Another local Hoffman! COLOR!

[Yamamaya42]

Originally Posted by Yamamaya42

1 is good, 2 is a charm, 3 is nuts! :P

http://suzaku.live-evil.org/crazy-color.jpg

Seems that all 3 of these gimmick lights are burned out. :O

Bad design.

NPN switch from the 6.3 fil power through a 1/2 wave rect, lighting up 3 2 volt bulbs through a 6.8 ohm resistor, as long as ALL 3 lamps are OK, all is fine, but if one burns out, then they ALL go because the voltage spikes.

they sell them in packs of 10, not gonna do it, I can get ultra bright yellow LEDs that run at 2-3 volts in packs of 20 cheaper.

[Electronic M]

Whenever I get a set that someone has converted to LED lamps I reflexively then switch it back to incandescent it's one of those things that gets under my skin about as bad as a set that someone painted some random ugly color.
I'm pretty well stocked with bulbs thanks to an estate sale of a mid-century EE who had 2 mason jars of spares, but when I use that up I plan to hit up rockauto...When I was doing my 6V 1947 Oldsmobile I had a look at every part they had and found a number of radio bulbs it used for the interior lights were DIRT cheap compared to mouser, and better than bob's capacitor who was my supplier before the estate sale. I think if I browse around 40s cars on rockauto enough I should find almost everything I typically need for consumer electronics.

[Yamamaya42]

I really don't mind using LEDs at all, they are cheaper than bulbs, and outlast them.

On second thought, since the source is 6.3v, and the drop across the transistor is pretty much nothing, w/o any bulbs, the switched on output should be about 6-7v so by adding a dropping resistor to ground, like 6-7 ohms should get me the 3.1v needed to use the ultra bright white LEDs, like I used in the GE TV.

Will just have to play till I find the right resistor value.

[old_tv_nut]

Originally Posted by Yamamaya42

I really don't mind using LEDs at all, they are cheaper than bulbs, and outlast them.

On second thought, since the source is 6.3v, and the drop across the transistor is pretty much nothing, w/o any bulbs, the switched on output should be about 6-7v so by adding a dropping resistor to ground, like 6-7 ohms should get me the 3.1v needed to use the ultra bright white LEDs, like I used in the GE TV.

Will just have to play till I find the right resistor value.

Trying to picture this. Wouldn't a separate series resistor for each LED make more sense?

[Yamamaya42]

Originally Posted by old_tv_nut

Trying to picture this. Wouldn't a separate series resistor for each LED make more sense?

The current draw of the old lamps was 3x .06a (180 ma total)
the draw of the 3 LEDS is 60 ma 3x20 ma.
The entire circuit in question is mounted on terminal strips behind where the bulbs go in.
I'm pretty sure all I need to to is add a resistor to gnd at the far side of r160, to keep the voltage about 3-4 volts, the LEDS are pretty forgiving about what you give them, and even if I damage a few while working out the correct value, I have 100 of them to experiment with, and they are small enough to solder into the shells of the old bulbs after the glass has been removed.

[Yamamaya42]

What has me scratching my head is 2.5v on the collectors of the NPNs, the source is 6.3v via a 1a SI rectifier, same type used for the main bias, which has a forward voltage drop of .6v, so is it really down to 2.5v from 6.3v via half wave?
Perhaps that there is no filter on the cathode of X11 that it's just being very inefficient?
Will have to look more closely at this.

[old_tv_nut]

1) It looks like the power is supplied as half-wave rectified AC through X11, so the DC reading doesn't tell the whole story.
2) The schematic doesn't give two sets of voltages, one with color present and one for black and white. Since the waveforms show color, I'd presume these are the voltages for the lights being on, but again it's not clear if the emitter of Q2 has plain DC or pulsating DC. 2 V DC is not going to be enough for the LEDs.
3) LEDs, like all diodes, have a sharp turn on, so trying to match the voltage is not good practice. Instead, you should look at the difference between [EDIT] the emitter of Q2 [END EDIT] and the diode drop and install a current limiting resistor in series with each LED.
4) In this circuit you are served a curve ball if all the voltages are pulsing half-wave rectified. Checking with a scope would be a good idea.

[old_tv_nut]

5) what you are hoping to find is that the peak of the pulsed DC on the emitter of Q2 is more than what's needed to make the LEDs conduct.

[Yamamaya42]

Well, what ever I end up doing will have to wait till i get the chassis back in and powered back up with the tuner in a position to play with it!

I just got finished with re-caping all the multi section capacitors, and some were REALLY tired, I'm surprised it worked as well as it did, for example some of the 80UF sections checked as low as around 32UF with horrid esr.

New ones all tacked under the chassis, and tacked with silicone, waiting for it to cure before i apply power to see if I messed anything up!

Then there is just 3 more topside.

[Yamamaya42]

https://www.youtube.com/watch?v=WmKhHiD1tUw

Recap complete and successful!

I may have to replace the Horz phase det.

[Yamamaya42]

as I said, I suspect that the phase detector is a bit weak, as I saw a little side to side jitters, and that there is many things to replace it with, I have one of these from work, https://www.st.com/resource/en/datasheet/stps41l60c.pdf

that should work fine from what I understand, Correct? :O

[Yamamaya42]

After searching and looking, I can really see no reason why this dual schottky diode (common cathode) I have should not work as a replacement for the old selenium horizontal phase detector, it even has almost the exact same footprint as the old part, so it should go in rather easily.
Will also replace the 2 390k resistors that bias it when I do it.

Will most likely do this at a future time when I adjust the HOT cathode current, if I ever figure out where the heck they hid the HV adjustment on this silly thing. :O

But for now, this weekend I'll be working on the LED replacements for the burned out bulbs.

[old_tv_nut]

Originally Posted by Yamamaya42

After searching and looking, I can really see no reason why this dual schottky diode (common cathode) I have should not work as a replacement for the old selenium horizontal phase detector, it even has almost the exact same footprint as the old part, so it should go in rather easily...

I'd guess it's OK too, unless the reverse voltages in the circuit are higher than 60v.

[Yamamaya42]

It's just as I thought with this trio of lights behind the controls, w/o any bulbs, the voltage on the emitter was not @ 2v, but at 5.5 with no load. I even stuck in 1 6.3v lamp I had, and it lit that up to 1/2 brightness.

for the LEDs, i just have to find the right load balance to keep them happy.

[Yamamaya42]

Originally Posted by old_tv_nut

I'd guess it's OK too, unless the reverse voltages in the circuit are higher than 60v.

http://suzaku.live-evil.org/phase.jpg

not close I don't think.
they are used in a 60v buck pws circuit, so I come across them all the time, and they looked perfect for the job, so I nabbed one from work with a unsuitable mounting hole, they were just gonna toss it! :O it works just fine!