Marshall JCM800 Questions

[novosibir]

Electrolytic capacitors have a shorter lifespan than tubes, in general.

Are you saying your tubes will last longer than 30-40 years before they need changing?

 

[novosibir]

It's a lot like having the mechanic just replace standard wear parts in an engine while it's opened up. You're not doing it because they're bad. You're doing it because you're there, and it make sense to just do it all at once. Capacitors are cheap and most of the labor was paid getting there.

That's the typical statement of a modern-day engineer with no empathy for the amp owner's desire to keep the old vintage sound of his amp.

Would you also advise the owner of an old 1964 Strat to repaint the body because the guitar already has some scratches, scrapes and scuffs?

 

[rstites]

Are you saying your tubes will last longer than 30-40 years before they need changing?

Nah, it's more of a historical statement. You used to have to change capacitors out more often because modern dielectrics hadn't been invented. Again, pulling from the old radio guys.....and I'm not really one of them. It's just their warnings on replacing caps.

In industry, we don't tend to run electrolytics for nearly that long though.

 

[Racerxrated]

ARS are the electrolytics that come closest to the LCRs in terms of sound - and yes, they are ok, but unfortunately a little thinner than the originals and therefore a bit tricky to get them firmly in the clamp.

However, if you install F&Ts or JJs for a very vintage sound-oriented guitarist with (still) good ears instead of the Daly or LCR, he may tell you that he no longer recognizes his amp and immediately afterwards he will cry. I've experienced it exactly the same way, otherwise I wouldn't write it.

I did experience this very thing, on an 87 Jubilee 2555. The caps were replaced by F&T. The amp had a kind of 'graininess' to the gain, grittiness or something but it wasn't the smooth Jubilee tone I expected. Sold the amp. Then, an 82 2204 had the same thing to the tone, again with F&T. Bought some ARS and swapped them in, and the tone was back to normal.
Most say caps don't affect the tone, but I know 3 others here on RT that feel the same way about F&T caps in a Marshall.

 

[rstites]

That's the typical statement of a modern-day engineer with no empathy for the amp owner's desire to keep the old vintage sound of his amp.

Would you also advise the owner of an old 1964 Strat to repaint the body because the guitar already has some scratches, scrapes and scuffs?

It has nothing to do with empathy. It's why it's a very common recommendation. It also isn't something I'm personally recommending for or against. Don't assume that me making a factual statement about why something is done is taking a position on the desirability of doing it.

 

[Chubbs]

Crazy idea, but try both. Personally I hated the stock daily’s in my 79, which were not leaking nor bulging. Newer replacements brought out a fuller, less harsh/ice picky sound. It’s not like you can’t swap them back in.

 

[glpg80]

ARS are the electrolytics that come closest to the LCRs in terms of sound - and yes, they are ok, but unfortunately a little thinner than the originals and therefore a bit tricky to get them firmly in the clamp.

However, if you install F&Ts or JJs for a very vintage sound-oriented guitarist with (still) good ears instead of the Daly or LCR, he may tell you that he no longer recognizes his amp and immediately afterwards he will cry. I've experienced it exactly the same way, otherwise I wouldn't write it.

I’ve experienced it too. I recapped a 79 2204 to flip with F&Ts and it made the amp sound cold and lifeless. I’ve learned ARS are the only ones I care for.

I disagree that ARS are thinner. In my experience they sound warmer and give more detail. Their value determines their electrical response and more tonal pallet as you know which is amplifier specific.

 

[glpg80]

It has nothing to do with empathy. It's why it's a very common recommendation. It also isn't something I'm personally recommending for or against. Don't assume that me making a factual statement about why something is done is taking a position on the desirability of doing it.

+1

Would you run original tires on an all original collector car knowing damn well you’re taking a chance they could cause an accident? Or would you put decent safe look-alike tires on it to assure your safety and the vehicles safety? The same analogy applies - if all you’re going to do is look at it, and never turn it on, then the originals will do fine. But if you’re going to play it, there’s zero reason not to change them out. The LCRs in my 74 leaked from the inside of the chassis and were the reason I got the amp at a discount - it was a corrosive catastrophe. It corroded all of the mains switches and even permanently stained the internal of the chassis. Not to mention the cancerous PTFE hazards including the fumes. They need to go and be gone for a plethora of reasons.

 

[Greazygeo]

I have never had an old amp wth original caps that sounded good. They either hum, ghost note or have loose low end or all of the above. My main 69 plexi has been recapped twice I have had it so long.

Even my Wizard had to be recapped and it was made in ‘05. Freakin ghost notes….

 

[BesaMoogie]

This comment has nothing to do with this amp, but is intended to shed some light on the subject of electrolytic capacitors - and to diplomatically lead the battle between glpg80 and Racerxratet to a peaceful solution.

In principle, every EE learns during their training that electrolytics (depending on the country and the applicable VDE, RU, CSA, etc. regulations) must be replaced after 10, 15 or 20 years. In addition, new Electrolytics may only be installed if they have not yet exceeded a storage age of 5 years.

These are the basics in school, training and that's what the textbooks say - just like you should throw away a can of beans after the expiry date has passed, although the contents could still be enjoyed for a few years longer without any problems.

That's just the theory - but now to practice (electrolytics, not beans )

The Erie electrolytics could be critical due to its age of meanwhile 55-60 years and should therefore be carefully checked for capacitance, ESR and leakage current (which requires unsoldering the positive contact and inserting a mA meter) after a gentle discharge.

The later Daly and especially the even later LCR electrolytics have (contrary to the laws of physics) an apparently (almost) unlimited life span.

However, this only applies if the amp has NEVER been out of use for more than half a year since it was first fired up as a new amp.

Unused electrolytics gradually deform, which, to put it in understandable terms, means that the oxide layer, which acts as the only insulator between the two aluminum foils in an electrolytics gradually dissolves, is dissolved by the electrolyte - and thus both foils come into electrical contact with each other. This process begins gradually after about 6 months without any voltage being applied and is completed after 2-3 years at the latest.

Now, when someone finds an old Marshall in a friend's basement or attic that hasn't been used in several years, they are at first delighted and can't wait to fire it up and hear the old sweetheart - but the joy is there usually only short and is abruptly ended by an ugly crash, followed by a massive hummmmm. One or more electrolytics have died due to a internal short and in the worst case even burst or explode.

In order to avoid this, you MUST form the electrolytics of an old amplifier that has not been in use for more than 6 months before switching it on again for the first time, so that the insulating oxide layer on the internal aluminum foil, which has since dissolved can form again.

I described how this works with Marshall amps almost exactly 16 years ago here:

http://forum.metropoulos.net/viewtopic.php?p=81922

Btw - I still use good old NOS LCR electrolytics for my new builds, which were produced in 1993 & 1994 and of which I had bought plenty of them in good time before the end of production.

Of course I have to form these electrolytics, which is a 36-48 hour process before I start my newly built DINO, British Purist, Rock Wizard or Pure Metal Machine with the tubes applied for the first time - but...

... I haven't had a single 'old' LCR of my newly built amps fail due to a defect - and my DINOs in particular are sometimes used live up to 150 shows a year for several hours each

Thanks Larry for the intel.
I did read the section in the metro forum. So my question is, can this be done without the desolder work? Some of my amps are a bit more "complicated" to get easy access to the caps etc.

So I was thinking of using a variac (and a current drawer like a 250W light bulb before the amp) and then slowly increase the voltage. So like starting at 50V for 2 min and then go up in 50V steps every 2 min till I reach the final 230V. All tubes are installed during this process.

What do you think about this method?

 

[novosibir]

ARS are the electrolytics that come closest to the LCRs in terms of sound - and yes, they are ok, but unfortunately a little thinner than the originals and therefore a bit tricky to get them firmly in the clamp.

I’ve experienced it too. I recapped a 79 2204 to flip with F&Ts and it made the amp sound cold and lifeless. I’ve learned ARS are the only ones I care for.

I disagree that ARS are thinner. In my experience they sound warmer and give more detail. Their value determines their electrical response and more tonal pallet as you know which is amplifier specific.

Just as shit happens, so do misunderstandings

I didn't say that ARS' sound thinner in sound, but that they are a bit thinner than e.g. LCRs - a bit thinner in diameter

 

[novosibir]

Thanks Larry for the intel.
I did read the section in the metro forum. So my question is, can this be done without the desolder work? Some of my amps are a bit more "complicated" to get easy access to the caps etc.

So I was thinking of using a variac (and a current drawer like a 250W light bulb before the amp) and then slowly increase the voltage. So like starting at 50V for 2 min and then go up in 50V steps every 2 min till I reach the final 230V. All tubes are installed during this process.

What do you think about this method?

You just had to read my second post in this thread on Metroamp Forums, which is right there as post #3, then you would have already had the answer to your question, because there someone asked the same question in post #2 as you did here

But anyway - there I wrote:

"That's at least better, than not at all forming the caps.
The first problem is, that with the variac you're limiting the voltage to the caps, and not the current - the current only is limited indirectly.
The second problem is, that you can't sense, how slow the caps need it to be formed or how fast you can proceed - you're deciding the process in this case.
The third problem is, that most of the people don't have so much patience, to regulate up the variac every 10-15 minutes a tad further, and that sometimes over a duration of up to 24 hours.
But the benefit of the resistor method is, that the caps are regulating all by itself - and you only have to check the proceeding result.
So why the stress with the variac?"

 

[BesaMoogie]

You just had to read my second post in this thread on Metroamp Forums, which is right there as post #3, then you would have already had the answer to your question, because there someone asked the same question in post #2 as you did here

But anyway - there I wrote:

"That's at least better, than not at all forming the caps.
The first problem is, that with the variac you're limiting the voltage to the caps, and not the current - the current only is limited indirectly.
The second problem is, that you can't sense, how slow the caps need it to be formed or how fast you can proceed - you're deciding the process in this case.
The third problem is, that most of the people don't have so much patience, to regulate up the variac every 10-15 minutes a tad further, and that sometimes over a duration of up to 24 hours.
But the benefit of the resistor method is, that the caps are regulating all by itself - and you only have to check the proceeding result.
So why the stress with the variac?"

Thanks! Was only reading the initial post of yours

 

[novosibir]

How often and for how long do I have to fire up my amps that aren't used daily to prevent this from happening?

Putting the amp into operation for about 20 minutes every 6 months is completely sufficient. You don't even have to play through it - it's enough if it's only switched completely (!) on, of corse with the speaker cab connected.

 

[Racerxrated]

I have never had an old amp wth original caps that sounded good. They either hum, ghost note or have loose low end or all of the above. My main 69 plexi has been recapped twice I have had it so long.

Even my Wizard had to be recapped and it was made in ‘05. Freakin ghost notes….

My 72 sounds like God if he played rock. Maybe the Daly caps throughout are re formed replacements, by some restorer? Who knows. All I know is, it sounds incredible with no ghost notes, hum, nada. It's been very obvious to me when an amp needs the caps replaced. Sounds like shit.
I've been tempted to change them to ARS, in my 72 just to see if it might even sound better than it does. But it's damn near perfect the way it is. In the last 16 years I've had over 60+ Marshalls, all 1990 or earlier, stock and modded. Only 1 had obvious leaky caps, sounded like shit, GE 6550s were biased around 15ma. Re capped and re biased and it was golden. But the other 60 had original LCR or Daly caps, no leaking, hum, ghost notes etc. I guess I'm just lucky.

 

[Arch Stanton]

Putting the amp into operation for about 20 minutes every 6 months is completely sufficient. You don't even have to play through it - it's enough if it's only switched completely (!) on, of corse with the speaker cab connected.

You're never gonna be able to play CHUGGA CHUGGA REEEE! CH-CH-CHUG-CHUGGA CHUGGA SQUEEE like that, Larry.

You have to work at it.

 

[japetus]

Guys, I can solve everyones problem right now. Just send me all of your rarely played old Marshalls. I will make sure they get cranked up and played enough so the caps never go bad. It's a win win situation for everyone involved. Feel free to PM me for shipping info!

 

[Greazygeo]

My 72 sounds like God if he played rock. Maybe the Daly caps throughout are re formed replacements, by some restorer? Who knows. All I know is, it sounds incredible with no ghost notes, hum, nada. It's been very obvious to me when an amp needs the caps replaced. Sounds like shit.
I've been tempted to change them to ARS, in my 72 just to see if it might even sound better than it does. But it's damn near perfect the way it is. In the last 16 years I've had over 60+ Marshalls, all 1990 or earlier, stock and modded. Only 1 had obvious leaky caps, sounded like shit, GE 6550s were biased around 15ma. Re capped and re biased and it was golden. But the other 60 had original LCR or Daly caps, no leaking, hum, ghost notes etc. I guess I'm just lucky.

Hope you got a lottery ticket . Every single Marshall 100 watt amp I have ever had had ghost notes…even the 1959RR. All mine have been the 73 and earlier. The later JMP 03-04 didn’t.
The older 60’s Fenders don’t seem to ghost note, but the caps pretty much always leak. Just recapped a blackface Super Reverb, low end was gone in that one. Some caps were bulging out. That amp sounded great after.
Just my experiences….

 

[bubbastain]

Not a Marshall and not LCR caps, but my recent VTM60 amp sat unplayed in a garage for 25 years before I bought it off the original owner. I was kinda expecting some hum or to see some leaking caps or just something. No problems that I'm aware of so far. Sounds just like a healthy VTM. Should I change out the caps?