Standby bypass

[Farrerdale Records]

Howdy!

With the AD30 I'm wondering how critical the standby switch is, as it has a valve rectifier which theoretically acts to slow the heat and power flow to the rest of the tubes on startup. Some guys say the standby is actually dangerous as it can bypass the fuse.

Is this the case with AD30? Does the standby on power up actually save tube life?

[fiveightandten]

IMO, the standby switch is useless in the AD30. It can put stress on the rectifier tube when the amp is in standby, and it causes a voltage surge when you flip the amp off standby after it's been warmed up.

I leave mine in the "on" position at all times, effectively acting as if it wasn't even there. It will take 60 to 90 seconds for the amp to ramp up to full operating voltage after you turn it on with the standby switch closed (in the on position). Use that as you minimum wait time, and ease the volume up from there as normal.

[Farrerdale Records]

Thanks! I figured as much but sometimes I think I think too much, so I thought I'd see what everyone else thought

[Jondog]

Best thing for any tube amp is to turn it fully on and have no signal at the input for warm up, so I’ve learned.

[Ade]

This is blowing my mind. Should I do the same with my AD15?

Ade

[Les Paul Lover]

You can simply leave it in on rather than standby mode.

To be honest, both school of thoughts make sense. A nice gentle warm up (using stand by) or avoiding current surge on the valves (no stand by).

In any case, we're talking about small percentage deterioration that may not necessarily be all that meaningful.

Amps work with both- I can't say one is better (I certainly haven't got the technical knowledge for that), but I can say that my amps with stand by have been working fine for years, so I'm not gonna sweat it.

[fiveightandten]

You can simply leave it in on rather than standby mode.

To be honest, both school of thoughts make sense. A nice gentle warm up (using stand by) or avoiding current surge on the valves (no stand by).

In any case, we're talking about small percentage deterioration that may not necessarily be all that meaningful.

Amps work with both- I can't say one is better (I certainly haven't got the technical knowledge for that), but I can say that my amps with stand by have been working fine for years, so I'm not gonna sweat it.

Using the standby actually does not yield a nice gentle warmup (for the amp). It yields a gentle warm up for the tubes (and only parts of them at that). When you use the standby switch, the amp sees no high voltage while the tubes are being warmed up. Then when you flip the switch, the tubes are hot enough to function pretty quickly. You flip the standby switch and the components in the B+ rail see a voltage surge. It ramps up above normal for a short time, then stabilizes.

When you *don't* use the standby the amp sees a slower warmup. The tubes get hit with high voltage immediately. So do many of the components in the amp, but they do not see a voltage surge above normal operating voltage.

I'd summarize it like this:
-Using the standby switch has the potential to be easier on the tubes (this is not always the case, taking the big picture into account), but it stresses the parts in the amp more.
-Not using the standby switch is easier on the components in the amp. It is harder on parts of the tubes.

This is assuming that we're talking about an amp with a solid state rectifier. In an amp with a tube rectifier, a standby switch is nearly useless. In that case, it's better for both the tubes and the amp to *not* use the standby switch.

[Les Paul Lover]

You can simply leave it in on rather than standby mode.

To be honest, both school of thoughts make sense. A nice gentle warm up (using stand by) or avoiding current surge on the valves (no stand by).

In any case, we're talking about small percentage deterioration that may not necessarily be all that meaningful.

Amps work with both- I can't say one is better (I certainly haven't got the technical knowledge for that), but I can say that my amps with stand by have been working fine for years, so I'm not gonna sweat it.

Using the standby actually does not yield a nice gentle warmup (for the amp). It yields a gentle warm up for the tubes (and only parts of them at that). When you use the standby switch, the amp sees no high voltage while the tubes are being warmed up. Then when you flip the switch, the tubes are hot enough to function pretty quickly. You flip the standby switch and the components in the B+ rail see a voltage surge. It ramps up above normal for a short time, then stabilizes.

When you *don't* use the standby the amp sees a slower warmup. The tubes get hit with high voltage immediately. So do many of the components in the amp, but they do not see a voltage surge above normal operating voltage.

I'd summarize it like this:
-Using the standby switch has the potential to be easier on the tubes (this is not always the case, taking the big picture into account), but it stresses the parts in the amp more.
-Not using the standby switch is easier on the components in the amp. It is harder on parts of the tubes.

This is assuming that we're talking about an amp with a solid state rectifier. In an amp with a tube rectifier, a standby switch is nearly useless. In that case, it's better for both the tubes and the amp to *not* use the standby switch.

You're a star, always so helpful with detailed technical explanations!!!

My point, really, is that isn't the amp designed to have parts to cope with the surge when the stand by is released?

Aren't the multiple RC power filters designed to absorb that variance, cope with it and protect the rest of the circuit?

[Jondog]

The story I heard on stand-by switches (and I can’t remember my source, an old amp builder I was listening to) is originally, they were service switches for techs. So they could power on and off without losing the filament heat. Leo Fender started putting them on his amps coming from a service tech background and everyone followed suit.

This wasn’t where I heard it, but talks of the same thing basically
http://www.londonpower.com/standby-switch#intro

Misunderstood and Hazardous

The design of the earliest guitar amps was not so much "beginning with a clean slate" as it was an application of hifi circuits for use with pickup-equipped guitars and basses. Portable hifi gear was not new - all that was novel was the intended use. Clean sound reinforcement was still the mandate.

Tube manufacturers "of old" provided application circuits for their products, and included advice for designing within the safe limits of the tube. It is generally advised that the cathode of the tube be at its operating temperature prior to application of the plate voltage, to prevent "cathode stripping". Cathode stripping shortens the life of the tube and reduces the amount of power that the tube can control. For very expensive and high-powered tubes operating with extremely high voltages >1kV, separate switching for the heater and the plate supply is recommended. The plate supply switch is called a "standby" switch, as the tubes are standing by with warmed cathodes, waiting for B+ to appear.
Many tubes have controlled warm-up times for their heaters, minimizing heater surge currents and allowing plate voltage to be present before the cathode emits electrons. This appears to contradict the concern about cathode stripping - but here is where the application makes a difference. Plate voltages for tubes equipped with controlled heater warm-up are always <1kV, and most often <500V. The danger of cathode stripping is insignificant, so the need for delayed turn-on of the plate supply is unnecessary.

Guitar amp power tubes are inexpensive compared to the cost of, say, a transmitting tube for a radio station. Guitar amps operate at 500V or less - most at under 100W. Low cost, low voltage, and low power: three reasons that guitar amps should not require standby switches. So why do many have them?

Answer: Fender essentially misinterpreted the requirements, and everyone else copied Fender. Leo tended not to put anything into the circuit that he felt was unnecessary - but he came from a repair background where a standby switch is a service convenience. There was no other logical reason for its presence: proper use of the standby is lost on most players. Many modern safety agencies even insist that the standby be removed, since the standby's removal of the plate voltage reduces the idle power dissipation and quiets the amp, and in such a state, it is easy for the user to forget that the amp is still on, which produces a fire hazard. Fender's rationale about the service convenience is also flawed: a B+ fuse works just as well, as does any easily unsoldered connection in the plate wiring. Although cathode life is theoretically extended - if so, by an infinitesmal amount - heater life is not extended.

Apart from misinderstanding when to use a standby switch, Fender also chose a poor implementation. Their switch is in the DC path, between the main filter caps and the feed to the output transformer and the rest of the plate supply. This leaves the main filters charged during standby, producing no useful advantage, especially for servicing, as this leaves high DC voltage present in the circuit. Mechanical switches arc when DC is present, so switch life is shortened in this application. Despite the fixed bias voltage also being present at all times, there is often a surge of current through the tube upon transition to the operating mode. The situation is improved quite a lot if the standby is used only to switch the screen circuit of the output tubes. Tube dissipation can still go to zero except for the heater being powered, but the current through the switch is reduced by 10-100 times. Other manufacturers switch the plate winding AC, which does lengthen the switch life, as AC switching is what most switches are designed for.

A few older amp models had standbys that simply muted the audio signal. There are several ways to go about this, and it does not alter the idle heat of the amp. Such circuits allow the use of a physically small switch that is easier to fit into the front panel. However, the quieted amp still presents the same fire hazard described above.

How to Use a Standby If You Have One

The best way to use a standby switch is to leave it on all the time - that is, leave it in the operating position. If you feel compelled to manipulate it since it's there, flip it when you flip the power switch.

Never leave the amp in standby between sets. Just turn down the volume control.

Rewire the standby to control just the screen circuit. Switch stress will be reduced by 10-100 times, and the output tubes will run at zero plate current. Or, rewire the switch as an audio mute.

In a Power Scaled amp, the standby should be rewired into the screen circuit after the Power Scale regulator. This is especially important in amps with a ground-lift standby in the centertap of the plate winding.

There are alternate preferred wirings for standby switches, as shown in The Ultimate Tone (TUT) series: all are safely implemented using a subminiature switch such as those in the C&K 7000-series.


The Safest Standby Switch

Bypass the standby switch internally so that it does nothing.



~by Kevin O'Connor

[Ade]

Wow, that’s really good information that even I think I get my head around.

But quite seriously and not attempting to be deliberately provocative - I own a Custom Shop AD50 designed and hand wired by Mr Ade E himself. Why did he design/build it with a standby?

[caldurham]

Why did he design/build it with a standby?

because tube amp users expect there to be a standby switch. after fender put them in amps for the first time to facilitate amp servicing EVERYONE else copied them. now users EXPECT there to be a standby switch, but you don't need one in a tube amp. look at all the other electronics that use tubes, like older tv, radios etc etc, none of those have a standby switch.

i think most tube amp manufacturers would LOVE to get rid of the standby switch.

[bclaire]

Why did he design/build it with a standby?

because tube amp users expect there to be a standby switch. after fender put them in amps for the first time to facilitate amp servicing EVERYONE else copied them. now users EXPECT there to be a standby switch, but you don't need one in a tube amp. look at all the other electronics that use tubes, like older tv, radios etc etc, none of those have a standby switch.

i think most tube amp manufacturers would LOVE to get rid of the standby switch.

I prefer to have an amp with a standby switch. I need to know that my amp is on and ready and not humming through the PA while I wait for the band to go on.

[caldurham]

Why did he design/build it with a standby?

because tube amp users expect there to be a standby switch. after fender put them in amps for the first time to facilitate amp servicing EVERYONE else copied them. now users EXPECT there to be a standby switch, but you don't need one in a tube amp. look at all the other electronics that use tubes, like older tv, radios etc etc, none of those have a standby switch.

i think most tube amp manufacturers would LOVE to get rid of the standby switch.

I prefer to have an amp with a standby switch. I need to know that my amp is on and ready and not humming through the PA while I wait for the band to go on.

lol i'd just always turn mine on when the band was ready.

[Ade]

Why did he design/build it with a standby?

because tube amp users expect there to be a standby switch. after fender put them in amps for the first time to facilitate amp servicing EVERYONE else copied them. now users EXPECT there to be a standby switch, but you don't need one in a tube amp. look at all the other electronics that use tubes, like older tv, radios etc etc, none of those have a standby switch.

i think most tube amp manufacturers would LOVE to get rid of the standby switch.

Yeah I get all that, hence my question.

The AD50 and Retro 50 were hand-wired Custom Shop models. Old Oranges didn’t have standby switches. Ade E being who he is, I just thought if anyone would’ve bucked the trend it would’ve been him.

Ade

[bclaire]

because tube amp users expect there to be a standby switch. after fender put them in amps for the first time to facilitate amp servicing EVERYONE else copied them. now users EXPECT there to be a standby switch, but you don't need one in a tube amp. look at all the other electronics that use tubes, like older tv, radios etc etc, none of those have a standby switch.

i think most tube amp manufacturers would LOVE to get rid of the standby switch.

I prefer to have an amp with a standby switch. I need to know that my amp is on and ready and not humming through the PA while I wait for the band to go on.

lol i'd just always turn mine on when the band was ready.

And if the amp is dead, there is no time to switch it out without eating into your set time. Thinking about the multi-band bills I have been on when your set time is, say 10:00 - 10:45, and if your gear isn't working, oh well. You are still finishing at 10:45 whether you go on at 10 or later. Been there - never gonna let it happen again.