Since there appear to be some interest in the correct working dilution for Pyrocat-HD I thought that some of you might be interested in the following comments.
As noted in my email message to Eric, my general recommendation is 1:1:100 for silver printing and 2:2:100 for alternative printing. This works well for modern films with tabular grain (TMAX 100 and 400) and with medium and slow speed traditional films such as Ilford FP4+. There is nothing sacred about these recommendations, however.
Some recent tests I have conducted indicate that films with very thick gelatin layers, such as HP5+ and BPF, which tend to develop high levels of general stain, or b+f, with long development times in rotary processing, will benefit by changing the dilution to 2:1:100 (for silver) or 3:2:100 (for alternative). What this does is increase the amount of preservative in the working solution, thereby cutting down on oxidation during development, which as we know is the primary cause of high general stain. The logic is as follows.
Pyrocat-HD consists of Part A and Part B concentrates. Part A contains the reducers, Pyrocatechin/Phenidione plus the preservative and restrainer. The preservative (sulfite) in Part A serves to control the amount of oxidation. Increasing the amount of sulfite in the working solution reduces the amount of stain, whereas decreasing it will lead to more stain. So you can reduce the stain just by increasing the percentage of Part A in the working solution. You can also decrease the stain by adding a small amount (say about 0.4g per liter) of sodium sulfite to the working solution but I think it is easiest to just increase the amount of Part A.
Part B of course is the alkaline accelerator. If you increase its amount in the working solution you get faster development times, to a point.
Increasing the ratio of Part A in the working solution should not be necessary when developing in tray, or when using tabular grain films and slow and medium speed films. However, when developing with rotary processing emulsions such as HP5+, BPF, Forte, and perhaps even TRI-X increasing the amount of Stock A in the working solution may lower general stain, or b+f, and significantly shorter exposure times.
Hope this all makes sense.