Jesstaa

Okay, so a while ago I sent Eurotubes an email asking what tubes would sound best in my Marshall JCM900 (For mostly thrash/NWOBHM), and they suggested KT-77's (It was sent out stocked with 5881s).

But I've been getting a little confused lately, people have been saying that KT77's run exactly the same as EL34s, meaning that I would have to modify my amp to run them, while others are saying they're between EL34s and 6L6/5881's, meaning I would only have to adjust the bias. Which of these is true? If modification is required, could someone provide me with a list of parts I'll need/instructions.

Also, will the tube retainer things need to be replaced, because they sit pretty tight on the KT77's (I haven't fired it up with them in, but I've chucked them in just to see if they'd sit in nicely)

Thanks,

Jesse.

Edit: Don't know if it really means anything, but the top of one of the boxes for the tubes says 46, and I also asked for a hotter grade of tubes when I ordered them.

Double edit: It'd be helpful if I could have this answered by tomorrow, because that's when I'm gonna try and get it working again.
Also, the forums are telling me there's a reply, but I can't see it, if other people can see it, could you please quote it for me.

Uber final edit - Nvm, installed them, and they sound GREAT. But I think my amp was already modded o.0

Marshall Amps

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MartyStrat54

You like to skate on thin ice, don't you? You did bias the tubes, right? I doubt if your amp has been modded. Did you tell Eurotubes that your amp came with 5881's? Do you know what your plate voltage is? Just curious. You just can't put tubes in without biasing them. I didn't read any place where you stated you biased the tubes before using the amp. I hope you did.

Marty

Jesstaa

Yeah, I biased it, it was the only reason I hadn't changed the tubes earlier, cause I didn't have a multimeter. And I told eurotubes I was putting it in an amp that came with 5881's.

My only problem is my bias doesn't stay put, I can get it up way past 50 (I just chucked it up to see what my limits were, then put it straight down (When I had my old tubes in)), but it wont stay where I set it, I set it at 38 the other day and it went up so high that the tubes almost red plated (saved them).

I'm gonna take it to get serviced and hopefully fix this bias issue, because now if I set it to 32 it'll end up at like 40 within 10 minutes.

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