[Collins] [collins_radios] Re: help needed

[Glen Zook]

The problem with the final amplifier tubes in his 32S-1 sounds like either 6146B/8298A or 6146W (with a code date of after mid 1964) were used in the transmitter at one time.  Unfortunately, all the 32S-1 and 32S-2 transmitters, as well as the earlier versions of the 32S-3 and 32S-3A transmitters and the earlier versions of the KWM-2- series transceivers, used a ceramic trimmer as the final neutralization capacitor.  When the 6146B/8298A or 6146W tubes are used in those transmitters there is well over a 95% chance that the ceramic trimmer WILL burn up!  Collins had to redesign this neutralization circuit to utilize an air variable capacitor.  There were 3 other components changed in the neutralization circuity as well.  However, the easiest way to tell if the transmitter can use the 6146B/8298A or 6146W tubes is to look at the neutralization capacitor in the final amplifier cage.  If it is a ceramic trimmer then do NOT use the later tubes.  If it
 is an air variable, then it is OK to use the later tubes.

Collins changed the neutralization circuit in those units that were on the production line and all subsequent units.  Collins also supplied a modification kit to the military to change the neutralization circuitry in the units already in service to facilitate the use of all of the 6146 family of tubes, thus allowing the use of the 6146B/8298A and 6146W.

Unfortunately, if the neutralization capacitor is burned, the only "fix" is to replace it.  Since it is a "pain in the posterior" to change this capacitor, I strongly suggest rebuilding the circuit to use an air variable and change the other components as well.  Although a specific value air variable is specified by Collins, just about any air variable that comes close to the specific value and that will physically "fit", can be used.
 
Glen, K9STH Website:  http://k9sth.com


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