120v Light Assembly: Interferes with Power?

[greg]

Hello.
I have used a Radio Shack pilot light which runs on 120V. I have it wired in to the power switch for my amp. I am wondering if this affects the power to the amp at all. The reason I ask is that I notice a slight, quick bump in volume right when I turn the amp off (as it powers down). So, the light immediately goes dark and there is an increase of volume for a split second, then the amp goes down.

Is it better to run pilot lights off the heater windings?

Thanks,
Greg

[Tom Phillips]

No logical reason why the light should affect the power to the amp. You can do a test to see for yourself. Disconnect the pilot light and see if you observe the same "quick bump" in volume when you turn the switch off.

[greg]

Thanks for the reply. So, in general, this not a "known bad" practice then. I suppose my question still stands - is it better to run status indicator lights off the 6.3v taps or before the PT at 120v?

Thanks,
Greg

[Ray Ivers]

Greg,

The only reason I can think of for the 'volume bump' behavior is that the neon might have caused the switch to momentarily 'micro-arc' and make contact again before completely opening up. I have absolutely no evidence to support this claim, just a thought-experiment kinda thing.

You might want to be careful how close the leads of a 120V neon indicator are placed to sensitive preamp stages, and IME neons have a tendency to flicker after a while, but those are about the only differences between the two I can think of off the top of my head. I think if I had the choice I would probably go with LED's (there are many 'LED bulb' replacements available), both for reliability and color/brightness/viewing-angle options, but YMMV.

FWIW, I just replaced 1 ea. 120V neon (standby) and 6.3V incandescent (mains power) indicators in each of two Marshalls I've been working on, just to have the same indicator brightness/color/appearance, not for anything performance-related.

Ray

[Steve Conner]

I seem to remember both my tube amps do that "volume bump" thing if you turn the power off while leaving the standby switch in the play position. AFAIK, it's down to the bias supply dying quicker than the other supplies and giving the output tubes a brief boost of current. Or weird things happening while the preamp supply voltages collapse.

Neither of them has any neon lights anywhere, they're all LEDs.

[Tom Phillips]

... I suppose my question still stands - is it better to run status indicator lights off the 6.3v taps or before the PT at 120v?

Greg,
I don't think one way is "better" than the other. If I was doing a build I would use the method that is easiest to wire up and gave the best lead dress to keep the AC away from sensitive circuits. Usually this is not a problem because the indicator light is already in the area near the PT and power switch. Other than that, you may have a preference to the look of a neon lamp vs. an incandescent.
Tom

[greg]

Great information. Thanks for the help everyone.

Greg