Ok, I have a MARSHALL "JCM 900" that takes 5881 tubes. I have 5881 "Sovtek" tubes I would like to install. Is there any chance that I could install them myself without taking them to a professional? (which lives hours away and I do not drive)

if they're the same you should just be able to pop 'em in. sure it'd be nice to bias them and you should for each tubes but if thay are the same dont worry about it.

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Exactly. Turn the amp off and wait a while for all the high voltage to drain to ground, then unplug it. Exchange the tubes, clean off any fingerprints or whatever with alcohol. You should thoroghly clean all the dust out while you're back there (used compressed air can preferrably). If it sounds funky to you, then take it in to get biased or have a friend with an oscilloscope (and a signal generator) do it for you.

Unless you know how to bias an amp then have a tech install them.

Buying new tubes and not biasing them is retarded and a waste of well earned money.

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I wouldn't mess with a tube amp if I didn't have skills. Just take it to a tech so you dont screw something up.

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has anyone here actually sucessfully installed power tubes ?

yes. but I had them biased by a tech.

but if they're the same type they should be vary similarly biased right?

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Not necessarily. If you buy a matched set from Groove Tubes or similar, you will get a cleaner sound, but the bias is set in your amplifier and all tubes are slightly unique so you should definitely adjust the biases any time you replace the tubes unless you're flat broke and don't have a clue how to do it yourself. If you know it's not adjusted, just don't crank it past 7 on the volume and you shouldn't have any problems other than some non-harmonic distortions.

my amp has auto bias circitry.ita kinda sketchy if you ask me but hey at least i don gotta get it moddoed.

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Not really, all tubes draw different currents.

Auto bias is a crock of shit if you ask me..

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anyone wanna buy a practically new pair of groovetube 6l6's? $25+shipping.

i was cleaning my band room and i found them... i remember i bought them and then had to give the the amp they were supposed to go in, a bv120h i was barrowing at the time with two blown powertubes, back.

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yeah i am interested but i need to wait till later to confirm if im ready to buy them. where do you live? will you take a money order?

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ok i emant to post this here.
what are the tonal charactoristics and differences between 6l6s and el34. what are thier tendecies and which do you prefer?

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Quotes are from "The Tube Amp Book" by Aspen Pittman:

"The EL34 has smaller components than the 6550 (roughly same as 6L6) and they are sealed in a thin bottle with a softer vacuum. This means they run hotter and distort sooner when you attack the string. They kind of act like light gauge strings in that they "bend" easier and so the distortion character is more controllable and less penetrating. Straight rockers and R 'n' B player usually prefer the soft compressed tone of the EL34, while bass players and heavy metal guitarists will like the powerful and tight sound of the 6550's. For what it's worth, Jim Marshall dislikes the 6550s in his amps and is a strong promoter of the GT-EL34's."

The author specifically recommends the European EL-34B

"The 6550 is heavier and more reliable."

6550a is made by GE
6550c made by China and has less power but distorts earlier

STR 6L6 - "These STR 6L6's are widely regarded as the best tube available and are standard equipment on Fender, Peavey, Acoustic, Mitchell and Boogie."

6L6C - Made in China, has 20% less power, softer tone and earlier distortion tendency than other 6L6's.

That's enough typing for me. I would highly recommend the book. It also has schematics of all of the classic guitar and bass amps. I'm in the process of constructing a 1970 marshall amp in a rack box from scratch with the help of this book...

wow. good luck with that.

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Thanks, but I don't think I'll have any problem with that project. I need luck figuring out how to tab "Kill as One" by Death Angel. The second riff is breaking my balls...

Sidenote to guy who started thread... The 5881, KT66, and 6L6 tubes are the same tube. 6CA7, KT77, and EL-34 are the same tube.

You always want to have the bias checked and adjusted if needed everytime you change power tubes. Some amps such as most Peavey and Mesa amps have the bias set to a cold value that usually allows you to just plug tubes in and not worry about bias. The problem is that some tubes are outside the normal range and could cause a problem. There's also the fact that you just spent your hard earned cash on the best tubes you could buy and you're not gonna get the best tone out of them if you don't have it biased.
The other side of having a tech check the bias is that this gives him a chance to get in there with test equipment and see what's going on inside your amp. MANY times I bias an amp and find problems that the owner wasn't aware of. Many time a failed tube will take out a screen grid resistor and without a tech going in your amp you'll never know. A good tech will also give the pots and jacks a cleaning while he's in there. Your amp needs some TLC every once in a while to keep in running at 100%. Filter caps should be tested and possibly replaced on amps 10 years old or older.
If you like crappy tone just plug them in, if you want the best tone possible take it to a tech and have it biased.
The only amp I'm aware of with auto biasing is the BV combo. There's basically two types of bias, fixed bias and cathode bias. Cathode bias does self adjust but only to a point. Fixed bias could be set with hard wired parts or it could have a bias pot, it's still called fixed bias because once the bias value is set it doesn't change.
Jerry

The god of tube amps has spoken.

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ha i have an old bv combo(yes). the univalve seems to have the most advanced autobias ive seen. seen it work, it was cool. the guy just played one thing on certain tubes then took 'em out and plugged diff kind in.

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I'm no God..... believe me! But I do appreciate the pat on the back.
Jerry

anyone else like thd amps.good a class amp imo.

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