[MFJ-Ameritron] AMERITRON AL80A UNSTABLE ON 20 MTRS

[Robert Bacharach]

Hello,  New to the List.

I have been having difficulty on 20 mtrs with an AL80A that works fine on the lower frequencies.  The linear IS equipped with the QSK-5 internal board.

The symptom is this:

When tuning up (following published procedure) on 20 mtrs after adding a small amount of loading I hear what sounds like a "snapping" noise.   It is similar to an arc, but occurs only momentarily and then output drops to zero, at which time I cease the operation.

I had a new spare 3-500Z on hand and replace the final thinking that perhaps there was an internal problem with the tube on higher frequencies.  No joy....  exactly same results.

I'm not certain if I have a complete manual or not, but suspect that neutralization of the final may be required or perhaps the tuned input for 20 mtrs is malaligned.  However I see no instructions for either the input alignment or neutralization process and would like to do this PROPERLY rather than be the proverbial bull in a china closet.

Any suggestions?

73 and Thanks,
Bob Bacharach  WA2EMF,  Rock Hill, SC