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Marshall Lead 100 MOSFET 3210 Head

Started by aoresteen, April 21, 2017, 11:10:29 AM

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aoresteen

Hello all!  The Marshall 3210 MOSFET amp was my first decent amp that I bought around 1990 with the Marshall 1965B 4x10 cab.  Never had an issue with it. I sold it in 2000 to my nephew (who I understand still has it) but recently acquired another 3210 (vintage 1990, Y0xxxx) a few months back off of the local Craig's list.  I have yet to plug it in although the seller said he had been using it regularly and had verified that all functions work.





I have both the Marshall 1965A & 1965B cabs that I use with my Carvin VT-50 tube amp head.



The Marshall cabs are 8 ohms each so using them both would put a 4 ohm load on the 3210 amp.

Last night I did a bit of research on the 3210 head's past problems and found out that they have a tendency to blow the MOFETs taking out the rectifier & a few other parts with them.  This seems to occur when you put a 4 ohm load on the 3210.  I always ran my old 3210 with a single  8 ohm cab so I never had the problem.

1. Before I plug it in, should I put a 16ohm speaker load on it first?  Or should I give it a shot with an 8 ohm load?  No way will I start out with a 4 ohm load.

2. As a preventative measure should I replace the MOSFETS with a pair of Exicon 10N20 & 10P20 before I run it with a 4 ohm load?  They are cheap at $35 for a pair.


My current MOSFETs

http://www.ebay.com/itm/282407099589?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

3.  While I am at it, should I replace any caps that have been problematic in the past?  Or just replace them all?  I checked the filter caps.  One read 1980 mf, the other read 2160 mf.


Filter Caps

4.  The board looks clean an un-modded.  No sign of a previous repair.  The ICs are not in sockets - they are soldered to the board.  Should I socket them and stock some replacements?


My 3210 board

5.  Should I beef up the rectifier with an 8 amp one?  Any recommended replacements?

As I plan on keeping this amp for the next 10 years at least, what spare parts should I stockpile?

Thanks!

Tony Oresteen
Peavey Bandit Silver Strip, Revolution 112
Marshall MOSFET Lead 100 3210
Squier SP10
Newnan, GA

Enzo

Make sure I understand, you bought a used amp that at least was claimed to work.  You have not even plugged it in, and you are proposing to tear it apart and replace half the insides?


WHY?


Online discussions may demonstrate that WHEN these amps fail, it is more often blown outputs than other parts, but how many of these worked flawlessly their entire lives?  Those amps never get mention online.  SO it is like hanging around a hospital emergency room to decide what your life is going to be like.   There is a difference between "these blow up" and "this is what burns on the ones that blow up".

You measured a couple caps in circuit, and they both are within 10% of value.  They could have measured the same the day they were new.  it isn't the value that wears out, it is the ESR and leakage inside.

A beefier rectifier bridge would just mean that someing else burns up when you have an output failure.

aoresteen

#2
Quote from: Enzo on April 21, 2017, 11:36:54 AM
Make sure I understand, you bought a used amp that at least was claimed to work.  You have not even plugged it in, and you are proposing to tear it apart and replace half the insides?


WHY?


Online discussions may demonstrate that WHEN these amps fail, it is more often blown outputs than other parts, but how many of these worked flawlessly their entire lives?  Those amps never get mention online.  SO it is like hanging around a hospital emergency room to decide what your life is going to be like.   There is a difference between "these blow up" and "this is what burns on the ones that blow up".

You measured a couple caps in circuit, and they both are within 10% of value.  They could have measured the same the day they were new.  it isn't the value that wears out, it is the ESR and leakage inside.

A beefier rectifier bridge would just mean that someing else burns up when you have an output failure.

Enzo,

Why?  Because I'm cautious.  I have no idea how long the amp has set or the past history of the amp.  In the tube world techs never just plug in an amp that they know nothing about.  They put them on a variac and bring the voltage up  s l o w l y.

The 3210 has a past history of failure that is well documented here and elsewhere.  So let's do this again:

I'll just plug it in and see what happens. 

Me: "I bought an amp I knew nothing about it and plugged it in and now it doesn't work.  Help! "

Enzo: "You bought an amp that you knew nothing about and plugged it in without checking to see the history of these amps?  Their failures are well known and had you been a bit more cautious we could have helped you avoid a catastrophe".

Sometimes Enzo you can be a real PITA.  In spite of your electrical genius.

I have 6 amps floating around here and I don't need the 3210 right away.  And yes I will replace known components that have a history of failure.  Before I even use them.  Like the brakes on my 1990 Ford Ranger I bought used and had dropped off at my mechanic and had them overhauled right away. I don't like catastrophes.

So I will replace the output MOSFETs and then run the 3210 at 4 ohms and see what happens.

Also, I've been sick for the past year due to my injuries in Iraq and I have not been able to do much like I used too.  So the 3210 had to wait a while.

Tony Oresteen
Peavey Bandit Silver Strip, Revolution 112
Marshall MOSFET Lead 100 3210
Squier SP10
Newnan, GA

Enzo

Sorry I interfered, best wishes for your recovery and success.

mexicanyella

I had a college roommate, circa 1987, who had a Lead 100 Mosfet head and the 4 x 10 slant cab. He used it with an early-mid 80s Ibanez Roadstar II, which was sort of strat shaped but with bound, square body edges, and a bridge humbucker/neck single coil pickup arrangement...and a Kahler trem. He played  in a sort of Fugazi-ish punk band and I remember thinking it was a pretty great crunch amp.

Later on he sold it to another friend of mine who played it with a Les Paul Studio through a Crate 4 x 12 cab. That guy used to get some pretty lively clean-ish tones by using the dirty channel but with the guitar volumes rolled back.

So I can see why a person would like those amps.

g1

Quote from: aoresteen on April 21, 2017, 12:22:01 PM
I have no idea how long the amp has set or the past history of the amp. 
Yes you do, you told us exactly that in your first post:
Quote from: aoresteen on April 21, 2017, 11:10:29 AM
the seller said he had been using it regularly and had verified that all functions work.

No, tube amp techs (or any other type of tech) do not power everything up slowly under the assumption that the owner was lying when they said it was working recently.
If you choose to see it that way, not much sense in telling us otherwise in the first post.  I don't think Enzo was at all out of line with his response.
Did you pay the sellers "working amp" price or buy it as a "non-working" unit of unknown origin?

DrGonz78

$35 for a pair of transistors is not a happy price to pay for me, and I do not consider that to be a "cheap" price. Before I went and ordered new outputs I would surely check to see if they were truly fried.

No problem running an amp on a light bulb limiter to avoid an issue on first power up and it takes no time to do this.

From my past experiences Enzo's logical questioning should have been something I had already tried or figured out first. It can be challenging when someone, with such deep wisdom on the matter, points out very logical questions regarding a post. Someone new to this whole thing might incorrectly take it as just criticism without intent to help. Sometimes we need someone to point out the hard truths, even bluntly. So I am guessing the "PITA" comment might have been made sort of tongue in cheek?
"A person who never made a mistake never tried anything new." -Albert Einstein

Enzo

Um, I'd rather we move on from me...

I was going to sit this one out, but here:
I don't look up model history, because in my own opinion WAy too much weight is put on "common problems".  Yes, many models do have certain issues that come up more than they should.  But the internet amplifies the problems at the expense of the overall record.  Someone goes to a forum like this and sees three threads about some model and assumes then that model must be unreliable and break a lot.  But in most cases, we see the most threads about failures on the models that sell the most.  When you sell 100,000 amps of a model and 200 of some other model, we will always see way more repairs of that 100,000 unit run.  A failure rate of 2/10 of 1% in 100,000 units is the same number as the entire run of the smaller run unit.  They don't compare.

Another factor is that just because some part fails more often in some model, that doesn't mean that is what failed in the unit we are looking at.  SO a tech can spend time running down lists of "common" failures, hoping one of them will be the solution.  Sometimes it is.  Other times, well we just spent an hour we could have been repairing.  SO I don't spend any time looking up what other people have done to their amps.  Not saying no one should, but I don't.

Everyone's approach is different, but to me if I have a list of check this and check that, I learn nothing.  If I troubleshoot my problem, I learn a lot about the circuit.  And chances are I get a better idea of the overall health of the unit than I do by the one from column A approach.  It is the difference between a Gerald Weber book and a Merlin Blencoe book.  Weber can tell you how to convert a SIlverface to a Black face, or how to make reverb work on both channels.  But if you follow his instructions, you still have no idea in the world why it works.  A book like Merlins tells you how circuits work.  Weber tells me to change the third cap from the left to increase my gain, while Merlin tells me to change the cathode bypass cap of the input stage for that result.

But I am wandering.  Hey, I'm old...

So, what do I do with an old amp?  I plug it into my variac, and run it up while I watch the current.  If it starts to ramp, then I back off and proceed as a blown amp.  If it comes up to 120v, fine, off the variac and plug into the wall.  Then I assess its operation.   I am not forming the caps or anything, I am just looking to see if the unit will be drawing excess current.

Absent a variac, a bulb limiter will do the same task.

I am not patting my own back, any competent tech can do the same thing, but in the majority of cases, we pretty much know what we are up against as soon as we check out an amp.

My personal philosophy is always to make it work first, and then, and only then, go about updating caps or whatever.  Unless they are shorted - in which case the bulb limiter goes on - weak caps won;t hurt it, you get hum or distortion.  SO I can leave them in while I sort out the rest.  I don't buy the "as long as I am in there" idea.  I liken it to a doctor.  If you are going in to have your appendix removed surgically, chances are you would not tell the doctor to go ahead and do some liposuction "as long as you are in there already."

You may well need some new e-caps.  I see a couple smaller ones have the shrink label peeling back.  That happens from excess heat around them.  Your power MOSFETs work or they don't, they don't usually get weak like old power tubes, so unless they have failed, I myself would continue to use them for whatever life they have.  Nothing says those FETs won't last another 30 years.

That is how I would approach it.  I am sure there are other valid approaches here.

J M Fahey

QuoteSometimes Enzo you can be a real PITA.  In spite of your electrical genius.
Ihope you choke on that statement.
QuoteI have 6 amps floating around here and I don't need the 3210 right away.
Which means?
QuoteAnd yes I will replace known components that have a history of failure.
Not in your amp.
Hey, you might take some Diabetes medications because panchreas have a history of failures.
And some heart medicines too, those are *known*  to fail.
CDC statistics can´t be wrong  :o
What about Parkinson medicines ...or Alzheimer .... or ... or ... or ....
There´s thousands of *common problems*  in Human bodies.  ::)
QuoteBefore I even use them.  Like the brakes on my 1990 Ford Ranger I bought used and had dropped off at my mechanic and had them overhauled right away.
Here is the main fallacy in your reasoning: mechanical parts wear out, tubes wear out, solid components (active or passive) do not ... they either work or die, unless abused and that kills them in a short time, often with visible results ... not the case here or at least you are not reporting that.
QuoteI don't like catastrophes.
Nobody does, and I don´t see any caused by "parts wear" either.
Only parts where some of that might apply are electrolytic caps, and even so I´d try to detect some problem first, such as increased ripple.
You have checked nothing yet.
Quote
So I will replace the output MOSFETs
Why? they do not wear; they either work as in the first day or die, which is very unlikely.
But ... but .... I read about of them blowing!!!!  :-\
True enough, but they didn´t "die" , they were "killed", not the same by a country mile. Hope you see the difference.
The Guitar Amp World is abusive on amplifiers and that´s an understatement; amps DO get used at full power for long hours, horrible shorted/cracked plug/stepped on/yanked/poorly plugged cables are *routinely* used to plug them into cabinets, users often get (cabinet)  trigger happy and connect any odd box they find laying around, never check impedance (what???  xP ) , THAT is the "common problem"  behind 95% of published failures.
Quote
and then run the 3210 at 4 ohms and see what happens.
Then there is a reasonably high possibility that you will blow them  :o
new or old have exact same specs, will use exact same heatsink, both are just as capable of driving a 4 ohm load (or not) , so replacing Hitachi by Exicons will not improve your amp a bit.
As I said, there is not a "wear" factor involved, but a specs/rating one.

Since this is not a rant against you, but in any case a "get real"  one, now I´ll try to help you with your amp, but let´s address the real problem instead of imagined ones :
in my opinion, that is an excellent amp, with just one problem: the output devices are simply not enough for a 4 ohm load.
They are electrically too close to maximum specs (so rating same spec fresh ones will not help) and I *guess* they are poorly cooled.
Can you please post a couple pictures showing the heatsink and how are the transistors mounted?
If possible, from both sides (fins and inside the chassis) plus a somewhat farther away one showing its general position inside the cabinet, also showing the back perforated panel.
The idea is to check whether you can add an extra pair of power devices or if physically impossible, replace them by "double die" Exicons (essentially 2 chips each inside same TO3 case) and/or add a small PC type fan *somewhere*  to improve cooling.

As said before, the idea is to avoid killing them, they are not dying on their own .

On the same token, make/get a *good*  pair of speaker cables, keep a spare nearby just in case, make a point of always checking connections (valid for *any* amp) and you will have a reliable amp for the next 30 years (or more ;) )

aoresteen

Thanks all for your responses.  I am away in Alabama for a vacation with family and will not be able to post any new pictures of the 3210 until next week.

Please understand that the amp will ONLY be use with a 4 ohm load.  The two cabs are Marshall 1965A 4x10" and a Marshall 1965B modified with a 15" Weber California.  I currently use a Carvin VT50 head with it.



So I need to have the head able to drive a 4 ohm load without failure.

When I said that I have 6 other amps it meant that I am in no rush to use the 3210.  I don't have to have the 3210 working tomorrow.

When I get back home I will post some more photos of the interior & the heat sink.

Tony Oresteen
Peavey Bandit Silver Strip, Revolution 112
Marshall MOSFET Lead 100 3210
Squier SP10
Newnan, GA

J M Fahey

Cool  :dbtu:

In a nutshell: I think the amp "as original"  is just on the edge, too close for comfort, to drive 4 ohm loads.

Not that it can´t absolutely drive them, otherwise they would not have released them, but real world touring or even plain stage use (LOUD, matching a LOUD drummer) are hard on an amp.

I guess that you can add 2 more extra devices or replace the current ones with double chip Exicons, which work very well.

Whenever possible show us what´s making it tick :)

aoresteen

Just a quick update.  I'm still working on the 3210 but a number of higher priority projects have jumped in front of it.  I did invest in a new ESD soldering station :) and I love using it.

I hope to get back on it in a week or two.  Thanks for all the help.
Tony Oresteen
Peavey Bandit Silver Strip, Revolution 112
Marshall MOSFET Lead 100 3210
Squier SP10
Newnan, GA

Jazz P Bass

If you replaced the original mosfet's, I'll buy them.:)

solidstate2199

Hi there,

i have a 3210 and some other similar 80s Marshalls.
I use the amp once or twice a week for some years now
and never had any issues with it. (1965A+B)

I go with the first response and say dont do anything if not
necessary.

Mine has a little hum, probably 60hz, could be the caps or its normal,
because my 5275 which is bassically the same circuit has it too.
Or this hum has something to do with the Reverb Circuit, because
if you put the Reverb Knob on half without engaging the Reverb,
the hum lessens a little..80s Marshall Reverbs are always noisy in my
experience.

And this Amp pops sometimes when powering down, this is normal on
this model. If you dont want it to pop leave it on for about 10 minutes after
playing, if you switch off then 9 out of 10 times it doesnt pop.

Hope this helps.

Its a nice Amp, sounds nice, just feels a little stiff to me when i play,
has a hard attack.

Have fun.