Amp smells and One tube is brighter

[vonFrenchie]

Hey All,

So I brought my "new" amp home yesterday. Its a 1990 JCM900. It wasn't until today that I got the chance to turn it on because my speaker cable somehow got lost in my house.

So I turn it on and I'm playing some Metallica, Death, Slayer... you know things you'd play with as much gain as possible. I don't have the thing cranked. The preamp is around 8 and the master volume is at 2.

I play for a good 5 to 10 minutes when I start to smell something. So I turn my fan in my room off and keep playing. I locate the smell as my amp. I check out the back and one of the power tubes (this is the 50 watt model so there are only two) is much brighter than the other.

Both tubes are in all the way, both of their spring holder things are on. I tried running it in 8 ohm mode, 16 ohm mode (yes I had the right speaker load running both times), high and low power mode. I still can't figure this out.

I am willing to attribute the smell to burning dust, if it will ease my mind. But what do you guys think I should do about this?


edit: Even with the worry it sounds really good. I turned the preamp down and turned the gain sensitivity down and got some nice bluesy sounds out of it. Now I can start a BB King/Pantera cover band!

[JFrankParnell]

Ya know, there's just nothing like the smell of a vintage amp. Old tolex or tweed, nauga hide, hot glass and dust, 30 years accumulation of various smoke, dried beer. I love the smell of vintage amps in the morning They oughta bottle that smell and sell it in a spray bottle!

Sorry, vonFrenchie, I know this didnt help at all. Ima go out to the jam room and sniff my Bassman 8)

[vonFrenchie]

Actually Frank, it kinda did. I was worried that my amp was so angry that I had bought it that it was trying to kill it self. Turns out it was just angry because no one has taken care of it for a while. I wiped the dust out and made sure the tubes were snug. Smell - mostly gone from an old man's house strength to leather wallet strength.

Also... it rips! I know that the 900's aren't known for being "amazing" or "THE Marshall." But this puppy can scream. I run a Digitech Hardwire Valve Distortion into it. It goes from warm, round bluesy tones to full on metal without batting an eye.

It seems like this amp has been around the block a few times, then a few more, then a few more blocks. And that in no way is a bad thing.

[sumgai]

vF,

Is the tube is merely brighter all the time, or does it pulsate brighter and dimmer as you play? And for that matter, what color is that glow? Specifically, I'm looking for a blueish cast to the glow. That blue may be bright or dim, and it may be 'mixed' with the orange glow of the heater, or it may be blue all by itself. But if you detect any blue at all, no matter how small, the tube is on its way out the door - blue means a vacuum leak, period.

If it's a red or orange glow, that usually indicates a tube that's being driven too hot (low bias, or too much B+), or the heater (filament) is on the verge of failing. Tubes in this condition aren't necessarily going bad, they may live for years yet. 'Tuning' the voltages might (should) reduce the glow factor, but that procedure may also alter the tonality of the amp. Not 'for sure, it will' alter the tone, just 'might' alter it.

Hmmm.... I recall now a Rivera amp I once had in the shop. It had the craziest B+ supply chain I'd ever seen. But it boiled down to one of the output tubes going crazy, like yours, only occasionally. The real issue turned out to be the B+ to the inverter stage, it was heating up a resistor that was failing, and when the resistor temporarily 'shorted' due to that heating factor, it would drive the tube nutso (not Nutz!). Took me awhile to track that down, it was first for me. All of which points out that sometimes problems can be tricky to solve, but thankfully they're usually pretty easy (by comparison).

You should try swapping the tubes, and see if the brighter tubes moves to the other socket, or if if stays put. That will tell you if it's just the tube itself, or if there's a bad component that's "abusing" the tube.

HTH




sumgai

[vonFrenchie]

One tube is brighter. It is a solid, consistent bright... BUT the tubes will switch sometimes if I turn the amp to standby or off. I was playing for a few minutes and the right tube was brighter. Then I turned it to stand by, grabbed a sandwich and came back to fire it up and the left tube was brighter this time. So I assume it isn't the tube. I will however swap them and put a little mark on the plastic of the tube to keep track.

It is an amber orange. The typical tube color. It is pretty warm too, not piercing. The silver on the top of the tube is a very strong metallic color. Not milky or anything so I assume it is sealed.

vF

[sumgai]

vF,

Based on your reply above, I'd like to suspect the bias circuitry, but wait...... my schematic shows that your amp has a hi-lo power switch. What happens when you toggle the amp to the other position? Does the tube glow in both states (hi, lo), or only in one of them?



sumgai

[vonFrenchie]

I played it for 10 minutes in high power and 10 minutes in low power. Weirdly, there was no difference. I guess my amp was just having one of those days. Both tubes emit a nice, warm, fuzzy glow.

Thanks for the help,
vF

[sumgai]

vF,

Whaddya mean, have a nice day? Does the problem no longer exist?

And if the power switch seems to have no effect, then try the amp at, or nearly at, full-bore. (You might wanna consider some ear-plugs here....) If there still seems to be no difference in either the output level or the tonality, then we need to investigate what's up with that.



sumgai

[ijustwannastrat]

Is it possible that it was just your mind playing tricks on you? I know I've gotten caught with that before (right after reading about it in a magazine)

[sumgai]

Mar 8, 2011 9:49:49 GMT -5 ijustwannastrat said:

Is it possible that it was just your mind playing tricks on you?

Uh oh..... Looks like the Jedi have been outed! This ain't gonna have a pretty ending.

[vonFrenchie]

My satisfaction was premature. I turn the amp on, leave it in stand by for a good 5 or 10 minutes and then when I switch it on a strong blue glow lights up vertically across a third of the tube. I switch it into stand by, the blue is gone, stand by goes off once again... blue comes back.

Hopefully I can just call up the music show and see if they will retube it for me for free.

edit: I've been reading and a lot of people say that the blue glow isn't much to worry about.
www.tdpri.com/forum/amp-central-station/219934-can-someone-explain-blue-glow.html
forum.grailtone.com/viewtopic.php?f=16&t=30260

It sounds fine to me but I am far from a tube expert. I'll take a picture of it in a bit.

[thetragichero]

always retube and BIAS (have you biased the amp with YOUR wall voltage?) a used amp
i believe blue glow is okay in power tubes, but not preamp tubes... no?
for wit: www.marshallforum.com/workbench/12473-blue-power-tube-glow.html

[vonFrenchie]

You try retubing when you're working minimum wage. I was planning on getting some Tung-Sol or Golden Lions but college is more important than tubes.

[thetragichero]

i never had a tube amp when i was working minimum wage.. it was always solid state

no need to get defensive... we're all friends here

keeping an amp tubed and biased is more of a maintenance concern than anything else (like oil changes in a car) and can help avoid more serious problems down the line (not so much preamp tubes, but bad power tubes can take out your output transformer, which will cost a LOT more than tubes)

[vonFrenchie]

I wasn't "fighting back" or anything. My point just came out wrong. Sorry about that one.

I am going to let it it ride for a few days then we will see. Make sure its well documented and what not. If all else fails I'll spend the 50 bucks on new tubes after my next paycheck. I would take pictures now but I can't find my camera.

[sumgai]

tth,

vF has been here almost as long as I have, so I think it's safe to say that he's got a pretty thick skin, at least here in The NutzHouse.... Not to mention that even at an earlier age, he was always helpful towards others. IOW, he has good cred here, and I for one am glad that he's able to spend with us whatever time he can afford to spend.

But I understood what you said, too, so this isn't a flame or anything, I just thought you'd like to know.

~!~!~!~!~

Frenchie,

Take my word for it.... blue glow means vacuum leak. It's a product of oxygen oozing into the bottle and reacting with the 'getter', a supposedly inert gas that's used to neutralize the remaining heavier gasses as the tube is being evacuated. Once started, there's no going back. It may be quick, or it may be slow, but it's as sure a bet as death and taxes.

What's the cost of a college textbook? What's the cost of power tubes of reasonably good quality? When you need a textbook for next quarter, do you skimp on a few Starbucks coffees in the morning for a week or two? Try that plan for saving up for a pair of tubes.... ;D

Sorry if the news is bad, but at least the cure doesn't have to be equally as bad..... I hope.




sumgai

[vonFrenchie]

Actually, I am pretty fiscally responsible, no morning coffees and no every day lunch stops for me. I do buy too many books though. Definitely haven't used my philosophy book at all this semester.

A good pair, 50 bucks. With all my bills for this month coming up and my pay check I will definitely be able to afford a retubing and biasing. I'm sure you all understand my frustration though. You play something in the store for a long time, it works, sounds great so you buy it. Then once you get it home it causes problems. That's my only frustration, not anyone on here because everyone I've spoken too on here (at least as I can remember) have done their all to give an honest and clear answer.

Bad news is still good news to me. The way I see it I JUST have to get tubes right now. Not tubes, a transformer, new this new that, ya know? Hopefully...

[vonFrenchie]

So I found my camera and camera cable. I took a picture for each mode (high/low and 8ohm/16ohm). It is running into a custom built cab what has 2 Eminence Man-O-War speakers. Each are rated at 125 watts and are wired to be used in stereo (8ohms) or series (16ohms obviously). Like I said, I took a picture of it running at 8ohms/25 watts into an 8ohm load, 8ohms/50watts into 8ohm load, etc etc. All this work to basically get the same picture four times.

Here it is, what my tubes look like when they aren't in standby. Standby just lets off a soft amber glow.

As you can see there is a distinct line of blue and a reddish orange-ish purple-ish streak. I'm guessing new tubes. I should probably take off the screening caps from the preamp tubes to give them a once over just in case.

[cynical1]

Granted, my experience working in the shop is a bit dated, but some things remain constant. If you sell something to someone, and it develops issues, then you do what is reasonable to make it right.

The adage of "do it right they tell 3 people...do it wrong they tell 20 people" still rings true.

If it were me, and I just bought a used amp, and it developed tube problems, I'd drop by the shop I bought it from and calmly explain the issue. If the guy who owns the shop is cool he'll cut you a deal on a new set of tubes...as in "for cost". If he's really righteous he'll swap them for free. If he just shrugs and says "tough sht"...well, then it's time to politely excuse your self and tell him you've got to find 20 people to talk to...

At this point, there isn't a music store in Milwaukee that can afford a bad rap.

The only other advice I can offer is get the Hell out of Milwaukee after you graduate...

Happy Trails

Cynical One

[vonFrenchie]

1: My friend works at this shop. They all know me there, they all know that I wouldn't make up a problem, create a problem, etc. I am planning on doing exactly as you explained this coming Friday. I highly doubt the amp tech will dismiss me as a looney. This place has an impeccable track record for service... but there is always a first time for everything.

Its a place called Cream City Music. Off of highway 43 just outside of Milwaukee. If you're ever in the area, check it out. Sorry, I felt a little bad considering that I had fallen directly into the 3/20 rule. I figured I'd bump that 3 up to a few more people.

2: Yes, I am getting out of Milwaukee when I graduate. As much as I love the city.... I can't afford to go to law school at Marquette.

Thanks Cynical, Sum and TTH

[sumgai]

Mar 8, 2011 22:15:50 GMT -5 vonFrenchie said:

I can't afford to go to law school.....

Better watch out newey, a Young Turk is headed your way!

[sumgai]

vF,

That's just what you didn't wanna see, sorry to say.


BTW, the brown base(s) might date those tubes as pretty old. I'm thinking that they may even by the original units installed at the factory. Reason enough to think about updating them.




sumgai

[ijustwannastrat]

Just because I couldn't find the answer in previous posts, can....


vF keep using the amp in it's current state, with no negative side effects?

[thetragichero]

the answer is a 'maybe'
maybe it'll be peachy keen, maybe the tube will short and take out the OT
as i said before (admittedly not so eloquently), it's preventative maintenance
if only my girlfriend understood that about oil changes in her car...

[vonFrenchie]

I agree with TTH. From what I've read blue glow is either a leak, or its just a random occurrence. If it is still around by Friday I will get the amp retubed. If not I will wait until April to do it.

I don't let any girl I know (except for my sisters) go get their oil changed without a guy being there. Those guys at autoshops are pretty cheap. I don't really blame them though.

And sum, you could be right about the age. But I KNOW these aren't factory standard. They are Mesa tubes. Honestly, I don't really like them. A tad too muddy.

If newey is a criminal attorney then he has something to watch out for. If not, no worries. I'm looking to be a DA or something along those lines. Keep the streets safe, ya know?

[sumgai]

Mar 9, 2011 10:34:11 GMT -5 ijustwannastrat said:

Just because I couldn't find the answer in previous posts, can....

vF keep using the amp in it's current state, with no negative side effects?

As TTH states above, it's not a matter of if, it's only a matter of when. Even when they are new, you can realistically say that tubes are living on borrowed time.... it's only a matter of when.

Experience dictates that the small amount of blue I can see in vF's image shouldn't be cause for immediate replacement, like in the next 24 hours, but at the same time, I wouldn't play out, for a paying gig, until they've been replaced. As a practice amp, they could go for perhaps another year, but they might go only another few weeks - you never know.

Things like the shock of traveling, heating up when cold (from the back of the van to the stage in 5 minutes or less....), all of these could contribute to a quick demise. Babying the thing, it might last for, like I said, a year or more, even if played every night. But I can't stress enough the embarrassment factor of having an amp take a dump on you, right in front of a paying audience. That's an experience that no one wants to, errrr.... experience. And particularly when it could have been avoided. Know what I mean?

I'll leave the obligatory car analogy to TTH.


HTH




sumgai

[Yew]

I used to play casually in a band with a guitarist that used an old marshall valve combo, my Little MG10 marshall was always in the corner, just in case....

[vonFrenchie]

So, found the problem. The plate on one of them is malfunctioning... maybe.
Here is the latest picture.


I realize that tubes have a short life. Two years if you're really lucky. So I figure I will show this picture to my amp tech and get a retubing and rebiasing. I just got the amp less than a week ago and they have a 10 day return or repair policy.

[newey]

If newey is a criminal attorney then he has something to watch out for. If not, no worries. I'm looking to be a DA or something along those lines. Keep the streets safe, ya know?

No worries here. When I was an idealistic young lawyer, I wanted to do criminal law, so I did a few cases. I soon learned that there are 2 major drawbacks. First, your clients lie to you, and second, they won't pay you.

I quickly found other things to do. Of course, things are different if you're a prosecutor- at least you get paid! Although, I'm not sure I'd want to be a State employee in Wisconsin anytime soon.

I applied to Marquette Law School, but as I recall they didn't want me, and I had already accepted elsewhere before they told me so. So, the feeling was mutual.

Anyway, good luck with both your amp and your future endeavors, vF!

[cynical1]

Mar 9, 2011 22:46:49 GMT -5 newey said:

Although, I'm not sure I'd want to be a State employee in Wisconsin anytime soon.

I'll give you a big Amen on that and second your sentiment, Counselor...

And they don't pay you here, either...they'll just give you cheese and used tractor parts...

HTC1

Escape to from Wisconsin