Tube amps without standby switches

Pantalooj

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3,650
What's the story here?

Do such amps have other means of protecting tubes during start up? Or do they simply wear tubes out faster?

Once they're fired up, is the idea to simply turn the volume down (guitar or amp) when they're not being played for a while instead?

Are they to be avoided?

I've got one at the moment (Classic 30) and I can't say it's ever bothered me. I'm also considering a new amp that doesn't have a standby either ... is it something that would put you off? Even if you liked everything else about the amp?
 

rhythmeister

Member
Messages
87
One part of the story is that if the amp is tube rectified (as opposed to ss rectified) then standby is superfluous b/c the rectifier tube fulfils the same role a standby switch would.

Cheers,
Blair
 

Blue Strat

Member
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30,694
One part of the story is that if the amp is tube rectified (as opposed to ss rectified) then standby is superfluous b/c the rectifier tube fulfils the same role a standby switch would.

Cheers,
Blair

...but ONLY if the particular rectifier is "indirectly heated" which results in slow turn on. The only common guitar amp rectifiers that do this are 5AR4/GZ34, 5V4, and some special 5Y3s. The others turn on quickly and slam the other tubes just as a SS rectifier does.
 

fullerplast

Senior Member
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6,781
I'm also considering a new amp that doesn't have a standby either ... is it something that would put you off? Even if you liked everything else about the amp?

Choose an amp based on tone, not standby switches!

If you eliminate those without, you could be missing out on some of the greatest amps ever made....like tweed deluxes, BFPR's, or AC30's!
 

Pantalooj

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3,650
Choose an amp based on tone, not standby switches!

If you eliminate those without, you could be missing out on some of the greatest amps ever made....like tweed deluxes, BFPR's, or AC30's!

Agreed. As I said I have an amp (C30) without standby now and it has never bothered me ... but I've read a couple of posts hear and there about this amp from people saying that it needs a standby, and even a mod to add a standby. I'm just checking to see if I've missed something. Definitely tone comes first.

Thanks
 

hasserl

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4,708
Standby switches, IMO, are greatly overrated for guitar amp use (meaning their value is greatly overrated, not the quality or specification of the parts used ;) ). They are handy for silencing an amp for switching guitars, etc. but for extending tube life there is no evidence they provide any benefit. If they make you feel better, that may be a side benefit. Certainly nothing to worry about, or waste time and resources adding one to an amp designed without one. JMO of course.
 

HKGuns

Member
Messages
92
Excuse me, could someone 'splain to me how turning the gain down replaces a standby switch? - I don't think so.

No evidence they provide any benefit? You don't think all that heat at idle has any effect on your tubes or it's circuits?

They're there for good reason.. Slamming cold tubes has never been and never will be a good idea.

They certainly aren't the tube equivalent of a mute button.
 

hasserl

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4,708
What I, or anyone else, thinks is not evidence, it is opinion. Show proof that "slamming" cold tubes has any harmful effect. Explain why slamming cold tubes is less harmful than slamming hot tubes, or is less harmful than slamming standby switch contacts, or less harmful than slamming filter capacitors.
 

somedude

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8,135
Excuse me, could someone 'splain to me how turning the gain down replaces a standby switch? - I don't think so.

No evidence they provide any benefit? You don't think all that heat at idle has any effect on your tubes or it's circuits?

They're there for good reason.. Slamming cold tubes has never been and never will be a good idea.

They certainly aren't the tube equivalent of a mute button.

Turning down the gain prevents you from hitting cold tubes with signal.
 

Pantalooj

Member
Messages
3,650
At this point I think we need an amp builder guru to chime in and explain the facts ... anyone?

I do know, for a fact, that amp makers' manuals for amps with standbys state that the standby mode should be used when powering up to prolong tube life:

From the Mesa Boogie Express manual:

STANDBY: Perfect for set breaks...this toggle switch also serves an even more important purpose. In the STANDBY position (switchup), the tubes are at idle so that during power up they may warm up before being put to use.

Before the power is switched on, make sure the STANDBY switch is in the STANDBY position. Wait at least 30 seconds and then flip the STANDBY switch to its ON position. Following this simple warm up procedure helps in preventing tube problems and increase their toneful life substantially.
From the Genz Benz Black Pearl Manual:

STANDBY SWITCH: The Standby switch removes the high voltage power supply from the plate circuit of the output tubes to protect the tubes from “cathode stripping” when first powering up the amplifier. The recommended start-up procedure is to place the standby switch to the standby position, turn on the power switch and allow the amplifier to warm up for at least 30 seconds before switching the standby switch to the operate position. This will help to prolong the life of your output tubes.​

and I'll ask again from my original post: Do amps without standby switches have other means of protecting tubes during start up? Or do they simply wear tubes out faster?
 

blackba

Platinum Supporting Member
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12,206
Amps like a fender champ have no standby switch, but I heard since they are class A, that they don't need one, not sure why or if this is correct.

A vintage vox AC50 has not standby switch and uses a Brimistor to help with the cold start, not sure what this device actually does.

Whether your amp has a standby switch or not, its a good idea to let it warm up before slamming it with your favorite boutique overdrive.
 

hasserl

Member
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4,708
Martin, titles mean nothing. Anybody can build amps, doesn't make them a guru. Pay attention to facts, not opinions. Mesa Boogie and Genz Benz are simply repeating the same urban myths they've heard themselves.

Search out the info yourself, there is NO empirical evidence of cathode stripping in guitar amps. NONE, ZILCH, NADA. Anyone that says otherwise, ask them to provide it, they will not be able to, it doesn't exist.
 

Pantalooj

Member
Messages
3,650
Martin, titles mean nothing. Anybody can build amps, doesn't make them a guru. Pay attention to facts, not opinions. Mesa Boogie and Genz Benz are simply repeating the same urban myths they've heard themselves.

Search out the info yourself, there is NO empirical evidence of cathode stripping in guitar amps. NONE, ZILCH, NADA. Anyone that says otherwise, ask them to provide it, they will not be able to, it doesn't exist.

I probably used the wrong terms ... by "amp builder guru" I meant someone who knows how tubes work and can explain whether cathode stripping (or other damage) is possible and detrimental in a guitar amp, under start up conditions.

I'm on the fence ... on the one hand the only evidence that I have now is that manufacturers go to the trouble of fitting standby switches to most tube amps, and then tell you to use it at start up ... why would they do that if there was no benefit? Then on the other hand there are tube amps with no standby switches that work perfectly well ... but I don't know if they have other tube protection mechanisms, other than the mysterious Brimistor on an old AC50.

Just curious at this point I suppose.
 

Jon Silberman

10Q Jerry & Dickey
Silver Supporting Member
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44,752
Internet tube expert hasserl will tell you that that is completely unnecessary, but apparently Brimar, a major manufacturer of tubes back in the day, would have disagreed with him. The fools.

Hogy

hasserl is far from alone in his views and the fact that a major tube manufacturer from decades back might have disagreed with him does not make him wrong.

Copyright 2006 © David B. Lamkins How to use a standby switch

There's a lot of information on the `net and in manufacturers' literature about how to use the standby switch on your tube amp. Not surprisingly, there are a lot of different procedures. In the words of at least one frustrated player, "there's not a lot of concensus among the experts."


Most of the experts cite the "cathode stripping" boogieman to convince guitarists to religiously follow a standby switch ritual. Their notion is that applying high voltage to the circuit before the cathode is fully up to working temperature will physically strip the delicate coating from the cathode and prematurely age the tube. You'll be left with a tube that doesn't work and has a bunch of white fluff (the stripped cathode coating) floating around inside the glass envelope. Expert opionions vary regarding how long you should wait before turning your standby switch to the "play" position; I've seen times ranging from thirty seconds to five minutes. And some experts even recommend that you put your amp on standby for some period of time to give your tubes a chance to "cool off" before turning off the power.


Let's look first at the range of "wait" times cited by the experts. Heaters come up to temperature in about 15 seconds. You can find out by powering-up your amp without using the standby switch. (I'll bet that makes you nervous, doesn't it? Read on...) Even if there was something to the threat of cathode stripping, the threat would be eliminated as soon as the cathodes came up to temperature and the tubes started functioning. So what's up with the recommendations to wait sixty seconds, or two minutes, or ... five whole minutes? If fifteen seconds is good, then three hundred seconds must be really, really good?


Cathode stripping is real. (Sit down. I haven't misled you.) It happens at very high voltages and currents. If you go back to the manuals and engineering texts of the `50s and `60s you'll discover that no one ever wrote about cathode stripping with respect to "receiving tubes" (as compared to "transmitting tubes"). "Small" tubes like the 12A?7, 6L6, 6V6, EL84, EL34, EF86, ... are receiving tubes. With the exception of a few tube amps having very high (~700V) plate voltages (like the SVT and a few high-powered Marshalls), you don't really need a standby switch except as a convenience for muting the amp; I'd rather just pull the cord from the input jack or turn down the volume control on the guitar. There is no way that cathode stripping can occur in preamp tubes, even in an SVT; the available energy is limited to a very low value by resistors in the plate circuits.


OK, so what about that bad tube you found with tiny bits of white fluff rattling around inside the glass bulb? Yes, that can happen. It's a result of poor bonding of the cathode coating combined with temperature cycling and vibration. It's not caused by cathode stripping.


Then you have to wonder about those amps that don't have a standby switch. The experts will tell you two things about that:
  1. You should probably have a qualified tech add one just to be on the safe side. Hey, techs have bills to pay just like the rest of us...
  2. Some amps don't need standby switches because they have "controlled warmup" vacuum tube rectifiers which don't reach their working temperature until all the other tubes are ready to go. Nice try, but not quite right or consistent with other expert advice... Rectifiers start working before they come up to full temperature, so there's some DC on relatively cold tubes throughout the amp. And given that the rectifier heats up about as fast as the other tubes, what becomes of the advice to hold off operating power until the tubes have warmed up for some number of minutes? Hmmm?
Standby switches introduce their own problems. They're not rated to break DC at the voltages present in any tube amp, let alone the bigger ones. (Check the ratings on a switch some day... The DC rating is always much lower than the AC rating.) When you break high DC voltages, the switch arcs and will eventually fail. It's a lot tougher to swap in a new standby switch than a new tube...


Switches are most prone to arcing as they open a circuit. In the case of the standby switch this happens when you switch the amp to standby. However, switch contacts "bounce" when you close a circuit; arcing may also happen on each bounce before the contacts finally come to rest. Arcing in this case is much less severe because there's less stored energy (see below) in the circuit as you're switching the amp off standby.


Arcing depends somewhat upon the circuit design. In general, though, standby switches are exposed to DC voltages well in excess of their design center. The reason it's so hard to make a mechanical high-voltage DC switch is because an arc is formed as the contacts open. The arc tends to continue so long as there's enough voltage to maintain it as the contacts separate. In circuits where there's a big inductor (like a filter choke) attached to the switch, the collapsing magnetic field (created by breaking the circuit) creates a high voltage that's sufficient to cause arcing. The duration of the arc is related to the amount of energy stored in the inductor.


A switch can and does arc with AC across it. However, the duration of the arc is limited because the AC voltage goes to zero 120 times per second (100 times per second in Europe). As the voltage approaches zero it very quickly becomes too low to sustain an arc, and once the arc is quenched it tends not to recur because the contacts have moved far enough apart that the voltage can't break down the air between the contacts. This is the reason that a switch has a higher rating for AC voltages than for DC.


Here's one more thing for you to ponder: "cathode poisoning". Normally the heated cathode throws off a cloud of electrons that get immediately pulled away from the cathode by the electrostatic field created by the plate voltage. When your amp is on standby you don't have any voltage on the plate, and that electron cloud hugs the cathode. Some of those electrons bump into the cathode coating and cause an electrochemical reaction which reduces the efficiency of the cathode coating which in turn reduces the useful life of your tubes. Unlike cathode stripping, cathode poisoning is not dependent upon how high the plate voltages are; when the amp is on standby there is no plate voltage. So now you have one more thing to worry about: If you put your amp on standby, how long before cathode poisoning becomes an issue? Is it cumulative?


You could lose sleep over things like this. Just keep in mind that no item of consumer electronics gear (and for that matter it applies to the small sampling of industrial electronics gear I've seen) made in the heyday of vacuum-tube electronics had a standby switch, except for guitar amps (which don't really need one) and ham radio transmitters (which really must have one). When you want to use the gear, you turn it on. When you're done, you turn it off. No rituals needed...


Frankly, with the exception of the arcing issue (which can cause an amp to become scratchy, poppy and to lose power because of carbon build-up due to arcing on the standby switch contacts), standby switches on most guitar amps (remember what I wrote about amps with very high plate voltages...) are harmless.


By all means use the standby switch if it makes you feel good. We all need rituals. But don't lose sleep over having powered your amp on (or off) the "wrong" way. It should be quite obvious from this discussion that guitar players follow a lot of different standby-switch rituals and no one's really suffering from having used any of the techniques described...


I leave my standby switches in "play"; they never move.


In deference to prevailing wisdom, though, I use the standby switch when cycling power on other people's amps; otherwise they get a bit pissy...
 

Pantalooj

Member
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3,650
Jon, thanks a million ... I think that's exactly what I was looking for. Even though David B. Lamkins is a software engineer (if he's the same guy I just found on the web) he sounds like he's done his homework and I like the way he thinks.

I shall continue along with my non-standby amp ... and will take this feature off the checklist when buying in the future ... not that it was ever there before really, until yesterday when I was comparing two possibles and noticed one had standby and the other didn't (same manufacturer by the way ... and same range ... Hughes and Kettner Statesman). That's, in fact, what prompted my opening post.

If I do end up with an amp with a standby switch, I think I'll use it at start up ... for 15 seconds :AOK
 

hasserl

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4,708
Thanks John, good info that should help Martin & others looking for truth.

Hogy, insults and personal attacks are the easy way out. If you have evidence of cathode stripping in a guitar amp go ahead an post it.
 

somedude

Member
Messages
8,135
Rivera recommends dropping the gain to zero for 30 seconds. It lets the tubes warm up with very little signal passing through them.

FWIW.... since no one seems to want to believe me on the gain knob thing.
 

Pantalooj

Member
Messages
3,650
Rivera recommends dropping the gain to zero for 30 seconds. It lets the tubes warm up with very little signal passing through them.

FWIW.... since no one seems to want to believe me on the gain knob thing.

Not a case of disbelieving you on my account ... in the end I was looking more for whether damage does actually get done ... is there a sypmtom to treat, rather than what's the treatment. Admittedly that's not how I phrased it in my original post ... I was just throwing the subject out there at first.

Thanks for posting!;)
 




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