Replacement LEDs for 200 neon bulbs

[Dogue]

What LEDs work instead of the neon bulbs in 200? The Vintage Vibe LED modification shows the LED wired across +42V, if I'm reading it correctly.

[sean]

Dogue,

Is that 42V supply voltage DC or AC?  Neon bulbs use AC current.  The Wurly schematic shows the neon bulb across the input mains - 120V AC in USA, 220V or 240V AC in most of the world.

Ahh, I see the 42V DC supply going up to the the collector of TR8 and TR9.  Good.  Use that.
----- ----- ----- -----

You can use any LED that you want to use. 

All you have to do is put a resistor in series with the LED to limit the current to what the LED is rated to survive (and still provides the level of brightness that you prefer).  I prefer dim lights, so I shoot for current of 3 or 4mA.  Many indicator LEDs can survive as much as 20mA.

You figure out the current in the LED using Ohm's law and the forward voltage drop specified for the LED.  The forward voltage drop for many indicator LEDs is 2V (sometimes as low as .7 volts).  In your case:  (42V minus Vf) divided by 4mA equals 10KΩ.  So stick a 10KΩ resistor in series with the LED, and the current through the LED will stay nice and low (4mA); so the LED will last for years.

You almost certainly don't have to worry about the power handling capacity of the current-limiting resistor.  When pushing 4mA through a 10KΩ resistor, the resistor is only handling 160mW.  A quarter-Watt resistor will work, but I would choose a half-Watt resistor for two reasons:  1) it will run cooler (infinitesimally maybe), and 2) the half-Watt resistors are physically larger, and easier to handle in point-to-point soldering installations.

The LED that I like for effects pedals is Wurth 151051RS11000, because it is DIM not bright, diffused not clear, and 5mm in diameter.  If I want a bright red LED, I use Kingbright WP7113LSRD.  I really hate any LED with a clear lens.  They are never comfortable on the eye, and are not great for off-angle viewing at long distance.

Standard LEDs are 5mm in diameter, little ones are 3mm in diameter, but you can order larger diameter ones if you want the light to be like a huge old neon bulb.

Sean

[Dogue]

Very thorough and helpful post—thanks, Sean!

FYI, I plan on doing this with a 200 with a non-functional neon bulb. Ken Rich indicated that the neon bulb isn't noisy (contrary to what the manual might imply), and so it's probably only worth replacing it with an LED if the bulb is no longer working.

[sean]

Dogue,

Is there room enough to stuff the LED inside the old neon bulb carcass so that you can use the same orange lens and mounting ring?

In that case, you might want a brighter LED with a clear plastic lens.  You can buy orange LEDs, but  I have no idea how orange and neon-ish they look.

Sean

[Dogue]

I ended up taking the approach suggested by VV and drilled out the hole a little larger to put a bezel in. I'm using a yellow LED, and with the original orange lens it's quite mellow.

[Electrickey]

It's been said that everything in a circuit affects the tone and that should include the pilot lamp/bulb/diode and some would argue negligible to none. If the original neon bulb is available I would opt for that and only change to another type if none.