Re: Jeez, prices on USA LM308 ProCo Rats have gotten stupid
On a side note; I can't imagine that the circuit changed when production moved to China
You're right - it didn't. But they did do their own PCB. I've spent far more time than is sane and looked at several schematics and traces (including two of my own for a vintage reissue and a 1990 turbo) and maybe hundreds of images of various RAT PCBs (FWIW I've been able to distinguish 2 different Chinese PCBs - the earlier one very similar to the latest - Deucetone - USA PCB). I've read a few accounts of cheap quality hardware on the Chinese RATs, and very thin traces on the PCBs (apparently one reason why Keeley and Allums won't mod them) and glued on knobs (resulting in shafts pulling out of the pots when they are removed forcibly - another reason for Keeley & Allums).
The changes to the RAT circuit over the years have been minimal. The first change was very early on in the late 70's when 5 tantalum caps were replaced by electrolytics. Not a real circuit change per se but nonetheless often brought up in vintage RAT discussions. What's interesting is that the most famous RAT - the original '85 whiteface - never used any tantalums.
The other major change was the op-amp as you mentioned.
Otherwise, basically the RAT-2 in 1988 introduced some changes which were carried into the Turbo RAT. Then starting in 2002, they switched over to a new PCB and reverted back to the original circuit, which was carried into the 2003 You Dirty RAT as well as ongoing production in the USA. I don't know for certain if any late USA RAT-2s ever used this new PCB and therefore the original circuit, but I suspect they probably exist since I've seen both Turbo RATs and late Vintage RAT reissues with this PCB. The op-amp change seems to coincide with this PCB change as well. There are a couple of other slight differences in RATs but this sums it up well.
That I've been able to determine, there were 5 different USA PCBs in total. The first one was used for the production of all of the original RATs. When the RAT-2 was introduced, the second PCB was released and had the ability to accommodate both the original RAT circuit as well as the RAT-2 circuit including the DPDT true-bypass LED indicator switching circuitry. This was used in late model blackface small-box original RATs (albeit without the RAT-2 changes or the LED cicuitry), as well as the RAT-2 and Turbo RAT. When the Vintage RAT big-box reissue was released, it originally had it's own PCB which was a clone of the original PCB. In 1995, a fourth PCB was release called the "Multi-RAT" which was used in all the RATs at the time including the Vintage reissue. It was basically the same as the RAT-2 PCB but had a different layout and included the capability for a minor mod to the output buffer - I don't know if that mod actually ever made it into production however. The 5th PCB is the one currently used which started with the Deucetone. It dropped the RAT-2 circuitry and the DPDT true-bypass LED circuitry, as they also started using 3PDT switches at that point, but gained a resistor and the indicator LED vs. the original circuit and PCB. These are easy to spot in pictures because they have three different holes for the 3PDT footswitch which allow it to be used in the Deucetone as well as single RATs. It's also easy to spot the circuit change simply by counting the number of resistors - the Deucetone PCB has only 12 - the original circuit's 11 plus the LED resistor. The Chinese boards have the same number. (And yes - I've checked the values and they are all to vintage spec.) This is about when the Vintage reissue was discontinued, and if you think about it that makes sense because now all the RATs were using the original circuit anyway.
Pretty much everything I've learned is summarized here:
http://www.aronnelson.com/gallery/main.php/v/diyuser/GGBB/Multi-RAT.png
One note - apparently some Chinese RATs use a sightly different value for the cap in the variable filter, resulting in a slightly different range for the filter control.
