Sunn Concert Bass questions.

[StandOutLoud]

Hello sun lovers!
im a newcomer to this wonderful forum, and come hoping to find some answers to some questions.

Just recently i bought my first piece of sunn equipment, a sunn concert bass head. So far its been a wonderful experience, and i cant wait to get it up and running fully, ill try to post a picture when i get a camera. From the sticker inside it was built in 74, and is the silver face model with distortion. I think its been modified to have a 3 prong power cable but apart from that it appears to be original (at least from what i can see) From what ive gathered from various threads its about 150-200 watts ,and 4 ohms.

My main questions are about running cabinets, im a noob to cabinets, before this i had an ampeg combo. According to a good friend of mine who i trust the two outputs of this amp are wired parallel, and that using only one of them to run your cabinet can make them a bit grumpy and cause it to overheat. I have tested the amp with a small test rig, to make sure it works, and it does and sounds wonderful, but im in the process of building a cabinet so i would like to know how i should wire it.

Basically should i wire my cabinet so that it has two outputs at 8 ohms each so that i can use both the inputs on the amp giving a 4 ohm load?

Or should i not worry to much and just run one at 4 ohms/8ohms depending on how the cabinet is wired?

Any other information people could tell me about this head would be great too! 

thank you in advance.

[george]

How many speakers are you putting in your cabinet? Most speakers are 8 ohms - if you connect two 8 ohm speakers in parallel (+ to + and - to -) you have a 4 ohm combination. That's the lowest imedance your concert should be connect to.

[jaywalker]

...the two outputs of this amp are wired parallel, and that using only one of them to run your cabinet can make them a bit grumpy and cause it to overheat.

Typically you would avoid (like the plague) running the amp below it's minimum impedance rating. For example if the minimum load is 4Ω then you would not run it at 2Ω or you will have a possible meltdown. You can run it at a higher load like 8Ω with some loss of output. So you could run one cabinet rated at either 8Ω or 4Ω (full power) using one output jack...  or you could run two 8Ω cabs using both output jacks. You don't need to use both jacks to make the amp happy.
You can wire your cab for 4Ω but then you can use only one cab. If you wire your cab with two seperate jacks with two 8Ω speakers wired completely seperate then you can consider that to be two seperate cabs with individual wattage ratings of each speaker (I would only do this for some special case versatility and it could be easily accomplished using a "plug and play" jack available at Antique Electronic Supply which gives you 4,8 and 16 Ω limited options if you're using two 8 Ω speakers )

[jaywalker]

I'd better qualify what I said. There are always exceptions. Some tube amps have a switching jack used for the output that taps the output transformer for a different impedance when a second cab is plugged in. The Ampeg B25B is an example. Don't think it applies to yours but the schematic that I looked at only shows one speaker output jack. 

[Isaac]

No, the switching jack was not used on the solid state heads, and the Concert Bass does not need to have something plugged into both jacks to be happy.

jaywalker, your description of how to connect cabinets to the amp is spot on.

[StandOutLoud]

Ok thank you all very much! All the cab talk makes total sense to me at this point now. I have to 15" speakers i am planning to use for my cab, can anybody actually confirm if the outputs of this head are wired in parallel or not? Or explain a way to check if they are? I will probably wire the cabinet for four ohms as i dont really have much ambition to have to lug more than one cabinet to gigs/jams/etc. Im not sure about the schematic mentioned, i have one on my desktop, but i cant read it/understand it, so im not sure if it has two speaker outs, but the amp does haha.

[george]

The output jacks are wired in parrallel - you can verify it with a simple inspection (take off the tree sided enclosure first).