Elimination of Spurious in MASTR II VHF PAs

Eliminating Spurious Emissions
in earlier MASTR II PA Decks
(PA's with 4 Output Transistors)
By George Burton
k7wwa@saber.net

Thanks to Pete Lascell, GE Tech Support for his assistance with the following problem.

Some of the early VHF GE MASTR II PAs (4 output transistors) would go spurious. I know, I had one but the fix in my case was very simple. Take 6 or 8 tantalum caps, around 10 uf, and solder them between the 12 vdc foil run in and ground. Do this in the area of the output transistors. The exact location is not critical.

Without the caps, if I tried to run more that around 60 watts the spectrum analyzer would light up like a Christmas tree. The other strange thing was if I ran the PA at maximum power it would stay clean also but I did not want to run the PA at 125 watts. Once I put the caps in place I could set the power from minimum to maximum and the spectrum analyzer stayed clean.

This process may also help a UHF PA from spurring.