Removing 2 of 4 Power Tubes

[EdHopper]

A few reliable sources told me I could remove 2 or the 4 power tubes in my Marshall Super Lead 100 watt amps. With the high cost of tubes, I though I would try it and save 2 tubes for later. The sources told me to remove the outer two tubes and to then reduce the impedance selector from 8 ohms to 4 ohms - even though my cabinet is 8 ohms. I tried it on my SLP and my JCM 2000. Both amps seem to work just fine with the two tubes removed.
I'm not sure but I think there is a bit of a difference in the sound. I don't play either of these amps very loud - I don't need 100 watts, wish I would have gotten 50 watt Marshalls. Without telling what I did, I asked my guitar buddy if he noticed any difference in the sound. He said the SLP sounded a bit thinner. Has anyone else tried this and noticed any significant difference in sound or tone? Both amps use EL 34 power tubes.

 

[MonstersOfTheMidway]

A few reliable sources told me I could remove 2 or the 4 power tubes in my Marshall Super Lead 100 watt amps. With the high cost of tubes, I though I would try it and save 2 tubes for later. The sources told me to remove the outer two tubes and to then reduce the impedance selector from 8 ohms to 4 ohms - even though my cabinet is 8 ohms. I tried it on my SLP and my JCM 2000. Both amps seem to work just fine with the two tubes removed.
I'm not sure but I think there is a bit of a difference in the sound. I don't play either of these amps very loud - I don't need 100 watts, wish I would have gotten 50 watt Marshalls. Without telling what I did, I asked my guitar buddy if he noticed any difference in the sound. He said the SLP sounded a bit thinner. Has anyone else tried this and noticed any significant difference in sound or tone? Both amps use EL 34 power tubes.

You do know that after you remove two tubes from an amp that normally runs on four tubes, you must bias the amp, right? Your post, which I quoted above, did not mention a bias of the amp after removing the two tubes. If you indeed did not bias the amp after removing the two tubes, I suggest you unplug that thing and get someone who knows how to properly perform a bias.

It's possible/reasonable/likely to believe that if you did not bias after removing the two tubes, your sound will be very different.

Side note: if 100 watts is too much for you, I suggest selling it and buying something else that is right for you.

 

[Micky]

High cost of tubes?

Personally I think tubes are at their lowest prices ever...

 

[dash8311]

Put them back in before you damage the amplifier. The cost of tubes will pale in comparison to the tech cost of a repair and a new output transformer.

Marshall has it printed on their website not to pull tubes in a 100 watt amp. I think I'd go with that, personally.

You could also read the entire three page thread that was dug up and posted in. Lots of good info there.

 

[iron broadsword]

FYI the impedance is different when pulling two tubes. Can't remember which way it goes but google it and change your settings or you could damage the amp.

Fwiw, I tried this in my jcm900 and I didn't like it. It knocks off 3db which is nothing, and it just didn't sound good anymore. IMHO get an attenuator instead.

 

[Rokinroller]

All above correct.Not worth removing 2 tubes as difference in loudness is negligible and the sound not as good.

 

[Ken]

If a 100 watt amp is too loud, a 50 watt amp will be too. In an emergency, like at a gig, if one PT dies you can pull its partner. But as a normal procedure it's not a good idea. Too many questions on changes of voltages and load to assume you're not slowly frying your amp. Or in some cases, quickly.

If the master volume isn't working for you, get a 1 or 5 watt amp. Be aware you'll lose a ton of clean headroom.

Ken

 

[ampmadscientist]

A few reliable sources told me I could remove 2 or the 4 power tubes in my Marshall Super Lead 100 watt amps. With the high cost of tubes, I though I would try it and save 2 tubes for later. The sources told me to remove the outer two tubes and to then reduce the impedance selector from 8 ohms to 4 ohms - even though my cabinet is 8 ohms. I tried it on my SLP and my JCM 2000. Both amps seem to work just fine with the two tubes removed.
I'm not sure but I think there is a bit of a difference in the sound. I don't play either of these amps very loud - I don't need 100 watts, wish I would have gotten 50 watt Marshalls. Without telling what I did, I asked my guitar buddy if he noticed any difference in the sound. He said the SLP sounded a bit thinner. Has anyone else tried this and noticed any significant difference in sound or tone? Both amps use EL 34 power tubes.

It's the other way around, with 2 tubes pulled:
4 ohm output becomes 8 ohms (connect 8 ohm cabinet)
8 ohm output becomes 16 ohms
16 ohm output becomes 32 ohms

And if you follow this rule (above), the amp will continue to operate without damage.
However you did not reduce the loudness.

And this is because you removed half the current carrying capacity.
The current load is now carried by 2 tubes instead of 4 tubes.
Therefore, you must also cut the load in half. (Or overheat the tubes...)

And you loaded the bias circuit differently, so you better make sure the bias is set right. There is not going to be a huge change in bias.

You did reduce the power from about 100 watts to 60 watts.
And there is almost no difference in loudness.
Because Loudness does not = Power.

It's speakers (not power) that make the amp loud, and that's almost a different subject.
But FYI, using 1 X 12 inch speaker instead of 4 X 12 Marshall cabinet
will do more to reduce the loudness.
Marshall 1912 1x12" 150-watt Extension Cabinet | Sweetwater.com

HOW to reduce the loudness:

A. Change the pentode output to triode.
This makes 100 watt amp 40 watts. This makes 50 watt amp into 18 watts.
This eliminates the need to pull output tubes, or recalculate impedance.

B. Use professional power attenuator. The impedance must be exactly matched to amp and speakers. (do not use a cheap $30 attenuator)

C. Reduce the number of speakers.
Use less efficient speakers.

D. Use a speaker emulator or Iso - cabinet.

The Important Stuff:
The impedance must be matched, no exceptions ever.
The speaker cables must be good, no exceptions ever.
Do not use a guitar cable in place of a real speaker cable.

 

[mott555]

You can remove two tubes if you have one fail and need to keep it running during a gig, but it's not something you'd want to do long-term. Tubes draw a lot of current and cause the power supply voltage to sag. The circuit is designed to handle this. But if you remove two tubes, you're reducing current draw from the power supply and voltages will go up as a result. Stuff that was in spec before may now be dealing with higher-than-designed voltage, and it may damage things.

There may be specific models that can deal with missing tubes, but in general Marshalls don't work that way. I can safely pull two tubes from my Mesa because it actually has a switch on the back to kill half the power tubes and the circuit is designed to safely operate that way.

 

[ampmadscientist]

You can remove two tubes if you have one fail and need to keep it running during a gig, but it's not something you'd want to do long-term. Tubes draw a lot of current and cause the power supply voltage to sag. The circuit is designed to handle this. But if you remove two tubes, you're reducing current draw from the power supply and voltages will go up as a result. Stuff that was in spec before may now be dealing with higher-than-designed voltage, and it may damage things.

There may be specific models that can deal with missing tubes, but in general Marshalls don't work that way. I can safely pull two tubes from my Mesa because it actually has a switch on the back to kill half the power tubes and the circuit is designed to safely operate that way.

The power level switch on a mesa might do 2 things:

1. disconnect 2 output tubes, same as pulling them out.
or
2. Change pentode to triode, leave all 4 tubes operating.

The industry standard is (now) changing pentode to triode.
This is because disconnecting 2 tubes causes an impedance mismatch.

Disconnect 2 tubes including mesa, there is very little loudness reduction.

The triode reduces loudness quite a bit more than removing 2 tubes.
This is because triode is less efficient than pentode.

 

[mott555]

On my Mesa, it definitely disconnects two tubes, it's a SimulClass amp where it runs the outer tubes (EL34's) in Class A for 15 watts and the inner tubes (6L6GC) in Class A/B for 60 watts. You can switch between full-power 75-watt SimulClass mode and Class A 15-watt mode which cuts the inner tubes. Right now it doesn't even have tubes installed in the inner sockets because Mesa 6L6's are expensive and I don't have a suitable replacement right now.

But my point was some manufacturers explicitly allow you to remove power tubes under certain circumstances, and that it's a supported mode of operation. That is generally not true for Marshalls, except for the AFD and YJM IIRC.

 

[charveldan]

Saying a 100 watt amp is too loud is like saying a Ferrari is too fast.


100 watts is 100 watts, can't handle it get something smaller.

 

[MartyStrat54]

Right now it doesn't even have tubes installed in the inner sockets because Mesa 6L6's are expensive and I don't have a suitable replacement right now.

Mott are you saying that you can only run a MESA 6L6? Or do you mean you only use MESA tubes so you don't have to bias the amp?

 

[mott555]

Mott are you saying that you can only run a MESA 6L6? Or do you mean you only use MESA tubes so you don't have to bias the amp?

I only use Mesa tubes because the amp isn't even biasable. I believe Mesa-branded (actually Ruby tubes, I think) ones are guaranteed to be in the right bias range, but I'm not sure what happens as the tubes age.

I bought a pair of Mesa EL34's for the outer sockets, they weren't too bad in price. Their 6L6GC's cost quite a bit more, but I really don't need 75 watts so I left those sockets empty and run it in Class A mode.

 

[EdHopper]

I thought I made it clear that I was not worried about volume - I have attenuators if that becomes a problem. What I am worried about is the cost of tubes. Someone said the price is at an all time low? Can you tell me where I an get 4 matched Svetlana winged C EL34s for a good price? Also...
One of the sources I used was Pittman's book (The Tube Amp Book) - the Groove Tube guy. In the book, there is a mod for changing a 100 watt to a 50 watt by removing two tubes - they don't say anything about changing the bias.

 

[EdHopper]

Oh, sorry - I guess I did not say I was not worried about volume and i did imply it because I was saying I wish I had 50 watt Marshalls rather than the 100 watts. As mentioned by a number of folks, the difference in volume between the 50 watt and 100 watt is not really noticeable - what is noticeable is the fact that when I have to re-tube it, I'm buying twice as many tubes.

 

[Sir Don]

You can pull two tubes if you want to save money on re-tubing in future but if you don't play very loud then you wont have to retube very often in any case I guess.

 

[blues_n_cues]

loudness-does nothing
tube cost- not that big a deal unless you replace them once a year
what it does do is reduce the headroom and that's why a lot of people do it.

also,you did make sure to pull either the 2 outer or inner tubes right? not 1&3 or 2&4? that will damage the amp.

 

[charveldan]

Just pull the PT, that will keep costs down ... lol.


Quad of EL-34B Tungsols is $100 bucks from Laura @ valvequeen.com

If you can't afford that theres always Clarinet.

 

[Micky]

Kids these days.
If they would just get a job instead of playing video games all day and complaining about how much stuff costs...