in the case of a blown tube...question

O

overwound

New member
Hey all. So my situation is a friend loaned me two amps to use on a recording project - a marshall JMP 100w and a Silver Jubilee 2550.

I am no tech, so what I don't get is in the unlikely/unfortunate event that a tube goes bad, what would you recommend I have on hand in the way of replacements?

If there's no multimeter and bias probe on hand in the studio (not like I would know what to do with them anyway), I'm assuming I couldn't just put new power tubes in there, or am I wrong?

What about the pre-amp tubes - do you have to bias for those too? Or can you swap a new one in?

I have already stocked up on fuses, but I realize the fuse really just indicates a problem somewhere else..Thanks for your help.
 
Re: in the case of a blown tube...question

If cost were no object....

..and it's okay with your friend...

I would take the amps to a tech, have the amps completely gone through, and then have him install a new set of say, Groove Tubes EL-34 power tubes with a 6 rating, and bias the amp. Then I would have an additional one or two matched quad sets around with the same rating--if I ran into problems, I could just swap in a new set with out having to have the amp re-biased. It's not hard, changing them is basically like changing a light bulb.

You could have him use Mesa tubes, and get the same results. Or go through the Tube Store, or Eurotubes, or Doug's, and get three or four matched quads.

Pre-amp tubes...the Marshalls use 12AX7/7025s, and these do not require re-biasing. However, the tubes from different makers can sound very different. If you like the current tones from the amps--don't mess with it. Having a couple of spares on hand matching what's already in there would be a good thing; they don't wear out like power tubes, but ca-ca happens. Be prepared.

If you want to experiment with tones (again, friend approval required), then a selection of 12AX7s from The Tube Store or another vendor, can allow you to swap in individual tubes one at a time in the various sockets to see what you like best. A Tung-Sol might work in one socket, but in a different socket a JJ or EH or Mullard might sound the best. This procedure is called "amplifier blueprinting", and you can search the web for more info. Most of my amps have a variety of tubes: I have power tubes from Mesa, Winged C, Groove Tubes and Eurotube JJ's. (Keep in mind, these are matched sets.) I have Mesa, Groove Tubes, Mullard, EH, JJ, and Tung-Sol preamp tubes...a couple of amps have three different brands. So you can see that having three or four of each brand of 12AX7 can get really expensive, really fast.

Hopefully, your friend's amps have been well-maintained and will sound great without having to do any tube swapping. Fingers crossed.

You are to be commended for your foresight and willingness to be ready for any contingency...that is really great.

Best of luck with your session...hope to see you on MTV soon!

Bill

P.S. If you want to talk EXPENSIVE...the guys at Mesa Boogie told me that Fleetwood Mac guitarist Lindsey Buckingham changes the 6L6 power tubes in his Mesa Tremoverbs for EVERY show while on tour. He does use Boogie tubes, and gets a modest artist discount...but dayum...that's a lot of tubes!!!
 
Re: in the case of a blown tube...question

At your level of understanding.....all you need are the tubes.
IF there is a problem, simply replace tubes one at a time in the preamp.
Hopefully you will not have any power tube issues.
If you happen to be recording near me.....shoot me an Email/PM if the need arises.
good luck
 
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