Marshall 25 Anniversary Silver Jubilee 50 100W 2555 Schematic. Marshall JCM2000 DSL50 Schematic Marshall JCM2000 TSL100 100W Schematic. Jul 12, 2015 - does anyone have the schematics for the following Jcm2-60-00 issue 6 tube board Jcm2-61-00 issue 3 pot board Thanks in advance.
The previous owner said he biased it himself, and after opening it up and measuring off the test leads, one of the tubes is set to 49.6 mV and the other is set to 46.6mV. Should i be lowering it or at least get them closer to gether at all?
Its to my understanding that they should be between 38mV and 45 mV, and they should be the same. Anyone got a JCM2000 DSL50? What do you have it biased to? Nick EDIT: after the circuit stabilized the one that was 49.6 is now 51.0, and the one that was 46.6 is now 48.8. The previous owner said he biased it himself, and after opening it up and measuring off the test leads, one of the tubes is set to 49.6 mV and the other is set to 46.6mV. Should i be lowering it or at least get them closer to gether at all? Its to my understanding that they should be between 38mV and 45 mV, and they should be the same.
Anyone got a JCM2000 DSL50? What do you have it biased to? Nick EDIT: after the circuit stabilized the one that was 49.6 is now 51.0, and the one that was 46.6 is now 48.8 I'm not a amp tech but it sounds like they are measuring voltage in each tube. The fact that it gets closer in value as the tubes warm up would tend to indicate this. I doubt a 3 mV variance is going to have an impact on the sound of the amp. Assuming the bias supply was adjustable for each tube you might try to match the voltages. The 51-48mv figure is possibly a compromise between two optimal bias points (one for each tube) or the correct BIAS point as determined by a scope.
BIAS probes, Current indicator LEDs etc don't really tell you whats going on as far as the actual output signal goes. Nothing beats putting the amps output on a scope. I suspect that 3nV is not going to make a difference. Does the amp sound good? Thats the REAL final determination. It sounds amazing But could it sound better?
That is what i'm wondering:P While the 3mV difference between the tubes may not be damaging to the sound, being 5 mV out of the top of the reccomended range is what makes me thing it should be re-biased. Nick Well that is pretty hot as far as BIAS goes. I haven't done any amp work since the early to mid nineties and and back then most tubes seemed to BIAS up at around -39 to -44.
Never mind - that was Bias Voltage. I'm not sure where Marshall is getting that mV reading from in the circuit. Just to note that tubes can vary wildly in current and voltage draw depending on many factors. So the -48 to -51 figure may be perfect for those tubes in that circuit running your wall voltage. I would say if the amp sounds good play it. If your really worried than balance the bench fee of a amp shop to check the BIAS against your peice of mind. It's my personal experience that tubes that are slightly over biased will sound better than those that are under biased.
Also its been a very long time since I worked on an tube amp. A broke buddy just gave me his broke Traynor to look at so I may be plugging my 1950s oscilloscope relatively soon. Make that fossilloscope. Ahh alright i might as well leave it then XD Nd i have 3 or 4 analog osciliscopes laying around. What would i be looking for in the wave form? Nick The classic bench method involves using a 1K sine wave test tone into the amps input. Then running the amps output into the same resistance as the intended speaker load E.G.
Set the amp controls so that you get a clean sine wave across the output. As you view the outputted sine wave you should be able to observe a distinct 'Notch' in the wave form. This is the cross over notch or bias point. By adjusting the Bias supply voltage you should be able to eliminate the cross over notch and at that point the amps output stage should be correctly biased.
You will need some expensive power resisters rated for the amps output. 50 watt 8 ohm power resisters are pretty expensive. Its probably cheaper just to let a tech look at it. All of the normal precautions about working with high voltages and tube amps apply.
I would suggest you spend some time looking about the web for info on amp biasing before you start. However since you have already noted the voltages it should be simple to put it back if you dont like the results. Hehe i work with high voltage all the time:P So i would use the signal generator in protools to send a 1k sine wave to output to amp 1 or 2, then replace the cab with a power resistor (i have plenty lying around from projects) and then measure with an occiliscope. Simple enough, sounds like a fun sunday project Nick Yeah pretty much. Thats the way my dad and the other old timers used to do it. (My late father held a amateur radio licenses since - well before there were transistors).
Opinions vary as to whats the best method and thats why I recommend doing some reading. My scopes are old EICO 460's and I have a old tube HP signal generater. They haven't been plugged in since Clinton was president. I need to bring them up an a variac and see if they will still work (or what smokes.
It would be nice to find a inexpensive solid state audio sine generater for doing this as the HP is about the size of a printer. Maybe theres a iPhone app out there.
I have an amp head of the model listed in the title. It blows the main fuse as soon as it is powered on. A little probing around shows that my primary winding in the main power transformer has a DC resistance of about 2.0ohms.
That would explain why the fuse pops immediately. I have managed to find an authentic replacement transformer as the company that makes them is no longer in business. But the folks in England want $150.00USD for it. Before I make the purchase I was wondering if anyone here in the states has one of these AMP heads and could put an ohmmeter on the prongs of the power cord and turn the power switch on and let me know what the DC resistance they read is? Much appreciated.
Glad you didn't Fedex your transformer. I don't think that your dc resistance test proves much of anything without a point of reference.
Hopefully somebody can help you out. Depending on how hard it is, you COULD disconnect the secondary leads, insulate them and see if the transformer by itself pops the fuse. You could also probe the power to ground on the other side of the power supply ( remember that the caps have to charge) to see if there's a short there. Then you coulsd probe around the power supply a bit. I hope that you have a schematic. This site seems to have schematics if you don't.
Also, I know that you're a high tech experienced guy but- please be careful with those 5v tube voltages. Good Luck, hj. University was decades ago now but I remember that an ideal transformer has zero ohms winding resistance. I measured a 200W toroidal 240V primary and got 3.5Ω.
I measured a 100W E-I core 240V primary and got 4.5Ω. I measured a 20W E-I core 240V primary with a known shorted turn on the primary and got 5.5Ω. I'm guessing you're at 110 VAC windings so you can probably halve my measurements; so your transformer doesn't look completely wrong. Do you have a Variac? You could drive it with 20 or 30V or so and take some measurements without popping the fuse.
Back on topic, I have determined that this transformer is shot. I took it out of the chassis, and connected the primary for 230v service and out a 3amp circuit breaker in series with my 120 vac mains and applied power. The breaker did not blow, but the transformer sitting there with nothing connected to its secondaries started to buzz pretty bad, then the smell of melting epoxy told me to cut the power. Transformer very hot, but still none of the winding's are showing shorts to one another no matter how I check. Tried connecting the primaries for 120vac and the breaker did not blow in time before the thing really started to Growl.
Time to tell the customer that we are going to have to order a new tranny from England. I still find it odd that the amp has been used at Gigs for 10+ years without fail, but leaving it on overnight with only the speakers connected to it caused the power transformer to burn out?
Here is hoping that there is nothing downstream wrong with the amp after the transformer is replaced. Kartman wrote: I would've thought Marshall would have wide support in the U.S.
Unless there's a trade embargo from the U.K for them stealing rock n roll! Oddly enough it's not simple finding parts here in the USA. Apparently the OEM for the power transformer is not in business, but their website is still running, albeit as more a museum of sorts. I have found suppliers of replacements units, that are either 'enhanced' models, or simple copies of the original, but they cost twice as much as importing one from the U.K.!!
As today is an unofficial Holiday of sorts here in the USA I will contact a local Marshall dealer and see if they carry the Transformer, and get a price, will get back to you on that. Ka7ehk wrote: The short does not have to be between windings. You can have a short between two turns in the same winding. That results in a shorted turn (or turns). The turn can get quite hot if there is enough power available. Jim Entirely possible as the epoxy impregnation looks pretty thin, and the enamel coating on the wires is also pretty thin looking as well.
Either way, the transformer is NG, I have an RFI in with Marshall and I have a replacement ready to go once I place the order. We shall see.
Jim - is it the model with the leaky Pcb? The replacement pcb assy isn't too expensive from what i was told (a friend fixes this kind of stuff). Then there's the tubes - they maybe getting a bit tired. To bad you can't just go down to radioshack and use their tube tester like in the old days! I'd suggest you talk to the Marshall reps and they should be able to tell you if your model/serial has the problem or not and suggest a course of action. My guess is it is not going to be cheap - but valve amps aren't cheap to begin with.
From the blogs(I have never read a 'blog' until now) the leaky PCB and resistors affect the series 3, 5, and 7 boards. This one is a series 5 unit do it has the leaky PCB, and I have not checked the tubes.I looked at purchasing a tester, but they start at $500.00 for a decent one. My email to MArshall Garnered an automated response saying thanks for contacting them, we will get back to you.yeah right. Kinda tough to find a MArshall rep here in the states.Sam Ash and Guitar center are the two retail biggies, but they are not going to be straight up with you as they want to sell amps.
Will look online for a Marshall rep that is independent and see if this is worth the effort. I did a quick Google and there is around a dozen Marshall service centres within coo-ee of long island. I'd expect the service centres will want to repair the amp, not sell you spares. At least they should be able to give an idea of the cost. I suppose the question is why the transformer died - did it simply die due to a shorted turn, or did something else help it on it's way? I can't recall what effect the leaky pcb has, but if if it makes the thing oscillate or otherwise turns on the valves, they're going to get pretty pissed off and need replacement - they're not cheap - probably around $30-50 usd each at a guess.
Or if the transformer did die of natural causes, the pcb may have already been replaced - it helps to know the history. I've been told the bias for the output valves drift due to the leaky pcb.
Biasing of valve guitar amps is the thing of myth and legend - it changes the 'character' of the sound since distortion is good in a guitar amp - but only the 'right' kind of distortion and that's why valve amps are preferred. Eddie Van Halen knows a thing or two about tweaking bias to get the 'right' sound. But I digress. Kartman wrote: I did a quick Google and there is around a dozen Marshall service centres within coo-ee of long island. I'd expect the service centres will want to repair the amp, not sell you spares. I am well aware of how many service centres there are on Long Island.many of which are not MArshall certified, and most will not just tell you anything over the phone.minimum bench charge.as I am a repair centre this route would not be helpful. The blogs are pretty informative though.mostly telling to not bother.the transformer is $150.00 and a PCB is 250 British pounds.the amp in good condition is $800.00usd so not sure if it is worthwhile.
Well this amp has quite the press on the internet with the leaky PCB, bad mains transformer, wrong bias resistors etc.I contacted Marshall, and two days later I get a terse email telling me 'Yep, sounds like the transformer is bad' Good luck, and Good Bye. There are aftermarket transformers for the thing, but they are twice the size and over $300.00usd plus shipping! A close replacement is $117.00usd plus shipping.
The customer wants an ORIGINAL Marshall Transformer. Too bad Dagnall, the manufacturer is out of business. Turns out some searching produced two placed in Europe that have stock on the original!
One wants $129 Euros plus shipping, the other wants 75 pounds Sterling plus shipping. I went for the one in Britain and for a grand total of under $140.00usd they shipped a 4Kg hunk of steel and copper FedEx OVERNIGHT!
Had it here at 10am this morning. Installed the replacement and the amp is working again. I was told not to correct the bias as he likes the sound as-is. The replacement tranny does buzz somewhat, but there is only so much I can do. Tubes get really warm/Hot during play time so I am hoping this thing is fixed.
One lesson learned in this is these newer amps are very poorly built. I had a spade terminal break off the PCB just by bumping it.I wonder if these things break off from the vibrations of the road abuse, and the heat/cooling. I'd still like to know what failed in the transformer to begin with where the thing DC meters out ok, no winding's shorted together, DC resistances looked ok too. Oh well.not going to pull the other one apart to find out.
Thanks for all the suggestions everyone. Tubes get really warm/Hot during play time That's what tubes do even if not playing, otherwise they are dead. Are you saying that the anodes start to go Red? If so there is an overload or the biasing is not correct. Output transformers with shorted turns would do that and of course eventually may take out the mains transformer if the user keeps on putting larger fuses in because the correct size blows.
I guess you are aware of the old technicians trick to leave a hot valve or a charged electro in hand reach of pestilent kids who would not leave you alone while you are trying to fix their TV and want to stick their noses everywhere.not that I ever did anything like that of course!