Fender tremolo roach LDR dark resistance?

[nuke]

What are you guys seeing on new replacement tremolo "roaches" for the LDR in total darkness, versus old original ones that seem to be in good working order?

There seems to be no "spec" published and I've got a few I'm seeing numbers all over the place. Some light leaks in past the shrink tubing, so I'm testing in full darkness. I'm seeing everywhere from 500k to almost 4 megs.

[R.G.]

I don't know.

But your question make me wonder what the effective range for the resistor side is. That is - how high and low does it need to go to get an effective tremolo sound?
Knowing that would let you know whether 500K, or 1M or whatever is good enough.

[Astronomicum]

But your question make me wonder what the effective range for the resistor side is. That is - how high and low does it need to go to get an effective tremolo sound?

Attached is an attenuation curve I produced for a Bandmaster AB763 tremolo while developing an LED/LDR mod I did a few years ago. It was developed from bench test results on an actual circuit. As you can see, most of the "work" is actually in the a resistance range below 250K.

However, since an LRD has rection and decay curves (hysteresis), you need the LDR to have a much wider range than would otherwise be indicated by the graph. This effect also causes the dB attenuation range to decrease with increased tremolo speed.

I found for this project that an LDR dark resistance of about 1M5 worked well.

[nuke]

Interesting graph. The circuit is kind of interesting, since the intensity control is only a 50K reverse audio and present all the time loading the circuit. The wiper goes to the LDR, at maximum the LDR is in parallel with the 50k at the signal leg of the pot. At minimum, the LDR is on the ground leg of the pot.

I've got a 1967 Super Reverb on the bench at the moment, and the reverb/vib channel is a bit weak compared to the 'normal' channel. The tremolo lacks a bit of depth. Over the years, I've replaced a number of the roaches for either the bulb not firing or the effect lacking depth. I've seen a few where the LDR had gotten really low.

The one in the amp is original and reads 600k in total darkness with the leg lifted. It goes down a bit more fully warmed up.

I have a new one that came from New Sensor probably 25 years ago in my stash of parts. It reads 5 megohms fully dark. Just shining a penlight down the hole on the neon side, it quickly drops down to about 60k from just that little bit of light.

[Astronomicum]

You can see on the graph how that 50K drags the signal down. Keep in mind that this resistance to ground also creates a high pass filter. That 50K coupled with the larger coupling cap on the vibrato channel really alters both gain and tone.

[nuke]

You can see on the graph how that 50K drags the signal down. Keep in mind that this resistance to ground also creates a high pass filter. That 50K coupled with the larger coupling cap on the vibrato channel really alters both gain and tone.

I was just going to ask whether your curve calculation takes into account the 50K intensity control that's always in circuit in the AB763 type amps?

[Astronomicum]

The graph does not include the 50K although shows what 50K does to the signal. It was removed (replaced with various resistances from a decade box while measuring the channel AC Signal Voltage) so I could get a complete picture. The graph would look very different otherwise, essentially stopping at 50K with nothing to the left. As you can see on the graph, a 50K intensity would brings the signal down 4.3dB, basically the baseline loss :/