67 Vox Cambridge Reverb AUX SPKR OHMS RATING?

[SPARKLEJET]

Does anyone know the ohms rating for the aux speaker output on a 1966/67 Vox Cambridge Reverb? The manual is no help. Thanks, Barry

[Chuck H]

Looking at the schematic the "aux" speaker jack is parallel to the "in amp" speaker which is 8 ohms. So ANY load you plug in will affect the amps "ideal" load in a negative way. If the amp ideally wants to see an 8 ohm load (as the schematic suggests) I would say that if you want to use an external cabinet it would be best if it were 8 ohms AND you disconnect the internal speaker. Short of that I would assume that the intention of the jack is similar to that of the old Fender amps as the arrangement is similar. That is, the amp wants an 8 ohm load BUT you can plug another 8 ohm load into the "aux" jack making it a 4 ohm load. This isn't going to give you the most efficiency from the amp but it shouldn't hurt it either. Most amps can operate safely with a +/- 100% mismatch. And I would assume that since your amp has a jack at all that it's up to the task. What else would the designers expect or suggest as a use for that jack. So...

The amp is best with an 8 ohm load. To run an 8 ohm load you must use either the internal speaker OR an 8 ohm cabinet plugged into the aux jack and the internal speaker disconnected. The amp is also fine with with a 4 ohm load though that isn't the most efficient way to operate the amp. A 4 ohm load would be the internal 8 ohm speaker in place and another 8 ohm cabinet plugged into the aux jack, OR the internal speaker disconnected and a 4 ohm cabinet plugged into the aux jack.

FWIW you could safely plug a 16 ohm cabinet into the aux jack with the internal 8 ohm speaker in place. The amp itself won't mind since this would present a 5.33 ohm load (in between 4ohms and 8 ohms) but the internal speaker would recieve most of the power since it has the lower impedance.

Also FWIW you could change the internal speaker to a 16 ohm model and plug another 16 ohm cabinet into the aux jack. Since the aux jack is in "parallel" with the internal speaker this would present the ideal 8 ohm load to the amp and the internal speaker and the extention cabinet would recieve equal power.

I hope this is more helpful than confusing.

Chuck

[SPARKLEJET]

Thanks Chuck. Understood clearly. Barry