running a 100watt H&K head at 50watt

[rabies]

just bought a h&k switchblade 100 head for $450 (!!!)

if i pull the two inner or outer tubes, will i need to rebias and what ohmage should i connect to on the speaker cab? thx.

 

[Jackie]

Ohmage is split as well I think.

If you intend to leave it like that then it's a good idea to rebias, yes.

Though I don't recommend pulling two tubes because you don't gain much... Today's amps have a very clean poweramp that doesn't distort much unless the amp is dimed and if you dime a 50W amp and a 100W amp the difference is very small (apparently it's 3dB), so you just lose a bit of clean headroom if you run it at 50W AFAIK.
BTW some folks that pulled two tubes actually popped them in and prefered the amp as it was.

Not saying you shouldn't do it, just sharing my opinion on the matter.

 

[94Tremoverb]

You don't need to rebias.

Set the amp to half the impedance of the speaker cab. (eg 4 ohms on the amp, 8 ohm cabinet.)

You need not necessarily re-set the impedance, and *not* doing so may get you more of the earlier breakup and compression that you normally want if you're considering pulling tubes, but you will be loading the two remaining tubes more heavily if you don't.

I also generally prefer four-tube amps with all four tubes in, I think they sound better even if you have to turn the MV down a hair to get the same volume.

 

[mbman]

What are you trying to achieve by pulling two tubes? As was stated earlier you'll lose some headroom and the difference in volume (approximately 3dB) is barely perceptible.

Martin

 

[rabies]

trying to cut the volume. I've cranked a 50 watt 2205 head and it wasn't as loud as the TSL100. not sure what tubes, I think the JJE34L have more headroom or are louder than regular EL34 so maybe that was the difference..