To stand-by, or to not stand-by?

[Jared Purdy]

I just came acorss this question on another thread and thought that I would isolate it as it is somewhat of a seperate issue from the other poster's issue of blowing fuses repeatedly in his amp. Once you turn the power on, how long should you wait before turning the stand by switch to on? Secondly, if you are jamming for a few minutes and need to go start dinner, but know that you'll be back in 15-20 minutes, or maybe less, do you turn the amp off completely, or to you put it into stand by? Bear in mind, that in my house, on some nights, this could go on for a couple of hours, resulting putting the amp into stand by mode several times over a couple hour period. I know this might seem germain to many of you, but I am not an amp technician, and I recently had a problem with my Mesa LSS where the fuse was blowing repeatedly, and the 5Y3 was arching. It was suggested in the manual, and by people on various forums, and at the store where I bought it, that it is likely due to a fautly power tube. I changed the power tubes (same Mesa brand), and put in a new Mesa rectifier tube and new fuse) and so far, after almost a week, so far so good. However, I had the amp new, from the shop for a month before it started blowing fuses, etc. During that period, I'm sure I used the standby switch quite a bit. Could I have inadvertantly damaged one of the power tubes by using the standby switch, thereby causing a power tube failure??
I never had this problem with my PRRI or my C30, as they don't have a standby switch. Not using it, turn it off.

[Euthymia]

Standby switches don't really do much one way or the other. They make a good mute switch, but use or imagined misuse is not likely to do anything to an amp that did not already have a marginal tube or tubes. Your issue would have happened with or without a standby switch.

The reason the tube died after you got it was that it started getting used, period. It was X hours away from a failure when it left the store. If it had stayed at the store and gotten those hours on it, it would have happened before you got hold of it.

My theory is that guitar amps have standby switches because players who were doing multiple sets a night told Leo Fender that it would be nice if they could leave their amps warmed up during smoke breaks, but not have to turn the volume down. The tubes also age more slowly when they are running on heaters only.

So Leo added them, and everybody copied that feature, and somewhere in there it got mixed up with transmitter tube theory that says you need to thoroughly warm your cathode before applying your many thousand volts to the plates, and here we are.

Been fixing amps for a living for half a dozen years and I have yet to see one that I thought had been injured by using the standby switch the "wrong" way.

In the amp I just designed that will be at NAMM this year (Coming Soon - Future home of something quite cool), I put in a standby switch because people have come to expect the feature, and it does have its small utility as a mute.

[Jared Purdy]

Thanks. After the fuse and tube issues, and my irratation died down (it's a failry expensive amp, and I had already had a couple of amp issues this year) I started thinking that with the time that amp had been in the store (likely upward of a year, as I called Mesa for the shipping date), it's quite likely that mutitudes of people turned the amp on, off, standby first, standby last, etc., and in those dozens, possibly hundreds of off ons (properly and inproperly), a tube was proabably nearing the end of it's life when I got it. At least that is what I amp hoping. I have a new set of Mesa power tubes, a new Mesa 5Y3 and a new fuse, and so far, for the last week, so far so good. And, I'm being consciencious as to how I use the standby. I hate amp issues!

[Steve Conner]

Oh no, don't reignite the old standby switch debate!

In many amp designs (including your LSS, as far as I know) the rectifier tube gets hit with a surge of current when you flip the standby switch. If the tube is weak, that can send it over the edge. And, it probably uses up a few hours of tube life every time you do it, much like the old debate about the economics of starting fluorescent lamps.

The effect of the standby switch on the other tubes is controversial. While in standby, no current is passing and they're cooler, so the usual wear mechanisms of gas emission and cathode wear are stopped. But, every time you bring them out of standby, the tubes are subject to a thermal cycle that makes things expand and contract, and can loosen the innards over time, making them microphonic or just plain out of spec. However, the thermal cycle is not as bad as if you turned the amp off completely.

[MWJB]

Do not leave your amp in standby for long periods, they don't like it, I know of plenty of folk who have blown fuses simply by leaving in standby for extended periods, admittedly they are all RI 59 Bassmans with export PTs & fast blo primary fuses, but it happens.

Standby is there to allow the heaters to warm up before dc is applied to the tube (this happens when you throw the standby). This prevents voltage spiking. Your Russian "5Y3" that you temporarily used was indirectly heated & had a "slow warm up" irrespective of the standby switch (indirectly heated rectifiers like 5AR4/GZ34, 5V4 do not normally need standby, because it takes for them time to start supplying dc) in most amps you only need to leave in standby for 30 seconds, maybe 4-5 minutes if usuing very large tubes like 6550/KT88. If you are going to be away from the amp for 25 minutes then just turn it off. Your PRRI came with a GZ34 with a slow warm up, AFAIK the C30 doesn't run its tubes at as high voltages as the LSS, the diodes in the C30 trectifier are probably more robust than the 5Y3 in the LSS.

The standby switch, or lack of it is unlikely to quickly kill a power tube, the rectifier is more susceptible to damage. If the power tube is drawing too much current however, this will damage it and excacerbate any weakness in the rectifier too...I have the strangest feeling I may have said this before...

But then, you know all this already Jared, if you don't believe any of the responses you get why ask a question? Or, do you just want to hear answers that fit your perception? People who contribute to this forum do so because they like to help people, so they freely contribute their time to field queries, often when they have better things to do, like paying work...like I do now. Goodbye.

[redelephant]

This is one of those everlasting subjects. There are many theories why guitar amps have standby switches. Other tube gear does not, even tho they have tube rectifriers and power tubes running at full class-A steam. I have yet to have amps without standby switches die on me, and as an experiment I often throw the standby switch first on my amps that do have them, no probs there either.
Fact1 : The tube with the world record in life span was seldom (if ever) switched off. According to 'how to get the most out of your vacuum tubes' book. Granted, this is an old book, so the record has probably been beaten, but I bet in that case the tube has been seldom turned off.
Fact2: Tubes that are cold, can be viewed as switches in the open position, no current is drawn from the supply. The voltages used in guitar amps are harmless to the tubes, the tubes take no damage from the high b+ on cold cathodes.
Fact3: If no load is connected to typical vintage amp's power supplies, in other words, if all tubes but the rectifier has been removed, or the tubes are cold, the voltage on the supply will be 15-20%, perhaps more, higher than the voltage when the circuit is drawing current.

Many 'experts' claim the standby switch was put in b/c times were hard, and condensers (caps) were expencive, so minimum rated caps were commonly used. If power was applied before the tubes drew current, the b+ might rise above the voltage rating of the caps. If you analyze vintage designs, it's easy to see they designed for most bang for the buck, so the story is believable to me. Having the tubes warm before applying b+, ensured the tubes loaded down the power supply as designed, and served as a cheap safety for under rated parts.
I've serviced amps with b+ almost right at 500volts, and the caps are rated for 500volts. Modern caps can handle overvoltages, but could the old ones?

I dunno, sound plausible, but I'm sure guitarists also wanted a muted amp they quickly could go to and play without delay. With humming power amps a mute switch on the input of the amp wouldn't make it muted enough. The constant hum would probably drive the sound tech mad. If only for muting, the standby has nothing to do with tube life.

Anyhow, this has been discussed at length at diyAudio, so if interested, go search there.

[jpfamps]

Standby switches are unneccessary for ensuring compoent reliability in most designs; tons of valve domestic electronic equipment, eg wirelesses, TV etc, operated without standby switches.

In amps with a valve rectifier a standby switch actaully be counter productive as switching on the HT when the mains is nera it's peak with a hot rectifier will cause a very large inrush current that could destroy the rectifier valve. My and others experiences with the current Vox AC30s would suggest that this is a real problem.

It is worth noting that in older Fenders with valve rectifiers the main filter caps charge slowly through the rectifier even when the amp is in standby, and my guess is here that this is to avoid stressing the rectifier.

As stated above, the first filter caps after the main filters in Fenedrs is also vunerable to the unloaded voltage, and again I've seen more caps in this position fail on old Fenders than any other.

Having said this, players expect to have a standby switch on their amps so it would be harder to market a standbyless amp abd I'm sure you would lose sales if your amp didn't have one.

Regarding the voltage compliance of older capacitors, destructive testing of electrolytics capacitors by a friend of mine (it was a slow day at his work) implys that older caps are more tolerant of over voltage than newer electrolytics. The reason for this is almost certainly due to the fact that modern electrolytics can be made to tighter tolerances.

[MWJB]

All well and good, but point 2 isn't quite correct, some amps run tubes close to their limits...& sometimes it doesn't take much to tip them over the edge. Anyhow, this particular post is not specifically concerned with power tubes, but with rectifier tubes & 5Y3 in particular. When a rectifier is running close to its limits all bets are off, it's possible that the PIV of the 5Y3 could be exceeded in the LSS, it's possible that the current rating is running close to max to the 5Y3's limit - again the Russian rectifier tube worked fine with its slow warm up & higher current rating (we don't know what the power tube idle current is, just that Jared has changed his tubes & still doesn't know whether this is for the better or worse).

Most amps are designed not to stress their rectifiers (1st filter cap largely is irrelevant, voltage & current draw are more pertinent), but ocasionally an amp comes along with marginal headroom in these respects (e.g. 5F8A twin, 5F6A RI when run with a GZ34 & very high idle currents). In short, there is more to this specific case because obviously everything is not running quite as it should be. I agree that in most amps, throwing the standby & power switch together, even with a directly heated rectifier, won't cause any issues...but we're not talking about "most amps", we're not even talking about most LSS, we're talking specifically about Jared's LSS, which obviously has an issue/marginal reliability. Telling him that all is fine & that not paying attention to rectifier fragility/power tube voltages & currents/standby procedure is all very well until his 3rd Mesa 5Y3 pops....

Jared, you said your shop has a tech, get them to have him look at it (at their expense) on condition that if it blows again, it's refund/trade in time. I know you only use the amp at home, but they don't need to know that & if you were gigging with it you would be in the mire.

[Jared Purdy]

I'm glad I asked this question, as being a newbie to the electric guitar and all things included (i.e, amp), and having had two previous amps where I didn't have to contend with a standby switch (Peavey C30 and PRRI), I was really in the dark on this and ill informed. I'm not sure where I got the idea that if I was playng, and took a break, I should hit the standby, which is what I have been doing to my LSS since I got it. There's a very good chance that the reason the tubes failed (the 5Y3 and potentially at least one of the EL84's) is because the amp was at the store, on the floor, for a least a year. In that time, how many people came in and turned it off and on - inappropriately? Possibly hundreds! The store in question is not a Mom and Pop shop, it's one of the busiest music stores in Toronto, in Canada for that matter. Hundreds of people go through the doors every day. So why the hell do they put a standby on amps any ways??? There's a very interesting article posted ovedr at tdpri on this subject as I asked trhe same question there. The article was written by Peavey Hartley, and does a bit of fascinating hisory on the orgins of the tube, and the differences between some of them. It woudl appear from the article (asuming tat it is correct) that the 5Y3 is possibly the worst of the rectifier tubes as it is a "directly heated cathode" as oppossed to an 5AR4, "indirectly heated cathode". Why would Randal and co use an inferior tube in an amp like the Mesa LSS? Also, while I'm asking,what is the post popular rectifier tube in tube amps?

[MWJB]

5Y3 are perfectly reliable when design limits are taken into consideration (you even see tweed champs & early tolex princetons with original rectifiers, same goes for 50's Danelectros with 4x6V6 or 2x6L6), most other tube rectifiers will result in more plate voltage on the EL84s...the LLS runs them pretty hard as it is, without knowing specific voltages I couldn't comment further. Simply swapping a 5Y3 for a GZ34 will result in a voltage hike of up to 40vdc (less in many amps drawing moderate current).

Unless voltages & bias currents allow higher voltage rectifiers (needs measuring on your specific amp), your best bet is probably the Weber WY3 copper cap. There is no "bad/worst" rectifier (it really is a question of taste as far as tone & response go), just rectifiers used in sub-optimal environments.

[Jared Purdy]

Thanks for clarifying that.

[ThermionicScott]

To attempt to button up the standby issue, take a gander at the example circuits in the old (and later) RCA tube manuals. You'll see a telling lack of standby switches, and they weren't feeling the same cost constraints that might lead an amp manufacturer to leave out parts. If they didn't think the switch is necessary for tube health, neither do I!

- Scott

[MWJB]

People don't play amps made from RCA example circuits though, amp manufacturers typically run tubes in much more hostile environments than data sheets etc would suggest. If a tightwad like Leo Fender decided to spend money on standby switches, one kinda thinks that there must have been some reasoning behind it? Of course, it's the user's choice as to whether they employ it or not.

[ThermionicScott]

Hostile when they're being played through and drawing lots of grid and screen current, sure. Not really at idle. Methinks Leo just used one method for a "mute" switch (note that the early ads didn't promote tube health, it was a quick "silencing" switch), and players didn't want to give up that feature once it had been offered.

- Scott

[MWJB]

Hostile is hostile...if your rectifier blows every few weeks, you don't even get to "idle"...which is where we came in on this thread. If idle is "too high" this can blow rectifiers when you throw standby in to play mode/when you actually play and shorten tube life. Amps can redplate at idle when they're not working right...which is the point here. What other amps are doing, not doing, might do doesn't help Jared. Context is everything.