My First Tube Amp-Some Questions

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paulmckenna

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Hello, I have used solid state all my life, pretty much just because I havent had enough money for a tube amp. Well last week I went for it and bought a Marshall JCM2000 TSL 60 Watt Guitar Head. It was cool, except for today I turned it on and one of the power tubes wont light up. I bought it used, so I am figuring that I should replace them all, just to start fresh, and if one goes out, the others are sure to start going out too. The amp takes 2 EL34'S and 4 12ax7's. I am going to buy all Mesa Tubes. Now here are my questions.

1: Does this amp have auto biasing, or do I need to take my amp in to a pro to bias it when i replace the tubes?

2: I read somewhere you can mess your amp up by running it with no speaker attached. My amp has a direct out, so would that damage it by just running the amp attached to my computer through the direct out?

Any help would be greatly appreciated. Thanks!

Paul
 
Hi,
Pull out from it's socket the (presumed) dead EL34 and measure it between pins 2 and 7 with an Ohmmeter.If it shows around 1,4~1,7 Ohms,the filament is OK and the trouble is elsewhere.If it shows "infinite resistance",the filament is open and you have to replace it.Eventually,to be more convinced,you can test the other (health) tube in the same manner.
About replacing EL34's:Mesa's are OK but a too expensive for what thy offer (both sound and reilability).Go for "C-winged" Svetlanas and forget any hassle while enjoying a GREAT tone.
I don't have that Marshall's schemo on hand right now but AFAIK these amps aren't auto-biased but have fixed bias.Therefore,you'll need a matched pair of outputs.Just plug them in the sockets and follow what's happening:within 1-2 minutes,is one of the tubes developing some kind of a blue glow inside the glass envelope,more than the other?Or one of the tubes is redplating?Is there a significant hum coming from the speaker with all the volumes and tonestac corrections down?In this case,the settings of the trimpot(s) inside the amp,the one(s) responsible with the bias,are wrong FOR THE NEW PAIR (the settings were made to match the old tubes).
The safest way of being sure that everything is OK is to take your amp to a tech.The bias alignement is a 15-20 mins.job tops.
About your last question,yes,it's true.Running a tube amp without a load on the OPT's secondary can destroy the tubes AND the OPT (...let's hope your amp has survived the second situation).However,if such an amp runs into a PC through a DEDICATED direct out (NOT the loudspeaker's jack,the impedances are way too different) it shouldn't be a problem.
HTH!
Regards,
 
I forgot...

And,by the way...
Welcome to the next level!
...or should I call it "The Road To Hell"?!? :D
 
paulmckenna said:
Hello, I have used solid state all my life, pretty much just because I havent had enough money for a tube amp. Well last week I went for it and bought a Marshall JCM2000 TSL 60 Watt Guitar Head. It was cool, except for today I turned it on and one of the power tubes wont light up. I bought it used, so I am figuring that I should replace them all, just to start fresh, and if one goes out, the others are sure to start going out too. The amp takes 2 EL34'S and 4 12ax7's. I am going to buy all Mesa Tubes. Now here are my questions.

1: Does this amp have auto biasing, or do I need to take my amp in to a pro to bias it when i replace the tubes?

2: I read somewhere you can mess your amp up by running it with no speaker attached. My amp has a direct out, so would that damage it by just running the amp attached to my computer through the direct out?

Any help would be greatly appreciated. Thanks!

Paul
Click to expand...

Go to www.eurotubes.com
 
Le Basseur said:
Hi,
Pull out from it's socket the (presumed) dead EL34 and measure it between pins 2 and 7 with an Ohmmeter.If it shows around 1,4~1,7 Ohms,the filament is OK and the trouble is elsewhere.If it shows "infinite resistance",the filament is open and you have to replace it.
Click to expand...

If It does show that the problem is elsewhere, what could be wrong with it? Not my new amp!!! Also, thanks for that link to Eurotubes. They have a retube kit for my exact amp model. Has anyone used JJ tubes? They look to be pretty good.
 
paulmckenna said:
Has anyone used JJ tubes? They look to be pretty good.
Click to expand...

If they are good enough for Yngwie Malmsteen, they are good enough for me
:D
 
Yeah, thats pretty much why i decided on them. If Malmsteen uses them, then they must be the best. I am just scared that the problem isnt the tube though. Does anyone have any ideas of what the problem may be if it isnt the tube?
 
Tube amps are pretty reliable. My bet is it's just the tube. My mesa rectifier had a bad tube when i bought it. It sort of worked for a day and then went to shit in a hurry.
 
JJ tube are the best. I use them in all my heads. I think if you want to use the recording on the Marshall you need to put the amp in standby. This allows for silent recording. If you don't get anything out of the direct out in standby, you can't do it. NEVER EVER NEVER IN A MILLION YEARS run a tube amp without a speaker (or load) You will melt you output transformer.
 
paulmckenna said:
If It does show that the problem is elsewhere, what could be wrong with it? .
Click to expand...
It could be anything (of a smaller magnitude,if it's only a heater circuit problem).A loose contact in the socket,a broken heater wire,a cold solder,etc.Really,it's hard to say blindly but,I repeat,nothing to be scared of.
As I said,take the amp to a tube tech and relax.
About the JJ Tesla issue,it seems I'm a maverick here :D but I must confess that I don't love them very much in Marshalls.I don't say they're bad,but they just don't ring me that "Marshally bell".
Winged-C Svetlanas,however,do.
The statement "...if they're good for Yngwie,then they're the best" doesn't compute.Malmsteen's heads are highly tweaked in the voltage gain/tonestack stages and this is what makes them sound like they do,much more than brand X or Y of output tubes.I have the utmost consideration for the Eurotubes' guy because he's a real pro but the fact that he sells JJ's and treats this brand as an "one size fits all" eventually means something else (he loves fanatically these tubes,gets them cheap,etc).Of course,after all,it's a matter of personal taste/business opportunity.
...but...
In a stock head as yours,you'll never get Malmsteen's sound...
Just my 2 (Euro) cents,
 
What are some obvious things that will happen to an amp if you ruin the output transformer?
 
problems are almost always the tube. An old amp can go through caps, that's hip for some piece in side the head, I think it's some kind of capacitor or something heh. A few times I've taken my amp into the shop and the guy just swaps out a tube and it's fixed. Eventually I'll get around to hassling with this myself, but right now I'm fine paying someone who knows what they are doing to fix it every once in a while. There's enough voltage back there to fuck you up really bad and kill you, so be carefull.

Running your amp without a speaker attached is probably a bad idea, maybe this isn't a problem for newer amps? I'd want to know from the source.

Personally I stay away from eccentric tubes and just stick old fashioned quality in there. I suppose different tubes have different tones so maybe some research...
 
Ok, one more question. Thanks for the help so far guys. I have heard so much about how there are lethal dosages of electricity that can shock you while working on a guitar amp. When i replace my tubes, is it possible that I could be shocked?

Paul
 
paulmckenna said:
What are some obvious things that will happen to an amp if you ruin the output transformer?
Click to expand...
Actually,running a tube amp without a load (either speaker or dummy) doesn't "melt" the OPT.If the OPT's primary is wound with a gauge capable of handling the extra current occuring due to the lack of load,the tubes are the first to go and you'll have to replace the tubes.This is the most common case.
If,instead,the OPT's primary has a flimsy wire gauge (wired economically,just with a slight margin of tolerance),the tubes are "working hard" and,when the current has surpassed the saturation's upper limit for that wire gauge (this translates into an increased temperature of primary windings),the primary heats excessively the isolation between windings and leads to a breakup.
(I used deliberately simpler words just to explain you what's the process,without too many tech dedicated terms wich may confuse you).
About changing tubes:in a EL34-based amp,it's a big chance to deal with voltages around 550-600 VDC.However,this voltages appear only on well-defined places (output tube sockets,standby switch,OPT's primary wires,HT electrolitics' leads) INSIDE the chassis.Assuming that a tube replacement doesn't involve opening the chassis,you don't have to worry.Before replacement,make sure that the amp was unplugged from the mains and wait 4~5 mins.Usually,there are so-called "bleeder resistors" bypassing some of the high-voltage electrolitics and these resistors are actually discharging gradually the remaining HT voltage after switching off.
There is another dangerous case regarding EL 34's:please inspect carefully and closely the two big sockets after you pulled out the power tubes:do the sockets look as they melted a bit between two leg holes?Are there some burn marks?
If yes,please tell your tech to replace those sockets (preferrably,with ceramic ones) because they're prone to arching.
Doug H said:

"...An old amp can go through caps, that's hip for some piece in side the head, I think it's some kind of capacitor or something heh. "

He talks about the high-voltage electrolitics wich are,in fact,prone to aging.
If your amp is newer than,say,7-8 yrs,you have no trouble.If,instead,you have an older model and those caps are the original ones,you should change them because:
1.Old caps "dry out" and loose their ability to perform filtration
2.As a consequence of pt.1,with worned-out caps you'll have more hum than it should AND what's called "ghost notes" (weird sounds when you strum a chord).
Don't be dissapointed about your amp because my extended rant...the cap stuff happens in EVERY amp,being tube or SS.Once that your Marshall is set up properly,it will give you years of hassle-free enjoyment.
Regards,
 
Le Basseur said:
Actually,running a tube amp without a load (either speaker or dummy) doesn't "melt" the OPT. when the current has surpassed the saturation's upper limit for that wire gauge (this translates into an increased temperature of primary windings),the primary heats excessively the isolation between windings and leads to a breakup.
Regards,
Click to expand...
So how is the laquer insulation on the coils breaking down because of excessive heat any different than melting? OK maybe burnt or fried.
 
Farview said:
So how is the laquer insulation on the coils breaking down because of excessive heat any different than melting? OK maybe burnt or fried.
Click to expand...
:D
No matter what you call it, the smell of a burnt transformer is unmistakable.
 
Farview said:
So how is the laquer insulation on the coils breaking down because of excessive heat any different than melting? OK maybe burnt or fried.
Click to expand...
The laquers used as trafo insulator are slightly different than the ones in wood industry.On the ambient temperature,these (trafo) laquers polymerize very slow (resembling the polyester laquer used on hi-gloss furniture).Therefore,the technique is to wrap the entire trafo's bobbin using tar-or-wax-impregnated paper (on older models) or high-temperature resistant,low-conduction polypropylene foil (on newer ones) and,once the entire trafo is assembled (laminations included) is immersed in a laquer bath.
The next phase is heating the "wet" trafo in a special oven on a temperature between 80 and 110 degrees Celsius for a faster polymerization.
The polymerized transformer laquer DOESN'T melt...it eventually burns.
What I said in my past post about primary's wire breakup has nothing in common with the isolation (it's really a rare case of a short between the windings because the isolation has gone).The primary will eventually break up (open) at the most weak (thin) point of the wire itself.
...and yes,a burned transformer has it's own flavour... :D :D :D
 
Le Basseur said:
Doug H said:

"...An old amp can go through caps, that's hip for some piece in side the head, I think it's some kind of capacitor or something heh. "

He talks about the high-voltage electrolitics wich are,in fact,prone to aging.
If your amp is newer than,say,7-8 yrs,you have no trouble.If,instead,you have an older model and those caps are the original ones,you should change them because:
1.Old caps "dry out" and loose their ability to perform filtration
2.As a consequence of pt.1,with worned-out caps you'll have more hum than it should AND what's called "ghost notes" (weird sounds when you strum a chord).
Don't be dissapointed about your amp because my extended rant...the cap stuff happens in EVERY amp,being tube or SS.Once that your Marshall is set up properly,it will give you years of hassle-free enjoyment.
Regards,
Click to expand...

Are there any other symptoms of a "dried out" cap? My amps been hummin' more than my ex-girlfriend lately... :)

Can you explain what "ghost notes" might sound like?
 
One thing that I have learned about tube amps, in my dealings with them, is that ALOT of the time just putting new tubes in the amp will cure all your ills.

I bought a used Fender Hot Rod Deville and the guy said "I loaded it with groove tubes...its ready to rock" Its sounded pretty good but was bassy as hell...had to turn the bass almost all the way down and turn the treble almost all the way up to get a decent sound. I thought it was screwed up, but I decided to try a new set of power tubes before taking it to "the shop". Man, it was like a totally different amp...the highs were there, the boomy bass sound was gone.... and it had alot more power.

From now on, when I buy a used tube amp...THE FIRST thing im going to do is put in brand new power tubes (even if it sounds good and seems to be fine). Thats "square one" from now on with me.
 
cellardweller said:
Are there any other symptoms of a "dried out" cap? My amps been hummin' more than my ex-girlfriend lately... :)

Can you explain what "ghost notes" might sound like?
Click to expand...
Other symptoms...hmmm,hard to say blindly because different amps had different configurations (number of filter stages) and different electrolytic values.
What amp do you have?
But...
Generally,except the hum thing as a result of insufficient filtration,a worn-out stack of caps make the amp sound thin on lows.Not only thin (as,in fact,this is a primary sign of worn-out output tubes and it should not be confused with the above) but,rather,a "muddy" and poorly-defined low end.
It's really hard to explain (taking into account my poor English) this sound but it's a very clear notion,at least for me!:)
On the other hand,"ghost notes" appear when you strum a double-stop (two strings hit simultaneously,being a forth or a fifth...whatever) on your guitar (say,like in the most common guitar riff) and,except the known resulting sound,you hear some other(s) strange sounds who apparently don't belong to that specific chord (like some unusual upper harmonics...again,hard to explain).
Please note that in this case these weird sounds are located in the middle spectrum,not in the high freq. as you might understand when I said "upper harmonics".
Another "ghost notes" can appear when you play a single,long note on the guitar.Listen to that note carefully,from the attack 'till it fades away:does the note have the same consistency/colour all the time,or it gets some sort of an "aura" after the attack?In the second case,(assuming that you didn't played through some pedal or processor but guitar direct to clean amp),you might consider a closer look on HT electrolytics :) .
Cheers,
 
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