RF Return

Here are some TL-922 specific mods that will also improve stability.

In the TL-922 the tubes are mounted on a metal sub-chassis.  Likewise, the Plate & Loading caps, are mounted on a different sub-chassis.  The RF path between these two sub-chassis is very poor.

I used a small piece of aluminium flashing material that was soft and easily shaped to make a straight backed Z to join the two.  In my case I started by cutting the flashing 11cm long x 6.1 cm wide. Aluminium flashing is really soft and so easy to work with. I bent it at 4 cm initially and this is the piece that sits down on the tube socket sub-chassis then I bent the top by hand and pushed it under the the 2000 pf capacitor, and the plate tune C angle support.

The plate tuning variable has a vertical aluminium angle as a support but it is also the only Plate C ground path.  You can see the aluminium angle in the back LH corner of the 2000 pf cap.  I wanted to maximise the return path as much as possible. The Z flashing is sandwiched between components like the angle bracket as well as the 2000 pf cap. 

Socket side the flashing is secured by two screws and flat washers aiming for a good RF connection.  This RF ground path is very important.