how to connect a 2.67 ohm load on a tube amp

Devo-lution · #1 08-03-2011, 05:31 AM

So, hearin the experts like Alex and Bill, it should be possible to connect a 2.67 load on my 4 and 8 ohm tube amp without endangering it (using the 4 ohm tap).

My gigworthy cab is kaman era trace 2x15 (400 watts 4ohm). Saw on our local ebay variant that someone is offering a kaman era trace 1x15 (200 watt 8 ohm) almost for free.

Seems like a too good chance to let pass. 3x15 would be quite cool for those 'extra loud gigs'.

But how to connect this load? Use both outputs of the amp or link the cabs to each other? It seems logical to me that the second answer is the correct one (as the first one might provide each cab with 50 watts, which is not what I want). But I'm not sure and I have no technical amp knowledge, so talkbass community, what say you?

billfitzmaurice · #2 08-03-2011, 06:00 AM

Quote:

Originally Posted by Devo-lution

But how to connect this load? ?

With speaker cables.

Whether you run separate cables to the amp or daisy chain the cabs it's parallel wired either way.

Devo-lution · #3 08-03-2011, 06:11 AM

Quote:

Originally Posted by billfitzmaurice

With speaker cables.

Whether you run separate cables to the amp or daisy chain the cabs it's parallel wired either way.

LOL

So, there is really no risk for the amp involved?

And yeah, I know I can connect it both ways. I just want to make sure that the 1x15 receives +/- 33 % of the output and the 2x15 66%.

Son of Bovril · #4 08-03-2011, 06:11 AM

+1 it doesn't make a difference if you link the cabs or run them from separate speaker outputs, the amp will see the same load

hover · #5 08-03-2011, 06:14 AM

might as well get a pack of franks because you're gonna cook that amp (specifically the output transformer[s]) in record time. Just might take some other circuits out too with the potential small fire that may follow. Mmmm, franks.

So in short, no. don't do it. Use the 4ohm cab alone. Or, the 8 ohm cab alone. The amp won't like that as much, but certainly a LOT better than a 2.6ohm load.

billfitzmaurice · #6 08-03-2011, 06:26 AM

Quote:

Originally Posted by hover

might as well get a pack of franks because you're gonna cook that amp (specifically the output transformer[s]) in record time..

-1. Tube amps aren't bothered in the least by low impedance loads, even shorted outputs for that matter. It's too high an impedance load that toasts output transformers.

hover · #7 08-03-2011, 06:30 AM

I find this news surprising. I had always been taught otherwise.

nashvillebill · #8 08-03-2011, 06:57 AM

Quote:

Originally Posted by billfitzmaurice

-1. Tube amps aren't bothered in the least by low impedance loads, even shorted outputs for that matter. It's too high an impedance load that toasts output transformers.

Exactly. Some amps such as the Ampeg V4 even have shorting speaker output jacks. So if you turn on the amp without a speaker attached, the OT's secondary is shorted (zero impedance) and averting the problem of an open (too high impedance) secondary.

staindbass · #9 08-03-2011, 07:02 AM

2.67 ohms? is that what is says on the cab? if you measured it with a multimeter, a 4 ohm cab will show less than 4 ohms. its a nominal measurement

hover · #10 08-03-2011, 07:04 AM

Staind, He wanted to add a second, 8 ohm 1x15 cab to complement his existing 4ohm 2x15 cab and wanted to run them together off the 4ohm load.

I am glad to hear this new info though re: amps, definitely.

eyeballkid · #11 08-03-2011, 07:05 AM

staind: 2.67 is what ya get when ya put a 4 ohm and 8 ohm cab together.

billfitzmaurice · #12 08-03-2011, 09:08 AM

Quote:

Originally Posted by hover

I find this news surprising. I had always been taught otherwise.

No knowledgeable source that would say that. SS amps are bothered by too low a load impedance, while they're able to drive a high impedance load or even no load/infinite impedance. Tube amps are exactly the opposite.

staindbass · #13 08-03-2011, 09:27 AM

Quote:

Originally Posted by eyeballkid

staind: 2.67 is what ya get when ya put a 4 ohm and 8 ohm cab together.

gotcha, thank you.

hover · #14 08-03-2011, 09:33 AM

Quote:

Originally Posted by billfitzmaurice

No knowledgeable source that would say that. SS amps are bothered by too low a load impedance, while they're able to drive a high impedance load or even no load/infinite impedance. Tube amps are exactly the opposite.

Point taken. It could be I had heard wrong too, but thanks for the clarification. Then again, I'm usually a one head / one cab type so it's not an issue for me.

jmpiwonka · #15 08-03-2011, 09:52 AM

Quote:

Originally Posted by hover

Point taken. It could be I had heard wrong too, but thanks for the clarification. Then again, I'm usually a one head / one cab type so it's not an issue for me.

my tech has told me it's ok to run a higher cabinet impedance but lower is bad...
of course it's best to match them though...

will33 · #16 08-03-2011, 09:59 AM

Quote:

Originally Posted by jmpiwonka

my tech has told me it's ok to run a higher cabinet impedance but lower is bad...
of course it's best to match them though...

A lot of you guys are confusing tube and ss amps.

Tube amp--lower impedance is ok, higher is not.

SS amp--higher impedance is ok, lower is not.

jmpiwonka · #17 08-03-2011, 10:03 AM

Quote:

Originally Posted by will33

A lot of you guys are confusing tube and ss amps.

Tube amp--lower impedance is ok, higher is not.

SS amp--higher impedance is ok, lower is not.

we were talking about the impedance switch on tube amps...my svtII
he also told me the same thing when i had a V4B serviced by him.

fenderhutz · #18 08-03-2011, 10:09 AM

Solid State amps. Running lower Impedance is a BAD thing. If it's rated at 4 ohms don't run lower than 4 ohms. However 4, 8, 16 is fine.

Tube Amps. If it says 4 or 2 ohms DO NOT run an 8 ohm cab. 2.67 ohms would be in that range and be fine.

Hopefully I am right and that cleared it up.

will33 · #19 08-03-2011, 10:35 AM

Quote:

Originally Posted by jmpiwonka

we were talking about the impedance switch on tube amps...my svtII
he also told me the same thing when i had a V4B serviced by him.

Where did you go? The best in town used to be Jon at Tonecraft (R.I.P.), now I don't know where to go but haven't needed any work done since then.

Old fenders can run on an upward mismatch....may not be the best idea but it won't kill them. Don't know about ampegs. The OP's 2.67 load I'd run on the 4ohm tap. Running 5.33 on the 4ohm tap may be close enough? Don't know.

jmpiwonka · #20 08-03-2011, 10:39 AM

Quote:

Originally Posted by will33

Where did you go? The best in town used to be Jon at Tonecraft (R.I.P.), now I don't know where to go but haven't needed any work done since then.

Old fenders can run on an upward mismatch....may not be the best idea but it won't kill them. Don't know about ampegs. The OP's 2.67 load I'd run on the 4ohm tap. Running 5.33 on the 4ohm tap may be close enough? Don't know.

i usually take my stuff to Chuck at Guitar Rez, especially the tube amp stuff.
the V4B he retubed for me sounded great.