LED firebox bulb replacement

The flickering LED that you show is NOT a direct substitute for a traditional incandescent bulb.  Specifically, if you apply the specified DC voltage, a flickering LED flickers while a bulb will just be solid on.  That is, there is a tiny electronic circuit built-in to the LED itself that modulates/pulses the LED to make it flicker.  Likewise, you can buy LEDs that blink by themselves upon application of steady DC voltage.

So to make a bulb "flicker" to simulate firebox, the electronics generates a modulated/pulsed DC voltage.  At least this is what the PS2 steam electronics does on the firebox light outputs.  I am not familiar with the PS1 electronics.

In general, if you apply the PS2 firebox light output voltage to a flickering LED, it will not work because the flickering LED is expecting a steady (smooth) DC voltage.  So there are various scenarios:

1) Use a pre-wired solid LED (not flickering).  Then the PS2 flickering voltage directly drives the LED as if it were a bulb.  There are some details such as matching the voltage which can be explored.

2a) Smooth the flickering voltage from the PS2 firebox output so that it's steady/smooth DC.  Then use this to power the flickering LED.  There are some details such as matching the voltage which can be explored.

2b) Smooth the voltage from a PS2 generic light output (could be headlight, interior light, etc.) so that it's steady/smooth DC.  That is, there are some PS2 engines that do NOT have a flickering light output.  But these outputs are nevertheless a pulsed (not smooth) DC.  There are some details such as matching the voltage which can be explored.

3) There are some MTH engines where the engine lights are not driven directly from the PS2 board itself.  There could be a so-called constant-voltage light board or the like.  Such a board may already have a source of steady DC voltage which can be applied to a flickering LED.  There are some details such as matching the voltage which can be explored.

I make Flickering firebox boards for upgrades.  Each consists of four flickering LED's, Red, Orange, and two Yellow.  I sand the tops to diffuse the light.  I also cover the firebox opening with a plain piece of white paper, further diffusing the light.  The effect is a very realistic firebox look.

None of my PS1 nor PS2 steam locomotives appear to have any flicker effect in the firebox at all.  The current seems to be steady.  These flicker LEDs have a resistor and the flicker circuit built in, so they should work fine with the fixed DC voltage that is supplying the current steady firebox bulb.  Is any of that incorrect?

Actually, the PS/2 bulbs are not supplied with steady DC voltage, but rather a PWM (Pulse Width Modulated) voltage that is effectively 6 volts for the bulb.  In order to use that with a flickering LED, you would have to add filtering to make it into pure DC.

The PS/1 locomotives do have a CV (Constant Voltage) board that outputs 6VDC, so that would work with them.

So wrt a generic, non-flickering PS/2 output, as GRJ says you need filtering to convert the pulsing DC voltage to smooth DC.  This is what I was calling option (2b).  It's not that the components to do so are expensive...maybe 25 to 50 cents in parts.  But it would involve soldering and trying to buy these components in small quantity will overwhelm you with shipping and such so you may be spending several dollars just for the smoothing electronics!  And of course you still must buy the flickering LED.  I am mindful that you did mention easy!

You might take a look at the pre-wired flickering LEDs from Evans.  They have one version that accepts 7-19V AC/DC.  This kind of suggests there is some kind of smoothing electronics as shown below in what they call a "rectifier unit".  That is, if it can handle AC input, then one would think it has some kind of smoothing electronics.  And perhaps someone else has already tried this and can chime in as to whether it works with a PS/2 generic, non-flickering light output.

If experimenting with the effect, consider using more than 1 flickering LED...maybe even with different colors...red, orange, yellow. The multiple color technique is most commonly associated with campfire simulators; whether or not this is realistic in a firebox it arguably provides an additional element of dynamism (is that a word?) suggesting action. 

This module I make has four LED's and an AC power supply to run from track power.

So is your 4-LED module for sale?

I'd also think if your module can operate on track AC...it could also operate from a PS/2 pulsed DC output?  In other words if powered by a PS/2 light output it could turn on when the engine electronics starts up rather than whenever it is on the track (if connected directly to track AC).

OTOH, the firebox had to be fueled and flickering hours before any engine operations...

I've never made any for sale, there's a bit too much manual labor.  You have to sand the flanges of the LED's so the fit close enough to display in the typical firebox.  I suspect it would run from the PS/2 lighting outputs as the PWM waveform peaks at around 18-20 volts.  OTOH, I could certainly share a BOM and the PCB design.

Installed one of these flicker bulbs in my PS1 Allegheny and it works fine.  I ended up attaching it to the red firebox window with a drop of hot glue and found that the hot glue gave some nice rippled fire / hot coal texture to the light as well.  For as much as you see the firebox on this engine, it gives a good effect.