[Milsurplus] Brands to 1625 tubes to convert to triode operation?

[C Eus]

Hello to all:
I understand that there were a few 1625 tubes that could be operated as a
triode after all three grids were paralleled.  The caveat is that a grid,
which was connected to the cathode,  had to be physically removed from the
cathode.  This was done by cutting the base and gaining access to that
connection point that joins the grid and the cathode together and doing the
appropriate modification.  There were a few tube brands that were not
modifiable in this way.  RCA comes to mind.  However, I know there should be
some others that could be modified.  Does anyone know of these brands? What
about the Russian 1625's?

I appreciate this and thanks.

Cal, N6KYR/4.