Retubing an old old marshall head

M

moho

New member
Hi I want to retube my marshall head i bought second hand about 2 and a half years ago. I don't know the tube maufacturer that is in it at the moment, however i know they are EL34s. I have read about biasing and am completely confused by it. Also is there any SAFE way to make a 100watt head into a 50watt by just using 2 power tubes instead of 4? My amp needs to be put up way too loud to get the full tone at the moment. It's a Marshall JMP Superlead from '79. I have two spare power tubes and two spare pre tubes at the moment but have no clue as to their quality as they came with the amp when i bought it (ebay).

Thanks!
 
people on this board have recommended Eurotubes a number of times. i've checked it out and there is a wealth of information there including videos on biasing. marshalls are covered.
 
I don't think you can operate the amp with any of the tubes removed. They all work together and depending on the design, share the workload of amplification. The best thing to do if is too loud is to trade it down for a smaller one. You may be able to sub the tubes with ones of lower gain, but that will most likely change the sound significantly. Big amps are built to sound good loud, will be hard to get around that.
 
Soundmind?? said:
I don't think you can operate the amp with any of the tubes removed. They all work together and depending on the design, share the workload of amplification. The best thing to do if is too loud is to trade it down for a smaller one. You may be able to sub the tubes with ones of lower gain, but that will most likely change the sound significantly. Big amps are built to sound good loud, will be hard to get around that.
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actually, you can on most all tube amps. i think there may be a few exceptions but i can't remember. check the link i posted above. i learned a LOT about tube amps from reading the web site.

my carvin v3 has a switch to go from 100 to 50 watts and it does just that. it disables/enables two of the four power amp tubes.
 
Thanks Castlerock, I posted my response before refreshing the web and did not see your post. Been a long time since I studied tube circuits. Didn't know guit amps were designed that way. I will be reading up on the subject now that I own a couple of them again. We learn something every day...if we pay attention in class!
 
Here is the big problem with this idea: 50 watts isn't that much quieter than 100 watts. Especially when pushed into distortion. It will break up faster, but it won't sound like a 50 watt head. 50 watt heads have 50 watt output transformers that saturate faster. Tube amp saturation comes from more than just the tubes, there is also transformer saturation and power supply sag that adds to it.
 
Soundmind?? said:
Thanks Castlerock, I posted my response before refreshing the web and did not see your post. Been a long time since I studied tube circuits. Didn't know guit amps were designed that way. I will be reading up on the subject now that I own a couple of them again. We learn something every day...if we pay attention in class!
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that's cool bro. i've picked up a lot of good info and resources here. i'm just keeping it circulating. =]

i've learned a lot from the eurotubes site. it's an excellent resource. i'll have to send bob a thank you note.
 
Farview said:
Here is the big problem with this idea: 50 watts isn't that much quieter than 100 watts. Especially when pushed into distortion. It will break up faster, but it won't sound like a 50 watt head. 50 watt heads have 50 watt output transformers that saturate faster. Tube amp saturation comes from more than just the tubes, there is also transformer saturation and power supply sag that adds to it.
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good point. for those on a tight budget though, that's the most economical option.
 
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