[Amps] SB-220 on 6 meters

[Chuck Sudds]

Greetings!

I am new here and have an amplifier question.  I just recently purchased an 
SB-220 that has had the 15 meter portion of the amp converted to 6 
meters.  The party that did this used the article in QST from back in 1987.

I am using an Icom 706MkII to drive the amp on 6 meters, which, 
unfortunately, does not have a built-in antenna tuner.

My problem is that, when I hook up the 706 directly to my beam, I have a 
perfect 1:1 match on 50.125 and 100W output but when I go through the 
SB-220, the 100W output drops off to about 50W and the SWR goes up to 
almost 2:1.  I am still getting 400W out but with only 50 watts drive!

I am assuming that there is a problem with the input matching 
circuit?!?!?!?!  The 15M coil and capacitor were modified per that article 
but I am not sure if there is an adjustment or something somewhere to "fine 
tune" it.

Any comments or ideas??  I will be happy to summarize and post the results 
at a later date.  Thanks, in advance!

Chuck  KØTVD