Series/Parallel wiring

surfguy13

Hi guys

I have been using an old Selmer T&B amp which has an 8 and 16 ohm out which makes life easy.  However, I have just acquired an old '72 Marshall PA 20 which doesn't have an ohms selector on the back.  There is a choice of 4,8 or 16 ohms tabs which are hard wired but.....this means you can't mix and match.  The amp is currently set up for 8 ohms.

Question....I have a pair of early 70s G12Ms that are both 8 ohms.  Clearly parallel would half that and series would double it.  Is it possible to series/parallel wire a 2x12 cab and if so what is the resultant ohmage using two 8 ohm drivers?

I guess I could wire the G12Ms to 16 ohms and then re-wire my other 2x12 to 16 ohms and change the ohmage inside the amp. 

Also, is there a difference between the amount of volume when wiring to 8 or 16 ohms?  This amp is not loud needless to say so if changing the amp to 16 ohms would give me a bit more volume that might be the best way to go.

Cheers

Guy

Sporky

With two drivers you can only wire them in series or in parallel, so with two nominally 8-ohm drivers you can only get 4 ohms or 16 ohms, nothing else.

With more than two (usually four) you can do series/parallel wiring, and then with four drivers you can get 8 ohms overall (either two series pairs in parallel or two parallel pairs in series). Or all in parallel for 2 ohms, or all in series for 32 ohms. There are other potential arrangements but none are sensible.

surfguy13

Thanks Sporky, at least I know what my options are.  I reckon I'll just hook it up to the 16 ohm tab in the amp and re-wire the cabs, makes the most sense.

Sporky said:

With two drivers you can only wire them in series or in parallel, so with two nominally 8-ohm drivers you can only get 4 ohms or 16 ohms, nothing else.

With more than two (usually four) you can do series/parallel wiring, and then with four drivers you can get 8 ohms overall (either two series pairs in parallel or two parallel pairs in series). Or all in parallel for 2 ohms, or all in series for 32 ohms. There are other potential arrangements but none are sensible.