[R-390] Geartrain Alignment Question (Band Switch)

[Flowertime01 at wmconnect.com]

  On page 112 of the TM 11-5820-358-35 Field & Depot Maint Manual, it shows 
the position of the "intermittent switch drive".  Not too absolutely clear as 
to how to verify it's set right, but it gets me in the ballpark.
+++++++++
Dont' get too happy with that one, it still requires
generous applications of "technicians' license".

Joe

Amen Brother.



I care not what the manuals say about you can do a band switch alignment with 
a meter probing into the pins of tube sockets. Sure you can do a lot of 
things. The question is should you do it?

Drop the front panel, pull the RF deck, turn the deck upside down on the 
bench and put the MC knob back on the shaft.

Roll the MC through the ranges both up the bands and down the bands. Look at 
the switch and the amount of contact mesh at each wafer section and at each 
change point going both up and down. As you move the MC change knob through the 
receiver range you will see the band switch change as you roll up or down 
across (.5-1 , 2-3 , 4-7 , 8-15, 16-31 ). At each change point, the switch should 
move over one contact and seat as the MC change knob sets into its detent 
position.

Now this is a judgment call. Depending on the free lash slop, mechanical 
exact construction of any given wafer and straightness of the switch assembly, how 
much contact mesh you will get varies. Resist thoughts of touching or 
adjusting wafer switch contacts of section. Just do not go there. 

Now looking at the switch contacts do the adjustment of the band switch. Your 
goal is to get the maximum contact overlap at all switch sections on each 
band.

You will find that one end the wafer is just making to the left of a contact, 
and when you dial to the other end of the receiver, the same wafer will just 
be making to right of a contact. One switch wafer will be lining up real good 
and another wafer will just barely be making contact. Remember, that receiver 
has worked for over 40 years, what ever adjustment is needed is very small.

The idea of doing this adjustment visually is to get maximum switch contact 
area. When you are doing the meter check, the meter current is very low and 
contact will "test" OK. You can get close with a meter and start burning the 
switch contact in actual use. Also the meter test is only one switch section. One 
section may be making contact while another switch section is not quite making 
it.

The first indication you may need a band switch adjustment is when you change 
bands and have to roll over (up or down past) the switch change point to get 
switch contact.

As long as you have the RF deck and crystal OSC deck there on the bench, 
check the crystal oscillator switch also. It chages every MC. Again contact area 
will drift from end to end. Also some contacts in the mid range may not be 
exactly spaced so some judgment must be applied to where best to set the switch. 
Check the contacts tuning both up and down as the gear lash will be different 
each way.

Roger KC6TRU

P.S. Am I using the correct detent spelling here?