5E3 Standby switch...........

[mozzaburger]

Good day to all...........

Where is the best place for a standby switch?
Betweeen the PT CT and ground ?
Or between the rectifier and first filter cap?
Also, why do some schematics show the first filter cap(s) connected to the
hot side of the standby switch and others on the cold side?
Is there any appreciable difference or advantage/disadvantage?
This is my first ever build, though I've overhauled other old tube amps.
Also, if the power filter(s) are on the cold side of the standby switch, why do some people recommend adding a cap to ground on the hot side?
(Like a .033 polypropolene)?

Trust me when I say I am all ears..................


Thanx
Mozza

[tubeswell]

I vote for the center tap of the High voltage winding (for no other reason than it works for me). I believe the other way (i.e. lifting the B+) is also fine.

[PeaveyBandit]

You'll get better advise than mine I assure you but I just built/assembled a princeton and the advice I got here was to put the switch on the hot coming from the rectifier to the first cap. It seems to be working fine, no pops or funny business when using it. I haven't been using the amp long enough to know if there will be any issues with the switch. It's rated for 250v. I hope you get some good responses. I'll learn something too.

[Enzo]

WHy are there so many ways to do it? because it doesn't matter how you do it.

You can interrupt the B+ to the whole amp.
You can open the CT.
You can open the secondary to rectifier connection.
You can put it before or after the main filter.
You can interrupt the B+ to the screens and preamp.
You can lift the cathode connections to the power tubes.
You can short the opposing grids together on the power tubes.

All a standby switch is there for is to silence the amp while letting the heaters stay warm. Then you can flip the switch and instantly play - no warm up time. Of course you can also just zero the volume control.

You can put the standby switch anywhere you want in the circuit that does the job. There are no advantages, ther are just rationalizations from each builder as to why the way he did it is better than all the other ways. This amp simply does not need one. You install one because you want one.

You will hear a lot of tallk of things like cathode stripping, but that doesn't happen at the low voltages and current in a Deluxe or a Princeton. Got a 50,000 watt radio transmitter? Then I'd worry. Your tubes are going to bust loose a screen grid winding and short out or something long before cathode stripping might occur.

Wherever you decide to put it, there will be electrical repercussions. One way is more likely to make a pop when the switch is flipped as the empty caps charge. ANother way might be more prone to switch arcing. You small cap on the hot side will charge up to the B+ voltage more or less. Ther is no current draw to drag it down. Perhaps it reduces switch sparks. That doesn't mean one way is better, just that each way must be accomodated in the circuit.

Once it is on, it might as well be a wire as far as the circuits are concerned, so unless the switch fails, it will have zero impact on performance. And Fender and everyone else has been using those same 250v switches for the last 50 years, I have to think they'll be OK.

[d95err]

All a standby switch is there for is to silence the amp while letting the heaters stay warm. Then you can flip the switch and instantly play - no warm up time. Of course you can also just zero the volume control.

Agreed. The label should be "Mute" rather than standby. The only advantage compared to using the volume control, or simply removing the input cable, is that the poweramp hum is also muted.

[PeaveyBandit]

Nice post Enzo thanks but one major point. If you leave power to the first stages of lets say two channels on a fender super reverb, deluxe etc you can have that first stage go crazy. Like a bad tube, bypass cap and the amp will go crazy on stage and nothing you can do short of powering off will silence the amp squeeling. That's one reason the standby is pretty nice. When you hit that and walk off stage you are virtually assured the amp will not make noises. I had this happen to me a while back for the first time. The culprit was a bad tube socket #1 and that amp almost cleared the club before I could get back to it and flip it off.

[sjhust]

Just my 2 cents - I can't get any switches rated at 400V DC, but I can get switches rated at 400V AC. So I use a DPDT between the secondary and the rectifier, so that I'm switching AC instead of DC.

If I were a commercial builder and a standby switch failed for some reason and caused enough damage that someone hauled me into court, I'm not sure what would happen if it turned out I was using a switch which wasn't rated for what I was using it for, but I'll bet it wouldn't help my case. IMHO, if it doesn't matter where you put it, then put it where it's operating within spec. Ok, the filter caps have to charge when I take it off of standby, but so what.

steven

[d95err]

Just my 2 cents - I can't get any switches rated at 400V DC, but I can get switches rated at 400V AC. So I use a DPDT between the secondary and the rectifier, so that I'm switching AC instead of DC.

There should be no problem finding a proper switch. A switch will stand up to at least 1.41 times the AC rating, so a switch rated for about 250V AC would work fine.

Also, switches are usually rated based on current. E.g. 2A 115V, 1A 230V. The B+ supply is usually less than 200mA, so you can go a lot higher in voltage. You need to look at the switch datasheet to find the maximum voltage it can take before it arcs. Even miniature toggle switches can usually stand up to 1000V AC (1400V DC).

So, for a standby switch you could basically use just about any switch.

[sjhust]

Look at the specs here for an APEM 600 series - a very good switch

http://www.apem.fr/pdf/uk/section_a/...0H-600NH-A.pdf

you're saying this switch is good for 350V DC?

steven