Tube gear standby switch.

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Zander

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Joined
Jun 25, 2012
Messages
267
Location
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I always wondered about this. Why do guitar amps almost always have a standby switch and outboard gear almost never? It would preserve the life time of more expensive tubes, would it not?


Zander
 
The 5E6 Bassman was the first amp with a standby. There are two plausible explainations for this: Fender used smoothing caps after the standby switch that were lower rated than the main reservoir cap before the standby switch, which must have saved money and space. A standby switch was therefore needed to protect the lower rated caps from overvoltage, until the heaters warmed up enough for the valves to pull the HT down to normal working levels. The later 135 Bassman schematic even shows labelled voltages exceeding the cap ratings during standby.

The other possible reason is that the 5E6 was the first amp where Fender used a DC-coupled cathode follower. This stage will sometimes arc between grid and cathode at switch-on if the cathode has not yet warmed up. (These days you should put a diode or neon-lamp between grid and cathode to prevent this, not rely on the user).

Marshall copied Fender without questioning it, and everyone else copied them both.
boom-history.jpg
 
merlin said:
The 5E6 Bassman was the first amp with a standby. There are two plausible explainations for this: Fender used smoothing caps after the standby switch that were lower rated than the main reservoir cap before the standby switch, which must have saved money and space. A standby switch was therefore needed to protect the lower rated caps from overvoltage, until the heaters warmed up enough for the valves to pull the HT down to normal working levels. The later 135 Bassman schematic even shows labelled voltages exceeding the cap ratings during standby.

The other possible reason is that the 5E6 was the first amp where Fender used a DC-coupled cathode follower. This stage will sometimes arc between grid and cathode at switch-on if the cathode has not yet warmed up. (These days you should put a diode or neon-lamp between grid and cathode to prevent this, not rely on the user).

Marshall copied Fender without questioning it, and everyone else copied them both.
My DIY home power amp I built in the early '70s is built into an old western electric chassis (32C or something like that from the 1930s?).

There is a three position rotary power switch. Off, then first on position is to turn on the tube heaters and let them warm up before applying full power at second on position. I repurposed the switch to limit mains turn on surge current through a resistor, and only connect the loudspeakers using relays after the amp is on and settled (second on position that also shorts the current limiting resistor).

Apparently not a modern concept.

JR
 
In John's WE amp the tubes were directly heated triodes and it was all run on batteries, so the purpose of the switch was to turn on filament batteries first and adjust voltage with a rheostat before applying B+. 
 
The "value" of an electronic toy (before GUI) was the number of knobs, switches, and watts, times the brand name.

A standby switch cost about a buck but the show-room value of another feature-switch might be 2 bucks. So the maker had no strong reason to leave it off.

Aside from electronic concerns, there is a real operational reason for standby. Guitar amps HUM. Moreso in days of 2-pin power. It could be more obvious in days when venues did not have background music systems going constantly. It would be very obvious if you got a Wedding Gig. This is times of playing and also times when the band must Shut Up to let the preacher, father, and friends speak to the crowd, often without a PA mike. The standby shuts-up the amp. But then the father of the bride finishes his toast by calling for a tune. The band must begin playing Right Now. If tubes are off, this takes some seconds. From standby to play can be under 1 second.
 
I have always been of the opinion that a standby switch has two purposes.

1) Instrument changes between songs.

Song ends, hit standby, yank 1/4" cord out of instrument and fling over amp, set instrument down in empty stand, grab new instrument and hang on shoulder, grab 1/4" cord and slam in hole, standby off, and ready for the next song, assuming whoever is driving the show follows the damn set list.

All this during the ten seconds while the yapper of the band goes on about "Make sure to tip your waitresses and bartenders, they work hard for you. Tee-shirts for sale at the booth."

2) Breaks between sets.

Set done, you make a point to remember to hit standby and set your bass in the stand.

Head for the bar for your well-earned "one per set, per the contract" free beer. You order it up, and survey the scenery for that one woman trying to make eye contact with this rockstar that just got off stage. Nope. None. Damn. They are all eyeing the guitar players. Bunch of.... well, you know.

As your comped beer is served, you heat a faint tone. You can't quite localize on it, with room reflections, standing waves and all. You move your head around to try to localize better, like a dog cocking his head when hearing a strange noise, but it doesn't do any good. Your ears just  go in and out of standing waves, and it is getting louder, and others are now noticing it. You feel a rather strong anxiety, having a clue as to what it may be. You look across the dance floor at your bass guitar in the stand next to your amp, and even from a distance, you can see that one of the strings on your early '60s Japanese copy of a Hofner hollow-body bass, looks blurry.

With only half a grip on your freshly served free beer, you manage to dump it over in great haste/panic to run across the dance floor, jump up on stage and hit the standby switch before the full RMS of the sextet of 6L6's in your Mesa Boogie D-180 rapidly approaching the point of clipping, well above the rating of your precious EV SRO 15s with the original, irreplaceable cones and voice coils, destroys them.

Now you get to walk back, tail between your legs with head bowed down to sarcastic applause, get to the bar, and then have to BUY another beer.

Fictitious story, no, this didn't really happen.

Completely made up.

A falsehood, I tell ya.
;-)

Gene






 
PRR said:
Aside from electronic concerns, there is a real operational reason for standby.
Gene Pink said:
I have always been of the opinion that a standby switch has two purposes.
A mute switch is indeed a useful feature on a guitar amp, but a standby switch is the most egregious way to implement it. It demands an expensive high-voltage switch, the absence of anode current for too long leads to interface resistance (= tube death), if designed very badly it results in hot switching of the rectifier tube (= tube death), and it can cause an annoying thump in the speaker.  If a mute switch is all that is required then it is far easier, cheaper, and safer to short one of the grids to ground.  Even switching off the screen grids is an improvement on cutting the HT to the whole amp.
 
Some Gibson and Epiphone amps implemented standby by shorting power tube control grids together. http://schematicheaven.net/gibsonamps/ea_10-deluxe.pdf With enough power tube plate current imbalance it'll probably keep on humming and buzzing annoyingly when on standby.

 
merlin said:
Even switching off the screen grids is an improvement on cutting the HT to the whole amp.

Sounds like this is a good approach. I saw for instance those Peavey Classic tweed amps with a standby-switch indeed do it like this (and even get a bit ridiculed for this by some magazine-reviewers ...  ::)  )

While having contact with Peavey support about something else recently, the standby-switch also came up. Their approach is inrush-current limiting for some kind of 'automatic' standby-switch function (to prevent cathode striping).

As it seems, later on the demands of the market became too strong to not longer skip it, so they added the switch.

FWIW, Hartley Peavey even wrote an whole chapter about it:

http://peavey.com/support/technotes/hartley/Chapter_6.pdf

Would be good if their product manuals also tried to 'educate' people w.r.t. the standby-switch. The manuals I saw gave the same impression as the usual other brands.... perhaps they gave up...  ;)

Bye
 
clintrubber said:
Would be good if their product manuals also tried to 'educate' people w.r.t. the standby-switch. The manuals I saw gave the same impression as the usual other brands.... perhaps they gave up...  ;)

Aah, FWIW, here's from the Classic 20 MH manual:

STANDBY switch

Placing this switch in the“STANDBY”position will effectively shut the amp off while leaving the tube
filaments on. Leave this switch in the“STANDBY”position for a minimum of one (1) minute after engaging
the POWER switch (#11). This is also a useful feature, since much tube wear comes from the heating and
cooling of the tube itself. Leaving the unit in“STANDBY”when you take a break allows the tubes to stay
warm while you are not playing. To immediately resume normal amp operation with no warm-up delay,
place the switch in the“ON”position. NOTE: This switch does not replace the POWER switch (#11). When you
are ready to stop playing for an extended period of time*, it is better to turn the amp off via the POWER
switch (#11). To prevent any undesirable noise, it is recommended to switch the amp to “STANDBY” for at
least a few seconds before switching fully off.

* Excessive time off (more than one hour) in "STANDBY MODE" can damage OUTPUT TUBE by "poisoning
the cathodes".


* For an informative description of the STANDBY function, please read the Chapter 6 (Standby...For the
Truth) of Hartley Peavey's White Papers
 
I've gathered not..... from above and.....

Standby Switches and Folklore
Many guitar amps (too many) include a standby switch. This is meant to let the heaters warm up before the high voltage is switched on. Old books called it 'preheating'.
But let's get one thing straight: a standby switch does not extend the life of the valves, in fact it is more likely to reduce their useful life. The valves do not care if you switch on the heaters and HT at the same time (with a couple of exceptions explained below). Now, I know what you're thinking, "but every guitar magazine in the land says the exact opposite?" Yes, they do, but guitar magazines know next to nothing about electronics, they just repeat the same old wives' tale each year.


http://www.valvewizard.co.uk/standby.html
 
clintrubber said:
Aah, FWIW, here's from the Classic 20 MH manual:

STANDBY switch


* Excessive time off (more than one hour) in "STANDBY MODE" can damage OUTPUT TUBE by "poisoning
the cathodes".




Radiotron manual advises 15 minutes.....
 
mjrippe said:
Because there is no high voltage until the rectifier warms up?
The old Western Electric amp/PS that I got the 3 position (1st position warm up) switch from had vacuum tube rectifiers, 4 huge ones sitting in external tube sockets, poking out the front of the main chassis.  But this was a design from the 30's so who knows?

I am not and don't claim to be a tube guy... I hear they will be replaced by solid state at some point.  ::)

JR
 
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