[Collins] More re: 6146/A vs 6146B/W

[James Monk]

 Gentlemen....... there has been much discussion and controversy concerning
 the use of 6146 and 6146A's  versus 6146B and 6146W's in Collins S-Line
 transmitters and KWM-2/2A transceivers, particularly the early units which
 utilize the variable ceramic PA Neutralizing capacitor.

 The problem apparently involves minute differences in the design and
 manufacture of the 6146B's which have somewhat different internal
 "interelectrode capacitances" than the earlier tubes. Thereby creating
 difficulty in obtaining neutralization of the PA.

 Further, apparently, later S-Line and KWM-2 designs incorporated the use of
 an air variable neutralizing capacitor, which solved the neutralization
 problem with the use of 6146B/W's.

 My question is: has anyone developed an effective modification which
 satisfactorily  replaces the original variable ceramic neutralizing
 capacitor with a suitable air variable of sufficient capacity and voltage
 rating to permit neutralization of the 6146B/W's and eliminate the problem
 in early Collins S-Line transmitters and the KWM-2/2A. Or perhaps developed
 some other method of overcoming this problem, as it is perceived.

 If such a modification exists, it would be a boon to Collins users, who
find
 the B/W's much more readily available than the earlier PA tubes.

 Comments?

 73/jim/W0JJL