Joe -- I may be taking your comment here too literally -- but maybe not, either. When you said that you "changed the chokes to 68-ohm resistors" -- you can't just do that in the literal sense. If you did, that could certainly be a significant part if not the heart of your problem, besides the weak tubes that others have mentioned.
The earliest 225s used RF plate chokes placed in series with the 7591 plate leads to control any parasitic oscillations that might otherwise form. These chokes measure about 0.1Ω dcr each to prevent any power loss due to their presence in the plate circuit. Therefore, if you simply replaced the chokes with 68Ω resistors, that would in fact reduce your power output significantly as you are noting. It would also upset the 50/50 distribution of power developed in the plate and cathode windings of the Unity Coupled output stage.
When Mac moved away from using the chokes, the 7591 plate terminals then connect directly to their relative output transformer lead, and then the 68Ω resistors appear between the relevant output transformer lead and screen grid terminals. In other words, in the first scenario with the chokes, they are placed in series with the plate leads, while in the second scenario, the resistors are placed in series with the screen grid terminals.
As a result, if you did a simple resistor for choke change out, then that won't work, and the resistors need to be removed, and the chokes need to go back in. Or, if you want to in fact update the unit to the revised design using the resistors, I can tell you that it is a fairly involved task that requires swapping out transformer leads and even drive leads to the output tubes as I recall, if you are going to mimic the original factory wiring change that was made when the change to using resistors was made. I know this well, because I did this very work on my own 225 a few years back, and it is much more complicated that just swapping the chokes for resistors would suggest.
I would suggest then that if the chokes were simply swapped out for resistors, that is likely the heart of your problem. Or, if you did go to the considerable effort to revise the wiring so as to properly revise the unit to the updated design, then I would suggest that you go back and check that work carefully, as again, it is a rather involved process, and can easily result in problems if not done correctly.
I hope this helps!
Dave
