[R-390] PTO

[Flowertime01 at wmconnect.com]

KA9EGW,

The cam alignment at 7+000 is spot-on.
The rf band switch rolls over between 7 +000 & 8 +000 just like in the 
tutorial.
7+000 equates to the 7 showing in the window on the crystal oscillator deck.
Visual inspection before reinstalling the rf deck/crystal deck assembly 
confirmed the contacts were right in line.

Is it somehow possible to have the crystal oscillator bandswitch mis-indexed
to the indicator drum inside the crystal deck, without having done anything
to the crystal deck on a previously-working receiver?

No. you are likely good here.

Tubes and alignment.
It worked yesterday. Today it does not. Only one thing is likely wrong.

As you will learn alignment, is every thing. A little bit goes a long way 
in the RF deck.

Sanity check: 2455 equates to +000, yes? True
Conversely 3455 equates to 000.

Assuming I'm at the full CCW stop on the pto, where should it be?  
It's a Collins PTO FWIW. (FWIW is good money) Something more than 3455. 
Three turn should get you 300 K hertz more than 3455. Its still linear (well 
mostly). Like wise the other end should get you 100 K hertz less than 2455 for 
every turn of the shaft. The real value at the limits will vary with every 
VFO. 

I won't even go into my planned 'someday' change to the Cosmos I have on the
shelf. Once you get the receiver operating, you may want to swap in the 
Cosmos just to make sure it works. From an electric point of view the models 
are equal. The Cosmos may have a higher output thus higher mixer level and may 
or may not provide an overall better signal to noise ratio. You do not know 
until you can compare what you have on hand and see.

There are two PTO's in any R390.
Which do you speak of? (BFO VFO)
They both have like stops and get treated the same. 
Finger resistance is the end point.

When I say 'stop' I mean that point where the resistance of the bare VFO 
shaft to my bare fingers just starts to increase marginally I am being very 
careful not to run the VFO past it's physical limits

3455 is about 3 or 4 turns clockwise from the full CCW end stop.
Does that seem about right for a Collins pto? True

Lacking access to a freq counter, but having a decent sandstate general
coverage rx, [a Rat Shack DX390 which is possibly too sensitive for this
use] how do I go about telling where the pto is really at? 

The VFO puts out a nice 4 plus volt signal from 3455 to 2455. 

On the back panel of the R390/A should be a mini BNC to BNC connector. Most 
days it couples the 455 K hertz IF out to the back panel. Pull this 
connector off the back panel and use it to couple the VFO to a BNC cable and then a 
wire to your receiver. The connector will match the VFO cable to BNC cable. 
Do include a cap in the line between the VFO and the receiver. The VFO 
should put out more than 4 volts and easily over drive the receiver. The VFO 
should have a nice output from 3455 to 2455. you should be able to tune the VFO 
and receiver along nicely.

Expect all kinds of mixing between the VFO and every signal in the 
universe. As you have no way to isolate the antenna input of the Rat Shack DX390 
receiver, the receiver will accept every signal and the VFO and then mix every 
combination you can imagine. Only if you can couple the VFO through a good 
attenuate and directly into the receiver antenna input and isolate all that 
from any outside sources, will you get just the nice VFO.

As you have found the 3455 and 2455 points, you can say the VFO is good and 
it is time to proceed. 

Put the VFO back into the R390 and perform the best mechanical adjustment 
and alignment you can. Mechanical adjustment is green screws and Oldham 
coupler spacing. Alignment is getting 3455 at 7000 or 2000 depending on model.

Now you must ask your self, Self, why am I trying to shot gun a receiver 
with a rifle?

Indeed jam one frequency into the antenna input, listen for one signal out 
of the head phones and believe you can determine the exact ill of a very 
complex receiver. Not knowing what the problem is, it is time to systematically 
trouble shoot the receiver one stage at a time until you isolate all the 
problems and resolve each of them. Easy can do with a 4 hour time horizon. 
Because any R390 can be fixed in 4 hours by an experienced repairperson. 
Caveat, parts are on hand to effect the repair.

Tools required, head phones, signal generator, analog volt meter (two 
preferred), 600 ohm resistor (1 watt [2ea 1200 ohm 1/2 watt]), tweaker for caps, 
magic spline wrench. Other things are nice, but not required, but may make 
the task more fun. All real time experiments have shown that other item only 
divert time into superfluous tasks. When your done with the extra fun toys, 
the receiver does not receive any additional signals as determined by a 
human with head sets. It just takes longer to get the job done while playing 
with the toys. You need not start with a set of known good tubes. The 
"inspection and alignment process" will select and grade all the tubes you wish to 
include in the process and should leave the best tubes in the receiver in the 
optimum location. 

You may not be able to hear any signal from / through your receiver because 
it cannot pass any signal through itself, for any number of reasons that 
have nothing to do with the VFO.

By the way, I'm using a known-good, plug-and-play IF deck just received from
Fair Radio. 

So you used the IF output cable and that back panel adapter to put 455 into 
the IF deck like it shows in the Y2K manual or any of the TM's. You get 455 
to peak through the .1 Kilohertz band width and thus the 455 crystal. You 
did look under the lid of the first IF can and did find a crystal?

Then set the bandwidth switch to 2 KC.

Not having a calibrated signal generator, you find something around 150 
micro volts will provide - 7 volts on the diode load. When you hang the 600 ohm 
load on the local output you can measure about 1/2 watt of power when you 
use a modulated signal from the signal generator. Your meter may read in 
power watts (nice), or DB (ok) or just AC volts (some math required 14 volts = 
27 db = 500 mili watts)

The IF gain is about mid adjustment. The diode load is -7 volts the BFO is 
off.
With the modulation on you get 1/2 watt out.

Wiggle the generator level to get 24.493 AC volts across 600 ohm load on 
the local audio output.

Turn the modulation off. The AC volt meter must drop to .775 volt. At most 
1 volt.

This is a 30 DB difference in level between a modulated and un modulated 
output. If you cannot get this difference, then the IF deck and audio deck 
need tubes replaced and or additional work until you can get 30 DB difference 
and a 1/2 watt out put.

If you cannot get the receiver to pass this test, post some mail and more 
details will come your way.

Put the RF to IF cables back to gather and put the 455 through a cap and 
into the 3rd mixer test point. The gain should be 10 times the level that goes 
into the IF deck.
The 1 volt CW should become 2.449 volts CW and you will need to back the 
generator level down before you turn on the modulation.

With 30 % modulation on, adjust the generator for 24 volts on the local 
audio output.
Turn the modulation off and the level should be under 2 volts (about a 25 
DB difference).

Now you have to get out the manual and start moving back through the stages.

You have the mechanical alignment good. Bad tubes will stop everything. 
Just because a tube reads good on a tester does not mean it will provide good 
low noise performance in the receiver. A tube can read good on a tester and 
generate so much noise it swamps any signal.

Having trimmed the cams to exact alignment you can expect all of the RF 
deck alignment to be off. You may have to drive high levels of signal through 
the RF deck and make more than one pass to get the alignment close enough to 
start receiving signal from an antenna. You may have to inject signals into 
the mixer test points and align the second and first variable IF stages of 
the RF deck before you can get signals through the RF deck. 

You can set the signal generator to your other receiver to help you get it 
on frequency close enough to help you peak it through the R390.

Let us know where you are at and how its going and we can off some more 
specific detail.

Enjoy

Roger AI4NI

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