light bulb limiter / startup question

[Bob Simpson]

Will the startup dim/glow sequence be different if the standby switch circuit is after the first filter caps rather than before?

I don't want to make a mistake starting mine up...

TIA

Bob Simpson

[Gibsonman63]

The light bulb limiter is just a current limiting device, so it really doesn't care. You have the same circuit all over your house, except you have a straight piece of wire instead of an amplifier, so the bulb glows at full power. You're basically checking for dead shorts and protecting the amplifier at the same time. Mine paid for itself many time over just in fuses. Your amp can be considered resistance in series with the bulb, so some of the voltage is dropped across the amp the the rest is dropped across the bulb. Normally, most of the voltage is across the amp, so the bulb glows very dim.

[Structo]

To add to that, no it doesn't matter where the first filter is in relationship to the standby switch but the way the bulb acts will differ.

If the filter is before the standby the bulb will flash brightly when you first throw the power switch because when a large cap is first energized it appears almost as a short because it passes current to ground for a split second before it charges. Then the bulb will go to a lower glow, then when you throw the standby switch you will get another flash as the other caps charge, then down to the lower glow.

If the first filter is after the standby switch then you won't get much of a flash when you throw the power switch but you will when you throw the standby.

If the bulb stays brightly lit for more than a second or two, you probably have a short circuit or wiring mistake and you should immediately turn the amp off.
Then troubleshoot your wiring, especially the power supply and see where the mistake is.

For a brand new build and first power up I usually use a 25w bulb first.
This limits the amp to less than 250ma.
No tubes in for the first power up.
Then if it has a rectifier tube I will install that and do it again.

Once that test goes off with out a hitch I install a 60 watt bulb and do it again this time leaving it on for 5 minutes or so. This helps form the caps before you slam them with the high voltage.

Then I will install a 75 w bulb, install all the tubes and try it again.
MAKE SURE TO PLUG IN THE SPEAKER WHEN POWER TUBES ARE IN AMP!

If no shorts or faults, take out the limiter, plug in a guitar and make some noise!

This simple device can save you from burning up transformers and other expensive parts. A really neat invention IMHO.

[jhaas]

I built a bunch of amps in the 20W and under range, used the bulb limiter on every one. Then recently I build a 4 x 6V6 Rocket, which is probably in the 30-35W range. When I powered this one up for the first time bulb was glowing much brighter than I was used to. I spent probably 3 evening trying to figure out what the problem was.

Turns out that everything was fine. It was just that this amp was drawing much more current than the lesser powered amps I was used to, so the bulb was glowing brighter.

[tubeswell]

And the lower the wattage of the bulb, the more you will see it dim (if the PT is good) 2CW

[Bob Simpson]

Thanks for the replies, folks...

It made sense to me that the flash/dim sequence might be different based on whether the caps came before or after the standby switch.

Of course, making sense to me doesn't necessarily make it so...

Bob Simpson

[Gibsonman63]

If you truly had both sockets in series, you would have an open circuit unless you had two things plugged in at the same time. I guess you could just plug a lamp into one of the sockets and accomplish the same thing though. It should be wired:

incoming Hot to the switch
Switch to hot on the first socket
Nuetral on the first socket to hot on the second socket
Nuetral on the second socket to incoming Nuetral
All grounds tied together and taken to incoming ground.

I am thinking that you should plug the lamp into the first socket, but given the oposing theories of hole flow vs. electron flow and the fact that it is alternating current, I cannot reconcile the logic in my mind.

Meter it out before you plug it in to be sure. It sounds like you have a dead short.

[wsaraceni]

i figured it out. i have a shorted wire. and i typed it out incorrectly so ignore what i typed above.

[Masco]

I've got my limiter rig set up series w/ 3 bulb sockets in parallel and a bypass switch across the whole thing. You can halfway screw in/out paralleled bulbs as needed for different wattage, then bypass all the bulbs out for normal operation via switch.

[wsaraceni]

i went with 3 of these.

http://www.amazon.com/Leviton-Ivory-Soc ... B000VL4CFC

one for each bulb. and i just wrote on the base what bulb is which.

here is my fixed "schematic" any issues?

[img:764:1024]http://img.photobucket.com/albums/v217/ ... 9e3cb9.jpg[/img]

[Structo]

Nope, looks good.

Just be sure to break off the tabs between the two receptacles.

[wsaraceni]

thanks. i actually cut them out so there is a big space between the tabs.