tube amp experts care to chime in?

atyourlasthourrr said:
Apparently, warming up tubes is not only unnecessary but can have detrimental effects on the tubes themselves.
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Yes, it's true.

I have an AC30TB that was modded by a tech. guru and he actually removed the standby switch altogether. He used the spot to install my power scaling pot. So all I have now is just the main power switch. When I flip the switch, it takes a few seconds for the power light to come on, but once it does, I'm good to go. I've had my amp. for about 7 years now. The power scaling helps with tube life too, but I haven't noticed any detrimental effects by not having a standby switch.

Edit:

Here's the information on the reasons why it's not needed, on an AC30TB/TBX or CC at least, from the person who modded my amp.
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by Lyle Caldwell on Sat Jul 26, 2008 3:22 pm
I don't know how many times the collective gurus here have said it in various threads, so I'm making a thread just about this subject.

Do not use the Standby switch on an AC30TB/TBX or CC. It is not needed, and can damage the rectifier tube due to inrush current and a voltage spike that over time will cause the tube to fail.

Do not use it. Ever. Just don't. It's dumb.

I'll paste the technical reasons in below after I've had more caffeine.

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by Lyle Caldwell on Sat Jul 26, 2008 5:35 pm
The current inrush is one issue, and could be fixed just by adding series diodes to the rectifier from the PT secondaries.

But there is also a voltage spike (over 700v) which can damage the rectifier tube, the output transformer, the filter caps, and the standby switch itself, though the rectifier tube is the most likely one to fail.

This can also be addressed with a varistor across the switch.

But how many mods must one make to safeguard a non-needed switch?

I posted this in a less technically-inclined forum, but I think it explains the issue well:

Better for the amp if you either just leave it on with the master down or turn it off until 5 minutes before you start playing. Standby offers no benefit but every time you engage the standby switch there is a large current inrush and voltage spike. This gradually damages the GZ34 and eventually the filter caps and output tubes. Nominal B+ on these amps is about 325vdc, and the filter caps are rated 400-500vdc. When you flip the standby switch, voltage spikes of over 700vdc with brief but heavy current surges are common. These put undue stress on the parts mentioned above, as well as eventually causing the switch itself to fail.

Sometimes its a lot of fun when the spike/surge causes the rectifier tube to actually arc weld itself. You get a light show and a funky smell. The light show is over fast, but that smell lingers. And sometimes it takes out other parts of the power circuit! Yay!

And the reason people tell you TO use standby is so there is no instantaneous plate voltage on the tubes until the heater filaments in the tubes are warmed up. Thing is, no B+ (plate supply) flows in these amps until the filaments in the GZ34 have warmed up themselves, by which time every other tube in the amp also has its filaments heated.

So there is no valid reason to use standby, but lots of empirical, explainable, and predictable reasons not to.

Note, for the sake of this argument, I am only discussing amps that use a GZ34 rectifier tube or the Weber replacement. So JTM45, AC30, Bassman, etc. Amps with other tube rectifier types or solid state rectifiers are not part of this discussion.

Though really, unless you're talking about an extremely high voltage amp like an SVT (700+vdc B+) cathode stripping is really not a danger, so there still is no compelling reason to use Standby on a Twin or Marshall either.

Lots of techs "know" things based on what they have been told. That really is not knowledge. That is just a good memory.

Let me put this in less technical terms.

It's rare for you to be sitting in a room reading a book and the light in the lamp just goes off.

But it's common to switch on a lamp and have the bulb die at that point.

In the first scenario, the light has a steady voltage and steady current through it. Unless physically vibrated, that filament inside that bulb will keep on going a long long time.

But that same bulb when subjected to the voltage spike and current increase due to the electricity quickly being switched on will fail. The filament that could withstand hours and hours and hours with a steady voltage and current will fail instantaneously when the voltage and current briefly exceed its threshold of failure.

Now, that same bulb on a dimmer would not fail at power up if the dimmer was all the way down when the switch was turned on, and then you slowly brought the voltage up with the dimmer.

This last scenario is what happens when you let the filaments of the GZ34 control the voltage sent to the rest of the amp, rather than using the Standby switch.

Standby = instant on.

GZ34 = slow dimmer increase.

Hope this helps.

http://www.vintageamps.com/plexiboard/viewtopic.php?t=75667
 
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Toopy14 said:
Yes, it's true.
Click to expand...

I've owned several tube amps in my lifetime, some new some used. Most of them are gone now, but I do recall reading a manual for an amp I bought new (I think it was a MESA or a Peavey, don't remember) that specifically said to put the amp on standby for at least 10 seconds prior to switching it on.

If what your guru tech claims is correct, then why is this information so widespread and accepted?

Reading that article really blew my mind!
 
atyourlasthourrr said:
If what your guru tech claims is correct, then why is this information so widespread and accepted?
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Not sure if you read what I just posted, but the caveat may be that it depends on the amp. design. Having said that though, here's what the AC30 manual says about the standby switch;

"Standby Switch:
This switch allows the amplifier to attain the correct working temperature before
applying the H.T. supply. Before connecting the amplifier to the Mains supply, ensure the Power and Standby switches are in the off position. Turn on the Power switch first and then wait 2–3 minutes before turning on the Standby switch. Doing this each time you play helps prolong tube life. The Standby switch is also very useful for playing live as it allows you to keep the valves at a functional temperature between sets."

As I mentioned in my previous post, I've had my amp for quite a while and I've never had any issues by not having a standby switch.
 
I've built a few amps myself and know quite a bit about them. The typical justification for standby switch is cathode stripping, that is, the removal of oxide coating from the cathode by the electric field. This argument is bunk for low power tubes used in guitar amps: in order to have a demonstrable effect, the field strength has to be truly insane, and your EL34 or 6L6 (let alone EL84) is just not going to get anywhere close to that. There's a lot of "voodoo bullshit" in the tube amp community. Like changing tubes frequently (including preamp tubes), the widespread belief that all "vintage" tubes sound "better", the belief in the magical powers of tube rectifiers (whereas their effect can be easily replicated with diodes and resistors), etc, etc. And people can't be disabused of these notions, much like audiophiles believe in $3K power cables (which they use to connect to the shitty, frayed wiring in the wall).

Aside from fairly modest power savings I don't see much of a reason to have standby switches.
 
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