[Collins] 6146B Circuit change

[Laird Tom N]

>>If I recall, running 6146B's at full power required a change in the screen
> voltage.  But, I agree with Jerry, it is not worth it. Jim
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from the WC9M archives:


When the S-Line and the KWM-2 were initially produced the neutralization
circuit was designed around the parameters of the 6146. You must remember
that the 6146-B had not yet been made. To recognize the rigs designed for
the 6146 look at the neutralization cap. If it is an 8 - 50 pf ceramic
type, then your unit was designed for the 6146.
The 6146-A had essentially the same inner electrode capacitance and would
work quite satisfactory in the units. The 6146-w tubes of that day were the
same except that they were a ruggidized version of the 6146-A tube. They
also worked very well in S-Lines and KWM-2`s that were being produced at
that time.

Along came the 6146-B. This was a different tube as far as the inner
electrode capacitance was concerned. It would not neutralize properly or if
by chance you did get it neutralized, it would not stay that way. The use
of the 6146-B tubes in the earlier rigs is not recommended. These tubes
cause excessive current to flow through the components and the
neutralization 
cap will over heat and will ultimately arc over causing it to burn up.

Collins realized the problems and redesigned the neutralization circuit and
went to a lower value cap. and changed it from a ceramic to an air
variable. They also changed two or three other capacitor values and a
resistor to make the radio happy with the new style tubes.

The current 6146-W tubes are the ruggedized version of the 6146-B and for
that reason should not be used in the earlier S-Line and kwm-2 gear.
You can however use any of the 6146 series tubes in the later units.

There is no way to determine which 6146W is which. However those @ SSN are
the ruggedized "B". The only ones that are the ruggedized "A" type are those
made prior to about 1965. John Bess WA5VVT

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Hope this helps,

Tom Laird WC9M
Moline, iL.