#1
My jcm 900 has a stamp type thing that I don't usually see on these type of amps. The stamp reads "Marshall 5881". The strange thing is, that I bought the amp with EL34's in it. Is this a sign that my amp has been modded?



I've been thinking about replacing my tubes, and any advice will help me out a lot.

I also have a side question: Is it normal for these amps to have Sovtek preamp tubes in them? From what I've heard, ECC83's are the standard for 900's.
#2
First, many 900s came with 5881s. Most preferred EL34s though and made the switch. So yes, it was technically modded but it's no big deal.

Second, Sovtek is a brand. ECC83/12AX7 is a type of tube. And Sovteks are quite common and cheap so it's likely a previous owner put them in,
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#3
Quote by mmolteratx
First, many 900s came with 5881s. Most preferred EL34s though and made the switch. So yes, it was technically modded but it's no big deal.

Second, Sovtek is a brand. ECC83/12AX7 is a type of tube. And Sovteks are quite common and cheap so it's likely a previous owner put them in,
yep
#4
So if I changed tubes, would I be safe installing any kind of tube? (though I'll prob stick with EL34's) Besides biasing, is there anything keeping me from the type of tube I could put in?
#6
Quote by andyhatescrass
So if I changed tubes, would I be safe installing any kind of tube? (though I'll prob stick with EL34's) Besides biasing, is there anything keeping me from the type of tube I could put in?


For the preamp, you can install basically any preamp tube you want. For the power amp you're going to have to rebias (even if you stick with the same type of tubes) if the amp is not cathode biased or fixed resistor bias.
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#9
Quote by forsaknazrael
if it's been properly modded, as in, the screen resistor values are correct for an EL34, all you would need to do is rebias.
I hope they did that right, haha.


How can I tell if the resistor values are right for my tubes?