Pulling powertubes for less wattage

[metalchurch79]

I was on the plexi palace and read up alot on this topic and after a while it got me thinking about doing it myself.
So the other night I dove into it and did just that.

They say that as long as the amp is biased properly for the powertubes that were in it, that you can pull 2 of them without any problems at all.
Since the amp is 1/2 the wattage (nominal) then you should use 1/2 the original ohms used, and set the cabinet accordingly.
For example:
I was running 16ohm mono on the 9200 and 16ohm on the 1960 cabinet, so now the 9200 is @8ohm mono, and the cabinet is still 16ohm mono. (as opposed to 4ohm)

Here's the equipment that I was working with:
Marshall 9200 Dual MonoBloc 100w poweramp.
It has a Side-A and a Side-B, so it's essentially 2 amps in 1, and they are completely seperate units.
Someone on here has the little brother to mine, which is the 9100.

The 9200 has 4 powertubes and (1) 12AX7, and (1) 12AT7 per side.

My Side-A was recently gone over by my tech this past June. He put (4) Tung-Sol 5881 Powertubes, and (1) Electro-Harmonix 12AX7, and (1) Electro-Harmonix 12AT7 in it.

Side-B was completely stock with (4) Sovtek 5881's, and (1) Marshall 12AX7, and (1)Marshall 12AT7.
But my tech went over it and re-biased it to make sure it was in great shape.

I pulled (2) of the Sovteks out of Side-B and replaced the Marshall pre-tubes.
I had a bunch of different brands, so I swapped them in and out for about an hour until I found a nice pair.
I tried Sovtek, Groove Tubes, Marshall,Ruby,Chinese no name, and some tue with no brand or size markings at all.
The Sovtek 12AX7 had the best voice out of them. I had 2 of those, so I used the best sounding one, and tried every tube paired up with that one. Surprisingly both Sovteks together didnt sound all that great to me.
I ended up using (1) Sovtek 12AX7, and (1) No-name/no-size.
I'm guessing that it's a 12AX7 because it has as much if not more gain than the Sovtek AX7.

Anyway, I am extremely impressed with the results that I got from merely pulling out 2 of the powertubes.
They say that by removing 2, it essentially makes it into a 50w poweramp.
But I also read that it really only drops it down to a realistic 70w, and that seems to be a better description.

I mainly did this to achieve a faster tube breakup, and not to lower the watts, but it ended up doing both very nicely.
It is surprisingly alot cleaner than I expected, and it almost has a better overall tone than Side-A.
Even with the mismatched pre tubes and the old Sovtek powertubes it has a nice smooth gain structure.

They say that guys have been doing this to their non-master volume Marshall Plexi's since the 1970's with no inherent problems at all, so that there is what re assured me to try it with mine.

So far I've played it for about 4 hours+ with no problems, and no unusual noises or anything, so it's so far so good!

By the end of this week I should have my Yellow Jackets to try out in Side-B. I'm gonna try them by themselves and with 2 of the 5881's to see which one is better.

Has anyone else done this yet?
What results have you gotten?
Do you guys really think this is safe to do?
Anyone have any thoughts on this?

Thanks
Joe

[bibz]

I've done it with my jsx to try out some 6l6's I only had three of (used two). On the official peavey forums a peavey tech said it was fine to do aslong as it was an outside or inside pair. Ohmage must be changed also as you mentioned.

[Spivonious]

I've heard that you can do this before, but I never heard that the "ohmage" had to be changed too. It makes sense, but then why don't you have to change it on amps that have half-power switches?

[DonP]

Has anyone else done this yet?

Yeah, since 1990.

What results have you gotten?

I don't think it makes a big enough difference. I don't do it any more.

Do you guys really think this is safe to do?

Yes.

Anyone have any thoughts on this?

Thanks
Joe

Yes.

You need to keep a close watch on your power tubes. You want to wear them out at the same rate to keep the matched set of 4, unless you plan on always running 2 only. This means keeping track of how long you use one pair of tubes, swapping, keeping track of the time on the second pair, swapping, etc.

To make it easiest on yourself, you need to make a decision to either go for 2 or 4 tubes and be done with it.

Personally, I think louder is better and that's why I got a DSL100 instead of a DSL50 head. I've had thoughts of making a 2203 with 6550's or KT88's for a real ass kicker.

[metalchurch79]

Yeah, since 1990.
I don't think it makes a big enough difference. I don't do it any more.
Yes.

Yes.

You need to keep a close watch on your power tubes. You want to wear them out at the same rate to keep the matched set of 4, unless you plan on always running 2 only. This means keeping track of how long you use one pair of tubes, swapping, keeping track of the time on the second pair, swapping, etc.

To make it easiest on yourself, you need to make a decision to either go for 2 or 4 tubes and be done with it.

Personally, I think louder is better and that's why I got a DSL100 instead of a DSL50 head. I've had thoughts of making a 2203 with 6550's or KT88's for a real ass kicker.

Thanks Don, I already had plans on rotating the powertubes for even wear and I'm keeping track of the playing hours.

Like I said it is a Dual Monobloc amp, so Side-A is still set @100w with all of the tubes in it. All that I do is unplug the input and speaker cable and connect them into Side-B when using that side.
They are seperate amps, but in 1 chassis.

It doesn't make a huge difference, but enough that I can notice a change.
It's nice to be able to mess with different sounds, because this is the only amp that I have.

But yeah as pointed out, you have to either pull the inside or outside pair and reduce the ohms in half.

Due to the sideways layout of my poweramp I had to pull these tubes:

The 9100 50w version of this only has (2) powertubes per side, (which would be the ones that I left in Side-B)

Thanks for the replies!

[Shawn Lutz]

I'm not sure how to do it on the mono bloc but I pulled two tubes outta a 2203 head and ran it at 50 watts. In a typical 100watt head..you either remove th outter 2 tubes or the inner 2 tubes. I also use the only YJ's in the 2203 and knocked it to about 20 watts or so.

I think an attenuator is a better option in taming beasts like that....