Zander

Tube gear standby switch.
« on: August 31, 2016, 04:17:28 AM »
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


Heikki

Re: Tube gear standby switch.
« Reply #1 on: August 31, 2016, 04:33:51 AM »
Standby switches in guitar amps do not extend tube life.

gyraf

Re: Tube gear standby switch.
« Reply #2 on: August 31, 2016, 04:45:12 AM »
..and the idea is only really usable for high-power tubes (power amplifiers, RF transmitters)..

Jakob E.
..note to self: don't let Harman run your company..

Re: Tube gear standby switch.
« Reply #3 on: August 31, 2016, 04:52:11 AM »
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.
« Last Edit: August 31, 2016, 05:01:59 AM by merlin »

Zander

Re: Tube gear standby switch.
« Reply #4 on: August 31, 2016, 06:20:51 AM »
Thank you all. I saw a switch on a Thermionic Culture compressor ( http://smhttp.39666.nexcesscdn.net/801433B/vking/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/t/h/thermionic_phoenix_mastering_plus_front.jpg ). I must ask why do they bother then?

Zander

EmRR

Re: Tube gear standby switch.
« Reply #5 on: August 31, 2016, 10:51:10 AM »
Because people expect them on some level. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

JohnRoberts

Re: Tube gear standby switch.
« Reply #6 on: August 31, 2016, 11:46:40 AM »
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
John Roberts
http://circularscience.com
Tune it, or don't play it...

EmRR

Re: Tube gear standby switch.
« Reply #7 on: August 31, 2016, 12:08:17 PM »
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+. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

PRR

Re: Tube gear standby switch.
« Reply #8 on: August 31, 2016, 01:18:23 PM »
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.

Gene Pink

Re: Tube gear standby switch.
« Reply #9 on: September 01, 2016, 03:33:51 AM »
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








Re: Tube gear standby switch.
« Reply #10 on: September 01, 2016, 04:40:17 AM »
Aside from electronic concerns, there is a real operational reason for standby.
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.

Heikki

Re: Tube gear standby switch.
« Reply #11 on: September 01, 2016, 09:14:07 AM »
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.


clintrubber

Re: Tube gear standby switch.
« Reply #12 on: November 01, 2016, 08:03:10 AM »
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

Re: Tube gear standby switch.
« Reply #13 on: November 01, 2016, 11:46:23 AM »
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

saint gillis

Re: Tube gear standby switch.
« Reply #14 on: July 13, 2018, 06:00:37 AM »
So it is not bad for a low power tube (e.g 12AX7, EF86 etc) to get full High Voltage on the anode when the filament is not completely warm yet ?

scott2000

Re: Tube gear standby switch.
« Reply #15 on: July 13, 2018, 10:39:50 AM »
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
"Give me a 25-stack of 9V batts, I'll monitor my truck's spark or fuel injection on the magic eye." PRR

isophase

Re: Tube gear standby switch.
« Reply #16 on: July 14, 2018, 04:49:35 AM »
Most tube amps that uses tube rectifier don't have a stand-by switch, why?
"we'll fix it in the shrinkwrap" fz

EmRR

Re: Tube gear standby switch.
« Reply #17 on: July 14, 2018, 08:38:18 AM »
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.....
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

mjrippe

Re: Tube gear standby switch.
« Reply #18 on: July 14, 2018, 12:36:52 PM »
Most tube amps that uses tube rectifier don't have a stand-by switch, why?

Because there is no high voltage until the rectifier warms up?

JohnRoberts

Re: Tube gear standby switch.
« Reply #19 on: July 14, 2018, 10:35:25 PM »
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
John Roberts
http://circularscience.com
Tune it, or don't play it...