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That sounds reasonable.
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Education is what you're left with after you have forgotten what you have learned. -
The reasoning behind standby switches as I understand it is based on whether your amp has fixed or cathode bias.
If you have a fixed bias circuit..... then, at the instant you throw the power switch, your bias voltage is 0 which allows a rush of current through the power tubes until such time as the bias voltage comes up to establish the proper operating point. It was an electronic "race condition" that depended on the amp and the components as to how often or how badly it happened.
With a cathode bias circuit..... when you turn the power on, sure, the plate current starts flowing. But the current through the cathode resistor is what establishes the bias .... so the bias is coming up with the plate current and serves to stabilize the operating point "on the fly" without providing a really large shot of excessive current through the tube.
It always made me sleep better.....Comment
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Actually, that is backwards as most all fixed biased amps have the bias supply running with the amp in standby so the tubes are fully biased when you flip the switch to play.Originally posted by bob_ruth View Post
Cathode biasing is the one that takes a moment or two for the bias to develop....full pop, high B+ with zero bias until the tube conducts current.
However, neither will really suffer much at all without a standby switch in the real scheme of things.Comment
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All true! But the discussion was...... what does standby DO for you? Why is it THERE? So if that big fixed bias amp did NOT have a standby switch.....
now go back and read it!Comment
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Don't stand-by switches also allow instruments to be un-plugged / plugged-in without the sound coming through the amp? I have a Gibson GA30RV w/ reverb in one channel only. The standby function is a switch position on the power switch; off/standby/on (off/on/on). I have a newer Univox U305R w/ reverb in one channel however its standby function is different; standby/off/on (on/off/on).
In both these amps, the channels are voice differently so for someone wanting to switch channels - without benefit of a footswitch, relays, or opticouplers - standby would make it easier. In the case of the Univox, to get from standby to on, you have to shut the power off briefly as the switch is moved from standby to on (and again to get to standby from on).
In looking for replacement power switches to match the GA30RV - and to add standby function to amps without it using a GA30RV type switch - the market doesn't seem to support off/on/on - just on/off/on. Do I have it wrong about the plug/unplug thing and does anybody know where I can find an off/on/on DPDT switch? Thank you, JohnComment
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Yes, standby keeps the amp warm for instant operation, but with no output. You can flip it off to change what is plugged in, sure. You could also just dial down the volume.
That very brief momentary visit to the off condition while switching between run and standby is irrelevant. it doesn't take long enough for anything to cool off or discharge appreciably. If using an on-off-on switch doesn't appeal cosmetically, then so be it, but electrically it doesn't matter. I won't get into the mojo of it.
SOme rotary switch power switches have off-standby-on-on. The two ons being also reverse mains polarity options. A rotary could be wired most any way you want, and would likely fit in the hole.
Not in a toggle that I know of, but I am aware of sequential-on rocker switches.Education is what you're left with after you have forgotten what you have learned.Comment
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Hi Enzo; thanks ... yes, it's partly mojo but it also matters if the control panel is already lettered off/standby/on or, in the event of adding standby function to an amp that doesn't have it but whose control panel is already lettered off/on. Thanks also for the confirmation that no off/on/on toggle switches out there ... at least now I know there's no needle in the haystackOriginally posted by Enzo View Post
. John
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