#1
I have a bogner shiva head which has 3 speaker outs..2, 8 ohms and 1, 16 ohm... I have a bogner 4x12 cab rated at 16 ohms and a dr.Z 2x12 rated at 8...both cabs have 16 ohm speakers. I know it is imposible to wire the 4x12 speakers to be 8 ohms and also the 2x12 speakers are imposible to wire to 16.. so my question is this.. I have never heard of a 32 ohm cab..but what if I wired my 2x12 speakers in series to make it 32 ohms..and then ran it in parallel with my 16 ohm 4x12 making a total resistance of 10.6 ohms and plugged that into a 8 ohm jack?

..is that safe for the amp?

..or is there any other possible solution other than buying new speakers or mod-ing the amp?
#2
You don't have to use all the outputs on the head. I would think it's meant so you can use one 16 ohm cab or two 16 ohm cabs.


edit: from the Shiva manual:
e) Speaker Outputs


NOTE for older Shivas made prior to 12/1/05: If you put the amp in play make sure you have a load or speaker cabinet hooked up, otherwise you could damage the output transformer and the power tubes. This older Shiva does not have an ohm selector, it has 3 speaker output jacks each labeled with an oval containing 2 numbers in it. One of the numbers in each oval is marked out with a black marker, so only the other number is important to you! If you hook up only one cabinet, the impedance (ohm value) of amp and cabinet should match: 4 into 4, 8 into 8 or 16 into 16. If you hook up two cabinets (they must have the same impedance, same ohm value). The total ohm value is half the value of one cabinet since they run parallel now: so two 16 ohm cabs plug into the two 8 ohm jacks, two 8 ohm cabs plug into the two 4 ohm jacks if your amp is wired with two 4 ohm speaker outputs of course, see the following for more details: The EL 34 Model has one 16 and two 8 ohm speaker outputs (the transformer has an internal 4 ohm tap also, so the outputs could be wired to 8 4 4 or 16 8 4 ohms if you wanted your amp customized)

NOTE for 6L6 Shiva's made June 2002 and newer are wired with one 16 and two 8 ohm speaker outputs, just like the EL34 models. Shiva 6L6 models made before June 2002 approx. do not have a 16 ohm tap. The older 6L6 Model have one 8 and two 4 ohm speaker outputs (the transformer has an internal 2 ohm tap also, so outputs could be wired to 4 2 2 or 8 4 2 ohms if you wanted your amp customized) Keep that in mind because most of the 4x12" cabinets are 16 ohms.


...so just plug your 16 ohm cab into the 16 ohm jack and enjoy.
Last edited by Roc8995 at Mar 18, 2008,
#3
I know it's an old thread, but I found this in a google search and one of the OP's original questions went un-answered. Whether he sees it or not, perhaps it could be helpful to someone out there.

If you were to have an overall speaker-load of 10.6 ohms, the answer to your question is yes, you can run your amplifier at 8 ohms without risking damage to your equipment. However, there will be some power loss, though perhaps negligible.

It may not be necessary though. You can wire two 16 ohm "dummies" into your 212 cab. You don't have to have 4 16ohm speakers to attain that load - simply 4 sources of resistance at 16 ohms apiece. Might be kind of tricky, I've never actually attempted it, just heard of it being done.

Really you should just get another 412. Full stacks kick the most ass, by rule.