Hello again, and a couple new questions

[Weez]

Hey all,

Been a while since I've visited. Been busy with my project(s), and of course the bs that real life throws at you.

My first amp project was a PR clone. I recently finished it, and man does it sound nice I ran into some problems, of course, but that was expected, so no biggie. It may have been what many would consider a bit complicated for a first project, but I took it slowly and followed procedures I gleaned from the 'net very strictly. It works like a charm.

So, now that I'm hooked, I've been collecting the schematics for potential future additions to the arsenal. I ran across a couple of schematic symbols I can't identify, and I'm hoping maybe you guys can help.

I've attached two pics of the symbols; they are from a Fender Vibro-King. The first is of what looks like a resistor, enclosed with an oval. "TH1" is written above it. There are no values and it isn't assigned an R number.

The second pic shows two symbols. The one on the right appears to be some sort of photoresistor or photovoltaic component (I'm assuming this because of the two arrows pointing down at it). Just to the left of that component, are two horizontal bars inside a circle. This component is wired in parallel with R50. I'm thinking that, if the component on the right is in fact a photoresistor or similar, then the component on the left is a lamp or led? The problem is that there are no values listed, or other markings or notes on the schematic.

Any clue as to what they are?

Thanks.

[Enzo]

It isn't assigned an R number because it is a TH. Thermistor. A temperature sensitive resistor-like item used as an inrush limiter. Fender likes them, as do any number of other makers. They have a negative temperature factor, swo the warmer they get the lower the resistance. In series with the amp it starts out at higher ohms and then warms up to a very low figure, thus soft starting the amp.

fender part # 0028503000 10 ohm 5A type C60-11

From Digikey:
CL-60 GE Sensing | KC006L-ND | DigiKey

The other thing is often called a "trem bug" or "roach". It is a made up optocoupler or optoisolator. The left half is a neon lamp, and the right half is a photoresistor. They are placed together face to face in a piece of black heat-shrink tubing. Neon wire leads out one end and photocell leads out the other. The trem oscillator drives the lamp, which flashes, lowering the resistance of the cell. That is then used to modulate the signal in the amp. Fender has used it for decades. Part # 0037836000

[Weez]

Excellent, thanks Enzo.