[R-390] RF GAIN pot ?

[Roy Morgan]

On Mar 17, 2016, at 5:45 PM, Craig <hamfish at comcast.net> wrote:

>                                                       AND THE PLOT THICKENS
> To Jacques & All,
> 
> The 14-PH-56 rings a bell, got one of those also! It appears to be
> normal.......has CTS line & local pots 2.5K audio (log) taper. 

I have here (only) a beat up front panel from Motorola Contract 14-PH-56, and measured the pots:

Resistance numbers are at these knob dial positions 0 to 10, from the “0” terminal to the wiper:

0    2-1/2   5   7-1/2   10

RF Gain  CTS Type 320 320 4PJ 565  5 k
 0   2.5k  4.4 K  (open  open)*

Local Gain  318K146  CTS722 2500 ohms (Measured 6.4 k)
0     0.4k  0.8 k    3 k  6.4 k

Line Gain  318K146 CT 722 2500 ohms (measured 4.9 k)
0     0.2 k  0.5 k   3 K  5K

Limiter  318A145 500 K  CTS717 (measured 470 k)
0  50 k  220 k   400 k  470 k

*I have to wonder if the whole radio was scrapped because the RF gain pot was open on one end!

For reference, I measured an unused Ohmite type AB  No. CU-1041 pot  0.1 megohm (measured 113K)
(similar to the Allen Bradley Type J pots)  This seems to be a linear pot.

0  30 k    60 k   90 k   113 k

Can anyone point to online graphs of pot tapers?  I have seen graphs, but it might have been back when we had only paper.


Yours in happy resistancing,
Roy

Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958