standby switch

[sbirkenstock]

Hi everybody,

most switches you can buy have an ampere rating for 125V and 250V.
The standby switch is switching around 500V though.
Is it ok to just double the ampere for the 250V value?

Best regards,

Stephan

[stuben]

I've always used Carling switches rated 6A @ 125V, 3A @ 250V. Since we are only switching a few hundred milli amps at best we are fine.

I no longer use standby switches after reading Kevin O'Connor's books. They are not needed.

[Phil_S]

Merlin also says we don't need them. I stopped using them, too. One less hole to drill, one less thing to connect.

To be clear, components are of better quality today, particularly caps. In the bad old days, I think maybe those s/b switches were really there to soften the blow to the caps, not for the tubes. From what I read for guitar tubes, the cathode stripping argument is a red herring.

Some people want them just for the vintage look. I suppose no harm is done by having one.

[sbirkenstock]

Thanks for the feedback
I found the Kevin O´Connor books. Thanks for that tip.
Can´t find the Merlin books. Do you have a title or any other further info?

I think standby is still good if you have a break (especially if you leave the room).

I read several times that you can or even should go without standby switch if you have an indirect heated rectifier tube.

[xtian]

Designing Tube Preamps for Guitar and Bass, 2nd Edition
by Merlin Blencowe

http://www.valvewizard.co.uk

[Phil_S]

http://www.valvewizard.co.uk/standby.html

[R.G.]

If you wanted to be Really Sneaky, you could use a 1200V MOSFET to actually switch the high voltage, and an LED-to-photovoltage module to turn it on an off.

This also has the advantage that you can incorporate a few parts with the MOSFET to make the MOSFET clamp the current through it to being more than the amp ever needs while running, but less than the huge pulse when switched out of standby and get a soft-on standby.

see http://www.geofex.com/FX_images/Return% ... Fol....pdf

[pdf64]

When switching dc, what matters is that the switch has a quick make / break action, see p6 (p4 of the paper) http://www.aeroelectric.com/Reference_D ... Manual.pdf

and note http://www.carlingtech.com/sites/defaul ... _COS_0.pdf

I don't think that slow make / break switches would be suitable, even if rated for comparatively large ac currents.

I think that the regular Carling SPST eg 110-63 traditionally used for power and standby is quick make / break, see http://www.datasheets360.com/pdf/1977147183663097080
Even though standby switches act on circuits well above 250V, historically they're probably proven suitable for our application.

Bear in mind that to meet approvals / certification for use as a line switch, they must be able to cope with repeated transients from lightning strikes on the distribution system. The protection systems can only take so much energy out of such events.
So the voltage switches can withstand across their terminals is probably way above guitar amp B+, though it'll probably be above the voltage they're rated to switch.

Some good discussion on this topic at MEF http://music-electronics-forum.com/t38483/

As Merlin demonstrates, note that traditional standby implementations are nonsense and should be avoided.
Avoided like the plague in the case of those used with tube rectifiers.

[V2]

following up on pdf64's post, I think that the 'slow action' switches like the Carling F series would be ideally suited for the AC power switch but not for the conventional standby switch.

The additional stress put on the switch by high VDC is one of the reasons Kevin O'Connor and others implore people not to install or use the conventional stand-by. If one wants the muting and power-reduction functionalities of the stand-by, the switch could be wired in different parts of the circuit to reduce switch-related problems.

[Structo]

How many standby switches have needed replacing on the old Fenders?

[Gaz]

How many standby switches have needed replacing on the old Fenders?

5,345

[Structo]

[Gaz]

I called up Fender HQ, and that's what the secretary told me.

[pdf64]

Here's http://www.thegearpage.net/board/showpo ... stcount=17 the view of Alan from Carol-Ann Amps.

THe failure of a standy switch is quityr common and one of the most puzzling problems that techs can come across because they rarely just burn out. The most common symptom is a ticking sound every few seconds. The switch starts acting like a capacitor that charges up, breaks down and discharges to ground causing the tick/slight pop. The number of seconds between ticks is always very similar usually in the range of 15 to 30 secs. This fault is rarely detected or repaired unless the tech has seen it before. But most techs have come across it, even if they didn;t manage to trace it down.

However, even given the above, my view is that the big issue with traditional standby arrangements is not the stress on the switch, but rather the stress that use of the switch (and the consequential current surge) places on other components.

[Structo]

Thanks for the info.

I was half joking when I asked, how many Fender Stby switches have been replaced.

I can see where a tech would miss the Stby switch if it was making noise.

I think I will install a knife switch, that should last a good long time.

[img:220:200]http://upload.wikimedia.org/wikipedia/c ... switch.jpg[/img]