replacement LED bulb for princess phone

[flhusa1]

here is a direct replacement bulb that looks better and will last forever. it is a direct replacement with no mods needed. already using them in two of my phones.

http://www.banggood.com/10X-T10-158-168-194-W5W-501-White-LED-Side-Car-Light-Bulb-p-908120.html

i originally bought them to use in my landscape lights and had a few left over.

[jsowers]

Are you using a 6VAC transformer like a Princess would use, or 12VAC or DC? Just wondering because the lamps say 12 VDC.

These lamps would only be for the 702 Princess. The 701 used a miniature screw base #46 lamp. Also "forever" is a relative term. I've used three different 702 Princesses beside my bed in the last 25 years and still haven't burned out the first lamp. The incandescent ones last a very long time.

[poplar1]

The LED lamps I tried did not reduce brightness in night-light mode with the existing resistor found in a 702.

[unbeldi]

The LED lamps I tried did not reduce brightness in night-light mode with the existing resistor found in a 702.

Your finding is not surprising. The dimmer resistor of the lamp in the Princess has only 27 Ω resistance. When the bulb is hot its resistance should be about the same, I would expect.

The use of an LED, which has much higher resistance and draws perhaps only 10% of the current of the incandescent lamp, completely changes the operating characteristics and renders that resistor useless.
Not a good (=authentic) experience.

Actually, come to think of it, we can calculate the hot resistance of the bulb:
The bulb is powered by a 2012A transformer, its spec are 6-9 volts output at 1.75 VA.  Let's take a full voltage in the middle, say 7 volts:
1.75VA / 7V = 0.25 amps

Now, by Ohm's Law:  7V/0.25A = 28 Ω.

Bingo.

I once measured a current of 0.25 A at 6.7 V, so that is right in line with the calculation.

QED

[unbeldi]

So, perhaps one should really keep a supply of these:

I've never had one of them fail, IIRC, though.  No wonder stashes of these can be found.

[Bartonpipes]

I'll be honest, I really don't like LEDs in any use other than electronics, especially not in a vintage piece of equipment. Sure, I would say that if LEDs had been developed before 1959, it's possible that Western electric would have used them. I really think we got it right with the basic incandescent bulb- extremely cheap to produce and buy, and made out of recyclable materials.

Before you go calling me an old goat who's afraid of change, I'm 18, haha. 

[princessphone]

I believe that this topic has been discussed before. I've tried these LED's and consider them a novelty specially with choices of different colours. As mentioned, the light stays in bright mode at all times. One member posted that by replacing the resister with a much higher ohm resister, the dimming effect can be working again.
My opinion, unless you really want a bright night light, keep the phones original.
John     

[unbeldi]

Certainly, a 1 or 2 kΩ resistor would limit the LED current sufficiently to dim it down, but that is quite an intrusive modification—IIRC, the 27Ω resistor is soldered into the bulb base—for a dubious benefit.

[Kenton K]

Or you could place the resistor on the terminals of the transformer outside the telephone. No soldering necessary.

KK

[unbeldi]

Or you could place the resistor on the terminals of the transformer outside the telephone. No soldering necessary.

KK

No, because then the switch wouldn't work either, and the result would be the same as with just replacing the bulb, albeit just dimmer.

[Kenton K]

yup, your right. i was thinking about a general current limiter for the bulb.

KK