Can the Marshall JCM 800 2210 be used as a 50-watt head with only two power tubes?

[d3vCr0w]

Hi people, hope y'all doing great. I was wondering if a Marshall JCM 800 2210 can be used with only two power tubes and if so which ones are to be removed?
Has anyone done it? And is there a risk to blow the remaining two tubes from over-current?

 

[V-man]

Yes. All 100w Marshall are capable of this.

Assume the cab load of 16 ohm...

1. Double impedance from 16 ohm to 8 ohm
2. remove either 2 outer tubes (1&4) or 2 inner (2&3).

Done.

 

[d3vCr0w]

Yes. All 100w Marshall are capable of this.

Assume the cab load of 16 ohm...

1. Double impedance from 16 ohm to 8 ohm
2. remove either 2 outer tubes (1&4) or 2 inner (2&3).

Done.

I'm using an 8ohm cab, would I have to use the amplifier with a 4ohm load then?
And is there any internal modification needed or does this just work out of the box without risk of blowing the tubes?

Thanks for the reply.

 

[V-man]

I'm using an 8ohm cab, would I have to use the amplifier with a 4ohm load then?
And is there any internal modification needed or does this just work out of the box without risk of blowing the tubes?

Thanks for the reply.

You always double.

Have a 16 ohm load normally? Set to 8ohm w 2 tubes.

Have an 8ohm load? Set to 4ohm w 2 tubes.

Have a 4 ohm load? You’re SOL pulling tubes w this load.

No mod needed. Just observe the common sense rule when pulling speaker cables or switching impedances to ALWAYS begin at low volume as a disciplined practice. Catastrophic failure usually occurs with volume.

 

[Pete Farrington]

Note that due to the resulting higher, stiffer HT supply than an equivilant 50W model, the remaining valves are likely to be under more stress at medium / high power output levels.
As such, it may not be a great idea to crank the amp, eg into an attenuator or speaker,
Hence unless you're skint and can't afford a full set of functional output valves, I view this as a 'non recomended', retrograde move.

 

[Gutch220]

just to avoid confusion I see here, and feel free to correct me.....

If you were at 4-tubes at 16-ohms, then you remove two tubes and turn the amp to 8-ohms.........you'd still want a 16-ohm load. You just need to "half" the amp's impedance while keeping the same speaking load.

 

[Gene Ballzz]

just to avoid confusion I see here, and feel free to correct me.....

If you were at 4-tubes at 16-ohms, then you remove two tubes and turn the amp to 8-ohms.........you'd still want a 16-ohm load. You just need to "half" the amp's impedance while keeping the same speaking load.

^^^^^ A very appropriate and well worded clarification, right there! ^^^^^

This is still a much les than optimal means of shaving a very minimal (at best) amount of volume from a 100 watt amp, as correctly alluded to by @Pete Farrington ! A really good attenuator (like the @JohnH ) while running the amp with all four power tubes (as designed) would be a far superior solution!

Just Thinkin'
Gene

 

[d3vCr0w]

just to avoid confusion I see here, and feel free to correct me.....

If you were at 4-tubes at 16-ohms, then you remove two tubes and turn the amp to 8-ohms.........you'd still want a 16-ohm load. You just need to "half" the amp's impedance while keeping the same speaking load.

Oh, that makes sense now, in my case I have an 8 ohm cab and the impedance selector from my amp is set to 8 ohms obviously, so I should set the impedance selector to 4 ohms and still use my 8 ohm cab, is that correct?

 

[Gene Ballzz]

@d3vCr0w
What the heck model is that Ampeg amp?
Just Curious?
Gene

 

[Gene Ballzz]

Oh, that makes sense now, in my case I have an 8 ohm cab and the impedance selector from my amp is set to 8 ohms obviously, so I should set the impedance selector to 4 ohms and still use my 8 ohm cab, is that correct?

Correctamundo!
Gene

 

[d3vCr0w]

@d3vCr0w
What the heck model is that Ampeg amp?
Just Curious?
Gene

It's a VL-502 (the 50watt version of the VL-1002) designed by Lee Jackson and built by Ampeg SLM, it's basically a JCM 800 on steroids.

 

[d3vCr0w]

^^^^^ A very appropriate and well worded clarification, right there! ^^^^^

This is still a much les than optimal means of shaving a very minimal (at best) amount of volume from a 100 watt amp, as correctly alluded to by @Pete Farrington ! A really good attenuator (like the @JohnH ) while running the amp with all four power tubes (as designed) would be a far superior solution!

Just Thinkin'
Gene

Not really what I'm after, I already have a Marshall Power Brake to tame the volume, and also I don't mind about the headroom/breakup difference between 100w and 50w.

What I'm exploring, since I have now two EL34 amplifiers, is to take a pair of JJs from my JCM800 2210 to have as spare in case I need in the future, tubes are very expensive now so I might do that.

 

[Gene Ballzz]

Not really what I'm after, I already have a Marshall Power Brake to tame the volume, and also I don't mind about the headroom/breakup difference between 100w and 50w.

What I'm exploring, since I have now two EL34 amplifiers, is to take a pair of JJs from my JCM800 2210 to have as spare in case I need in the future, tubes are very expensive now so I might do that.

As mentioned by @Pete Farrington , using just two tubes may possibly shorten their useful life. So, what are you really gaining?
Your Amp, Your Tubes, Your $$, Your Choice!
Gene

 

[d3vCr0w]

As mentioned by @Pete Farrington , using just two tubes may possibly shorten their useful life. So, what are you really gaining?
Your Amp, Your Tubes, Your $$, Your Choice!
Gene

Oh, don't know how but for some reason I missed Pete's comment, yeah that's what I really needed to know, I read somewhere else that the current levels would increase inside the amp, and that confirms it, therefore in the long run doesn't seem to be a wise thing to do. I'll leave it as it is.

Thanks everybody for the replies.

 

[Gutch220]

Oh, that makes sense now, in my case I have an 8 ohm cab and the impedance selector from my amp is set to 8 ohms obviously, so I should set the impedance selector to 4 ohms and still use my 8 ohm cab, is that correct?

yup.......the amp knob will be 4 ohms but the speaker cabinet will be 8 ohms

 

[Dogs of Doom]

that amp has a built-in attenuator...

but... it also has a design flaw, where, if you run it hot, it has a few failing points. #1 being the molex connectors between the main board & the output board. There's a couple more things, Lee outlines in his fix/repair video...

 

[d3vCr0w]

that amp has a built-in attenuator...

but... it also has a design flaw, where, if you run it hot, it has a few failing points. #1 being the molex connectors between the main board & the output board. There's a couple more things, Lee outlines in his fix/repair video...

Yes, in fact I got it for a bit cheap because it has exactly that same MOLEX connector problem (it burned out as usual). I'm going to fix (hopefully) it whenever I have time.

Lee Jackson designed this amp but Ampeg cheaped out on certain things to save money, however after doing these mods, the amp should be good to go for years and it's quite a beast!

 

[Dogs of Doom]

Yes, in fact I got it for a bit cheap because it has exactly that same MOLEX connector problem (it burned out as usual). I'm going to fix (hopefully) it whenever I have time.

Lee Jackson designed this amp but Ampeg cheaped out on certain things to save money, however after doing these mods, the amp should be good to go for years and it's quite a beast!

yeah, but, in the meantime, I wouldn't do anything that will push the power section. On that one that Lee fixes, he reroutes a high voltage wire direct to the power board, because it fried a spot on the main board.

I'd do everything he does in that video...

also... the attenuator will be hard on the power section.

anything that causes heat to build up.

I have a VL5001 (single channel), that needs worked on still.

 

[d3vCr0w]

yeah, but, in the meantime, I wouldn't do anything that will push the power section. On that one that Lee fixes, he reroutes a high voltage wire direct to the power board, because it fried a spot on the main board.

I'd do everything he does in that video...

also... the attenuator will be hard on the power section.

anything that causes heat to build up.

I have a VL5001 (single channel), that needs worked on still.

That's right, I intend to do everything he does in the video, I won't really use the built-in attenuator because I have a Marshall PB100 that's more than sufficient.

What have you done to your VL5001 so far?

 

[Dogs of Doom]

That's right, I intend to do everything he does in the video, I won't really use the built-in attenuator because I have a Marshall PB100 that's more than sufficient.

What have you done to your VL5001 so far?

nothing yet...

it was working fine, then I had it in storage for a while. When I dug it out, it had a hum, so I just turned it off & it's back in storage. I don't have time to mess w/ it at the present, as I've been pretty devoted to bass, keyboards, harmonica & vocals for certain projects...

I hardly have time to plug in a guitar right now (for the last 2 years or more, really). So, I'm running my SVTs & at home, my PF-50T.