tube swap question for Marshall 25/50 - Jemsite
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post #1 of 3 (permalink) Old 10-14-2010, 10:46 AM Thread Starter
Join Date: Oct 2010
Location: North Carolina
Posts: 11
tube swap question for Marshall 25/50

ok, I 'have searched the forums and can't find an answer to this question:

I have an old Marshall Anniversary Jubilee series head that has el34's currently. can I safely use 6l6gc's without a re bias? I am handy with a multimeter and feel comfy with doing it myself. thanks in advance :-)

This is only my second post so the forum won't let me attatch a link for the schematic but it can be found by googling "Marshall 2550 schematic" has the easiest to read. Mine is the version 2 2553 and my serial number is in the 7k's

Thanks for your time
Pinfinity is offline  
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post #2 of 3 (permalink) Old 11-09-2010, 04:19 AM
Join Date: Aug 2009
Location: Red Hook, NY
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Re: tube swap question for Marshall 25/50

You shouldn't even replace the EL34 tubes with new EL34s without a rebias. I don't know if you can run those tubes in that amp at all. At minimum you may require a few resistor changes to allow the amp to be properly biased. Try posting on the Marshall forum. There are a few techs that hang out there and will give you a quick answer on this.
Riffraff is offline  
post #3 of 3 (permalink) Old 11-09-2010, 09:53 PM
Join Date: Oct 2010
Location: Modesto, Ca
Posts: 36
Re: tube swap question for Marshall 25/50

they will more than likely work, but the bias and plate voltage may be incredibly off which will both sound bad and possibly cause damage depending on how far off it is. As riffraff mentioned.....this is because of the resistor changes in the power supply section that is usually requires to run 6L6 instead of EL34

but i have a question..............why do you want to run 6L6 in that amp anyways?
Kev-o-matic is offline  

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