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

[Joe Foley]

Thank you, Roger!

I should have said that in more exact detail, I guess
I was waiting for more questions to be asked.

I agree with what Roger said he covered some that I
forgot.  It's exactly as he said.

That's one for the manual!

Joe



--- Flowertime01 at wmconnect.com wrote:
>   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?
>
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