Mel wrote,
> I have an MLA-2500 with soft tubes. Seeking information on modification
> using a
> pair of 4cx800 tubes in grounded grid.thus eliminating a seperate bias
> supply and screen supply.
A modification of the MLA2500 to other tubes is a good idea, but
it's my opinion that the modification you suggest is not a good one
for two reasons:
First, the power supply of the MLA2500 isn't adequate for a pair of
4cx800's. The original pair of 8875's have a combined plate
dissipation of less than one 4cx800a, so one 4cx800 is probably
ok.
Second, grounded grid is OK, but zero bias and no screen supply
are NOT good ideas. These tubes need proper operating bias on
both grids to work correctly. (They aren't like 4-400A's, for
example.)
The Svetlana website has articles for converting an MLA2500 to a
single 4cx800a or a pair of 4cx400a's.
73,
George T. Daughters, K6GT
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