[Collins] Info Needed Collins 30L-1

[Dr. Gerald N. Johnson]

I didn't find manuals showing the three section capacitor. The parts 
list and the schematic don't agree on the four section which is wired as 
three sections. Two sections are used alone on the top two bands, three 
sections on 20m and four sections on 40 and 80. The parts list doesn't 
mention sections, just says 14 to 432 pf. The schematic says 56 to 1580 
pf. 56 is 4 times 14, but four times 432 is 1728 pf.

Its conceivable that if one section of the three section capacitor is 
twice the number of plates as the other two that a three section could 
be the perfect equivalent to the four section. Its possible that the 
lowest band(s) could have a fixed capacitor added (like each band of the 
32S transmitter). Or when the loading capacitors are switched separately 
from the coil taps, to use a single section capacitor and add increments 
by the loading switch just smaller than the delta range of he variable. 
Like with a range of 14 to 432 pf, adding steps of 390 at a time would 
allow all possible loading capacitor values.

It is possible to compute the capacitance of a variable capacitor. I 
have a very old handbook with a nomograph for that which is quicker than 
doing the math. What it takes is the diameter of the rotor plates, the 
number of rotor plates and the number of stator plates plus the rotor to 
stator plate spacing. I'm guessing the plate spacing is probably about 
.030" but it could be smaller or larger. That the rotor plate diameter 
is about 1-3/4" but I could be wrong on both.

It was possible to have a capacitor made with twice the capacitance in 
one section than in the other two to be exactly equivalent to the four 
section with two wired in parallel, though typically a large value 
variable wasn't much more than 400 pf per section and a common value for 
an AM BC radio was 365 pf per section. Getting out to 800 per section 
would be very special but not impossible.

If you can come up with those numbers I can figure the capacitance of 
each section and see how much different the three section capacitor is 
from the four section capacitor.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 3/30/2012 4:45 PM, J Allen Call wrote:
>
>
> Why do some Collins 30L-1 linear amplifiers use a three section C33 (loading capacitor)
>   and other 30L-1 amplifiers use a four section C33 (loading capacitor)?
>   The schematic that I have shows a four section capacitor yet the 30L-1
> has only a three section capacitor.  Are both the three section and four section the same capacitance?
>
> J
> W7KSG
>   		 	   		
>