Standby REALLY necessary???

[vechap]

I dunno.

Are the Blues Jr. and Pro Jr. tube rectified?

Seriously, I dunno.

No.

 

[Splattle101]

Did your grandma's TV have a standby? Their radio?

Standby is a glorified, over complicated mute switch that can kill rectifier tubes in amps with poorly designed standby / power supplies.

If you need a mute, get a tuner.

If you can't afford a tuner, get any true bypass pedal and take out the battery: it's now a mute switch when you turn it on.

If you can't do that and you still need a mute between sets, try the vol control on your guitar. Leave the amp running. It'll keep the valves warm.

 

[CB91710]

Raises another question. I have and regularly play out with a Friedman WW 20 - special version of the JJ Jr, which I guess he doesn’t make anymore - which seems to be equivalent to the Runt 20 and JEL 20 in most specs. The website doesn’t say, that I can find on any documentation, what type of rectifier is in those amps, although it does call them all tube amps. The 50 W versions DO have a standby switch, the 20’s don’t, and my WW 20 DOES NOT have a standby switch. I’ve always had Marshalls that did have a standby and I used it. In the Dr Z video, he said you don’t need it on “smaller” amps, which doesn’t really answer the question.

But my question is, having an amp WITHOUT a standby switch, when I play 3-4 hour gigs with 15-20 minutes between sets, should I be turning off the amp at the end of every set? I don’t, currently (no pun intended!). This Friedman WW 20 doesn’t seem to take long to warm up to be played, either. Less than a minute, for sure.

Interesting thread!

Thermal cycling speeds aging of pretty much everything, including the components in an amp.

Think how long old TV sets and radios were on, compared to commercial equipment and how long they lasted between failures.
TV sets were turned on and off a couple of times a day, PA systems in department stores ran for 10-14 hours.
TV sets failed way more often than those Muzak PA systems.

I'm not saying leave it on 24/7, that will shorten the life of the filaments, but once it's on for a practice day or a show, leave it on until you're ready to load out.
Then TRY to allow it to cool before moving. Load out the guitars, PA cabinets, the board, and lighting first. Take the heads off of the cabinets and then load out the cabinets.

 

[cdemike]

There's not a simple yes-or-no answer to this. There absolutely are amplifiers that should be started using the standby switch, but most designs do not require it. However, some very popular designs use circuits that rely on the standby switch to avoid destroying tubes and prevent damage to other components in event of a failure related to not using a standby switch.

Many have correctly noted that most other tube-based electronic equipment does not require a standup switch, and that there's nothing about tubes that specifically mandates a standby switch. However, under certain operating conditions a standby switch is vitally important to prevent arcing within the tube.

One type of circuit that does require a standby switch is fairly common: the direct-coupled cathode follower, which is present in 5F6-A Bassmans and related circuits, including almost all 4-hole Marshalls and JCM800s (there are very rare exceptions to the 4-hole Marshall piece — Majors and a a very number of Super Basses did not use cathode followers despite the vast majority of Super Basses having them). Fender and Marshall biased their direct-coupled cathode followers extremely hot, which is part of the sound, but doing so places very high voltage on the tube's grid. If you start your amp without the standby switch preventing high voltage from reaching the B+ rail, that high voltage reaches the cathode follower's grid before the tube can conduct, which keeps the cathode's potential over 100V less than the voltage at the grid. Tube datasheets will specify the maximum voltage between the cathode and grid, which is germane to this start-up condition. For a 12AX7, that datasheet maximum is 55V, which is much lower than the kinds of voltages present on a cathode follower's grid at start-up. The specific amount varies depending on your specific amp, but it can be nearly as high as B+ at the first filter capacitor (generally between 300V and 500V for most amps) if starting with dead cold cathodes since it will take a few seconds to get the heaters hot enough that the tubes start conducting current; if your amp has looser filtering, it could take meaningfully less time to charge the filter capacitors than for the heaters to get hot enough to start conducting. An optimistic example might be to use the typical voltage at a DC coupled cathode follower's grid after the amp has warmed up, which is ~180V in a 5F6-A Bassman, ~155V for metal-panel era 100W Marshalls. An extreme example is in early Plexi-era 100W Marshalls which can have ~220V here.

Here's why all this very technical information matters: placing voltage between two points very close together (like a tube's cathode and grid) risks arcing between those two points. This won't happen all the time, which is why many people get away with using these amps without using their standby switches. But if your tube happens to be on one end of production tolerance where the grid is close enough to the cathode for an arc to occur, this will destroy the tube and potentially cause damage to other related components (e.g., if the tone stack capacitors are rated for less than the unloaded B+ voltage in a Bassman or Marshall, those capacitors could be destroyed as well).

There are ways to prevent this type of arcing from happening without use of a standby switch (see: https://valvewizard.co.uk/dccf.html), but none of the original tweed Fenders had this type of circuit protection, nor did any of the Bassman reissues. There similarly is no such protection on any vintage or reissue Marshall, nor on any of the reissue-adjacent designs like the Studio series amps.

 

[cdemike]

Sorry for the double-post. Just wanted to clarify since my first post was pretty strong and only clarified instances where a standby switch is necessary without also giving a fair shake to the counterpoint that standby switches aren't needed for most amp designs.

There are many reasons why standby switches, including many which have already been mentioned in this thread in amps that don't have directly-coupled stages. In those amps, a standby switch is totally useless and does in fact needlessly stress the tubes in while also introducing an unnecessary point of potential failure in the switch itself which sees a significant amount of mechanical wear-and-tear (not to mention cases with with poor design of the standby switch itself: https://valvewizard.co.uk/standby.html). While amps using circuits similar to the tweed Bassman (including nearly every Marshall) make up a large proportion out in the wild, the majority of amplifier designs do not need standby switches, including nearly every Orange amplifier and all of the common Black and Silver-era Fenders. Of course, there are exceptions: arcing could occur in some early-1970s OR120s where the phase inverter is directly coupled to the preceding gain stage, but a relatively small number of Oranges came with that circuit.

My point is that there's not a one-size-fits-all answer in terms of whether a standby switch is useless or even harmful to your amplifier. In some cases, it actually solves a potential problem in the circuit, whereas in others it's a lazy or misinformed design decision.

 

[Splattle101]

...If you start your amp without the standby switch preventing high voltage from reaching the B+ rail, that high voltage reaches the cathode follower's grid before the tube can conduct, which keeps the cathode's potential over 100V less than the voltage at the grid...

I don't think this can happen in a 5F6A or a JTM 45 or other amp with a valve recto. There can't be any high voltage reaching the cathode follower - or any other part of the amp - until the recto has heated up and had a chance to start conducting to charge the reservoir caps. By that time the 6.3 V filaments should have warmed up the cathodes, too.

In effect, the entire amp has a slow start up. Together.

 

[cdemike]

I don't think this can happen in a 5F6A or a JTM 45 or other amp with a valve recto. There can't be any high voltage reaching the cathode follower - or any other part of the amp - until the recto has heated up and had a chance to start conducting to charge the reservoir caps. By that time the 6.3 V filaments should have warmed up the cathodes, too.

In effect, the entire amp has a slow start up. Together.

That’s correct, my apologies for the misleading statement about the 5F6-A and JTM45. I must have been thinking about the version of the reissue “59 Bassman” which had diode rectification. But still an important caveat that if there’s no rectification, there can’t be B+ and as a result no arcing. Same caution applies to RI Bassmans (Bassmen?), however, as well as solid state rectified Marshalls, as well as 6G6A Brown Bassmans.

 

[Leee]

I experimented with not using Standby on my 100 watt Plexi (solid state rectifier). This shortened power tube life.

Do you know this for a fact?
Not doubting you - just asking.

There are a lot of factors affecting the life expectancy of vacuum tubes, eh?

 

[firehead]

I wouldn’t kill it and power it up repeatedly. As mentioned above, just roll the volume to zero on breaks.

If you aren’t changing guitars that works. I use standby to mute the signal path for switching out guitars between songs. And so I can unplug my guitar during breaks to help prevent mishaps with tripping on the cord.

Even with light gigging the power tubes in my amp have lasted several years. I dont know if that has anything to do with using standby though. For me it’s just a useful feature.

 

[Leee]

I mute with my trusty old TU-2 tuner.
Easiest way to swap guitars.

 

[zontar]

I forget which amp maker it was, but the guy being interviewed said the only reason they put standbys on their amps is because people expect them, want them, and hold to the old tales.
He said their amps don’t need them.
Then there’s the joke about wiring one that at most turns n the light

 

[hbucker]

Is this more complicated than, do what you want?

If you don’t want to use standby, don’t.

If you like it, use it.

There is no deep state conspiracy here. Why are we overthinking this?

 

[efstop]

There is no deep state conspiracy here. Why are we overthinking this?

This is a guitar forum, you know.

 

[Leee]

Why are we overthinking this?

I think there’s a moral to the story.

Standby switch - properly used - is necessary for the health of certain amps.

As mentioned up-thread, it pays to know if your amp is one of them.

 

[Dogbreath]

All I know is that I’m now really confused! I only have two amps with standby switches. I love the switches. I think I would have an anxiety attack without them. They give my life purpose. I need to talk this out with my therapist,

 

[cdemike]

I mute with my trusty old TU-2 tuner.
Easiest way to swap guitars.

From a purely technical perspective, I think this is the best solution. Although I'm not aware of any strong scientific testing on this, using the standby switch as a mute switch causes heat cycling in a similar way as turning the amp on and off using the main power switch since the output tubes' plates and screen grids will intermittently start and stop seeing current. It's not as drastic as powering the amp on and off since the heaters are still running, but plate and screen grid dissipation is not an insignificant amount of energy, especially since nearly all guitar amps run in class AB or A (i.e. run the tubes either near their maximum or at their maximum plate dissipation at idle).

Is this more complicated than, do what you want?

If you don’t want to use standby, don’t.

If you like it, use it.

There is no deep state conspiracy here. Why are we overthinking this?

Unfortunately yes. On the one hand, there's a risk in terms of potential for electrical arcs that could damage or destroy tubes and other components in an amp where a standby switch should have been used, while on the other hand there's also a risk of needlessly having to replace tubes due to wear from needlessly using a standby switch. So I don't consider this very different than making sure you're paying attention to how well your strap fits the guitar's strap buttons. In the overwhelming majority of cases, nothing happens if you're not specifically paying attention to how well strapped-in your guitar is, but there is a real, non-zero risk of breaking Gibson-style guitar's neck if it drops headstock-first (or of being unable to play a show if your amp cooks a directly-coupled gain stage without a spare tube on-hand. Even if the tube survives the injury, I'd hope I remembered to bring spare fuses if this happened to me). If a standby switch really bothers you and your amp is capable of being modified (i.e. was constructed with turret board or point-to-point wiring or has a PCB layout that allows for it) most techs will be able modify your amp to protect against arcing if that's the specific reason your amp should be used with a standby switch.

There are other risks beyond arcing. For example, some 50w Marshalls have their bias supplies tapped from the HT secondary downstream of the standby switch which makes startup a risk proposition since the bias supply essentially needs to race the main B+ line in coming up to operating voltages. That's poor design in the first place, but increasing the number of startup events increases the number of times when it's possible that the bias supply won't reach operating voltages quickly enough to prevent runaway plate dissipation. By the way, I'm not picking on Marshall — it's just the amp brand I'm most familiar with from a technical perspective, but these types of design oversights come up in nearly any brand that makes enough amps.

But as others have mentioned in the thread, some manufacturers put standby switches into amps that don't need them. To go back to the strap button analogy, I don't consider knowing how best to power up your amp to be too different than knowing the importance of avoiding dropping a Gibson-type guitar if you're playing a Les Paul, avoiding big, rapid temperature swings with acoustics with thinner tops, etc.

 

[firehead]

I mute with my trusty old TU-2 tuner.
Easiest way to swap guitars.

I should just do that. When I’m using my boards anyways.

 

[landguitar]

Thermal cycling speeds aging of pretty much everything, including the components in an amp.

Think how long old TV sets and radios were on, compared to commercial equipment and how long they lasted between failures.
TV sets were turned on and off a couple of times a day, PA systems in department stores ran for 10-14 hours.
TV sets failed way more often than those Muzak PA systems.

I'm not saying leave it on 24/7, that will shorten the life of the filaments, but once it's on for a practice day or a show, leave it on until you're ready to load out.
Then TRY to allow it to cool before moving. Load out the guitars, PA cabinets, the board, and lighting first. Take the heads off of the cabinets and then load out the cabinets.

Exactly what I do. And take it out of its soft case when I get home so it can cool more.