The REAL Reason some tube amps have Standby switches.... and how to use it.

There's a whole bunch of misconceptions about this... and I've even seen certain amp makers saying STUPID things about it. Although different circuits wire these in differently, the MAIN function is to allow the tubes to warm enough to DRAW CURRENT, and pull DOWN the HIGH VOLTAGE... saving your Filter Caps from eating more than their rated voltage.
Hope this low production video helps.

[@fullwaverecked]

I dig the way you explain stuff! Cheers!

[@DeadKoby]

I appreciate that!

[@fullwaverecked]

What a lovely explanation. Thank you.

[@DeadKoby]

Glad it was helpful!

[@fullwaverecked]

I'm 60 years old. Still trying to wrap my egg shell mind around why, whilst being confused enough, I've got to be more confused with bias, stand by, current flowing both ways, AC riding on DC, Visa Versa, What the Heck? I feel like I'm tryin to play Schrodinger's Guitar... Cheers! Great video as always.

[@DeadKoby]

Understanding bias is easier when you think of electricity as water........ and the tube as a valve. There's some good explanations out there, but I have my own style of thinking about it.

[@Polyphemus.]

​@@DeadKoby You mean the valve as a valve? Sorry. Had to. Open goal. 😁

[@Mikere5]

​@@DeadKobyThat's why we call them valves NOT tooobes!

[@edwardhannigan6324]

Great video, now I understand..Thanks for sharing..Ed..uk..😀

[@DeadKoby]

I'm attempting to explain what the world "bias" in a tube is for..... Since I've been asked to do so. Hopefully I won't fail miserably.

[@fullwaverecked]

That's kinda funny, Fender was the O Fender... He He He...

[@DeadKoby]

One of our (now retired) music store owners knew Leo Fender... "he was as much an accountant as he was a product designer"

[@fullwaverecked]

@@DeadKoby Well, I think he performed both well?

[@DeadKoby]

Considering that the amps his team designed are the basis for MANY others... and are still sought after means they did something right. The modern era stuff has tried to go "too cheap" and the reliability suffers.

[@jerrylondon2388]

You mention that the standby switch is only needed on diode rectified amps. What would make tube rectified amps not need a standby switch. Or is it that they sorta do, or do for a different reason? Thanks! Enjoyed the video, long time subscriber.

[@DeadKoby]

In a Tube rectifier.... the DC voltage is going to rise as the rectifier tube warms up... which is usually around the same time that the other tubes start conducting. Thus, in a tube rectified amp, the DC isn't immediately present... The Diode rectified amp has the high DC almost immediately on power up. The odds of the rectifier tube getting up to full voltage prior to the other tubes conducting isn't nearly as likely. Tube rectified amps have minimal benefit from the standby switch... compared to the diode rectified amp. In several amps, I've observed about 550v unloaded (standby) and then it drops to about 425v (operate)

[@jerrylondon2388]

@DeadKoby This would make a good follow up video. Thanks!

[@komodomoe]

That was a great video! Can you explain why a tube amp should not be placed in operate without a speaker attached?

[@DeadKoby]

With no speaker, there's nowhere for the energy to go, and wild voltage swings and or oscillations can occur.

[@Craig52-zq1bt]

AND...perforations in output transformer insulation from errant transients BAD. Always have a load on transformers.

[@silasfatchett7380]

If an amp is operated with no load while attempting to amplify a signal, high voltage spikes are generated in the primary of the output transformer. This causes flashover between the electrodes in the output tubes which can damage them, and also cause conductive carbon tracks between the the pins on the tube socket. The worst case scenario is that the spikes can break down the insulation around the wires in the primary causing shorted turns, irreparably damaging the output transformer.

[@davidszep3488]

What if the standby switch is before the full wave rectifier? This was the main caps dont charge... If i ditch the standby switch should i use NTC thermstor to prevent high current draw when powering up the amp?

[@DeadKoby]

There's going to be huge voltage before the tubes warm and conduct. If you don't have a standby switch, thermistors can help. If your amp is tube rectified, you don't really need to concern as much... since that tube has to warm up also.

[@davidszep3488]

@@DeadKoby I did build two tube amp for myself, i am looking forward to improve the design, and tube lifetime, i have 6.3VAC spot on the filament, i did place the standby switch between the transformer secondary and between the greaetz/full wave rectifier. I planing using NTC too...should i place different NTC to the plate voltage, and the filament? They have different current draw after power on...

[@DeadKoby]

Thermistor is gonna work only on the positive rail after the rectifier. One is enough. Overthinking can be your enemy. Observing the voltages on a scope or with a probe .

[@paulcargo4233]

Even if I knew nothing about anything my first guess would have been money...its always about money.

[@DeadKoby]

Technically, a vintage 600v cap would have been mighty big also...... big and expensive. Some hi-fi amps (Elekit) actually used a digital controller to perform the standby/operate function automatically... That's some dedication there.

[@Lack0]

I have an Elekit and it has a microcomputer to control the soft start and also monitor voltages and alert before a tube fails. I find your video very informative. What I still don't understand about the cost effect is, why wasn't a thermistor used instead of the bypass switch?

[@curtiseverett1671]

why do you call yourself DeadKoby? that ruins your whole channel

[@DeadKoby]

Look under community posts. I explain it with photos. Koby was an electronic toy from the early 2000's

[@curtiseverett1671]

yeah, whatever, you know what you are saying shame on you ;;;;;@@DeadKoby

[@DeadKoby]

No... I've been using this name since 2001. It's just a coincidence. The spelling is different too.