Signal stops/Pilot Light dies: Coincidence? (3-3 build)

[JoeTele]

I was listening to my Ipod on my Mullard 3-3 build when the music stopped. I knew right away that my Ipod battery had died, but I also noticed the indicator light burnt out. The tubes were still glowing, so I put in a new light, variac'd up, and all was fine (though, interestingly, the El84 cathode was actually down a couple volts from the last time I measured, and my heater CT is connected to the elevated cathode voltage). I then put the old light back in and it was indeed burnt out, but everything else powered up. I measured my heater voltage to be about 6.9 volts, did some research, and of course realized it was due to the lightened load (PT is rated with a Deluxe Reverb load), which I factored in on the high voltage winding but not here. In fact I had noticed that the light was uncomfortably bright but hadn't given any thought to why. Given that stress, could the stopped signal have somehow been the straw that broke the Camel's back? Would it be wise to add resistors to bring the heater voltage down? Possibly anything more sinister going on?

Joe

[martin manning]

Given that stress, could the stopped signal have somehow been the straw that broke the Camel's back?

I doubt it, assuming your indicator lamp is simply connected across the filament winding.

Would it be wise to add resistors to bring the heater voltage down?

At 6.9V, you are within the usual +/- 10% tolerance for filament voltage, but you could add resistance to lower it a bit, possibly prolonging the life of the tubes and the indicator lamp.

Possibly anything more sinister going on?

Probably not.

[Phil_S]

A #47 bulb (typical pilot lamp) only draws 0.15A. That's not much of a load.

If you want to bother reducing filament voltage, a 0.25Ω 5W wirewound resistor on one leg of the filament winding will probably be about right. You must place the resistor between the PT and the first filament connection if you do this. It gets hot, so it needs some space. Really, as Martin notes, this isn't necessary. It is probably more trouble than it's worth.

I'd simply suspect that a cheap bulb blew its filament, and, with the replacement working OK, I'd just move on.

[tubeswell]

Loose IEC power cable plug?