modifying a 100 watt head

W

wannabecomedeat

New member
hey,

I own a 100 watt jcm2000 marshall head amp. I wanna turn it into a 50 watts amp. It's way to loud, can't get the tubes to saturate, it feels like my head will simply blow up, and the volume knob is only turned at 2.

I think I read somewhere that I just have to remove 2 of the 4 poweramp tubes and the job is done, no biaising to do. Can someone confirm, with personal experience? If that's true, which of the 4 should I remove? and how do I remove those things without breaking them, do I simply need to pull on twist or turn counterclock side? What if I remove 3 tubes?
 
Do some more research but I believe all you need to do is pull the tubes. Each has a power rating of around 25 watts so for each one you remove you'll be lower the power output accordingly. As far as removing the tube, I believe you pull them straight out, unless I've been doing it wrong.
 
Just a thought, but could you trade in the 100 watter against a 50 and still have cash to spare?
 
Or look into a power soak or something like Yellow Jackets. These are a couple of ways to do like you say and saturate the power tubes without liquifying your intestines.
 
I bought this amp used, half price, mint condition, so money was no big deal + I do about 8-10 gigs a year, big volume is still needed

Other then that it's exactly what I would have done :D
 
Also remember that the difference between 100W of output power and 50W of output power is barely audible. You'd want to reduce it to more like 15W to have it be noticably quiter.
 
Tadpui said:
Also remember that the difference between 100W of output power and 50W of output power is barely audible. You'd want to reduce it to more like 15W to have it be noticably quiter.
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Correct, try removing all but one power tube.
 
I understand this fact, but I feel it's a bit pointless. Let me explain; if my amp gets too loud at 2 with 4 tubes, it will get too loud at 4 with 2 tubes, if it's unbearable at 4 with 4 tubes, it will be unbearable at 8 with 2 tubes which 1)gives me two times more control over the volume and 2)tube saturation will be much more important with volume set to 8 rather than 4.

The problem here isn't one of human ears accuracy but one of "I don't have enough control on my amp"

I might be wrong, but if the ear acts like human eye and light, than there is a db level interval where the ear is really good at telling the difference, let's say between 50 db and 100db, and higher than 100db the ear can't tell (alltought with the eye the invert happens; a 1/10th brighter light feels like twice as bright)

I might be totally wrong, but from what I know a 30 watt practice amp will play much less louder that my head with volume set at 2
 
If you want to remove tubes, you have to remove them in pairs. They work in a "push- pull" fashion. As one is pushing, the other is pulling. The two outer tubes are "paired" and the two inner tubes are "paired". You can try removing the two outer ones. This will reduce the headroom a bit, but isn't going to make a huge difference. It'll still be a pretty loud amp.

You can't remove 3 tubes. I don't think it would be safe for the amp.
The tubes have pins that go into sockets. They pull straight out. Don't twist them. You should probably check some forums on the "jcm2000" and see if they work OK like this before you try it. Maybe someone else can shed more light on this.
 
Hum got this from the faq section on marshallamps site:
http://www.marshallamps.com/support/support_faq.asp#7a

7a -Can I remove two valves from my 100 watt to make it a 50 watt?

We do not recommend the removal of any valves as a 100 watt amplifier is designed to work with four power valves the removal of two can and will cause damage. One way to reduce the output of the amplifier will be to use a power soak this gives you a lower physical output allowing you to turn the amplifier higher to achieve the tone you are after
 
jonnyc said:
Correct, try removing all but one power tube.
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The marshalls are class A/B. If you remove all but one tube, you will only get half of the signal through. (ie the positive swing of the signal and not the negative swing)
The tubes work in pairs. Unless they changed, the old Marshalls were paired as inside pair and outside pair. You can either remove the two tubes in the middle or the other two. It's not recommended and it doesn't make the amp that much quieter.
 
I pulled 2 of the 4 power tubes from my 80-watt tube amp and it had barely any effect. It was certainly not any quieter of an amp while running at 40W versus 80W. It was not any easier to control either.

It sounds like the reasons are mounting towards getting an attenuator.
 
Farview said:
The marshalls are class A/B. If you remove all but one tube, you will only get half of the signal through. (ie the positive swing of the signal and not the negative swing)
The tubes work in pairs. Unless they changed, the old Marshalls were paired as inside pair and outside pair. You can either remove the two tubes in the middle or the other two. It's not recommended and it doesn't make the amp that much quieter.
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Yeah yeah, I was corrected earlier about this. My bad. Did you see where the original poster linked to the Marshall site where it says not to remove any? Is that true you can't do that?
 
There is no point in pulling tubes because the sound volume will not drop at all. To get 1/2 the volume you need 1/10 of the power. So 10 watts (but you can get away with even a 25 watt amp with a less efficient speaker.) If you are plugged into a 412, then plugging into a single 12 would also be a great improvement since you will be moving much less air.

But there is only one solution to this without a second amp. A THD HotPlate or another brand of power soak / attenuator.

What you need IMO is a practice amp (any wattage solid state, under 15 tube). The 100 watt head is only for play loud.
 
jonnyc said:
Correct, try removing all but one power tube.
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no you can't do that ...... it's a push/pull amplifier and so it needs at least two tubes ...... for that matter you can't just pull one ..... gotta pull 2 tubes
 
Lt. Bob said:
no you can't do that ...... it's a push/pull amplifier and so it needs at least two tubes ...... for that matter you can't just pull one ..... gotta pull 2 tubes
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And it has to be the correct two. :D
 
Lt. Bob said:
no you can't do that ...... it's a push/pull amplifier and so it needs at least two tubes ...... for that matter you can't just pull one ..... gotta pull 2 tubes
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Can any of you guys fucking read, you're the third fucking person to bring this up. Read the whole thread!!!!


Sorry about the language, I'm hung over and don't like multiple people correcting me. It's funny how, as soon as people read something, they're very quick to reach for the reply button so they can prove you wrong.
 
Pull the two inner or two outter tubes. The volume won't be that different, 3db is all. You will get better tube saturation so the overall tone will be better if you like power tube distortion. ;)

Oh and for the idea to only use one tube, that'll blow your output transformer so please don't take that advice.
 
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