My new..used Tube amp is always a warm distortion?

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CoolCat

CoolCat

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ok, my recent new -used Marshal 2000 401 is acting up.

the clean is always a warm tube distortion sound, and seems to have lost some volume.

its sad in that it sounds good still....but its not working right. there's no clean channel to be had!

Damn thing got really, really hot on the gold face plate too....or maybe that was my "hot playing"...nah,,, :p it's a malfunction.

Power Amp tube? Any help will be appreciated.

edit- found a decent forum music-electronics repair.

So I opened up the back plates and it has the original tubes. EL84 (4qty) and 12x7(3qty) stock Marshall
amp serial is 2005....so it appears the tubes usual suspects.
note- anything after 2003 the heat issues/solder were supposedly resolved on this amp. (good news!)

haven't seen anything else other than swapping out all the EL84's? and the replacements need to be JJ's as many other types won't fit thru the casing holes I'm no tube specialist by any means.

and will pop in a Celestion V30 also while she's opened up...

any info welcome.... maybe this will help someone else save a return trip with the EH's and Sovtek EL84's won't fit.

JJ's...it is ...whatever JJ means?
 
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bumping my own question.

so before I go spend $60 on tubes....

is there any quick troubleshooting tips to where I might be able to buy one tube and swap them out one at a time? to save money.


if no answer by noon, I'll go drop some more bread....but this sucks! If this thing can't play for a few years without needing more mo9ney dumped in her...she's out of here...

the tube tones are great, but $60 upkeep...not good. My Peavey SS-Discrete is a 1980 and has not cost one penny and plays as good as it did from day one.

Problem is it doesn't sound very good imo....maybe I should put the V30 in it?

arrrrrrggggggggggggggggg...unexpected bills!:mad:
 
Marshal 2000 401 tube problems?

ok....one more troubleshooting tip. to throw out there...I know I'm moving fast, before replies, and jumping ahead here...but! repair is in progress...

Two of the 4 power tubes EL84, are glowing super hot the other two are not.
Is this a clue?

Seems the clean tone is present slightly more when the amp is first powered on, as it warms the distortion starts up.

No schematic. No blue glow showing a leak/crack in the tubes. The preamp tubes, 12X7, appear uniform in their glow??

No cigar.

maybe I was too harsh? I put strings on my guitar and don't think anything of it.... $60 in tubes for a year or two life span (seems to be normal lifespan as I read the posts).


Note: the Power Tube hole in casing is .995". The Marshal came stock with the J/J EL84-Marshall printed on it. The Tube is .855 diameter.

The PreAmp tube hole-casing is .885 w/rubber gromit. Tube was 00055,WK42/05 Marshall .860" diameter.


EDIT 6:

I swapped the 4 EL84's and the High Glowing tubes followed. So it's most likely those two tubes, and the ultra brite glowing is not the "schematic location" for the overly glowing tubes. This may also insinuate its not the electronic board either as the the normal-glow tubes did not change.

So I'm thinking 2qty EL84's will need to be purchased... ????
 
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Let me ask you a few questions:

Well let me preface this with I don't know anything about that particular amp but more tube amps in general.

1) Do you mean EL34? or EL84? 34s are bigger in diameter than 84s. Are the tubes small (about as small-maybe a little smaller-than the preamp tubes)?

2) Do the tubes glow blue as you play?

3) Is the power transformer (the biggest one) extremely hot to the touch within the first 5 minutes or so of the amp being powered on?

4) I'm assuming this is a combo amp?

Get me some answers and ill try and return the favor lol.
 
producerkid said:
Let me ask you a few questions:

Well let me preface this with I don't know anything about that particular amp but more tube amps in general.

1) Do you mean EL34? or EL84? 34s are bigger in diameter than 84s. Are the tubes small (about as small-maybe a little smaller-than the preamp tubes)?
EL84
2) Do the tubes glow blue as you play?
No Blue Glow seen
3) Is the power transformer (the biggest one) extremely hot to the touch within the first 5 minutes or so of the amp being powered on?
Not sure...2 of the 4 were glowing really really bright. 2 of the 4 were normal-orange like the pre-amps tubes, slight orange glow.

I then took the glowing 2 tubes, and swapped locations with the normal 2, and the glowing shows to be the tubes not the location....as the Super brite glowing tubes still appear very hot.

4) I'm assuming this is a combo amp?
Yes
Get me some answers and ill try and return the favor lol.
Click to expand...

I appreciate it! I don't work on guitar tube amps but I'm cautious and technically inclined...many years working on equipment and calibrations.

I'm not sure of the tube inside's, but the large plate structure on the hot tubes is almost orange! the other two seem to be cool, and standard grey metallic....similar to the cool preamp tubes.

Is there any reason to change ALL 4 tubes at the same time?
Or is it ok to save a few bucks and do 2 tubes or even one tube change out at a time?


EDIT 8:...er......9
My mistake....There is a tiny blue glow on all 4..It's toward the bottom, little blue tiny plasma glow...like a pilot light on a gas furnace.

oops! my bad...I didn't know what I was looking for.... The decal even melted on the hot ones.

Checked the large transformer, it didn't seem to get hot.
 
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I was one of the guys who recommended the tube amp and perhaps I should've told you that you're going to have to maintain the amp. It's not like solid state at all when it comes to maintenance, you're going to have to put new tubes in it every few years or so, and if 60 bucks every few years is going to break you then by all means sacrifice your tone for a few saved pennies.
 
COOLCAT said:
Is there any reason to change ALL 4 tubes at the same time?
Or is it ok to save a few bucks and do 2 tubes or even one tube change out at a time?
Click to expand...

If the tubes are bad do not run the amp or you could damage the transformer.
Yes you need to change all 4 at the same time because the tubes need to be a matched set. Then you will need to bias the amp.
 
Thanks..Guitar Center opens in an hour. Appreciate the notes.

yeah, JC..I over-reacted, because, as you said, $60 or so every couple of years is not that much, its less than guitar strings really over 2yrs.
Just not a good month,,, and as you know I haven't had the amp 6 months yet!

but the tubes are original and the amp is serial date 2005.

Sounds like a full set of 4 EL84. This is the info I appreciate too, it'll save a dang transformer! and the all expensive gasoline too.

thanks....its 11:15....I'm about out the door with my calipers. Apparently this model Marshall has these holes the tube goes thru which some common EL84 tubes don't fit. I'm suspecting Marshall went less than 1" on the hole, and therfore many common EL84's don't fit. Total "doh! mistake" it appears.

thanks all.
 
Well, yeah if the bright/hot problem moves with the tubes, then its probably the tubes. Other possible issues could be the power supply and/or biasing circuit. Now, while there may not be an immediate damage to either items, there could be a flaw in the design or inferiority in parts. This kind of problem in power tubes after only a span of two years isnt really normal as such, unless the design sacrifices tube lifespan for tone (i.e. biasing REAL hot).

Dunno. lol. $60 bucks for a quad of power tubes aint much for good tubey-tone if your liking it. Maybe even save the bad tubes after you change them for that "brown sound" of your clean channel, haha.

Hope the tubes fix ya up. If not report back and let us know.
 
yes, thanks.
well, to finish this fiasco off...

bought a 4-pack of Groove Tube Gold "S" at Guitar Center (because it was the only ones they had.) measured them and they were a bit smaller dia than the J/J's at .849 ~...so they'd fit this 2000/401 metal cover/tube hole.
$71 something for the set of "matched" tube's. geeez?:confused:
Still will get some preamp tubes next month or something. The pre-amp tubes will have to wait for another payday.

Popped them in and that was that, problem solved.
no bias work done, but its up and has the clean channel back. Which is a "success".

Interesting, didn't notice any "blue glow" on these new tubes...maybe all 4 of the old tubes were leaking in?

Slapped in a Vintage 30 g12 while it was open, switched to 8ohm, didn't notice a huge, huge big :eek: type change from the Black Gold stock 16ohm Celestion. But I left the V30 in.

Is there a big bias shift from the J/J to the GT?



Luckily, nothing serious like a transformer or pcb!
 
think of biasing as setting the idle on your car... if you want it to respond quickly it's got to be done... the tubes will last longer as well... on some of the marshalls of that vintage the bias is adjustable and test ponts are already there for over all bias and side to side balance as well....
 
ok, a few days, no issues...nice to have some clean sounds back.

biasing. I understand the concept but how do I know what I'm doing exactly on this amp.

DVM? and a pot to set the voltage....what voltage is the goal?

I don't have a schematic.

And its working and the tubes look pretty mildly warm. I have a lot of gain, plenty for me.

but this longtivity of the bulbs is a concern or a positive... what do I need to do to set this up or at least check it?
 
thanks OC, but I don't see the access on the DSL401 , maybe I have to take the entire amp out and remove the black cover?

unfortunately, the video wouldn't play some error on the windows media or something. But I did get the pics.

I'll search around, bias setup sounds really easy to do 40-45mV...and DVM and pot-driver....thanks!


FYI- info:

MARSHALL SERVICE BULLETIN

SUBJECT: Bias Info/Procedure for JCM2000 series Marshall amplifiers

THEORY OF OPERATION: We are setting the bias using the current method instead of cross over distortion method. The Bias PCB assembly is as follows:
PR1: Bias mini-pot adjustment for pin1 which is one side of the push pull amp (two output tubes in a 100watt amp and one output tube in a
50watt amp). Pin1: Connected to the cathode of the output tube(s) which then goes through a 1 ohm resistor then to ground. Pin2: ground reference.
Pin3: Same as pin1 but for the other side of the push/pull amp. PR2: Bias mini-pot adjustment for pin3, the other side of the push/pull amp.


PROCEDURE:
Instructions:

1) unplug the amp and remove the head unit from the cabinet.
2) locate the 3 pin molex connector labelled (CON 5).
3) securely attach the red probe of the voltmeter to one of the outer pins (use aligator clips).
4) securely attach the black probe of the voltmeter to the center pin (again use aligator clips).
5) plug the amp in (make sure the head is connected to the speaker) and let it warm up for a couple of minutes.
6) then turn on the standby and let the circuit stabilize for a few minutes.
7) adjust the mini pot (PR1) until the voltmeter reads

DSL201 0.675 V
DSL401 1.375 V
DSL50 45 mV
DSL100 90 mV
TSL60 80 mV
TSL100/122 90 mv

I bought some nonconducting pot screwdrivers
from Radio Shack for this.
turn off the amp, unplug the amp, and place the head unit back.

1. Make sure amplifier is connected to a load with the proper impedance
selected. 2. Power up amplifier on STANDBY and let the circuit stabilize for a couple of minutes.
3. Locate the male three pin molex connector (CON2) with the two mini-pots (PR1 and PR2) on both ends found on the bottom of the tube bay. 4. Connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector CON2 and positive lead to pin1 on CON2.
5. Take amplifier off of STANDBY with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to the mV voltage that is listed in the chart below. 6. Repeat steps 4 & 5 for pin3 and until both pin1 and pin3 mV are the same.

BIAS CHART mV SETTINGS
(pin1 and pin3)

DSL50 45mV TSL60/1/2 80mV
DSL100 90mV DSL401 1.375V
TSL100/122 90mV DSL201 .675V
 
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I read the Bias and its only .555mV (DC).

So I cranked the pot to 1.375V as the notes state and at full max I can't get 1.375V on CON5 Pin 1 & 3(grd). DSL 401: Model. At full open, I can only get 1.025V.

Anyone think I should adjust it back to .555mV ?

Or leave it at 1.025V?


Great thread and pics in below link...but I still can't get 1.375V? I did find on the schematic it says Max. pot...ccw to reduce bias.

http://www.historiclespauls.com/music/index.php?option=com_content&task=view&id=22&Itemid=48
 

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Marshall's recommended setting seems a little hot according to Bob at Eurotubes. Anything between .8 and 1.0 volt is fine.
 
it would be hard for me to make a specific recommendation without knowing the B+voltage at the very least...on the one hand i would trust marshall to know their amp... but a quick look at the sheets from a bias probe indicates for instanc that a 100wt with 4 tubes running at 400-450V should have a plate current of 31ma per tube.... looking at the blurb you posted from marshall the pot reflects 2 tubes so i would expect it to be around 62ma of draw on that side....that's read from pin 1-2... to balance side to side i would check for a voltage between pins1-3 and zero them out... then recheck 1-2 again... alternating till it settles in.... check the B+ voltage and if it's not around 400V then PM me with the voltage and i'll look it up for you... if the voltage is lower you want more draw... higher less...
 
Some of the previous posts may have listed some other amps, some with a PR 1 and PR2.

This 401, only has one Bias pot, also its CON5 (connector 5) that has the voltage readings/ 3 pins. but 1 and 3 read the same thing. 2=ground.

401 has 4 tubes, and the 201 has 2 tubes.
I forget the name but the Pin 1,2,3, has 1 & 3 as the same reading which I found was true with the DVMeter.

I set the DVM to DC, 2V range....red lead on CONNECTOR 5- Pin 1 or 3, and the black lead on Pin 2....and tweaked the PR1 post with a small screwdriver.
The response was immediate. all that work for a 2 minute tweak?:confused:

I nearly scratched the front of the amp head, yanking this thing out of the cab, the tolex came unglued somewhat and bunched up making the head partially stuck.

Anyway, Looking at the setting, originally at .555mV upon first measurement, I wondered if it hadn't been setup at the factory as a 201 and not a 401? Everywhere states to set the 401 at 1.375V, the 201 at .675mV...which the .555MV is closer to? just a guess.........

Anyway, Thanks everyone for the help...good class, in tubes for the Marshall 2000 401.

Its been playing fine and the amp seems alright. 4 new GTEL84-S, with a Bias set at wide open 1.025V= 1,025mV...

Noticed..the original 2005 preamp tubes are in there still, better start saving!
 
just for shits and grins check the HT (B+) voltage and let me know... this is supposed to be 100wt right???? i got a sneekin suspicion you may have it under biased.... or maybe not... just curious...
 
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