5E3 Standby Switch Question

[lmolter]

I saw in another forum that some builders were switching the HV center tap to ground with their standby switch, instead of interrupting the HV to the reservoir caps. Is this common practice? Is it gentler on the caps and rectifier to do it this way?

Curious because I haven't started wiring my 5E3 yet.

Larry

[stingray_65]

This is exactly how I put the standby on my 5E3 and have had NO issues what so ever.

It does not "POP" when switched on and off and is super simple to wire.

On my next push pull amp I plan on running a DPDT standby switch.

half will switch the ct on the HT and be wired as a SPST. the other half will switch a diode in and out of my heater supply.

It's the heaters that age the tubes (in my understanding) the most and by shunting in the diode inline with the standby it will drop the heater supply voltage by about .6v which is a 10% drop. the effect is the heaters aren't cooking away while the amps in standby.

This mod was suggested to me by Tubeswell.



Ray

[fmarshall]

The original circuit of a 5e3 doesn't have a standby switch. The way I have seen others wired, that I also did, was to uses a SPST switch and interrupt B+ coming off the board.

Is that the right way to do it?

[bnwitt]

With a 5Y3GT rectifier tube you don't need a standby switch anyway as it comes up to voltage slowly enough.

[mbratch]

The original circuit of a 5e3 doesn't have a standby switch. The way I have seen others wired, that I also did, was to uses a SPST switch and interrupt B+ coming off the board.

Is that the right way to do it?

There seems to be a couple of popular ways to do it. Fender uses the same method on their re-issue '57 Deluxe that stingray_65 did: switching the HV CT on the PT (that sounds funny, dudn it?). Fender also adds a couple of diodes to the mix to avoid potential popping due to inrush. See the schematic available at their web site.

I'm not sure which way is best, that or the B+ switching. I've seen each done by reputable builders.

[mbratch]

With a 5Y3GT rectifier tube you don't need a standby switch anyway as it comes up to voltage slowly enough.

I have no intention of sending the thread on a tangent, but is this also true with the lower powered amps that use 5AR4 or 5U4, such as a BF Princeton Reverb? They don't have a standby and I've wondered whether that would be a problem.

[Five_E35]

Leo put them on the HV center tap in cathode biased amps that had them like the 5E5 Pro, moved it to the B+ when he went to fixed bias as on the 5E5-A and others. Just a guess, but I think this was to bring up the negative bias voltage while on standby. Later he moved it after the first set of filter caps, maybe to make life easier on the Rectifier Tube or to avoid blowing fuses.

Modern Fenders have an in rush current limiter(that NTC thing) on the 120 VAC side of the transformer. Some people claim this slow starts the tubes, but I looked up the specs once and it turns on so quick, I don't see how. Maybe it helps the Rectifier with higher cap loads or is there to avoid blowing fuses prematurely. Anyone know?

5AR4's are slow warmup, but I've always used standby to warm up the tubes anyway, but not for anything else. Every RCA datasheet that includes tolerance lists heater voltage as 6.3 volts AC or DC plus or minus 10%. 6V6's were used in car radios, so they probably ran pretty hot when the battery was charging.

[Enzo]

NO guitar amp needs a standby switch really. The only reason they are put on there is to allow the amp to remain warmed up but not producing sound. There is no "best" way to do it. You can open the PT CT, you can open the PT secondaries before the rectifier (MArshall), you can open them after the rectifier(Fender). You can open the B+ line after the first filter but before the plates. You can open the B+ after the plates, but killing the screens(Peavey).

You can open the cathode lead from the power tubes. You can short the opposing control grids together on the push pull output.

The standby doesn;t really protect the tubes from anything. At the small currents and low voltages of guitar amps, the vaunted cathode stripping just is not an issue. I can;t imagin dropping the heater voltage a half volt will make any difference. I'd be inclined to think heat cycling would be more harmful than just on-time.

[tubeswell]

I saw in another forum that some builders were switching the HV center tap to ground with their standby switch, instead of interrupting the HV to the reservoir caps. Is this common practice?

All my amps to-date have had the stdby off the HT Center tap. No issues

[txstrat]

I usually open the B+ line after the first filter. Some of my amps have a slight pop when switched into play mode. Unfortunatley those PTs don't have a CT. Is there another way to avoid the popping?

[mbratch]

All my amps to-date have had the stdby off the HT Center tap. No issues

Is that all that's needed for a pop-free switch, or do you also have the diodes a-la Fender's newer design, and/or a strategically placed cap?

[stingray_65]

first I believe that people have a stanby switch on a 5E3 because they have an unused hole after removing the polarity switch

what else you gonna use to fill a hole that already has a switch in it.

second to MRBRATCH, put the switch inline with the HV CT and you won't have an issue.

Ray

[mbratch]

first I believe that people have a stanby switch on a 5E3 because they have an unused hole after removing the polarity switch

what else you gonna use to fill a hole that already has a switch in it.

second to MRBRATCH, put the switch inline with the HV CT and you won't have an issue.

Ray

Thanks Ray. I wondered because Fender chose to add the diodes in their re-issue and I wasn't sure if they were necessary.

As far as what to do with the ground switch, I'm still trying to decide between:

• A 3-position ground switch (like a 70's Fender has)
• A standby switch
• Something else different and interesting.

[bnwitt]

first I believe that people have a stanby switch on a 5E3 because they have an unused hole after removing the polarity switch

what else you gonna use to fill a hole that already has a switch in it.

I have used it for a split/shared V1 cathode R/C setup, a bright switch, a half power switch, and a few other things. Before you laugh about the half power switch, I've had a handful of 5E3 customers complain about the amp being too loud for home use and that is why I have implemented it. Attached is a gif file of a cathode biased power section half, quarter and full power switch drawn by a member of the Hoffman amps forum some time ago.

[tubeswell]

Is that all that's needed for a pop-free switch, or do you also have the diodes a-la Fender's newer design, and/or a strategically placed cap?

Yep the switch is all that's needed. However, I also put reverse-biased zeners next to the switch on some of my amps, but that is for tweeking the HT voltage - nothing to do with the stdby switch.