Help needed with LED light project

Thread Starter

mike_drop

Joined Jan 7, 2018
5
Hi all,

I am looking to make a sort of table top light fixture out of this cool RCA tube tv circuit board. It is to my understanding there is no way to really light the tubes themselves, so my idea was to illuminate each tube from underneath with a bright LED. There are 17 tubes total, so it would be 17 LEDs used in a series circuit that’ll plug into and outlet. I’m very new to this DIY LED stuff and don’t want to get zapped or ruin the LEDs. I can’t seem to find the right info for exactly what I want to do so I’m hoping the experts here can help!

I’ve attached pictures of the TV circuit board I’ll be working with and the LEDs I’ve purchased and their specs. What I need to know is what kind of power supply you’d recommend for this set up, what kind of resistor(s) I’ll need, and where they’d go in the series. I’m happy to answer any questions and provide more info. I really appreciate you helping out a newb and hope this post isn’t a bother.


CFD4D0C2-13AB-4180-B803-D49C07F87FF0.jpeg 2FD5D964-6128-4F8C-918F-43B9D2F267F6.png 0AE93310-D50C-4963-8214-2D69B0277BF7.png 1A906207-1131-4F42-975D-F669B69CAD3C.png 3C65E8D2-C5FF-4AFF-930D-D0CC0506D6C1.png
 

dendad

Joined Feb 20, 2016
4,449
You need a 12V power supply as each LED has an internal resistor to set the current already.
They will work ok on 9V I would think too.
make sure you wire then the correct way around.
To work out the current the supply needs, multiply the single LED current bu the number of the LEDS.
17LEDs at 20mA each
17 x 0.02 = 0.34amps or 340mA.
Use a 12V 1Amp supply.
If you have an old 19V laptop supply around, run 2 LEDs in series and they will have 9.5V each and that will most likly do.
 

Tonyr1084

Joined Sep 24, 2015
7,829
As dendad said, each LED has its own resistor so there's no need to worry about adding a resistor. The drawing I posted has a 12 VDC 1 Amp supply. You can often find such wall warts on cordless telephones. Sometimes they're 9 volt so you'll have to watch for that. I've included SW1, a switch for convenience, but it's not necessary. If you have a switched outlet you can just turn on the light switch on the wall. OR you could plug it in when you want it lit ( bit of a hassle I'd think. ). Using a 9 VDC supply will work almost as well as a 12 VDC supply. The difference between 9 & 12 volts is minimal.

At 12 volts, a 20 mA current is going to have a 600Ω resistor. ( 12 ÷ 0.02 = 600 ). Since the resistor isn't going to change, using a 9 volt supply will look like this: ( 9 ÷ 600 = 0.015 [or 15 mA] ). So, you're going to have slightly dimmer LED's but you'll probably be happy with the brightness anyway. And at a lower brightness the LED's will last longer. One easy way to test that out for yourself is to get a 9 volt battery and connect the positive wire to the positive terminal using one LED and see if you like the brightness. Then connect the same LED to a 12 volt battery and see how that compares. I doubt you'll see much difference, if any at all.

Finally, I'm sure you've considered this, but each TV Tube (TVT) will be in a socket. Meaning there's probably a hole in the middle under the tube. I'd think that's probably a great place to put the LED's. But that's just my opinion. Build it as you see fit.

LED Table.jpg
 

MrChips

Joined Oct 2, 2009
30,618
Many tubes have a filament that requires 6V. These are usually wired in parallel (but not always the case). You can use a transformer to deliver the 6V to the filaments. You will need to know how much current all the tubes need. If this is just for display purposes, you may also be able to wire all the filaments in series and use a higher voltage (and hence lower current) power transformer.

If you want to go ahead and illuminate the tubes with LEDs then that is ok too.
 

ElectricSpidey

Joined Dec 2, 2017
2,754
For this kind of project I probably would have bought .5 watt LEDs with a wider viewing angle and made a brightness control. (possibly even more than one, due to the fact that LEDs can be a problem to match brightness)

A fixed brightness with “ultra bright LEDs” (not exactly the truth) is not always a good idea because unless you know exactly what the result is going to be…you can be disappointed.

I’m not trying to pee on your parade, just some advice from someone that has built a LOT of lighted displays.

Yes…it’s more work…but so is doing something twice.

But as a noob…you might want to keep it simple. :)
 

sghioto

Joined Dec 31, 2017
5,370
I agree with MrChips. I would try and resurrect the tube filaments first. It's possible they are already wired in series. Down side is the tubes produce a lot of heat and probably not practical as a table top fixture.
SG
 

Thread Starter

mike_drop

Joined Jan 7, 2018
5
Wow, you all are amazing. Thanks for the fast replies and extremely helpful advice. @dendad thanks for being the first to reply and the advice re: the wall wart. I actually have several of those hanging around at my parents. They are packrats and wouldn’t miss it or even know it’s there haha. And thank you and @Tonyr1084 for the help with the math(sweet diagram Tony and yes, that’s totally the thought process with the socket holes. Was planing on hot glueing the each LED below each tube in that socket. Also, I had considered a switch but didn’t want to complicate things and add one more thing I can mess up. Now I am reconsidering though...
 

Thread Starter

mike_drop

Joined Jan 7, 2018
5
@ElectricSpidey interesting... well, I ordered them so I guess I can try one of them out using a battery test and see how they look underneath. If I do end up disappointed, might be from how you explained it, I will return them. I don’t supposed you happen to know where to get prewired LEDs with the resistors in them with the wattage and brightness you mentioned. If I have to wire them myself, that’s ok I guess. Trying to keep it as simple as possible. More steps, more noob mistakes. I’m using the warm white LEDs for the tubes btw.

I totally hear what @MrChips and @sghioto are saying re: wiring up the tube filaments, but I’m to nervous TBH. That’s some old wiring and tubage there and could be dangerous on a few levels between me doing the work and everyday operation. As cool as it would look, it’s not worth the risk to me. I have thought about it for some time though after seeing someone who had actually performed this mod online. Looks awesome.
 

ElectricSpidey

Joined Dec 2, 2017
2,754
My first thought with using those 20 degree LEDs was the beam is so narrow that it is likely to be blocked by some “stuff” inside the tubes, and not really give you the results you are looking for. Of course it might just bounce around and look really cool…

Also the “ultra bright” LEDs are not really that bright beyond the tight viewing angle, and could get easily lost inside a tube.

I don’t know of any higher power LEDs that come pre-wired…sorry.

I would go ahead and do what you plan, and try some with a battery, you might just get what you want.
 

dendad

Joined Feb 20, 2016
4,449
It will be better to light the valves (tubes) in parallel, nor series. They will not all have the same power requirements so series will not work. The old amps and radios that did have series wired tubes used special ones with varied voltage requirements but the same current.
Have a look and you will no doubt see them wired already.
"Back in the day", this was my bible for valve data...
https://www.google.com.au/url?sa=t&...watt1962.pdf&usg=AOvVaw3UsGZpZxvlffL2n7GtE5bL
You will be able to look each one up to see the heater volts and current. The larger Octal based valves will be hard to get an LED to light as they have the black base. Carefully breaking the end of the locating center part of the valve base away may give you enough access to the glass to illuminate it. Be careful as the glass evacuating port is in the center part of the base.
To get a realistic display it may be easier to actually power the filaments with a 6.3VAC supply but it will take a few amps.
Please post a pic of your finished project so we can see it :)
 

philba

Joined Aug 17, 2017
959
I always loved the glow from tubes when I was a kid. Especially the ones from the old pentagrid tubes - like there was some secret source of power inside those little cans. Part of what got me hooked on electronics in the first place. This could be a neat project.

I too agree with Mr Chips. Though, putting a somewhat fine point on it, the filaments are 6.3VAC. Those transformers used to be cheap and plentiful in the "good old days" but not so much any more. Still, 6.3VAC is nothing to worry about. 6VDC could work as well.
I think I'd experiment with some reddish LEDs to add to the glow but think the filaments should be the centerpiece.
 

MrChips

Joined Oct 2, 2009
30,618
Sure, 6.3VAC. I just didn't bother with the extra decimal place. It really depends on how bright you want the tubes to glow for spectacular display purposes.
 

Tonyr1084

Joined Sep 24, 2015
7,829
20˚ viewing angle: I've sanded the top flat on an LED trying to make a laser pointer out of it. Didn't work so well. But when I transmitted the light through a lens I got a picture of the die (the chip LED) inside with the attaching wire. So you CAN change the viewing angle if you're good with a bit of fine sand paper. As it occurs to me, I think I'll grind a 45˚ angle on one and see what kind of beam it throws. Gonna do that right now. Let you know the results in a bit.

[edit]

Well, after trying it I'd have to say it's not worth it! In fact, it's counter productive.
 
Last edited:

k7elp60

Joined Nov 4, 2008
562
Looking at the picture of the TV set and the vacuum tubes, I see a possible problem. From what I see is all the tubes are in sockets, which is normal. But some of the smaller tube sockets are held together with a fastner, perhaps a special rivet in the center of the socket. This fastner my prevent much light from getting thru the bottom of the tube. If it were me on this project, I would check the filaments and the wiring of the filaments. If they are wired in series and all the filaments are good, I would use an isolation transformer to supply voltage to the filaments. I would add a surge protector circuit to prevent the full AC voltage being applied to the filaments. The reason for the surge protection is that tube filaments cold resistance is much smaller than the hot resistance. This means when power is first applied to the filaments the current is many times the current drawn when they are hot.
If all the tube filaments are the same voltage and connected in parallel, a transformer and a surge current circuit would be the easiest.
 

Thread Starter

mike_drop

Joined Jan 7, 2018
5
Yeah come to think of it, I think we can move past the “using the actual tubes filaments” convo all together(though you all do have me wanting to find another old tv to try this out on). Reason I say this- I had jumped the gun weeks ago while taking this whole tv console apt(the original idea was to make a bourbon bar-see pic- out of the cabinet itself and scrap everything else), but the tubes looked so cool that I thought “we have something here ”. Unfortunately, I carelessly ripped out parts of the sockets that I believe make the tubes light up-convinced LEDs were the ONLY way to go. I’m no expert, as you all know, but I believe this is the case- that I’ve ruined the tube sockets. So LEDs it is! I’ll update all you fine folks when the goods get delivered and I get a chance to take it all for a spin. Any suggestions on how to get the best illumination in the tubes using LEDs is more than welcomed in the meantime. Always willing to go back to the drawing board! Thank you!
 

Thread Starter

mike_drop

Joined Jan 7, 2018
5
Forgot a pic of the tv console bar concept for you all to enjoy. Kinda neat, eh? Hopefully mine looks as cool when I’m done with it. Other folks have turned these into a fish tank! Bizarre! 0C37297C-C1C2-4576-B863-B40785D8895F.png
 

MisterBill2

Joined Jan 23, 2018
18,061
I agree with MrChips. I would try and resurrect the tube filaments first. It's possible they are already wired in series. Down side is the tubes produce a lot of heat and probably not practical as a table top fixture.
SG
Tube filaments in many TV sets were run in series, and the tubes that needed more power for the filament had higher voltages, since the current in a series string is the same in all the series elements. The first number in most tube types is the nominal filament voltage, perhaps 4, 6, 12, 33, or even 50. So you would need to add up all of those voltages and then supply that to the series string of filaments. Lots of math but none of it hard. But if some of the tubes are failed then it will not work, in which case the LEDs will be a better choice. And you will need to feed them in parallel because different colors have different forward voltages.
 
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