[Ron Ramirez]

I'm currently restoring the chassis of my 42-761EZ. This is the chassis which came out of the cabinet I had so much trouble refinishing this past summer.

It's an AC/DC set, designed to operate from either 115 or 230 volts, and has a metal ballast with jumper wires for 115 volt operation, and two sets of resistance wire for 230 volt operation.

I suspect one or both sections of resistance wire are bad, but that does not matter since it will be powered by 125 volt AC.

This set is another nightmare of rotten rubber-covered wiring, and it's all bad. Yep, all of it is dried out and crumbling.

Anyway, here is my first question on the subject.

This set uses a pilot lamp which connects across the line, but with a Candohm resistor in series with the lamp to drop the line voltage down to the proper voltage.

The original lamp was 34-2397E.

I found a 34-2397 in my 1950 Philco parts catalog. According to it, the lamp is a #53, 12 to 16 volts, 0.10 amps at 15 volts. It is listed as having a cylindrical bulb like a 44 or 47, miniature bayonet base.

The series resistance is 1020 ohms.

So, following Ohm's law, E=IR so 0.10 * 1020 = 102 volts being dropped, so assuming a 117 volt line, this would be correct for this lamp.

However, modern specs for a 53 lamp indicate 14.4 volts at 0.12 amps, with a round bulb like a 51.

All of that really does not matter to me, and here is why.

I am thinking of eliminating the dropping resistor and installing a miniature bayonet lamp which will run on 120 volts. I found types 120MB, 120MB6 and 967, but it looks like I would be sacrificing candle power for the convenience of having no dropping resistor if I used one of those.

The lamp is used to light the top edge of the dial scale, and is movable so only one of the several scales is lit depending on which band is selected.

To me, a 1020 ohm resistor is a very inefficient way to run a dial lamp.

Neon is out of the question as the lamp needs to be very bright to properly light up the edge of the glass dial scale. An LED lamp is an option, as long as it does not generate enough RF to interfere with the proper operation of the radio.

So, I look to you, the Phine Philco Phellows, for your thoughts, suggestions, etc.

[Steve Davis]

My vote is for the 120 volt lamp, if it is not bright enough then go with plan "B"

Steve

[Ron Ramirez]

Well, the response was...underwhelming. Everyone must be hibernating and staying away from their computers?

Steve, I shall go with your suggestion. I think I'll order an incandescent bulb and an LED, and try both. If neither work, I can always add the dropping resistor and install a lower voltage bulb, I guess.

Meanwhile, almost all of the rotten rubber-covered wire has been replaced, along with most of the capacitors and resistors. I'll have to order some electrolytic caps and a dropping resistor for the filament string. The original section of the 2-section Candohm for the filament string was 28 ohms. That won't drop the voltage quite enough on today's higher line voltage, so the replacement will be 68 ohms which will allow operation on 125+ volts without putting too much voltage on the filament string.

[Chuck Schwark]

An LED will get you the brightness. I don't know about any RF generation, but if you're hearing it, I'd try a couple .001 uF/400v disc ceramic caps maybe to ground on either LED lead, or maybe one across the LED. Experiment, you can't hurt anything with such a simple circuit as and LED, dropping resistor and diode and a couple caps.

Breadboard the lashup and hold a transistor AM radio next to the circuit.

A quickie hard circuit beats three yellow pad pages of "what-ifs" and formulas.... Or wrap the lamp/circuit/fixture in grounded and insulated aluminum foil. Again, experiment.

There. Another Two Cents.
:-)

The Other Philco Guy

[Arran]

Is this lamp in series or in parallel with a resistor? I know that it was very common in an early AC/DC set to connect the dial lamp in parallel with a dropping resistor that was in series with the filament string but since this is a Tropic which is an oddball set compared to other Philcos nothing would surprise me. I think your idea of using a 120 volt bayonet bulb for a dial lamp sounds fine, or a C7 candelabra lamp, no doubt that arrangement has something to do with it being a universal AC/DC power supply export model.
I don't know how much interference a straight 120 volt LED would make, the puck lights over my kitchen counter create some noise but I think it may be the power supplies causing it rather then the LEDs themselves. You can't hear anything on AM broadcast unless the radio is within a foot or two of them, but on one of the lower shortwave bands you can hear noise all over the room, very likely caused by the switchmode supplies radiating RF junk through the wiring.
Regards
Arran

[Ron Ramirez]

OK, allow me to clarify things a bit.

The dial lamp is attached to a movable bracket which slides left or right on top of the dial scale. It is brought into position above one of the eight scales, depending upon the position of the band switch.

These photos may help to illustrate:

[Image: http://www.philcoradio.com/images/phorum..._00001.jpg]
Band switch in AM (Broadcast) position

[Image: http://www.philcoradio.com/images/phorum..._00002.jpg]
Band switch in band 5 position (25 meters)

The lamp must be a miniature size lamp due to the limitations of space. A C7 candelabra will not physically fit.

Now, about the Candohm. It is a two section resistor, 28 ohms (I erroneously stated 22 ohms earlier, I have since corrected that post) and 1020 ohms. The 28 ohm section serves as a dropping resistor for the filament string. The "hot" side of the AC line connects to the junction of the 28 and 1020 ohm sections. At the other end of the 1020 ohm section, originally, was the 14 volt dial lamp; the other side of which connected to the "neutral" side of the AC line. In other words, the 1020 ohm section was in series with the dial lamp.

One section of the Candohm is open, so it will be removed altogether.

The filament string adds up to 105 volts. Adding a 28 ohm resistor in series dropped 8.4 volts, which added to 105 equals 113.4 volts. Not enough of a drop on today's 125+ volt AC lines. A 68 ohm resistor will drop 20.4 volts, which when added to 105 equals 125.4 volts - perfect.

The other section of the Candohm dropped the AC line to allow the 14 volt pilot lamp to operate properly. But I think using a dropping resistor in this fashion is a very inefficient way to provide for a dial lamp. The 1020 ohm section wasted over 10 watts of power just to provide the proper voltage for the dial lamp.

Since the Candohm must be replaced anyway, I wanted to do away with the 1020 ohm section entirely and use a 120 volt lamp if at all possible.

LED lamps are made, with miniature bayonet bases, which can operate at 120 volts AC. An LED of this type is looking more like a good answer to this problem.

I was just thinking that I had seen somewhere how someone used an LED night light in a Philco table model which originally used one of those 4 watt 117 volt incandescent night light bulbs, and it worked out OK.

[brownie45]

Don't like to step in too much, but could you hide a 6.3 volt filament
xfmr. under the chassis & use an appropriate voltage bayonet base
bulb? I know the correct police will be all over me for this. Jim

[Ron Ramirez]

No, no, Jim, please don't feel that way. Feel free to step in anytime!

Very good suggestion, in fact. The only reason I'm not going to go that route is because I want to try the 120 volt bulb first. I could follow your suggestion if the 120 volt LED isn't to my liking.

And please remember...there are no "correct police" here. The only time any action would be taken against anyone is if (1) you start posting spam or (2) start picking fights with others.

[brownie45]

Was thinking along the lines of low voltage, since
the light has to "travel" across the band selection
& has a chance to chafe the wires on metal edges.
The correct police I referred to was about keeping
the radio/ chassis as original as possible. Jim

[Ron Ramirez]

Good thoughts, thanks for your input.

Actually, the wires themselves should be protected well from chafing, as the wires will not be rubbing against any part of the mechanical moveable parts of the lamp mechanism.

[Eliot Ness]

Ron, I have several LED lamps that I bought a while back to experiment with, unfortunately they are subs for #44/47 lamps so that would defeat your desire to eliminate the dropping resistor. I've not used small 120 volt LED's, but in any case they're going to be dropping that excess voltage in some manner.

I'd be interested to see the source of small 120V LED's that you're thinking of using and if they do fit your space requirements they'd be worth a try. Otherwise it'll be simple enough to add the required section to your Candohm and use the conventional bulb or modify the value to use a #44/47 LED lamp.

Personally I wouldn't worry about the wasted watts of the dropping resistor in the Candohm, but I'm interested to see how your experiment turns out.

[morzh]

There are good small 3 to 6W 120V bulbs, used anywhere from Hanukkah menorahs to lighted vanity mirrors.
Easy to use.

Why not?

[Ron Ramirez]

Why not?

No room for a candelabra or xS6 bulb. Only a bulb which is the same physical size of a 44/47 lamp will fit.

John (Eliot) - How did you like those 44/47 LED replacements? Good/no good?

[Eliot Ness]

Ron, I bought a pretty good assortment from a couple of different pinball suppliers, but haven't really experimented with any of them yet. I'm optimistic that at least one version will be a good substitute.

[Ron Ramirez]

John, I am planning to try a BA9SF-W-180-120VAC LED from superbrightleds.com:

http://www.superbrightleds.com/cgi-bin/s...9s_120.htm
http://www.superbrightleds.com/moreinfo/...b-1-led/4/

180 degree angle (great since the lamp has to illuminate the edge of the glass dial scale from the side of the bulb).

If it's not to my liking, I'll install a new dropping resistor and put in a 14 volt incandescent lamp as per original.