Can I remove tubes to change 100w to 50w?

[Richardjordan]

Hi, I have a JVM 210c which is 100w. I wanted the 50w version but managed to get a very good deal the the 100w and the £'s have a big influence!

I prefer to drive the amp and a friend told me I can remove two of the power amp valves and this will reduce it to 50W and allow me to drive the amp harder

Does anybody know if this can cause any problems with the JVM series amps?

Also, is it better to turn the channel volumes to max and control the master volume or thee other way around? I've heard different views for each method, I mainly use the overdrive green and clean green/orange.

Thanks guys.

 

[wulfgar1976]

You can remove either the inner or the outer pair but you must set the impedance to half of the value you would usually use. E.g., if you're using a 16 ohm cabinet, use the 8ohm output. This is perfectly safe.

Marshall actually built this feature in to their 30th Anniversary amplifiers but without the need to change the impedance.

 

[poeman33]

Yes it is possible, but won't make it sound any better, and it won't be much quieter. It can also be hard on the amp. Marshall does not recommend it, but no your amp won't blow up or anything.

Your amp gets most of it's drive from the pre-amps. It you want to drive the amp harder, turn down the gain. There's a gazillion threads on this on most forums I think.

 

[The Ozzk]

JVM's tone comes from pre-amp tubes.

You want to drive the power section? get a 2203 or 2204 and ear protection and give'er

 

[MM54]

 

[wulfgar1976]

Yes it is possible, but won't make it sound any better, and it won't be much quieter. It can also be hard on the amp. Marshall does not recommend it, but no your amp won't blow up or anything.

When I asked them about the practise, their tech support didn't say anything against doing it. Since they built this feature into the 6100 & 6100LM, it would be a strange thing for them not to recommend doing.

 

[MKB]

Be very careful when doing this, as Marshall has designed some of their 100W amps so that the B+ is close to the maximum the power tubes can withstand. If you remove two of the tubes in such an amp, the B+ can go over the tube limits, and the tubes can blow.

Not all of their 100W amps are like this, but for sure the Vintage Modern is in this category. The designer of the amp (Steve Dawson) has posted several times on the Vintage Modern forum that using only two power tubes in the 100W VM can kill the tubes due to overvoltage.

If Marshall does not specifically design the amp to use only two power tubes, and does not specifically endorse pulling two tubes, I would not use the amp with only two tubes unless a tech can carefully determine if it is safe or not (by verifying the voltages in the amp with only two tubes, and checking the data sheet of the tubes you are using to see if it is safe).

 

[charveldan]

You have to be smarter than the amp.

 

[poeman33]

When I asked them about the practise, their tech support didn't say anything against doing it. Since they built this feature into the 6100 & 6100LM, it would be a strange thing for them not to recommend doing.

It's been years since I actually looked it up, but there was at one time an FAQ on the Marshall site asking this very question. Basically they said if your amp has four power tubes, it's designed to run on four power tubes. If you want a 50 watt amp...buy a 50 watt amp.

I first heard about this practice in the 70's when I started playing professionally. Most of us tried it just for fun. And that's all we did was try it, because it wasn't an improvement...but the practice still lives on obviously.

 

[paul-e-mann]

The only reason to do it is if youre down a tube or two, or you want to run a smaller watt cab. I have a 100 watt amp kit I plan on running on two power tubes when its done so I can use it with my 2x12 greenback cab.

 

[MartyStrat54]

Try a quad of 6V6's. :eek2::eek2:

 

[MartyStrat54]

Just joking.

If you got such a good deal on the amp, sell it and get a 50 watt amp.