revalve a 900 with el34

[mkstylee]

Hey all,
Anyone? If i swopped my 5881's for EL34's in my 4100 ,apart from a rebias is there any known problems/mods/tweaks i should be aware of?

Thanks in advance.

[washburn 1]

Hi mate, I'm. Sure that when I've asked about trying 5881s in my MA, others have said its not just a straight swap so best not to chance it until you have researched a little more. Look at my early questions within MA section. Good luck. Would be nice to know what difference it makes if eventually done. What's wrong with the 5881s ? In my Sound City mk 6 they sound massive. cheers, kev.

[frank9310]

I'm pretty sure you also need to change the value of the grid resistors. Call an amp tech. He'll be able to tell you or check metroamp forum.

[Mats A]

Right i had a JCM900 SL-X in the 90´s that came with 5881´s and i had it modded to take EL34´s. Back then you could get a conversion manual from Marshall that was for modding Marshalls from EL34´s to 5881´s. But you could use it and work in reverse. You need to change some resistors and some caps. There are also circuit diagrams on the net of JCM900´s with EL34´s that they originally came with before they were changed to 5881´s.

[Naggus]

Hello Guys,

I have a JCM 900 SL-X. I put some 6l6 tubes in it. When I took the bottom out, the unit had a sticker that said 5881. I'm assuming this head came stock with the 5881 tubes, but the tubes in the head were actual GT El-34s. When I replaced the tubes, I was able to bias the tubes within specifications, with a plate voltage reading of 435V. I biased at .34. As far as I can tell, the head is working fine. Any feedback will be greatly appreciated.

[mkstylee]

Cool thanks guys ,seems like theres more to it than a bias so i'll leave it alone.sounds fine stock anyways.worth asking though.

[frank9310]

[youtube][/youtube]Mats A
How'd you like the 900 Sl-X with the EL34s? I know Robin Trower used 2 of them on his Living Out of Time Dvd and man the tone he was getting,was just incredible. Here's one of several youtube clips from that show. Had a shot at buying one of those 2 when he switced over to Vintage Modern amps but I was cleaned out after buying his main #1 U.S. touring 1976 jmp 100. Sweetest sounding amp on the planet. Its funny, because I used to change amps like my underwear but nothing sounds better than my Vintage Modern 2466 that I've been playing the past few years in stereo with the JMP. They both have different kimds of fatness, richness and sustain

[JCM900MkIII]

[youtube][/youtube]Mats A
How'd you like the 900 Sl-X with the EL34s? I know Robin Trower used 2 of them on his Living Out of Time Dvd and man the tone he was getting,was just incredible. Here's one of several youtube clips from that show. Had a shot at buying one of those 2 when he switced over to Vintage Modern amps but I was cleaned out after buying his main #1 U.S. touring 1976 jmp 100. Sweetest sounding amp on the planet. Its funny, because I used to change amps like my underwear but nothing sounds better than my Vintage Modern 2466 that I've been playing the past few years in stereo with the JMP. They both have different kimds of fatness, richness and sustain

Those are Dual Reverbs, not SL-X's...

Check the amount of dials/knobs.

DR's have 10, MkIII's and SL-X's have 8

[frank9310]

Ah! Thanks for the heads up! I had a 4100 Dula Reverb that sounded horrible as it had some high gain mod done to it and couldn't get any clean tones at all. I thought they were SL-X because when Robin sold off a bunch of his gear, there were two SL-X for sale but no dual reverbs. Then again, they were selling off his U.S. backline, not the Euro stuff which is where that video was filmed (Germany). I'd have loved to hear it without that high gain mod but my amp tech couldn't figure out where the mods ended and the stock circuit began.