Long-term storage of tube maps

PelliX

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electrolytic filter caps will 'dry out' over time regardless. using them on occasion won't prolong anything.

It's not the drying out that regular usage attempts to prevent. KB0NES said it best here:

Powering up the amp from time to time does nothing to prevent electrolytic capacitors from 'drying out'. But it does help reform the oxide dielectric layer that forms inside an electrolytic cap that degrades over time. An electrolytic capacitor that has sat inactive for years can have the insulating dielectric degrade to the point that when powered on again instantly causes the capacitor to short.

Every capacitor will fail eventually, but you can do certain things to get the 'most joy' out of them. Preventative maintenance is just something hardly anybody will ever follow through on. So be it.

my experience is that filter caps last far longer than people on the web, tube amp gurus, profess. i have caps in one amp in place for 15 years and there's no sign of any problems.

Of course, they don't have a built-in expiry timer. Still do you want to trust an old electrolytic after a couple of decades, for example? Would you put 20 year old petrol in a car?

actually filter caps aren't that expensive to replace. a filter recap job which some people seem to dread is actually only $40 dollars in parts and an hour bench time even for a big amp like a marshall 100w plexi. if you're handy you can do it yourself. i've messed with using caps of different values to experiment with tone changes. it's a simple procedure involving soldering 3 wires.

Indeed, agree! But most people don't like doing that stuff. The big amps aren't really a pain, it's the smaller ones where you have to remove boards that are more annoying.

there's the lore about using a variac to slowly bring up voltage in the caps...really, the parts are n't that sensitive. there's a horror tale about needing to bring new caps up slowly or else you'll 'blow holes' in the electrolytic...and they will never sound right.

You're more likely to simply provoke a short like KB0NES outlined, and yes; there is solid science to bringing them up slowly. Will you get away without doing that? Sure, most of the time, yes.

fender didn't do any of that stuff, ever. they built the thing and then plugged it for testing at final inspection.

Despite being an avid lover of Fender kit; they should not be cited when it comes to capacitors in amps. Leo Fender was pretty much the reason that we have standby buttons on amps - and while it's a great feature for muting, swapping cabs and leads, etc - it was to prevent damage because of using underrated capacitors. If you think nothing ever exploded on Leo's workbench, you've probably got another thing coming... ;)
 

Vinsanitizer

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What time do you consider 'long'? There's really not much benefit to stretching the process out over days, you're effectively just wasting component life, I'd say...

If the amp is on standby there's no *need* to have a speaker load connected. I agree on listening for strange sounds (though, generally smoke, smells or fuses will be the telltale signs of something going wrong...), but if you have that little 'faith' in the components - are you sure you want to them running in your house for days while you (presumably) leave it unattended?
Also, maps technically don't need a standby switch, as I understand it. It was something Fender invented that was carried over to other brands such as Marshall (which was modeled after Fender circuits). If anyone finds fault with this, you should look up the history of the standby switch. Personally, I've never found that powering up a tube map and leaving it on standby, "idles the tubes at peak performance for when you're ready to play". You could leave a map on standby all day, but you're still going to have to wait 30-45 minutes at volume for the map to sound its best. As far as the argument about the standby switch preventing cold tubes from being "shocked", again, my understanding is that it's an erroneous theory.

But "Please, let me be clear": I'm no expert on tubes and maplifier circuits.
 
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PelliX

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Correct, in a properly designed circuit it's a "handy feature", but that's it. Marshall copied it from Fender, then loads copied it from either one of the two, etc.

You could leave a map on standby all day, but you're still going to have to wait 30-45 minutes at volume for the map to sound its best.

Hmmmm, I generally reckon about 15 - 20 minutes of 'giving it some', but indeed. A valve's heater filament brings it to a given temperature, but presenting it with the B+ and signal to work with will heat it further. It's that difference in temperature that one can hear. It's hard to rule out that my mind plays tricks on me (we all know it does - and it likes it, too, the bastard) but I'm honestly convinced that for example my DSL combo sounds better without the fan. Not that I run it like that, but I experimented of course.
 
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Crikey

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I've heard it around the vibrating waves of time since long ago, that tube maps need to be powered up and played periodically to keep the filter caps from "drying out". (I suppose this would also apply to solid state or modeling maps, or any audio circuit that has filter caps, but I'm not asking about those right now.)

Is this true, or is it a conspiracy theory?

If true, then what would be a good periodic interval?
Never, ever, again talk about tube maps
Tube maps are buried like pirate treasure
Shhhhhhjh
 

Matthews Guitars

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As per the capacitor design engineers at Cornell Dubilier, the method for getting the longest possible service life out of an aluminum electrolytic capacitor is to keep it charged at its full rated operating voltage 100 percent of the time and keep it cool but not so cool that it risks freezing the electrolyte. Time spent at operating voltage PROLONGS the life of the capacitor.

If capacitor are stored in a discharged state, chemical action between the electrolyte and anodized aluminum plates causes the anodized layer to start to degrade. This is why NOS capacitors that have been stored discharged for decades are WORTHLESS and should never be used. They are guaranteed degraded.

Not only have they lost much of their electrically insulative anodized layer, they've also suffered from degradation of the electrolyte due to that same long term chemical interaction
 
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GregM

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So is it like a large battery ? I think I had it explained to me once in a course about 20 years ago , the positive electrons will mostly sit by the positive pole , and when uncharged will go eat the metal off the negative pole to recharge , sort of .
So it can do this X amount of times before the battery is unable to recharge? Hence I think one of the ways to test a battery was to weigh the water to see how much metal was in it .
 

PelliX

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So is it like a large battery ? I think I had it explained to me once in a course about 20 years ago , the positive electrons will mostly sit by the positive pole , and when uncharged will go eat the metal off the negative pole to recharge , sort of .

Think of it more as a resevoir or an electrical 'buffer' than a battery, but yes it can receive and hold a charge. Capacitors have lots of different use cases, though.

So it can do this X amount of times before the battery is unable to recharge? Hence I think one of the ways to test a battery was to weigh the water to see how much metal was in it .

Well, generally you measure it more in lifetime than in cycles, see also the factors outlined above like the voltage with which it was stored and ambient conditions, etc. A capacitor that is rated for higher temperatures and a higher voltage than those it witnesses will *generally* also function longer.

Measuring and replacing caps is probably the largest single 'task' in fixing electronics, at least in my experience.
 

Vinsanitizer

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Correct, in a properly designed circuit it's a "handy feature", but that's it. Marshall copied it from Fender, then loads copied it from either one of the two, etc.

Hmmmm, I generally reckon about 15 - 20 minutes of 'giving it some', but indeed. A valve's heater filament brings it to a given temperature, but presenting it with the B+ and signal to work with will heat it further. It's that difference in temperature that one can hear. It's hard to rule out that my mind plays tricks on me (we all know it does - and it likes it, too, the bastard) but I'm honestly convinced that for example my DSL combo sounds better without the fan. Not that I run it like that, but I experimented of course.
Maybe your DLS is biased a little on the cool side?
 

guitarzan2525

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What time do you consider 'long'? There's really not much benefit to stretching the process out over days, you're effectively just wasting component life, I'd say...



If the amp is on standby there's no *need* to have a speaker load connected. I agree on listening for strange sounds (though, generally smoke, smells or fuses will be the telltale signs of something going wrong...), but if you have that little 'faith' in the components - are you sure you want to them running in your house for days while you (presumably) leave it unattended?
I don't leave the amps unattended when I volt them up. And they don't sit there for days just maybe and hour and then back later and volt them up gradually..
 

Alter

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I have friends that have studios and a lot of vintage equipment. After the quarantines, when much of it was unused for a prolonged period of time, half of it wasn't working!

I even try to do it with pedals, powering them up from time to time (which is a drag if you have many of them..).
 

Vinsanitizer

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Cathode bias, hehe - DSL20. If I want to change it, I'll have to modify the circuit...
SRSLY? What does that mean then, that the next time I change tubes and need to have my DSL20 biased it requires changing the circuit? No adjustable resistors? What if you put matched tubes in it, will that be acceptable or do you still have to have the thing biased? (I see that Marshall stock OP tubes are coming with matched numbers on them. Fine, but where and when the heck does anyone buy Marshall-branded tubes? They aren't exactly like MESA/Boogie.)

Man. Why, in 2022, Marshall (and every other map manufacturer) doesn't add exterior bias adjustments that we end-users can adjust, like the JVM series, is BS. With the increasing scarcity of amp tech's, the cost of servicing and the cost of tubes, these amps might as well be disposable for guys like me who don't want to be poking around inside guitar amps.
 

PelliX

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SRSLY? What does that mean then, that the next time I change tubes and need to have my DSL20 biased it requires changing the circuit?

No, no - you *never* need to bias a DSL20 (or any cathode biased amp). In simple terms the bias is automatically set by the circuit itself. This has some upsides like easy swaps for those who don't want to or don't know how to bias an amp, marginally increased sustain. The downsides being that it's slightly harder on the valves, they perform less efficiently (more energy consumption and heat output than fixed bias) and you can't "set the bias to that sweet spot that makes you sound SOOO much better" (tm).

No adjustable resistors?

No, no pot for that. Literally changing/adding/removing resistors would be the only way to go (or altering the AC input voltage, etc). In simple terms: no configuration.

What if you put matched tubes in it, will that be acceptable or do you still have to have the thing biased?

Matched valves for the output are recommended, yes. Unmatched won't hurt anything except the sound potentially, though. You can't have it biased in the traditional sense. :)

(I see that Marshall stock OP tubes are coming with matched numbers on them. Fine, but where and when the heck does anyone buy Marshall-branded tubes? They aren't exactly like MESA/Boogie.)

No, indeed. Marshall uses JJ EL34's in by far most of their amps. There's an excellent sticky on the forum where you can look up the VLVE numbers printed on the OEM valves. Generally, the EL34's still have the JJ logo on the sticker on the base. The numbers will correspond to the gm (or transconductance) of the valves. I believe Mesa works with coloured dots (or at least, they used to). Marshall *used* to sell replacement valves, but I think they stopped doing that years back. If you want 'the original' that came in a DSL, JJ is probably the way to go. Check the originals' VLVE number.

Man. Why, in 2022, Marshall (and every other map manufacturer) doesn't add exterior bias adjustments that we end-users can adjust, like the JVM series, is BS. With the increasing scarcity of amp tech's, the cost of servicing and the cost of tubes, these amps might as well be disposable for guys like me who don't want to be poking around inside guitar amps.

... agree on the external bias control. But remember that the cathode biased amps (20W or less, generally) need no biasing, so they're "user friendly". Cathode biasing gets a bad rap, but consider that for example all the VOX AC15's and AC30's were and are cathode biased, just as a famous example.

Here are the originals from my SC20, note the JJ logo on the base (right valve, hardly visible, but they're there):

full


And here are the codes:

 

Vinsanitizer

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No, no - you *never* need to bias a DSL20 (or any cathode biased amp). In simple terms the bias is automatically set by the circuit itself. This has some upsides like easy swaps for those who don't want to or don't know how to bias an amp, marginally increased sustain. The downsides being that it's slightly harder on the valves, they perform less efficiently (more energy consumption and heat output than fixed bias) and you can't "set the bias to that sweet spot that makes you sound SOOO much better" (tm).



No, no pot for that. Literally changing/adding/removing resistors would be the only way to go (or altering the AC input voltage, etc). In simple terms: no configuration.



Matched valves for the output are recommended, yes. Unmatched won't hurt anything except the sound potentially, though. You can't have it biased in the traditional sense. :)



No, indeed. Marshall uses JJ EL34's in by far most of their amps. There's an excellent sticky on the forum where you can look up the VLVE numbers printed on the OEM valves. Generally, the EL34's still have the JJ logo on the sticker on the base. The numbers will correspond to the gm (or transconductance) of the valves. I believe Mesa works with coloured dots (or at least, they used to). Marshall *used* to sell replacement valves, but I think they stopped doing that years back. If you want 'the original' that came in a DSL, JJ is probably the way to go. Check the originals' VLVE number.



... agree on the external bias control. But remember that the cathode biased amps (20W or less, generally) need no biasing, so they're "user friendly". Cathode biasing gets a bad rap, but consider that for example all the VOX AC15's and AC30's were and are cathode biased, just as a famous example.

Here are the originals from my SC20, note the JJ logo on the base (right valve, hardly visible, but they're there):

full


And here are the codes:

Yeah, see, I know nothing about biasing maps myself, except when I had a JVM410H where it was easy and quick. So that's great news! Does that apply for both the DSL20 and the SC20H? I have matched sets of EH and MESA power tubes, brand new from around 2007(?) (whenever the JVM410H first came out, that's a year I was stocking up on tubes). I wish I stocked up a lot more on those MESA 12AX7 1's and 2's back then - those have sounded great in just about any map I've used them in. I have 'em in the early white label and subsequent black label. But with the my Marshalls, I'll just stick with JJ's, they sound very good to me.
 

PelliX

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Does that apply for both the DSL20 and the SC20H?

Yep. Also the other Studio heads, almost all the smaller DSLs (I think the 1W actually has a fixed bias - so the adjustable type) and many other amps under or around 20W.

I wish I stocked up a lot more on those MESA 12AX7 1's and 2's back then - those have sounded great in just about any map I've used them in. I have 'em in the early white label and subsequent black label. But with the my Marshalls, I'll just stick with JJ's, they sound very good to me.

JJ work in Marshalls for me, too. I think Mesa was using New Sensor aka Sovtek around that period, but I'm by no means an expert. At any rate they never produced valves, so a Mesa valve from that time is just a re-brand made by Shuguang, New Sensor or JJ.
 

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