[Boatanchors] 6146 vs 6146A vs 6146B or 6146W

[Glen Zook]

The easiest way to tell if the Collins equipment has the new neutralization circuit is to look inside the final amplifier cage.  If the variable capacitor between the 6146s is a ceramic trimmer then it is of the older type.  If the capacitor is an air variable it is of the newer type.

The original capacitor actually has a considerably larger capacitance range than the air variable.  There were 2 fixed capacitors and a resistor that were changed when going to the air variable.

All that aside, the comment "There is a difference in the tubes but I have not seen any radio that couldn't be made to work with either type. But it is not always a plug and play process" is exactly what I am talking about.  If someone thinks that they can just plug a 6146B/8298A into any transmitter designed for the 6146 or 6146A/8298 and be on their merry way, they are badly mistaken!  Sometimes you can, but more often than not, you are going to have make modifications.

Glen, K9STH

Website:  http://k9sth.com


--- On Tue, 7/5/11, Gary Schafer <garyschafer at comcast.net> wrote:

Neutralization IS a problem with some equipment. I have changed several early model Collins S line and KWM2 radios from 6146A to 6146B tubes. They have to be re neutralized  and if they don't have the newer neutralization circuit they will not neutralize properly. There is not enough range in the capacitor to allow proper neutralization.
 
I spent many hours trying to tame the finals in the Collins radios until I realized that they required changes in the neutralization circuit.
 
I suspect that lots of people just shove the tubes in and are not concerned about neutralization. Then wonder why the radio tunes funny sometimes.
 
You can easily check your Collins equipment for proper neutralization by observing the grid current when tuning the plate thru resonance. The grid current should dip at exactly the same point of the plate tune capacitor as where plate current dips. If there is any difference then the neutralization is not correct. This includes the feedback neutralization too.

Note that grid current dips rather than peaks at plate resonance when feedback is employed such as Collins uses.  A radio without feedback will have the grid current peak at the exact point where plate current dips if it is properly neutralized.
 
The screen voltage is often a little different in radios with the two different tubes.
 
There is a difference in the tubes but I have not seen any radio that couldn't be made to work with either type. But it is not always a plug and play process.