outside interference when you have no load. Look at at schematic and you will find that if you pull the main 1/4" speaker connection the jack will short to ground to protect the amp from this problem.


If you go any lower than 4-ohms on the 4-ohm setting you generate more heat and stress on the output components. If you put a 2-ohm load on the output transformer for any length of time at high output levels I would be fearful of having some sort of failure long-term but it would probably work fine short term if you weren't balls-out for hours on end.


That's my take on it...


Steve