Indicator lamp and fuse

[Smokebreak]

I've been voicing a new build for a week or so. All's been well, except that I've noticed when I flick the mains power switch, the 125V neon lamp takes maybe a half a second to come on. I can then flick on the standby and everything is fine.

Amp is 50W Fendery thing, and supply is basically old Fender : GZ34, reservoir cap bank before the standby, 300r 10W resistor after instead of a choke. I've attached a pic.

I've also just started using an IEC assembly with a fuse holder, 5X20, which I've used in a couple of builds with no problems.

Now, this has been bugging me, as something's not right. Today I flicked the mains switch back and forth at 1 second intervals, and the the fuse blew after about 5 times. I can put in a new fuse, fully power the amp, and all is fine. I repeat the multiple flicking, and the same thing happens.

I haven't got too far into it yet, but I did swap a GZ34, and the same thing happens, but again, only after repeated flicks. GZ34s are fine, and the amp still "works" after the fuse swap.

Also, after the amp has been on for a few minutes, then lamp comes right on(no delay) when powering the mains, but the repeated flicking gets the fuse every time.

What do you all think?

[Phil_S]

I'm no expert on this, but I think you need a load resistor on the negative side of the bulb. Why not just change this for an old school incandescent? They come in both bayonet and screw base.

[vibratoking]

I've been voicing a new build for a week or so. All's been well, except that I've noticed when I flick the mains power switch, the 125V neon lamp takes maybe a half a second to come on. I can then flick on the standby and everything is fine.

Amp is 50W Fendery thing, and supply is basically old Fender : GZ34, reservoir cap bank before the standby, 300r 10W resistor after instead of a choke. I've attached a pic.

I've also just started using an IEC assembly with a fuse holder, 5X20, which I've used in a couple of builds with no problems.

Now, this has been bugging me, as something's not right. Today I flicked the mains switch back and forth at 1 second intervals, and the the fuse blew after about 5 times. I can put in a new fuse, fully power the amp, and all is fine. I repeat the multiple flicking, and the same thing happens.

I haven't got too far into it yet, but I did swap a GZ34, and the same thing happens, but again, only after repeated flicks. GZ34s are fine, and the amp still "works" after the fuse swap.

Also, after the amp has been on for a few minutes, then lamp comes right on(no delay) when powering the mains, but the repeated flicking gets the fuse every time.

What do you all think?

The caps start at zero volts and the voltage doesn't come up fully until the caps are charged to a high enough voltage to light the lamp. I think that's the delay.

The fuse blowing is probably due to inductive kick back and the resulting current that occurs as you quickly flick the switch. Is the fuse a slow-blo?

[Smokebreak]

Phil, I believe there is a resistor inside the assembly, per the specs : http://www.ralphselectronics.com/Produc ... IDI-1050A3 , but both leads are black, and the same length.

VK, I'm powering from 120V primary side, so I thought there shouldn't be a delay? The fuses are indeed slow types. I just stuck a new 120V lamp in, and the same thing happens. I also switched over to SS rectification for a minute and the same thing happens.

Also, I've got a different, yet nearly identical amp here, only difference being a choke instead of the 300r 10W, and this is not happening with this other amp.

[vibratoking]

Also, I've got a different, yet nearly identical amp here, only difference being a choke instead of the 300r 10W, and this is not happening with this other amp.

That's interesting. I would imagine that an uncharged neon bulb has a turn on delay as it has to ionize. But this doesn't make sense if it works without delay in your other identical amp. Have you tried the bulb that shows the delay in the 'other' amp? Are you sure it is a neon bulb in the other amp? Incandescent bulbs light almost instantaneously, while neons have to ionize. Just pontificating on your issue.

Edited to add this link: http://home.comcast.net/~jlrmsousa/sign ... _lamps.pdf

Based on this, I would guess that you have both the ionization time lag and a voltage rise issue. Do you have a scope to look at the voltage at startup?

[Smokebreak]

Thanks. I don't have a scope but voltages seem to be acting normally during startup.

Here's what I've discovered : The amp with the same neon lamp(as the one that I just put in the problematic amp) has a T2AL . i.e. 2A slow blow, low breaking, glass.
The fuse in the problematic amp is a T2AH i.e. 2A slow blow high breaking, ceramic.
I put a glass, "L" type in the problematic amp, and problem solved.

Now, this makes no sense! I thought that the high breaking fuses(stronger composition) held up to high current surges better, and that ceramic fuses were preferred for mains fusing(though perhaps for a different reason - filament contained glass fuses leaving conductive remains after failure).

I'll have to wait a while and see if the delay is still there, as discharging the caps doesn't put it in the state where the delay shows up. It's only after its off for 15-30min. Weird.

[Structo]

I'm no expert but I can't imagine flipping the power switch back and forth rapidly is a good thing to do.
With an inductor and the first filter cap.....

I have used neon bulbs in the past and had a few quit or flicker, so I just use fender #47 type incandescent or a LED type.

[vibratoking]

Good that you got the fuse issue straightened out.

I'll have to wait a while and see if the delay is still there, as discharging the caps doesn't put it in the state where the delay shows up. It's only after its off for 15-30min. Weird.

I think the 15-30min waiting time is due to the atoms in the bulb staying closer to the ionization state and so it takes less energy for the lamp to light. You can check this with a flash light. Shine a light on the bulb when it hasn't been lit for a long time and nothing should happen. Shine a light on a hot bulb just after it has turned off and it will light. In the state that is close to ionization, it takes very little energy to re-ionize and emit photons. In this state, I am guessing that there is no noticeable turn-on delay.

[Leo_Gnardo]

I have used neon bulbs in the past and had a few quit or flicker, so I just use fender #47 type incandescent or a LED type.

If you want your pilot to last near forever CM #755 is your friend. I buy a hundred at a time.

If the neon in question had no dropping resistor, I could see it causing trouble installed across the AC line. Typically neon "assemblies" contain a "dropping resistor" 30K to 39K. If there was a dropping resistor involved in this question I don't see how the neon lamp could cause a fuse to blow. Those who use neons not assembled into a mini fixture with a resistor should add a resistor to keep out of trouble & extend the neon's lifetime. Note Ampeg put a neon pilot on their hi voltage supply @ 540V DC. The typical Rd value was 180 K.

Stay calm & shine on you pilot lamps