Ampeg 6x10" bass cab question

[John Phillips]

Apologies for cross-posting this... there are probably people who never look at the other area who may know the answer.

What is the actual impedance of an Ampeg 6x10" 4-ohm cab? ie, what speakers are used and in what configuration? Assuming standard 4-, 8- or 16-ohm drivers it cannot actually be 4 ohms, but since Ampeg have been known to use unusual individual driver impedances in the past (eg the SVT 810 cab, which has 32-ohm speakers), they might have done so here as well.

Why it matters is that I have a customer with a bass head (not Ampeg) and one of these cabs, and he's having problems with the head. I've tested it more than once and can't find anything obvious wrong with it. The fault symptom according to the owner is a cutting-out or loss of power that he thinks sounds almost like it's shutting itself down. I don't have the cabinet here to measure, and although I have not tested it into a lower impedance than 4 ohms (and would prefer to avoid doing since that's its rated minimum), I wonder whether the cab could be the problem. There is no logical combination of speaker impedances that would produce a load of just below 4 ohms that I can think of, and I assume they wouldn't have made it as low as 2.66 ohms (eg six 16-ohm speakers in parallel)... but I would like to know for sure.

Either a description of the speakers and their connection or even a direct DC resistance measurement of the whole cab would be useful.

Thanks in advance.

[Backstage Kent]

Initially they used 8 ohm drivers in a misbegotten series/parallel scheme that yielded uneven response and blown drivers. Within the first year they realized the error of their ways and went to 6 ohm drivers, wired as 3 series pairs paralleled, yielding 4 ohms. If he's got an early unit with the original drivers, I suppose that could be contributing to the problem, but it seems a bit of a stretch given the symptoms.

[John Phillips]

That's very useful information, thanks. I have no idea how old the cabinet is, so I can't rule that out as being a possibility. I think I need him to either open up the cab himself or bring it to me (which is quite a pain, obviously... ).

[Backstage Kent]

Just get the serial number, which should be 10 characters. The 5th character denotes the year. If it's an M (2000, AFAIK first year of production) or N (2001) the wiring issue is a possibility--I'm not exactly sure when the change was made, but it was definitely within that range.

[John Phillips]

Originally Posted by Backstage Kent

Just get the serial number, which should be 10 characters. The 5th character denotes the year. If it's an M (2000, AFAIK first year of production) or N (2001) the wiring issue is a possibility--I'm not exactly sure when the change was made, but it was definitely within that range.

Perfect! Thank you . I can just phone him for that...