novelty RCA plug indicator

[maxkracht]

Was doing a console amp rebuild/conversion for someone, and the old RCA in jacks were too convenient not to use as tie points for the heaters/ power indicator. Then I thought, even if I leave a note not to plug your aux and tape in, someone is going to plug something in there, so I better do it first.

Current implementation: LED and dropping resistor In RCA plugs, one anode to ground the other cathode to ground, other leg connected to the heater. Heater is elevated, 100R resistors to 6V6 cathodes. 



Power on, both led’s are running on AC. Amp warms up, DC kicks in and the backwards LED shuts off.



Thought I would check with the experts before sending this off. Good stupid or bad stupid?

[martin manning]

I like it, very clever! The only concern I have is the peak reverse voltage the LEDs see when running on AC, which is maybe 4.5V ? IIRC that's close to the max. From a mechanical point of view, are the LEDs likely to get knocked off when moving the chassis around?

[maxkracht]

Thanks Martin. So, if I want to do things a bit more right, use a gruntier diode in series with the red and parallel/flipped for the green? As is, if one or both fail, i'm guessing they would fail open. So, no more flashy lights, but ultimately no harm done. Not too worried about mechanical stuff. The plugs are pretty tight and should have plenty of cover when it's in a cab.

[martin manning]

So, if I want to do things a bit more right, use a gruntier diode in series with the red and parallel/flipped for the green? As is, if one or both fail, i'm guessing they would fail open. So, no more flashy lights, but ultimately no harm done.

I would put a higher PIV diode in series with both red and green, same polarity. 1N914 or 1N4148 would be enough. OTOH, they haven't failed yet, so you are under the max PIV. Right now you have an LED and a current limiting resistor in series going to ground from each side of the heater winding?

[maxkracht]

Right now you have an LED and a current limiting resistor in series going to ground from each side of the heater winding?

Yep, I regularly use that setup with another diode in antiparallel instead of a regular indicator lamp. Never had a problem running on 6vac, so 3 shouldn't be a problem.

IMG_2047.jpg

[dorrisant]

Very cool idea... kinda like a coil indicator in a diesel vehicle.

Can you post a back of the envelope diagram? I think I understand the concept but would like to be clear.

[maxkracht]

IMG_2096.jpg

[dorrisant]

And on the back of an envelope as requested... Stellar!

[WinnetouKoslowski]

Maybe put the leds in antiparalell and dont connect them to ground?

[maxkracht]

Maybe put the leds in antiparalell and dont connect them to ground?

Not sure what you are suggesting. Can tack a couple leds across the heater, but then you just get a light and no flashy status indicator. Also needs separate resistor values so the one lights up with just the 3vac and the other doesn't burn out with the 20something vdc.

[maxkracht]

Just an update to this idea incase anyone is interested. New version uses a flashing LED that runs on 3vac and a regular LED that runs off of the cathode voltage. When the amp is cold, the flashing LED is bright and flashes until the power tubes warm up. Once the power tubes are warm, flashing light turns off and the regular led gets bright. I've been able to fit the whole circuit into a hollowed out #47 bulb, where the flashing led sits behind the regular led. Video of the rca amp just has it sitting in some heatshrink tubing behind a lens. I have installed this in a few amps that have been running for 2-3 years without issue. Not worth the trouble mosta the time, but kind of fun. In both videos the tubes were already a bit warm, it flashes for longer if starting up cold.

Cap in parallel with the flashing LED needs to be at least .1uf but larger is better. Antiparallel diodes on either LED are optional but recommended.

https://youtube.com/shorts/z33cBuDcIf4?feature=share
https://youtube.com/shorts/tOidYYJoK7Y?feature=share

[martin manning]

Looks like it would be cool, but the videos are "private."

[maxkracht]

Looks like it would be cool, but the videos are "private."

Thanks, think i've got it fixed.

[dorrisant]

I have a cool little vintage PA that I will try this with. Thanks for sharing!

[maxkracht]

Shining through a PEC tube base with some pink leds.