[R-390] How is this gear supposed to work?

Sun Nov 30 18:42:28 EST 2014

Grayson,

I did not look at the drawing but from your description you have the Zero adjust assembly in hand.

--------
When I put it back together, it is extremely difficult move 
the back gear back and forth.  Problem is I am not sure how this assembly is 
supposed to work.
------------ 

The front gear location in relation to the back gear location can be varied within the range of the
three pins in the slots of the front gear.

But you can only change the relation of the gears when they are installed,
the dial zero adjust assembly is complete and installed and
the front panel is installed.

In life and real use,
the dial counter is rolled over to a 100Khz point,
the dial zero adjust is screwed in to push the three pins into the clutch mechanism in the gear set.
you can then twist the Kio Hertz knob through the adjustment range with out moving the veder root dial counter.
The adjustment range being the range the pins can move in the slots of the gear face.

You mostly go to CAL on the function switch,
Turn the BFO On.
Set the BFO pitch to zero.
Set the veder root counter to XX X00 where you expect to find a cal tone.
Engage the zero adjust by screwing it in clock wise to free the clutch.
Rotate the Kilo Hertz knob to a zero tone of the calibration oscillator against the zero of the BFO.
Release the zero adjust by turning it counter clock wise.

Never over crank a zero release counter clock wise. You will screw the shaft out of the bushing nut and force the
zero lock disk off the end of the zero lock shaft. This state would be a broken zero adjust assembly.

You should have a nice big 1 inch or so flat washer on the end of the zero adjust shaft.
If not you have a broken zero adjust assembly and you can not zero adjust your receiver.
The big washer is forced against the three clutch pins by the thread movement on the zero adjust shaft.
Forcing the pins in will cause the clutch to release.

With the clutch and gear assembly in hand you can not apply enough pressure to the pins to freely
change the setting of the gears to each other.
I think the assemble is riveted together and does not come apart.
You just have to give it a good bath to clean it up as best you can.

In real life every crystal in the second oscillator and it's used harmonics are not exactly on frequency.
The VFO may be linier to within 200 hertz from end to end but off many cycles along the way.

So you just run the receiver over to the nearest 00 cal tone spot.
Engage the zero adjust.
Dial the VFO to zero beat and release the zero adjust mechanism.
Then within about 50,000 hertz of the zero you can read the receive frequency 
to 1000 hertz.  from XX X00 to XX X50 plus or minus.

All the megahertz from 00 to 31 should let you zero beat the receiver on every 100 KHz cal tone.
If you have a mega hertz that is so far off that it will not zero you may need to change the crystal in the 
second crystal oscillator. 

While you try to set the zero adjust to mechanical center, 
release the zero adjust
and adjust the counter to XX X00 by loosing a counter gear and moving the counter,
and then setting  the VFO to match by loosening the clamp on the Oldham coupler 
with a counter  or to zero through the .1Khz crystal in the IF bandwidth as was done originally prior to the wide spread use of counters,

you may find one or more of the megahertz band will not zero beat with in the range of the zero adjust.
So before you just go seeking crystals, reset the zero adjust mechanical center to not exactly center and in a spot that
will let you zero every megahertz.
If the range gets so wide that some thing will not zero you have to decide which end you want to start making changes on.

Some crystals are easier to find than others.  You may not be going where you want to go that brings all the
crystals closer to center. But you pick what you can get to get your receiver back in range. 

Find the 4 or five wide ones two high and two low and go shopping.
Crystals use harmonics some use two and some use three.
If one harmonic is two far out then likely so will the other values of the crystal be off.
Maybe only the last highest value will be two far out to get it to zero.

When setting the second crystal oscillator trimmer caps you are looking for maximum output not exact frequency.

You will find that as you change megahertz each one will have a different zero point in the zero adjust.
Its normal.
If you have a fair set of crystals most will be close.
Most days an operator did not go changing megahertz that much.

If an operator was swapping two megahertz to chase some ditties and the two megahertz were way apart on zero we would swap
crystals around between several receivers to give the receiver some what matched crystals on the pair or three megahertz the operator needed so
when he called out a frequency or was given a frequency he could read the dial with some degree of certainty.

Not that any crystal was on exact frequency but the ones of interest were all about the same zero point with in a 100 hertz or so.
That close and the operator did not need to zero the receiver on the megahertz changed. The VFO from end to
would only be in that range.

If the operator was working  6930 and 7041 he would have to go end to end on the VFO.
Charlie know we were coping him on R390 and had this range problem and would work over a megahertz end just because.
I seen a few Viet Nam rigs that were miss aligned so that the high end would be a 1000 hertz over the end of the megahertz band.
The dials were just off the alignment by 1000 hertz and used that way.

Before an intercept op could spin to the end and flop over, the other end of the ditty conversation would have been completed and never copied by the 
intercept operator. Even if the intercept operator had his second receiver setting on the low end of the next megahertz he often could not find the 
second end of the exchange in time to get a copy or send it to the direction finding team to get a bearing on the transmitter.

But we never tried to get every crystal in a receiver to zero at the same point with the VFO.
It just was not done. Way to much effort invested plus crystal cost. 

Grayson,
I hope this helps

Roger Ruszkowski AI4NI

-----Original Message-----
From: Grayson Evans <wa4gvm at gmail.com>
To: R-390 HF Receiver List <r-390 at mailman.qth.net>
Sent: Sun, Nov 30, 2014 3:54 pm
Subject: [R-390] How is this gear supposed to work?

This is a bit of an obscure question.
I am having trouble getting the “clutch” gear (21 in the exploded diagram of the 
gear assembly) to work properly.
This is the gear on the front of the assembly where part of it engages the 
Kilocycle gear of the V.R. wheels.
This is an odd two part gear, a movable split gear on the back with a fixed 
gear, attached to the shaft, in the front.  There are two pins on the back gear 
that fit in two slots through the front gear.   Three more pins are attached to 
a plate sandwiched between the two gears.

I took this assembly apart to clean it.  It, like most of the gears, were 
totally gunked up.   When I put it back together, it is extremely difficult move 
the back gear back and forth.  Problem is I am not sure how this assembly is 
supposed to work.  I am assuming that at the stop of the kilocycle range on the 
VR counter, the two gears slip to allow some “overshoot” on the turning.   I 
have no idea if this makes any sense.
It looks like the clutch action adds some resistance to this movement, but I 
don’t know how much resistance.

Has anyone every disassembled this gear and put it back together successfully?  
when back together should it be easy (by hand) to move the front/back gears back 
and forth in the slots? or require a LOT of torque?

I haven’t been able to find any kind of exploded diagram of how this thing goes 
together.  I think I assembled it exactly like i took it apart, but maybe I did 
something wrong.

Grayson
TA2ZGE - Ankara, Turkey
KJ7UM

______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html