Don't warm your valves.......? I saw this earlier

Wolfetone

Do you believe that your standby switch on your tube amp is necessary?

Do you think that you need to warm your tubes up before playing?

Well, I have some bad news, it looks like you’ve been living a lie.  Don’t worry, until about 4 hours ago, I too was living this lie, but now I’m about to set you free.

Using the standby switch on your tube amp is more likely to damage tubes inside (especially rectifier tubes) than it is to extend their life!

There’s no real reason for having one on guitar tube amps, and the standby switch is there like a lot of things in the guitar world.  People would be upset if it vanished and aren’t very receptive to change.  The only reason that the very first guitar tube amps featured a standby switch is because they didn’t really know what they were doing, and nobody since has really bothered to remedy this.

A lot of guitarists falsely believe that warming your tube amps up with the standby switch is necessary to avoid putting wear and tear on your tubes.  This supposed wear and tear is cause by cathode stripping,which is when particles of the oxide coating are ripped from the cathode when the cathode is exposed to the extremely powerful electrostatic field from the anode.  There’s also the threat of cathode sputtering but…

You don’t actually need to worry about either of these when it comes to guitar amps because the only time it becomes an issue is when you are using extremely high power tubes (and I don’t mean KT88s!) that don’t really find themselves inside of amps.  According to London Power, guitar amps usually run at less than 500V – which is far below the threshold for tubes requiring anything resembling a warm up.

Warming up guitar tubes might even be bad for them because of something known as cathode poisoning.  Cathode poisoning is primarily caused by a fully heated valve without any anode current running to it.  Over time, a permanent undesirable layer is created between the oxide coating and cathode tube.  Valve Wizard claims that amps with tube rectifiers should not be used in conjunction with a standby switch because switching from standby into your amp’s operating position causes current to surge into your tube which eats tubes up very quickly.  This most notorious example of this are some Vox models.  Many familiar with tubes know this as hot switching…which is a practice most companies that manufacture tubes say is very bad for the longevity of a tube’s life.

If your amp does have a standby switch, fear not.  Simply stop using it and enjoy longer tube life!  Now spread the word by sharing this article on Facebook and enlightening your uncivilized friends that are chewing through tubes because of their standby switch.

Still curious?  Or maybe you don’t believe us?  No problem.  Check out the articles we linked above by London Power and Valve Wizard, you’ll see exactly what we mean.  Wampler also wrote a fantastic piece on how useless your standby switch is.

imalrightjack

I believe @ICBM agrees.

Wolfetone

I didn't write this (far beyond my scientific understanding! ) but I was intrigued as to it's basis in fact. ICBM? r u lurking? 

bbill335

I've heard a tech say the same. You just don't need it. I wish someone would tell major amp manufacturers they can knock a few quid off their production costs and RRPs.

capo4th

Does it not depend on the design of the amp some are ok to flick the switch and play others need the warm up via standby switch?

ICBM

No, I don't agree. Although it's not actually necessary, a standby switch is still very useful - although possibly more for techs than for players! Troubleshooting is a lot easier when you can turn off the high voltage while the amp is on.

A standby switch certainly can put more strain on the rectifier valve, yes - but *only* if the switch is fitted in the wrong place in the circuit, as seems to have become common on many modern amps. If it's upstream of the first filter cap then the rectifier will have to supply more than its rated current when the switch is turned on and the cap is empty, as Valve Wizard said.

But if the standby switch is in the *correct* position, after the first filter cap, then this is not true because the cap will charge slowly as the rectifier warms up. Leo Fender knew this perfectly well, some modern valve amp designers don't seem to! That does not mean standby switches are bad at all, it means the designers have done it wrong…

Other than that, a standby switch does not shorten valve life and can extend it in those which run the valves very hot at idle, simply by not leaving them cooking away if the amp is not being used for a while. Cathode poisoning doesn't seem to occur to any significant degree.

I always use the standby switch on amps which have one, except for those with a valve rectifier which I know have it in the wrong place.

Hoof

My Hayden Mofo doesn't have one and it's the most reliable amp I've ever owned. I also did quite a few gigs without using the standby on my Fender Dual Showman after the swtch got snapped off with no ill effect. I still got it fixed and went back to using it out of perceived good habits. 

I always drain the caps by letting a note ring out after I've cut the power. It seems like a good idea but I kind of enjoy the sound of it more than anything.

Voxman

I have two valve combo amps with standby switches. A Laney VC30 and Marshall jcm2000 dsl401.  I was told by an amp tech that using the standby on both amps at start up and shutdown would be beneficial in prolonging valve life.  ICBM/other techs , do you concur?  

ICBM

Voxman said:

I have two valve combo amps with standby switches. A Laney VC30 and Marshall jcm2000 dsl401.  I was told by an amp tech that using the standby on both amps at start up and shutdown would be beneficial in prolonging valve life.  ICBM/other techs , do you concur?  

Startup yes, shutdown makes no difference.

More importantly, it lets you 'rest' the valves if you're going to take a set break, without turning the amp fully off which introduces another cooling/heating cycle - which is a bad thing and one of the known causes of valve failure, as well as not being good for the amp in general. This might help the valve life on the Laney (hot-running cathode-biased) and certainly won't be a bad thing with the Marshall either.

ecc83

ICBM have gone 3 falls andno submission on this several times and I do not intend to rake over old coals.

His point about "correct positioning" is fine but in these H&S times there is a "technical" problem. Most toggle switches of the sort used for SB duty are rated at 250V* max and the vast majority of guitar amp HT rails are well above this, especially "off load".

Now, I have never had or heard of a SB switch breaking down and shocking anyone but if it did AND "they" found it only had a 250volt rating, all hell would be to pay!

*Looking at one of "our" super chunky switches I see the rating is 15A @125V, 10A @ 250V. I take these to mean CONTACT ratings and not insulation strength? Personally I be quite happy to have that contact set up at 500V+ but you know what lawyers are like!

Er? WRT "draining the caps" I would like to see 220k discharge resistors fitted to all amplifiers. Standard practice OTHER than the gitworld.

Dave.

Modulus_Amps

I generally don't fit them on my amps, switches are not rated for high voltage switching and its just another part taking up valuable panel space that could be a pot or switch for tone options.

For techs, If you need to turn the amp on without powering the valves up you can remove the HT fuse pretty easily, and every amp should have those fitted now.

ICBM

Modulus_Amps said:

For techs, If you need to turn the amp on without powering the valves up you can remove the HT fuse pretty easily, and every amp should have those fitted now.

Should, yes - many older and even some newer ones don't. It's often not worth the hassle of fitting one if it's a customer's job either.

That's actually something that Leo Fender *didn't* get right, and the modern Fender company is one of the culprits for not doing too.

Modulus_Amps

ICBM said:

Should, yes - many older and even some newer ones don't. It's often not worth the hassle of fitting one if it's a customer's job either.

Should have said every new amp should have one fitted

I probably would have agreed with that a few weeks ago, but recently had an amp that started blowing HT fuses and it took a bit to figure out what what wrong, anyway for £1.00 worth in parts I am glad I had an inline HT fuse fitted.

ICBM

I think you'll have seen this before, but this is a good illustration of what can happen if you don't fit one!



That's a recent Fender Twinolux, after I removed the burned-out wiring loom… the arcing was so serious it vitrified the ceramic valve socket between pins 2 and 3. What's stupid is that although there is no HT fuse, the white fuse is an entirely pointless filament fuse - which of course didn't blow.

I rewired the amp and used the holder for an HT fuse instead.

Modulus_Amps

@ICBM Not seen that but wow! and wow for not fitting an HT Fuse Fender, some designer needs sacked as they have not considered the failure modes properly.

capo4th

I love the thought of my valves warming up nicely

ThePrettyDamned

Hoof said:

I always drain the caps by letting a note ring out after I've cut the power. It seems like a good idea but I kind of enjoy the sound of it more than anything.

Is this true? I've never heard it before. 

My ac15 is valve rectified and has a standby switch... Perhaps I shouldn't use it? If that's the case, is it safer to leave the standby as always on, then just flick the power switch? 

And how about for switching off? I tend to just switch the whole thing off anyway... 

ICBM

ThePrettyDamned said:

Hoof said:

I always drain the caps by letting a note ring out after I've cut the power. It seems like a good idea but I kind of enjoy the sound of it more than anything.

Is this true? I've never heard it before. 

My ac15 is valve rectified and has a standby switch... Perhaps I shouldn't use it? If that's the case, is it safer to leave the standby as always on, then just flick the power switch? 

And how about for switching off? I tend to just switch the whole thing off anyway... 

It's best not to use it on a modern Vox.

Draining the caps by letting a note ring out doesn't really do anything different from just turning off, and it also depends on where the standby switch is in the circuit. With amps which have the switch in the wrong place it's actually most effective to put the amp on standby and wait a minute for the HT to drain through the valves, then turn off. With ones with it in the right place it's best to turn the power straight off and leave the standby in 'play' - that will drain the first cap too, and connect all the others to the divider resistors on it (if it has them). But it really makes no difference unless you're going to work on the amp - it doesn't matter at all if the caps retain any charge of not.

martinw

I almost always fit standby switches (unless a customer specifically doesn't want one), mainly for usefulness as outlined by ICBM above. I don't think wear and tear on the valves is significant either way for most people most of the time, but there are times when you might prefer to leave the amp on but on standby, such as where there's a long gap between sound check and first set, or when recording all day in a studio.

I don't think switch ratings are an issue. As ECC83 alluded to, the ratings on the switch are contact ratings, not dielectric strength. I think the data sheet for one of the smallest types I use shows an insulation strength of 1000V IIRC. A typical rating of "15A@125V, 10A @250V" sounds more like a power rating to me...as you can see the current is inversely proportional to the voltage.

I suspect the manufacturers stop at 250V because there are no common applications above that. As the current across the contacts on the HT side is very low, I don't think those ratings are relevant, except in that of course voltage across the contacts is relevant, but only while the switch is moving or open. I've never seen an issue of arcing across an open standby switch, and any arcing produced during switching seems, in practise, to be no greater than would occur at mains voltage anyway.

The proof is in the pudding. I've never had any problems with my builds, and I can't recall changing more than couple of standby switches in other amps, and then we're probably talking about 30-40 year old amps, and I've certainly replaced more mains switches.

randella

Interesting thread this.  Anecdotally, me dad taught me about the standby switch which I've always used religiously.  I noticed recently that he doesn't take his own medicine and just thumps everything on at the same time on his amps (i.e. his amp and one of mine hahaha).  We've never had a failure either way - I suspect @martinw is on the money when he says wear and tear is not significant either way for bedroom and weekend warriors like me.

chris_topher81

I always thought the point of a standby switch was so that you could keep the tubes warm without the amp emitting any sound onstage before a gig for example. I was told that when you turn on a tube amp, the tubes have to warm up a bit to reach their best sound wise? (but I'm no expert)