Tube Question
Whitty
Posts: 61
Hey,
Over the summer I bought a used Marshall JCM 800. It has Electro Harmonix tubes (red design on them, made in Russia). Anyways, I've owned this amp for about half a year, and have noticed that the tubes now have a purple glow when I turn the amp up higher, as opposed to the light orange glow they usually have.
Basically, I'm wondering if the tubes are going on me. Can anyone tell me from what I described?
Thanks,
-Mitch
Over the summer I bought a used Marshall JCM 800. It has Electro Harmonix tubes (red design on them, made in Russia). Anyways, I've owned this amp for about half a year, and have noticed that the tubes now have a purple glow when I turn the amp up higher, as opposed to the light orange glow they usually have.
Basically, I'm wondering if the tubes are going on me. Can anyone tell me from what I described?
Thanks,
-Mitch
"It makes much more sense to live in the present tense."
Toronto 2000
Montreal 2003
Halifax 2005
St. John's (2x) 2005
Boston 2010
Hartford 2013
Quebec City 2016
Toronto 2000
Montreal 2003
Halifax 2005
St. John's (2x) 2005
Boston 2010
Hartford 2013
Quebec City 2016
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that should help mitch.
I've never had that problem. Are there any sonic issues?
The thing that got me worried was when I was jamming with my band for a few hours last weekend. The signal would just disappear and then come back in a couple seconds.......I figured it was because I hadn't had my amp on for 4 hours straight before. But who knows. Hopefully it is nothing major.
What color should the tubes be glowing?
Toronto 2000
Montreal 2003
Halifax 2005
St. John's (2x) 2005
Boston 2010
Hartford 2013
Quebec City 2016
It's most definately time for a retube. Probably power and preamps. It might just be a bad pre amp tube making it cut out that is a tell tale sign you need to service it though.
check out http://www.thetubestore.com they have all the tubes you need relatively cheap pricing too.
what part of the tube is the plates? I've read that Trentino site and whatnot as well. There's nothing glowing red hot, but there's a nice orange glow in the tube, but around the bottom there is a purple glow as well, like a darkish purple-haze kinda. Almost looks like a gas or soemthing like that. Hard to explain.
Thing is, the music store here SUCKS at fixing gear, and they over charge like crazy. For example, I brought my old solid state Marshall in because it wouldn't turn on (blown fuse). Anyways, I didn't know it was a blown fuse, so I figured I'd trust them to fix the problem. 2 weeks later I get a call saying its done. Turns out it was a blown fuse.......$60 (Canadian) later, I have the amp home, and when I turn it on, it shuts off again.
Anyways, I bring the amp back to the store, the guy says "Oh yeah, he put the wrong type fuse in it. Leave it here, we'll fix it". Another week later, and another $20 bill, I get my amp back, and this time it works.
So basically, I'm a little hesitant to let this store fuck with my gear again, but it is the best Music Store in town, and the only one that services Marshalls.
Oh well
Toronto 2000
Montreal 2003
Halifax 2005
St. John's (2x) 2005
Boston 2010
Hartford 2013
Quebec City 2016
See if you can't find a few good sites on how tubes work they can answer your questions more accurately than I can.
Don't take your guitar amp back to that place, see if you can find a tube amp repair shop somewhere close to you. the JCM 800's are getting old enough in age now the Filter Caps and tube sockets probably need to be checked. Most likely they are fine. You just need to make sure you get a matched pair (50 watt) or quad (100 watt) of EL-34's so they are the proper bias and whatever 12AX7's you want. It's essentially a tune up like you'd do on your car. New tubes are like new spark plugs. Power tubes have to be matched, pre amp tubes are not as sensitive.
I suggest you contact http://www.plexipalace.com and ask them a few questions. They specialize on the older marshalls but they'll have seen more than a few JCM 800's. They are experts, just send them an e-mail.
Since we've all gone head-over-heels on analogies around here, I figured I'd put my latest up here...
Power tubes are like a team of horses. If you have one horse, you can have whatever kinda horse you want. Slow, fast, weak, strong, whatever. The wagon is still gonna move forward. Now, if you have two horses, those two horses have to work together. If one horse is fast, and the other is slow, you're gonna have trouble. Same if one horse is strong and the other is weak. If you have four horses, you have the same problem. The faster horses will wear out the slower horses, and the slower horses will hold back the faster ones. The strong horse will carry the weak horse for a while, but that just makes that horse wear out faster.
Power tubes are the same way. They have to work together, pulling (or pushing-pulling, to be precise) to make the speaker move and make sound. That's why it's so important to get matched sets, unless you only have a single power tube in your rig (like my Vibro Champ).
Now, preamp tubes are like stock-brokers. They all work together, but if one isn't doing so well, he doesn't take the whole group with him. He craps out, ends up a waiter at Denny's, and the rest of them are fine. Sometimes stock-brokers have partners, and if their partner doesn't show up to work, he can't do his job that day. So, he leaves a dead fish on his partner's pillow that night and finds a new partner in the morning.
In the same way, preamp tubes can be replaced as needed, and don't have to match. Sometimes preamp tubes are directly connected (many amps have dual-stage tube preamps, with one tube directly feeding another, usually in the "distortion" channel) and if one goes out, the other won't be able to carry the job, but that doesn't mean that the other tube can't just start working with a new tube once you replace it.
That was fun... what other things can I create metaphors for?