-
I've used valve/tube amps with standby switches for decades.
It's always been my understanding that you turn the amp on in standby mode until the valves warm up then flick thr SB switch. Then repeat the process in reverse to power down. (God forbid pulling out the mains plug before carrying out the power down "ritual!!!).
I know the SB switch is often used as a mute. I have never done this as once the amp is on and running I don't like messing with it just in case it craps out.
It's only recently whilst talking to an old friend that I have become aware of the "myth" associated with the switch and very conflicting opinions such as the valves are damaged in standby mode.
Who should I believe?
.
-
03-16-2024 11:02 AM
-
I've been using the standby switch on my Fender/Fender style tube amps for decades. I've never had any indication whatsoever that the tubes were damaged as a result of this. I think there is a lot of BS on the Internet (on all topics) that needs to be taken with a grain of salt or not taken at all. Unless somebody is posting about this from the perspective of being an electrical engineer, I would be skeptical.
-
If you look at the schematic diagrams of Fender amps, it's obvious that the only thing the standby switch does is cut power to the output transformer. It has no effect on the other components. Its only designed purpose is to prevent feedback if the guitar is left near the amp.
-
Neither of my current tube amps (20W and 10W, hand-wired, boutique, blah-blah) even has a stand-by switch! I've had others with SB, though, and if I ever forget to "follow the rules" when powering up or down, nothing (obvious) happened.
-
Trying not to disappear down the rabbit hole, in brief, it seems that amp makers that incorporate them say they are essential and electrical engineers say they can cause damage.
Originally Posted by Cunamara
Your average Joes have their opinions which differ considerably.
-
I may have had, in the dim and distant past, a slo blo fail when not 'following the rules'! Possibly coincidence? Originally Posted by marcwhy
-
It actually cuts the high voltage B+ supply to the output tubes. Many amps have it wired to the center tap on the OT too, but that has no protective effect other than to prevent switching transients from reaching the speaker. It’s only a B+ supply switch on some modern tube amps. Originally Posted by sgosnell
Tubes won’t conduct until they warm up. So there’s a voltage surge in the power supply if cold tubes are hit with high plate voltage. This drops as much as 400+ volts across the power supply electrolytic caps until the tubes heat up and start conducting. A SB switch lets the filaments heat up so there’s no voltage surge on the caps. That’s the whole story.
Fender (who was the first to use a standby switch AFAIK) used caps rated with very little voltage headroom, and that cold surge destroyed many caps over the years. So the standby switch was to be used when powering up a cold amp. It was never intended to be a “mute” switch or to be used on breaks etc. We can now get caps with 500+ working voltage tolerance, and I’ve never seen a properly rated PS cap fail like this.
Tube life is unaffected by having a SB switch, and I know of no reason to switch to standby before turning the power switch off after use. There’s also no reason to switch into SB when not playing. I leave the amp on and turn my guitar’s volume pot fully down on breaks. But if you have a vintage amp with vintage spec caps and a SB switch, stay in standby for at least 30 seconds after switching the power on before switching the SB on. By 30 seconds, the cathode will be emitting electrons and the voltage across the PS caps will be within spec.Last edited by nevershouldhavesoldit; 03-16-2024 at 12:24 PM.
-
Thanks. Originally Posted by nevershouldhavesoldit
Your explanation accords with a few accounts I have read. I've also read about 'stripping of this and poisoning of that' in SB mode. Is this anything to worry about? Does using the SB switch as mute for reasonably long periods damage anything?
I'm using an old Musicman RP65 1x12. I've had it repaired recently and these days, as now the components are old and breaking down, they can be difficult to source.
I need to handle it with kid gloves and not cause it any undue stress. Would the old PS caps be of the little voltage headroom type?
-
Tubes break just like strings. Use it how you want and expect to change them one day. I was told standby power on, standby off play. Then, to turn it off just cut the power “this gets all the electricity out of the amp.” Were the guys exact words.
My blues jr doesn’t have a standby.
-
I don't understand the electrical engineering side, but in my 10 years of constant gigging with a Mesa I always went by the rules and I think I replaced a tube maybe once. Maybe never? Can't actually remember for sure.
Before that it was Fender Super. Same deal but I did have to replace a couple in that.
Maybe it doesn't actually matter if you use SB or not? I never considered not using it.
-
Cathode stripping is a term for damage to the emissive surface of the cathode from bombardment by ionized gas molecules. When the tube is fully powered and conductive, the cathode has a cloud of electrons around it that protects it from this damage. But if the plate voltage is 0 (ie in standby mode), this cloud is not there. Originally Posted by garybaldy
Since the vacuum in a tube is never complete, there are many stray gas molecules in it. If stray electrons flying from cathode to anode strike a gas molecule and ionize it, that ion can be attracted back to the cathode and hit it with what for submolecular particles is a lot of force. This “strips” the cathode’s emissive coating, shortening tube life over time if it’s allowed to happen often.
The electron cloud that surrounds the cathode when the tube is conducting prevents those stray ions from returning to the cathode and damaging it. But if the tube is hot and plate voltage is shut off (in SB mode), cathode bombardment continues. This is the argument against leaving the amp in SB for long periods of time. Pure tungsten cathodes are immune to this damage. But thoriated and oxide coated cathodes are susceptible to it (oxide worse than thoriated).
If your amp hasn’t been fully checked and serviced in several years, you should replace the filter caps in the power supply and have it fully tested. I’m rebuilding a ‘71 Twin right now in which I found two of the original PS caps. The other 3 had been replaced in 2006 according to the tag left inside the capacitor board cover. All of the caps were rated for 300 or 350 volts. It was way down on power, with little bass response and a lot of audible IM distortion when playing two low notes together. I put in 450 and 500 volt replacements last night.
All older tube amps need proper grounded power wiring, removal of the “ground” switch and capacitor, and testing of the voltages at all marked points on the schematic. Just having problems fixed is not enough.
Yes, leaving your amp in SB for many hours (collectively) can shorten tube life. I power up in SB, wait 30 or more seconds, then switch from SB to on and leave it like that until the end of the gig / session / etc. I either turn my guitar volume pot or the amp’s all the way down for breaks.
-
Guitar tube amps never get anywhere near the voltages that actually cause cathode stripping. So, the Standby switch may work great as a mute switch, it's not really necessary to protect your tubes.
-
Another point, if your amp has a rectifier tube the stand by switch is obsolete for any warming up procedure of the tubes before B+ will be turned on.
Full B+ will be available only when the rectifier tube also has warmed up.
BTW, the tube amps I've built have no SB switch. Also the ones with diode rectifier.
Cathode stripping requires a very high plate voltage, higher than in normal guitar amps. And nowadays it's no problem to get large eletrolytic caps with 550 or even 600V rating. (As nevershould... already wrote above).
-
My 1983 amp has not been fully checked and serviced in several years, if ever. But it works just fine, so I see no reason to change anything.
-
Do you follow a particular procedure when using the standby? - that's if it has one. Originally Posted by Litterick
Thanks
-
You’re correct that full B+ will only be available when the rectifier tube is warmed up. But that only means that you need to wait longer before switching from standby to on. Some tube rectifiers need a minute or more, but some (like the 5Y3) ramp up very quickly. Originally Posted by bluenote61
The standby switch does not control power to the rectifier tube.
-
Yes, you are right. Originally Posted by nevershouldhavesoldit
But what I wanted to say is, once the amp has a rectifier tube, it works like a sort of smooth ramping up stand by switch. No need to use the SB.
Caveat: Some older Fender amps with rectifier tube have the SB switch BEFORE the first cap in the power supply. Using the standby here will give a high peak load onto the rectifier tube once you switch to "on" which will cause a faster wearout of the rectifier tube.
Later amps (I think from blackface on) have the SB switch after the first reservoir cap which solves this problem.
-
It has none — it is a Fender Princeton Reverb II. My other amp is a Hiwatt Custom 7, which does have standby. My startup procedure is to turn the power switch, wait about a minute, then turn the standby switch. My shutdown procedure is to turn the standby switch and then the power switch, in quick succession. I think I am following instructions, but I do not know where I read them. Originally Posted by garybaldy
-
nevershouldhavesoldit has it exactly right.
On my amps that have standby switches, on my amps that don't, I don't worry about it.
-
I have 39 years of experience as an electronics technician.
Use it, don't use it, it makes no difference in the life of the tubes or anything else.
-
No no no, You all have it totally wrong.
The function of the switches are this: about 20 minutes before the gig You tune Your spare guitar, take it to the stand in the stage and turn on the ON switch to announce the electrons in the amplifier that You are in a stand by mode, soon there will be something happening.
Then You stretch your leg muscles, warm up Your hand muscles, tune Your No 1 guitar, wish Your band members a good gig, climb to the stage before the roaring audience and now turn the stand by switch to tell the amp that now we'll make this joint explode!
Or something like that. A routine that prepares You for the gig.
-
The original way to protect the caps when switching on was to put a fuse in line with their power feed. If there was a voltage surge, it blew the fuse instead of the cap(s).
-
My 64 Reverberocket does not have a standby switch. Left the factory without one. It worked fine with the original tubes for 35 years. Then, they were replaced in error (the actual problem was in the reverb tank connection). Newer tubes seem a little more fragile. But I digress. Maybe Ampeg didn't use the lower overhead caps?
-
Remember that Leo didn’t use data to make decisions - he went by his intuition. ‘50s Fender catalogs say only that the “Fender first” standby switch prolongs tube life. There was (and still is) no evidence that it does. I suspect that protection of the caps was serendipity and/or a realization after the fact. He may very well have decided he could get away with lower voltage caps because there was a SB switch. Understanding Leo’s logic is a mythical quest. Originally Posted by rpjazzguitar
My bet is that the caps that have succumbed to turn-on voltage rises were pretty close to the end of life. I’ve never heard of it in a new or well maintained audio amp of any kind.
Look at any tube audio amplifier from any era - none has a standby switch. There’s no evidence that cathodes erode in audio output tubes. There’s no evidence that tubes last longer if the SB switch is used as intended. It’s all somewhere between anecdote and fantasy.
-
Mesa still uses a standby switch. fwiw.
Reply With Quote
Melody between melody
Today, 03:25 AM in Chord-Melody