[lasurveyor]

Hi all,
I have a Philco 52-547 that has a bug that I know I've read about but I can't find info.
If you turn off the radio and turn it back on abruptly the pilot lamp will burn out.
Can someone explain what is happening here and what a solution looks like?

Thanks,
Alan

[Paul Philco322]

It gets too much current from somewhere, maybe not so good rectifier tube?

Paul

[morzh]

Yes. The thing is, the rectifier is serialized with the pilot lamp.
So, when you turn it off (after it has been warmed up) and then on quickly, the rectifier is still conducting, and you get electrolytic cap inrush going through the pilot lamp. Which can be bad enough to burn it.
The inrush of a discharged cap can be very large. Possibly you could install a NTC thermistor in series, but I am not sure what value it should be, and whether it is really needed. No device should be cycled quickly; we even wait for computers to be off for a few seconds before turning it back on.

Just don't do it.

[Ron Ramirez]

+1 what Mike (morzh) said. Don't do it.

[lasurveyor]

Thanks guys, I'll take your advice and "don't do it" (but I'll keep a box of bulbs around for those momentary lapses).

I appreciate your responses, thank you,
Alan

[radiorich]

Hello Alan,
Well what I did some years ago is to put what they call a bucking transformer so it steps down the line voltage I have it mounted in a cabinet with fuse holder and outlet plus filter network and a rocker switch on the front what do is leave my radio switch on and volume set low the rocker switches it on .

Sincerely Richard

[morzh]

Rich

I kinda doubt that this would change anything. Your rocker switch will do to a radio with its switch on the same as the radio's own switch would do. So if you decide to flip your external rocker switch quickly on after you have just powered the radio down, there is no difference in the process. And the pilot lamp might (I am not saying "will", but "might") just burn again.
And the bucking transformer itself will not prevent the lamp from burning, as the same inrush will happen. A discharged cap will draw lots of current from almost any voltage, and so difference of 5% to 10% won't matter.

[radiorich]

Hello mike,
Yes ,but it does help keep from wearing out the radios on/off switch and I did think of using a NTC thermistor.

Sincerely Richard

[morzh]

NTC thermistor is always a good thing, especially if chosen correctly.
I had to use it a few times, especially when I had to design an off-line SMPS power supply.
The challenge is, the consumption has to be significant for a particular thermistor to cause it to heat up and drop the resistance, at the same time having sufficiently high resistance in the cold state to limit the inrush. This all goes to efficiency, as obviously there are extra losses associated with it.

Of course, with the radios we do not care much about efficiency

[Paul Philco322]

You know when I nod off I don't like be jarred back to work, I guess tube radios don't like it either. Buy bulbs.

Paul

[morzh]

Here.

Take a solid state relay.
Make the switch input powered through an RC. Or a 555 timer. With 20 seconds delay.

And from here you could be as fancy as you like. I do not exclude a possibility of using some microcontroller and even AI. In the latter case make sure it has a display, where for 20 seconds there will be a middle finger displayed and some pleasant voice will tell you were to go and what to do.

Then after 20 seconds it will say "OK, ok...now".