Standby bypass

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gtomax
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Standby bypass

Post by gtomax »

I'm building an 18 watt and noticed it has the standby between the power source and screens filter which is not a great design. I'm leaving it out all together and just putting in a switch not connected to anything for looks but it's straight power on/off no standby functionality.

I know 1986/7's have a similar problem but with the bias feed.

Is it unreasonable to (even, or maybe ESPECIALLY on vintage amps) wire up the standby switch with a jumper so it's "always on" an avoid the potential problems all together?

For vintage amps that's less intrusive and easier to reverse by some different owner than re-wiring the bias supply and it seems there is no disadvantage to the tubes doing a normal charge/warm-up?

After all if you want it quiet, turn down the volume!

Am I missing anything?
frankdrebin
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Re: Standby bypass

Post by frankdrebin »

In any guitar Amp standby is not required at all, period.
If you want, you can make a mute switch out of it, but with a different implementation than the usual hv interrupt, there are many different ways.

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populartsl
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Re: Standby bypass

Post by populartsl »

Merlins B's page has some interesting switching options for a 'standby switch' at the bottom of the page.

http://valvewizard.co.uk/standby.html
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pompeiisneaks
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Re: Standby bypass

Post by pompeiisneaks »

I agree wholeheartedly with frankdrebin I never put one on my new builds they're a mistake made by fender that everyone copies without understanding they're pointless. If you want a mute, then put in a mute that grounds the inputs, or something similar, super easy, doesn't require a complicated switch or anything. Standby switches were mandatory on high power (4kv etc) systems to protect against cathode stripping. that can't happen sub 1000V. Therefore standby is moot. On the other hand, it is super easy to accidentally configure an amp with standby to kill rectifiers. ;P

I wouldn't hesitate to jumper it, or convert it to some kind of mute mechanism that ties the inputs to it, and then to ground so you can lift the ground and have normal operation, and flip it to send all input away.

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martin manning
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Re: Standby bypass

Post by martin manning »

I think an effective mute could be made using the standby switch to disconnect the screen supply from the power tubes. Usually that will be just one wire, and a large resistor (say 220k) could be placed across the switch terminals to reduce arcing.
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pompeiisneaks
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Re: Standby bypass

Post by pompeiisneaks »

martin manning wrote: Thu Dec 21, 2017 8:43 pm I think an effective mute could be made using the standby switch to disconnect the screen supply from the power tubes. Usually that will be just one wire, and a large resistor (say 220k) could be placed across the switch terminals to reduce arcing.
I am sure that would work, but it seems tricky, requiring a well specced switch, etc. Why doesn't just shunting the signal to earth at the input work? It takes no special requirements, super low voltage, etc, and its safe.

?

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gtomax
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Re: Standby bypass

Post by gtomax »

Well usually the standby is on the opposite end of the chassis so carrying a signal wire down there could pick up some interference.

I think I'll just never turn it off on vintage amps and on new builds leave the switch for visuals only disconnected.
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martin manning
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Re: Standby bypass

Post by martin manning »

pompeiisneaks wrote: Thu Dec 21, 2017 9:28 pmI am sure that would work, but it seems tricky, requiring a well specced switch, etc.
Nothing special needed; the usual type of standby switch is fine for this.
pompeiisneaks wrote: Thu Dec 21, 2017 9:28 pmWhy doesn't just shunting the signal to earth at the input work? It takes no special requirements, super low voltage, etc, and its safe.
This:
gtomax wrote: Fri Dec 22, 2017 12:58 amWell usually the standby is on the opposite end of the chassis so carrying a signal wire down there could pick up some interference.
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Re: Standby bypass

Post by Stevem »

To me a standby switch is a good thing to have in place!
Number one, it gives a amp with big uf fixed bias supply filters a chance for the bias voltage to come fully up .

Number two, in terms of output tube life being able to cool the output tubes down slowly after playing by first allowing the amp to sit with the standby switch open for 2 minutes before turning the amp fully off has shown me in over 45 years of doing such, to lessen the rate of thermal expansion and contraction which leads many times to microphonic output tubes!

And last but not least, the standby switch also lets you drain the amp out to make it safe to work on.
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Re: Standby bypass

Post by sluckey »

Sears had an uncommon standby switch on it's Silvertone 1484 amp (maybe other models too). Just a SPST switch connected between the 6L6 grids. Really just a mute switch. The switch was located between the power and polarity switch on the front panel.
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martin manning
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Re: Standby bypass

Post by martin manning »

Stevem wrote: Fri Dec 22, 2017 11:36 am To me a standby switch is a good thing to have in place!
Number one, it gives a amp with big uf fixed bias supply filters a chance for the bias voltage to come fully up .
Unless the bias supply is very poorly designed, there should be plenty of time for that as the power tube heaters warm up.
Stevem wrote: Fri Dec 22, 2017 11:36 amNumber two, in terms of output tube life being able to cool the output tubes down slowly after playing by first allowing the amp to sit with the standby switch open for 2 minutes before turning the amp fully off has shown me in over 45 years of doing such, to lessen the rate of thermal expansion and contraction which leads many times to microphonic output tubes!
Presumably by turning off the idle current flow while the heaters are still on? If that is true then switching off the screen supply would have the same effect.
Stevem wrote: Fri Dec 22, 2017 11:36 amAnd last but not least, the standby switch also lets you drain the amp out to make it safe to work on.
If there is no standby switch, the tubes will drain the power supply caps as the heaters cool down. This is the same as the case where there is a standby switch, as long as the standby is left in the "play" position when the AC power is switched off, and that goes for the screen supply cut-off mute too. Many modern amps have some built-in means to insure that the power supply caps are drained, using either a dedicated bleed resistor or letting balance resistors used with stacked filters perform that function.
pdf64
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Re: Standby bypass

Post by pdf64 »

If a HT standby was beneficial to tube life, surely Tomer would have featured it http://www.tubebooks.org/Books/Atwood/T ... 0Tubes.pdf
but rather the opposite (standby and forgetful musicians might lead to a build up in cathode interface resistance).
And / or it would be noted on the manufacturer's info for the tubes we use.
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Re: Standby bypass

Post by dorrisant »

Some amp designs, like the Rocket, do good to have a standby switch. It will prolong the life of the rectifier, I believe.

Also, pull the guitar cable out of the input jack... This grounds out the input, no standby switch needed, right?
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pompeiisneaks
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Re: Standby bypass

Post by pompeiisneaks »

dorrisant wrote: Fri Mar 09, 2018 5:38 pm Some amp designs, like the Rocket, do good to have a standby switch. It will prolong the life of the rectifier, I believe.
That's basically a myth that won't die. Standby switches aren't hard on rectifiers unless you've put too much capacitance on the first stage (read the tube sheet, it will say the rectifier's max allowed capacitance. This is the limit of allowed inrush. ) Also the easiest way to slow down the inrush is to just put balance resistors on the caps to slow the inrush a bit. It also helps discharge them on power off. There's even a great video out there that D-Lab did on inrush current and standby switches if you want to watch it. He came to the same conclusion, they're not needed. They also CAN cause some damage to amps if the caps are slammed with heavy current draw on poorly designed amps when the warmed up tubes come on and all start conducting immediately on power on.

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xtian
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Re: Standby bypass

Post by xtian »

pompeiisneaks wrote: Fri Mar 09, 2018 5:42 pmAlso the easiest way to slow down the inrush is to just put balance resistors on the caps to slow the inrush a bit.
Really? My gut says nope. Happy to be proved wrong, tho.
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