Valve Jr. Power output

[cowgard]

Often amplifier specs say so many watts at 8 ohms and so many more at 4 ohms ect. Does the VJ head put out more power to an 8 or 4 ohm cab than it does to the 16 ohm cab? Just wondering. Thanks, David

[jwalin]

tube amps put out LESS power when the wrong impedance is used. you need to match the speaker to the impedance of the output transformer because this is directly related to the impedance of the power tubes and the primary side of the output transformer. if you have multiple taps for different impedances on a tube amp, only then should you run other cabinets of different impedances.

 

SS amps are different, they put out more power into lower impedances, until they run out of power and current capability. then they blow up or shut down.

[cowgard]

Cool. Thanks guys. I ordered a second VJ cabinet to daisy chain and was just curious if the lower impedence meant more power. So I guess I just plug 'em into the 8 ohm output (I made a splitter cable for this purpose) and get a total of 5 watts power. I've read that some have powered up to four 12" speakers with a VJ with good results. Once again thanks for the info. David

[jefrs]

I've got the EVJ head, it's got the transformer with 4, 8 and 16ohm output taps. Correctly loaded, you get 'full' power from any of these taps, but the full winding of the 16 ohm one is most efficient and the one to use if possible (imo it sounds best). I can't remember what outlets are on the EVJ combo.

 

If you run two 8 ohm speakers together, as you seem to want to, they are nearly always connected in parallel. Then you get a total load of 4 ohms - that must go into the 4 ohm outlet socket. (You could wire them in series and put them into the 16 ohm socket). If you have no option, it is better to place a higher load on the outlet than a lower one i.e. 6 ohms goes into the 4 ohm socket, not (no, not the 8 ohm one).

 

With a s.e. amp like the EVJ the power output to plate dissipation ratio is 1:1, i.e. you get 5 watts and like it. With a push-pull amp you get more output (due to the push-pull) but the ratio can theoretically be increased over 3:1. So it is theoretically possible for 4 of those little 5W dissipation EL84 to output over 90 watts. This may be accompanied by much heat and eventually, some smoke. Such amps generally have a more conservative rating, like 46 watts for the AC30/6. Same bottles as the one you have.