[Ron Ramirez]

Fun (?) with LEDs, Part 2.

As it was easy to convert the dial lamps to LEDs, I decided to try converting the Auto Magic lamp and the two tuning meter lamps.

The Auto Magic lamp was easy. I did add a 300 ohm resistor in parallel with this lamp since it is part of a switching circuit which I will show you shortly (plus, the Auto Magic lamp did not go out without the shunt). That worked fine once it was shunted. I just picked 300 ohms at random.

I then attempted to convert the two lamps behind the tuning meter to LED.

That did not go so well.

There is a circuit in the receiver which makes the tuning meter change colors depending on whether Auto Magic is on or off when the receiver is in FM mode. It is always green in AM, and is not illuminated when the receiver is in Phono or Aux mode.

When the receiver is in FM mode and the Auto Magic button is pushed in, the tuning meter is illuminated green.

When the Auto Magic button is off in FM mode, the tuning meter is illuminated white (actually, a bit off-white due to the incandescent lamp used).

Here's what happened.

Just by using 300 ohm, 1/2 watt resistors in parallel with each lamp, the tuning meter remains green whether Auto Magic is on or off.

Now, when I add a 47 ohm resistor in parallel with the white lamp, the lamps act as designed - but the resistor gets very hot.

I tried a 100 ohm, 5 watt resistor in parallel with the white lamp and it did not get hot - but at 100 ohms, the green LED does not go completely out.

With 100 ohms across the white lamp, Auto Magic on:

[Image: http://www.philcoradio.com/images/phorum/STA225_022.jpg]

Now with Auto Magic off:

[Image: http://www.philcoradio.com/images/phorum/STA225_023.jpg]

Notice how the green LED below the white LED is still on (although at low brightness)?

Here's a partial schematic. Click to enlarge it.

[Image: http://www.philcoradio.com/images/phorum...5_024a.jpg]

PL6 is the white lamp while PL5 is the green lamp. TR706 is another inverter, yes? That conducts when TR705 does not, causing the circuit to switch between lamps?

I could use some more help here, Mondial (or anyone else). I really don't want to go back to incandescent but I will if necessary...the LEDs light up the tuning meter much better than the incandescents did...