Just need to confirm (impedance)...

[some_dude]

Just need to confirm (impedance)...

Reference the speaker jacks, when I pull half the tubes out of a 100w head,

1)
4ohm becomes 2ohm
8ohm becomes 4ohm


or


2)
4ohm becomes 8ohm
8ohm becomes 16ohm


is it 1 or 2?

 

[proxy]

Re: Just need to confirm (impedance)...

They say the ohms halve, so 1. Just make sure your safe to do this with your head.

I do this with my amp and haven't had troubles. I do go through tubes much more quickly and I'm sure a real 50w amp would sound much better.

 

[proxy]

Re: Just need to confirm (impedance)...

Err actually I think he is right. I used the 16ohm out from my amp to a 16 ohm cab, and after doing this I was told to use the 8ohm out.

 

[J Moose]

Re: Just need to confirm (impedance)...

Acutally, I was always told that you didn't have to do anything...8 ohms is still 8 ohms because the tap on the output tranny is still the same...

So, we've got three different answers now...who's got the right one? :jester:

 

[muttonchopsrule]

Re: Just need to confirm (impedance)...

i always thought it was #2...8 ohms would become 16 ohms. at least i hope so, because that's the way i've been running my setup since i started running my amp at 50 watts about 3 or 4 months ago!

 

[J Moose]

Re: Just need to confirm (impedance)...

I checked with two buddies and my amp tech...

If you yank a pair of power tubes (inner pair or outer pair) then all it does it cut the power. The impedance stays the same and isn't affected...so 8 ohms is 8 ohms, 4 ohms is 4 etc

 

[Lee Bob]

Re: Just need to confirm (impedance)...

Hmmmm, this is interesting. I ran mine at half the ohmage when I ran at half power (8 ohm cab into 4 ohm output) based on an interview with a Mesa Engineering tech I was forwarded.
It states: "In the 50 watt application it just pretty much centers it. Also, in this situation, the output taps double - so that the 8 ohm tap becomes 16 ohm - the 4 ohm becomes 8 and so on. Take your 8 ohm cab and plug it into the 4 ohm tap, or your 16 ohm cab into the 8 ohm tap, and you will be lined up correctly."

I can email this to anyone who wants it. Just PM me about it.
Hope this helps.

 

[some_dude]

Re: Just need to confirm (impedance)...

The story I've heard a few times now (I posted this on a few forums) is that the actual impedance doesn't change, but the way the tubes react does.

So, 8ohm is still 8ohm, but the tubes will see a 16ohm load....and thus sound a bit darker as they're running cooler. To fix this, you run your 8ohm load in the 4ohm jack, which'll bring the tubes back upto where you want them.

That's how I've been understanding it anyway.