IMPROVED INPUT MATCH FOR THE EME ELECTRONICS 23150 P.A.
 
Having owned one of these amps for many years it has done good service on European DXpeditions and contests, once working 351 different stations in a 24 hour contest.

Mine is an old model and I found the input match appalling. I am not sure if more recent models still have this problem taken care of, but judging by recent conversations with those in the USA who own the same vintage PA the fix is unknown/unpublished. The following modification improves the input match, reducing drive requirement and was originally "disclosed" by the UK EME Electronics distributor.

As supplied my model had a large disc ceramic capacitor connected between the input connector and the cathode line as a DC Block. It was mounted vertically. The modification consists of mounting the capacitor horizontally and using the capacitor as one plate of an air dielectric capacitor to ground.

Remove all the screws from the cathode compartment cover. The input capacitor is rolled over horizontally and positioned on the centre line of the cathodes. A hole is drilled in the cathode compartment cover aligned with the centre of the capacitor. The hole is then tapped 4-40 and a 4-40 brass nut soldered on the outside of the compartment. A brass screw with locknut is then put through the chassis nut and a 4-40 brass washer soldered to the end, forming the other plate of the capacitor

With a directional power meter connected to the PA input, the screw is adjusted for the best match with the PA warmed up with all the correct voltages applied. The following summarises the improvement
 

 
 
Input Return Loss(dB)
Input Power (W)
Output Power (W)
Before Modification
7
15
150
After Modification
24
8
210
 
 
No input or output tuning drift was noted, even using the "as supplied" blower.