Ohmage Question? Please Help!

[Billy Apple]

I've spent my afternoon pulling my old Carlsboro 150w Stingray Combo out of the shed and cleaning it up. I got it when I was 16 and I can't believe I've had the thing for 30 years. Never let me down either. After clearing away the odd wasp and spider nest, and repairing a cracked fuse holder (£1.49 for a new one from Maplins ) she fired up first time, and everything seems to be in order. Some of the pots were a bit crackly, but that seemed to pass. She really only does one sound, but its not bad. Has a strange 5 button band by-pass filter that I ignore, along with a depth button, but we started getting there using my DHA VT1 Eq

But, all in all, a solidly built piece of kit that I can use for practise or chucking around, apart from one thing..

The speaker cone has a tear from the edge to half way in. So I'm thinking about replacing it with a light-weight neo driver, making the whole thing more manageable. I took the driver out and it's a 150w Carlsboro Powertone 15C 4Ohm. My question is, do I have to replace it with a 4Ohm driver? I only ask because most of the 15" neo drivers I have seen are 8ohm.

On the back of it are the following- 2 jack outputs that say 'Output 4-16 Ohms' (I have never plugged in additional cabs), a pre-amp jack output and two slave jack outputs. It also says 'max power achieved when total speaker impedance equals 4 ohms'.

This combo owes me nothing, so I don't mind spending a bit on a new driver, and if the whole thing packs up, I might take the driver and use it to build a BF cab.

[Musky]

Sounds like the amp is producing it's full 150w into the internal speaker and the speaker outputs are wired in series. Adding an extra cab with this scenario will result in a drop in the wattage. Some modern combos like Hughes and Kettner do this.

The other scenario might be that the original speaker has been replaced with a 4 ohm one, though if you've had it from new you can rule that out.

So you could replace the existing one with either a 4 or 8 ohm speaker, it just depends how much you want the full wattage and whether you're likely to want to use another cab. In terms of wattage alone there's scarcely any difference in volume between the 150w and 100w you're likely to get with an 8 ohm speaker. It's quite possible that a modern neo will offset any difference by being more efficient anyway.

[obbm]

There is nothing to stop you using an 8-ohm speaker however the max output would be just over half say around 90-watts when fully wound up. You could however add an additional 8-ohm cab to get the max.

BTW [i]"ohmage"[/i] is not an approved technical term, the correct description is [i]"impedance"[/i]

[Billy Apple]

[quote name='obbm' timestamp='1346105377' post='1785468']
There is nothing to stop you using an 8-ohm speaker however the max output would be just over half say around 90-watts when fully wound up. You could however add an additional 8-ohm cab to get the max.

BTW [i]"ohmage"[/i] is not an approved technical term, the correct description is [i]"impedance"[/i]
[/quote]

Please forgive my 'Impedance', and I pay 'ohmage' to your wisdom. I don't think I'll ever plug in another cab to this, so 4ohms it is!

[GregBass]

[quote name='Musky' timestamp='1346105086' post='1785456']
Sounds like the amp is producing it's full 150w into the internal speaker and the speaker outputs are wired in series. Adding an extra cab with this scenario will result in a drop in the wattage. Some modern combos like Hughes and Kettner do this.
[/quote]

I don't think the old Carlsbros were wired this way. The amp chassis was also packaged as a head, and the outputs were wired in parallel pretty much as you would expect. When they mounted it in a combo, I assume they anticipated no-one would want to cart an additional cab around so they packaged it with a 4 ohm speaker even though the speaker sockets were still accessible.

[Musky]

[quote name='GregBass' timestamp='1346150021' post='1785757']
I don't think the old Carlsbros were wired this way. The amp chassis was also packaged as a head, and the outputs were wired in parallel pretty much as you would expect. When they mounted it in a combo, I assume they anticipated no-one would want to cart an additional cab around so they packaged it with a 4 ohm speaker even though the speaker sockets were still accessible.
[/quote]
You might well be right, but it sounds like a recipe for disaster.

[brensabre79]

[quote name='Musky' timestamp='1346225320' post='1786593']
You might well be right, but it sounds like a recipe for disaster.
[/quote]

Yes, exactly!
Some of their stuff is great, solid workhorse stuff still going strong after 40 years of service in working mens clubs all over the country. But try and do anything slightly out of the ordinary like adding a speaker and BOOM! This is just the sort of corner cutting that earned Carlsboro their reputation among music shop managers for an unprecedented level of returned faulty amps.

and yet they have only recently gone out of business!

[brensabre79]

I'd just use the head and a separate speaker if you can get the head out from the combo. Replacing the driver will likely result in the new driver not being suited to the volume of the cabinet. Then you'll also be using the head as intended.