Proco Rat
The Rat was developed in 1978 (12 early versions made) and the first real run of pedals came out in 1979... or did they? See below.
UPDATE! Just found an early big box dated inside "5/31/78" with 2x 15th week of 78 pots, 1x 18th week of 78 pot, and possibly a 1974 National LM308N (numbers are "744" on the IC). So perhaps that Rat History link's info is not quite right. PCB silkscreen says:
PRO-CO SOUND INC KALAMAZOO, MICHIGAN U.S.A.
FUZZTONES FOR THE CONNOISSEUR THE RAT TYPE B
2 / 23 / 78 EIA 86-3
Early big boxes have the EQ control labelled "TONE" and it is a standard CW = brighter type control, unlike the usual RAT "FILTER" control where CW = darker. The RAT logo is all uppercase letters. Later big boxes use lower case "a" and "t".
Input jack and dc power jack are quite different than expected.
While most pedals use the ring terminal trick to ground the negative side of the battery, this early RAT interrupts the positive terminal, twice.
Input jack is a Switchcraft 113 type. This is a regular TS jack (like the 111 for the output jack), with an isolated "make" switch. The +9V from the dc jack is interrupted at the input jack, only connecting to the PCB when a plug is inserted.
dc jack is also unusual, in that it has 4 terminals. Both battery snap wires go to this jack. Two of the terminals appear to be sleeve terminals, and they do not appear to switch. The other two are the tip terminal, and a normally closed "break" switch to interrupt the positive battery connection when a plug is inserted. (The dc jack functions the same as later ones, but is unusual for directly grounding the battery negative since the input ring terminal trick isn't being utilized.)
Footswitch is DPDT, looks like a Carling, FX input common pole A, gets grounded in bypass, output jack common pole B. Input jack connects to both poles, opposite positions.
An unpopulated section of the PCB looks like it might have been for an optional LED driver. There is a TO 92 package spot, one terminal direct to +9V, and nearby access to an unused footswitch terminal connector.
Problem: No output when effect is engaged, and pedal is assembled. Works when pedal is disassembled (i.e. not in the metal box).
Solution: DISTORTION pot was shorted from the CCW terminal to the pot casing. When assembled, the 0V line would short the non-inverting input of the LM308.
Quite difficult to catch this one! Just holding the thing, I thought it was a bad wire, a connection, something like that. Because the voltage issue was fairly obvious on the LM308 input and output pins (they went low when output ceased), I had a clue, but it was still difficult to find.
Distortion pot is a Clarostat 100k, marked CM42548 100K Ω 19-7818, reverse vertical pc mount (pins face same way as shaft).
Tested the '78 RAT through my Pro Jr, and I have to say I really liked it. I normally do not think I like RAT pedals. Maybe there is something to the old circuit, or maybe I just need to try more RATs out.
General Circuit Description
The distortion effect is created by an op amp set for high gain and passively clipped by shunt back-to-back diodes. Changing the number, symmetry, and type of diodes will alter the character of the clipping and the many varieties of Rat and Rat inspired pedals explore these possibilities.
The LM308 Op Amp: S L O W . . .
The original Rat used a LM308 op amp, so it is not uncommon to get a request to replace the IC in later Rat pedals with a 308. Like the 741, the 308 is an old and slow device, and its limited slew rate is the characteristic believed to alter the final timbre is a superior way to other ICs. YMMV.