Marshall JCM 900 SLX Tubes - 5881 or el34?

  • Thread starter Thread starter Cap217
  • Start date Start date
C

Cap217

Active member
I just got another slx and it shipped with el34 tubes installed but when I took the chassis out it says 2100 slx 5881 on the side sticker. I forgot that some shipped with 5881 in the past along with el34.

How can I tell if this should run 5881 or el34? What do I need to do here? Are the interchangeable?
 
how do I tell? Seems that it ran el34 for a while.

I saw other slx that would say 5881 on the front. This doesnt.

25-BFB26-C-056-F-4214-B57-A-469-FDE6760-D7.jpg
E413-BC99-CAA8-46-C5-85-E0-2-FEA57-CE4-C97.jpg
CCB8-BCEF-10-BA-4-ACC-9-B8-E-178-AE020399-A.jpg
A624-E652-2-B86-4889-B5-AC-06-D46-F1-BB868.jpg
6555-FC34-08-BF-40-C9-A72-A-C4139969-D69-A.jpg
0-D88-AEE4-A1-A4-4-DC1-952-C-D43-B88-BFCE3-F.jpg
 
do you have a multimeter and/or bias tester
It won't hurt your amp to turn it on with the wrong bias tubes in there, but you don't want to play like that.
 
here is what i am finding:
5881: screen resistors 470 ohms, R28 47K
EL34: screen resistors 1K ohm, R28 22K
 
Yeah. You should post this in the tech side, someone will be able to easily identify. I am a novice. But I can tell you that piggy backed resistors are great. just gotta figure out which bias it is for. what came in the amp when it was shipped? If it was el34, then it that is probably good.
 
Smashedguitarist said:
Yeah. You should post this in the tech side, someone will be able to easily identify. I am a novice. But I can tell you that piggy backed resistors are great. just gotta figure out which bias it is for. what came in the amp when it was shipped? If it was el34, then it that is probably good.
Click to expand...
I know less than you here...

So looking at the resistors we should be able to tell?

And the difference is only biasing right? So if I get these el34 biased At 32ma then I’m ok, right?


I’m looking at other slx and the 5881 ones all have a sticker by the power tubes that say use 5881.

No other slx has piggyback resistors there though. All I see is the smaller brown one. 5881 or el34.
 
Last edited:
If I am reading the colors right on the blue it’s 470 x 10 = 4,700. I’m assuming the 4th color is brown here.
 
that bias resistor was added that originally came with 5881's
 
Seems that the 5w 1k resistors means el34. The amp is going from 470 plate voltage to 460 to 430 then stayed at 430. Im not sure whats wrong but I might just return this vs worrying about fixing it. It sounds like shit and I only did a few chords before I realized what was happening.

Or could the power tubes be bad and doing this?
 
I have a SLX 2100 EL34 do you want me to take pics of something on the board?
 
oh shit, man. you are golden then on returning if you cant get this figured out
 
You must log in or register to reply here.
Back
Top