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Hi Steve,
A friend notified me that this was on the space. I had turned off all email. Not many people are still working on these very nice radios. I have repaired many and given them to others to use. They are all still working fine. Almost all the parts are still available. Some links for pictures are below, but not specific to the transmitter.
Assumptions: I am assuming it worked before you replaced the IRF510..

1. I would make sure that the IRF510 (Q9) is good. VGs=3.46v, ID=2.5ma The tab is the drain. There are MANY Fakes out there.
1a. Make sure that the IRF510 is the rightdirection. Tab to the chassis. Face to the inside of the board edge.
2. Make sure the insulator is underneath the DRAIN (it is the tab)
3. Make sure there is no short to the chasis from the Drain (tab)
4. Make sure that the IRF510 is soldered in. Removing the old one can cause tabs or solder points to disappear or be burned off.
5. The bias pot R18, just set midway for now.. If set to high it will cause the rf tansistor to run very hot.
5. The driver 25C2166 (q8) is rarely bad.. It takes the RF input from the RF (top board) via a coax connected to the right edge of the board.

Replacing this rf driver is not the simplest thing as all the boards must be disconnected, cables removed, part replaced with no short to chasis and re-assembled making sure the rf cable is placed at j2 on the RF board (top most board) at the connector.





I am happy to help as much as I can.. I am home most days.
Working on these 40+ year old radios is fun! In the day it was not meant to be serviced by the normal joe.. ;-)

72/73 Guy ( guy at eastroad dot org)

PS.. there are fine schematics and drawings here: