Stand-by Switch reduce their useful life

KSTR

Member
Paid Member
2007-07-17 2:35 am
Central Berlin, Germany
There is an interesting statement here: "...a standby switch does not extend the life of the valves, in fact it is more likely to reduce their useful life..."
... when it is NOT used as intended.

The idea of the standby switch was to mimic the warm-up behaviour of rectifier tubes with solid-state rectifiers, therefore "standby" is a misnomer, actually.

If it is used properly (only at power-on for about 30 seconds), no problems.
Don't use it as a "mute" switch!
 
Hi, the paper looks quite good to me, but i do not agree with the following:
The two main causes of valve ageing are natural barium evaporation from the cathode, and interface resistance growth. Barium evaporation continues as long as the cathode is heated, so an ordinary standby switch has no effect on this. But a standby switch does encourage interface resistance growth. In other words, the standby switch is more likely to shorten the life of the valves!
In my understanding a valve ages, i guess due to barium evaporation, much due to anode-to-cathode current. Say, a valve of a Class-A amp ages faster than a valve of a Class-A/B amp, which is only played at soft levels. Due to the half-a-minute warm-up of the cathode, it is natural that, one switches the amp to stand-by if one is going to lunch, and switches it completely off if one is going away for the rest of the day. If we only had some numbers.
 
They will write papers about all sorts of rubbish.
If they destroy the valves, why do all manufacturers use them? Why do all backline guitarists, Bass included, leave their amps in standby whilst getting ready for their gig and during their break?
Valves age with electron usage. If they are in standby, the heaters are on but no HT goes to the screen grids, (many Boogies are like this) or no HT at all, (Marshall, Orange etc), so no emission just the light bulb heater to "wear out".
 

Printer2

Member
2010-04-02 6:34 pm
... when it is NOT used as intended.

The idea of the standby switch was to mimic the warm-up behaviour of rectifier tubes with solid-state rectifiers, therefore "standby" is a misnomer, actually.

If it is used properly (only at power-on for about 30 seconds), no problems.
Don't use it as a "mute" switch!

Standby switches predate solid state electronics. They were used on early radio equipment and migrated over to audio equipment because 'that is the way it is done'.
 
Stand-by switches (or even better, proper power sequencing) were used by engineers when they were needed (e.g. high power audio PA, radio transmitters). They became popular and then were used were they were unnecessary or somewhat harmful simply because some people expected to see them.

Cathode interface is real, and is well known among people who use valve equipment where one or more valves are rarely in use (e.g. the crystal calibrator valve in a communications receiver). However, it may be that it is seen less often these days as modern audio valves don't last long enough for the layer to develop.

JonSnell Electronic said:
If they are in standby, the heaters are on but no HT goes to the screen grids, (many Boogies are like this) or no HT at all, (Marshall, Orange etc), so no emission just the light bulb heater to "wear out".
These are precisely the conditions for a cathode interface layer to develop: full heater, no anode current.
 
Printer2,
Flog the Scott 299 to one of the many who would snap it up. Use the money for an 18 Watt kit.

Standby Switches are VERY bad with cathode biased amps. Until the cathode bypass cap charges you get a HUGE pulse of current thru' the output tubes. Popped a few HT fuses in one of my amp builds until this finally "clicked" and I deleted the standby switch and replaced it with an output tube grid mute switch.

If you MUST have a standby switch (fixed biased amps) then consider switching the output tube screen supply instead. That will drop their idle currents to a few mA but not turn them OFF entirely.

Cheers,
Ian
 
...
Standby Switches are VERY bad with cathode biased amps. Until the cathode bypass cap charges you get a HUGE pulse of current thru' the output tubes. Popped a few HT fuses in one of my amp builds until this finally "clicked" and I deleted the standby switch and replaced it with an output tube grid mute switch.
...

Yes that's a very good point.
Recent VOX AC30 reissue amps introduced a standby switch, even though the originals never had one. The reissue models soon got a reputation for eating up rectifier and power tubes. Many technicians recommended users to leave the standby switch in the 'play' position at all times.
If you want to mute an amp for a break, pulling the input jack half-way out will generally do it.
 
I thought it was well known by now... Stby switches are used to ensure a proper load on the power supply. Mainly to save the electrolytics which are not rated for the high voltage often found on unloaded power supplies. People just didnt have the extra money our generation seem to have and amps were built as cheap and sane as possible. The electrolytics in a Marshall or Fender are not rated for the voltages if the tubes do not pull some current. To extend tube life better to limit the inrush current into cold heater filaments.
Stby is a good mute tho.
 

Printer2

Member
2010-04-02 6:34 pm
Printer2,
Flog the Scott 299 to one of the many who would snap it up. Use the money for an 18 Watt kit.

No need for a kit, have more than enough parts for a couple of amps, other than output transformers. Amp is missing a knob or two, probably need to be recapped by now. Also am located in the middle of nowhere, shipping would eat up any money made. But no worries, have enough other projects and parts in the waiting it will be a few years before the Scott will be looked at again.
 

Printer2

Member
2010-04-02 6:34 pm
One thing I've noticed at live Gigs, is that in the interval, the road crew switch all the amps to standby. Switching them on full just before the band returns. What's that about?

That way they know the amp will not feedback with the musicians not on stage if one of the guitarists did not bother to turn down their amps. Let's just say the crew has seen it all and would rather be safe than sorry.
 
there's nothing worse than jumping up on stage to play sum harp on jam night to find
A: your amps been turned off by sum jerk who couldn't put up with a little buzzing and hiss
B: that by the time the valves (tubes for our American friends) heat up and start to work the songs almost ended.
and maybe I will only get a 1000 hrs to a set of tubes that's OK, i think lugging the amp round in the back of the car probably does more harm than a standby sw. each to his own tho more info on screen mute might be interesting
 

Printer2

Member
2010-04-02 6:34 pm
there's nothing worse than jumping up on stage to play sum harp on jam night to find
A: your amps been turned off by sum jerk who couldn't put up with a little buzzing and hiss
B: that by the time the valves (tubes for our American friends) heat up and start to work the songs almost ended.

Get on stage a minute or two earlier and you won't have to worry about 'some' (English spelling) jerk caring about the paying customers having a good night out.
 

infinia

Member
2005-05-15 9:51 am
SoCal
Originally Posted by SempiFi I thought it was well known by now... Stby switches are used to ensure a proper load on the power supply.
yes... the 'standy mode' allows the heaters to warm up before the HV section is activated, this was needed because of the power supply design E.g Choke fed filter only works well with constant current loads. Bad news without it, if the tubes don't conduct on initial turn on the PS chokes starve and regulation goes into anti-turbo mode, in those days the valuable HV electrolytic caps can go boom.
 
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