Can I just take tubes out to lower output?

[treymonfauntre]

I read in a Harmony Central review of my amp that the author took 2 of the 4 power amp tubes (6L6GC) out to bring the amp down to 60 watts. The amp has no bias. Is this really ok to do? Also, what happens if you mix different brand of tubes? Like, if I got 2 JJs and 2 GTs?

[Ilty]

U can do it, but it's not good way to go. in first, it's more hard for output transformer. Than, if you want to do it anyway, you must change impedance of the cab(8 on amp - 16 in cab, 4 on amp - 8 in cab, but i can be mistaken about ranges). Mixing output tubes isn't good idea also

[frans]

Hands off from mixing output tubes! The easier way is to get a good powersoak like the THD hotplate and use it sparingly to shave off 4 or max. 8 dBs or so - get's you in the same territory as unplugging 2 tubes. Or use a lower wattage amp anyway... who does really need 100 w tube output besides on a veryvery big stage?

[Blast9]

Yes you can... there should be no problem: have a read of this guy's Q and A page: ******//londonpower.com/faq.htm its all a really interesting read

Q: In a magazine Q-A, a player wanted to pull tubes to reduce power, but the "expert" said this would cause a meltdown of the remaining tubes. Of course, it was suggested that the expert's attenuator product was the preferred way to go. Is any of this true?

A: This is a person who should know better!

Removing tubes from a multi-tube fixed-bias output stage is never a problem. You can remove any number of tubes, and yes, that means you can take one tube out of a two-tube amp; one, two, or three out of a four tube stage, et cetera. This sounds heretical to techs stuck in the mire of convention, but it is something that has been known since tubes were invented.

The even-number tube extractions reduce power symmetrically. Neither the tubes nor the transformer will be damaged. Power will be reduced and so will frequency bandwidth - you will lose some bass and some treble. This is the point that switching the impedance selector to a less-than-load setting is supposed to correct, but it is completely subjective whether you should. The only 'should' of the matter, is do I like it this way, or do I like it that way?

In the uneven tube extractions, asymmetric power reduction occurs. Conventional thought says "the one tube on one side of the circuit will be trying to match the output of the two tubes on the other circuit half". This is wrong. The single tube can only produce so much power, and that's all it does. It doesn't melt down. The transformer does not blow up.

So, what's missing from conventional thought? The realization that tubes are "self-limiting power governors", which was stated in The Ultimate Tone (TUT), and explored in more detail in TUT2 and TUT3. TUT4 explores all of this in great detail. Our "expert" should get a copy.

In the end, you can pull tubes to reduce power, unless the amp is cathode biased - then you have to split the bias resistor. In any case, you do not have to worry about the impedance selector either.

Maybe dementedchord or other tech guys can chip in?

Interestingly there's a guy over at www.plexipalace.com called evhfreak or something, who has posted clips of his 100w plexi with just 1 power tube for that authentic EVH sound

[analogtodd]

You can get some really cool tones trying different things, but as in any experiment, you run the risk of blowing something up... including yourself!

I've seen guys run old Bassmans with one output tube and it sounds great.

If you plan on running the amp HARD (what kind of amp is it??)
you should really have it checked out and measure bias as you go and see what effect its really putting on the components.

It ain't rocket science, but a little education doesn't hurt.

If you are strictly going for a volume reduction though, I'd look at doing it some other way (hot plate, weber mass, blah blah blah)

[treymonfauntre]

well really i'm shopping for new tubes and it would save me a lot of headache and money to just buy 2 and see if i like how that sounds. and i agree 120w is ********ly loud.

[Blast9]

What kind of amp is it?

[dementedchord]

little or no reason you cant pull a pair of those tubes... just make sure that it's one from each side.... that is to say... most of these things are in a push/pull cofiguration and you dont want to just push... get my drift??? personally i wouldn't use tubes of diff brands.. unless one blows and you gotta finish the gig... the sound will in all likelyhood not be the same... part of what you guy's seem to like about tube amps can be traced to the output tranny... in particular when the thing is driven into saturation.... and it aint gonna get there easily with two pulled... which incedently is another good argument for a great front end amp with a modest output stage....

[max cooper]

I've been running 100w Super Lead Marshalls with two tubes out for about twenty years. Never a hitch. I always make sure my tech has gone over the amp before it goes out but even if I'm sloppy about it, it's never been a problem. I always make sure to pull 'em out in pairs.

I get the amps biased for one pair of KT88's and they sound excellent.

[themaidsroom]

again, i promote my friend curt emery

www.emerysound.com


best guitar sounds i know
from smart, modern
guitar amps





be well


- jack

[treymonfauntre]

Originally Posted by themaidsroom

again, i promote my friend curt emery

www.emerysound.com


best guitar sounds i know
from smart, modern
guitar amps





be well


- jack

uh.. thanks.... i'll keep that in mind next time i need a uh......

[softwareguy]

You can definitely do it.

I actually have a Showman that has been modded with a switch (pre-existing hole, don't freak out) so that you can pick
1. Inside pair
2. Outside pair
3. All four

Works great. Also lets me use just a pair of tubes with a single 8 ohm speaker and be balanced impedance-wise.

[softwareguy]

What I forgot to say is, it doesn't actually reduce volume that much. However, it does cut power in half, which is a LOT, so that if you use the amp with an attenuater you don't have to attenuate nearly as much to get it into the zone. Kinda weird, but it works.

[mrbobo]

One thing I noticed upon removing 2 tubes - that I never see mentioned in these discussions - check your bias!! I forget which way it goes now.... But it changes allot!

[dementedchord]

Originally Posted by mrbobo

One thing I noticed upon removing 2 tubes - that I never see mentioned in these discussions - check your bias!! I forget which way it goes now.... But it changes allot!

while i believe in rebiasing on tube swapping... and in general no reason you cant every day if ya want... doesn't seem to be any particular reason (need) to here...

bias is voltage used to shut down the tubes for the most part... think of it as setting the idle on your car... and that voltage shouldn't change because you've removed 2 tubes.... at least that i'm aware of.... YMMV