I have to buy some new tubes for my Marshall JCM900 4100.
From the web site it looks like four 5881 Power Amp tubes and three ECC83 Pre Amp tubes.
The local music store has a few brands to choose from according to the guy on the phone. He also says I might want to bias them and get matched pair. Not sure what that means but I'll probably get that done.....
What brand of these tubes do you recommend? Any reason some are better (long life/tone etc).....
I like the Sovtek or the Electro-Harmonix in my Peavey Butcher, and the Sovtek in my Fender evil-twin.
If you have 4 power-amp tubes you, ideally, want a "matched quad"--which means that the factory has measured the cathode "plate-current" on each of the 4 tubes to ensure that they're drawing a very similar (within 5%)
amount of current.
And, it's not really the tubes that get "biased", as much as it is the circuitry that the tubes complete. In other words, you should always have the bias adjustment after installing new power tubes. There are a few amps out there that don't require this bias adjustment, but it never hurts to use matched tubes.
Also, many amps have an "output balance adjustment". It's a trim used to balance the push/pull sections of the amp, and should be adjusted "after" the bias adjustment.
Your owner's manual should explain much of the details involved in these adjustments--i.e. you'll need a voltmeter set to the most sensitive DC scale, let the amp warm up first, exactly where the lead-probes should be touched, what VDC you should adjust to...
If you're not familiar with using a voltmeter, or you just don't feel comfortable poking around in places that could fry you or fry your amp, take it to the shop. That said, it's really not all that difficult to do--especially
with so much reliable reference material available.
Here is some good reading:
http://www.thetubestore.com/index.html
http://www.thetubestore.com/powertubeinfo.html
