I've heard from loads of sources while searching around the internet that if i pull my outer 2 power tubes on my 5150, I should Half the impedance.

I've also seen people saying you should double the impedance

When i talked to the rhythm guitarist in my band he said that there is no reason for changing the impedance as you are just halving the wattage and not affecting the impedance at all.

Can anybody please give me the correct answer on this, from experience, or from an engineering view as i don't fancy paying a repair fee for the 5150.
Last edited by Bullet_Fan at Aug 29, 2009,
impedance as in speaker? i doubt pulling tubes would effect the output ohms. why do you need to anyways?
no you need to run your amp at half the load impedance if you want to pull two powertubes.

and make sure you pull either the two outer ones or two inner ones.
Hey mate, I pull two tubes, dropping my amp down to 60 watts.

If my head was previously set to 16Ohm, I leave my cab on 16Ohm and drop my head to 8Ohm once the tubes have been pulled.

So in terms of numbers, after you pull tubes you make sure your head is set to half the Ohms of your cab.
kk thanks, does anyone know the reason for this, as in like technically so i can show my rhythm guitarist?

Oh and is there a reason that my friends Bugera 6260 has half the tubes pulled and works with the same impedance as before.
As well as my rhythm guitarists Laney and windsor.
Is running them it like this dangerous?

And thanks i'll half the impedance
Your power tubes will just die faster this way, no biggie.


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Yes it is dangerous since the impedance is mismatched.

I believe the impedance problem has to do with only using half of the transformer when the tubes are pulled. I don't know the specifics, but I know it comes back to the output transformer.
I don't give a shit if you listen to me or not
Basically dude, if they leave it as it is, it makes the amp work harder, which will make the tubes blow sooner, and just generally wear out the amp.

However, if they dropped it to say 4 ohms rather than leaving it at 16, the head would basically instantly explode.

Either way it is bad for the amp, it's just that the latter is obviously imminently bad, as opposed to long term damage.