[Milsurplus] R-390A carrier meters

[pete williams]

Hi... While  some of  you guys  have been getting legless from taking
the plate  caps off  807's,  some of us  at the  other end of the  day
have been  active in being practical in adapting surplus meters for
the carrier level function in R-390A.
The original meter has  an  internal  R of  around  10 Ohms and the
replacement meter I have (ex W5cab )has an  Internal R of  around 103
ohms. It has a  FSD of  1 mA.The  scale plate changed  per foto
details  available on the  net.
 Altho' it deflects, the reading is a  fraction of the original.
Following  suggestions  made by  David  Wise  and  Gary Gitzen  ,
modifications made to the  meter  bridge circuit gave identical
results to that generated with  original meters -

 Not only  was  meter  deflection approximately the  same (Even
readings from original meters varied under same  test  conditions  )
but the parameters of linearity and  AGC also remained identical to
readings obtained  with the  original meters during the tests .Time
constant values  also appeared to be the  same as original.
MODIFICATION..Refer to Fig 22 on page 36 of  manual TM
11-5820-358-35.
Replace R524   with a 600 ohm resistor.    Replace R548  with a 160
ohm resistor . Both are easy to  get at.

Remove R537 a 22 ohm resistor from the  carrier meter  adjust pot ..

Remove the  shorting link  from the center wiper terminal of this  pot
and  connect the white- blu -orange wire  to the  "hot end" of the pot
. The  white- blu  - green stays on the   center  wiper  and it is
already  connected to the  + side of  meter M102. The  white  ire
stays  going to  chassis.
Zero the meter as  per the manual and  that's it .
 NOTE.... other meters of  greatly differing  IR's  may require
modification of the   resistor  values... none  were  available  for
test.
 Thanks  to  Dave  and  Gary  for   interest and  assistance with
these  modifications .
 Purists can get on  with evacuating  807's  !

Cheers
Pete D . Williams
METUNG 3904
Australia
jupete at bigpond.net.au