Johnson Ranger I recommendations

[W4AMV]

Hello Forum.

I am finally and long over due in bringing a Ranger I on line. It is fully functional, very stable, no chirp and intend to use on CW only. Thanks to prior help from folks on the forum,  I addressed the only problems found. One, blown line fuse was due to one of the ceramic disks in the TVI filter shorted, a fused wafer contact on the meter switch, failed to read meter plate current. Thats it. I did replace HV and LV electrolytics on the assumption that they were bad.

My question, are there any other obvious things that should be addressed and that would lead to catastrophic failure rendering the Ranger I to a sad state ? I really DO NOT want to due a modernization or restoration. The Ranger is really in pretty nice shape.  

Thanks in advance !

Alan

[N8ETQ]

Hey Allen,

   A pair of "Back to Back" 1N4007's across the
Meter terminals can save a lot of grief. A 3 wire
cord and a fuse holder is also nice if you wish
to add a Hole, Inline fuse holders work too..

GL 

/Dan

[WQ9E]

Alan,

Since you are planning to use it on CW I expect you will be tuning the VFO more than the average AM op.  The grease in the ball reduction drive is going to be dry with age and contaminated by now so I would clean it up and lubricate with new grease, I use a modern synthetic.  Properly operating the VFO drive is very smooth but as the grease gets dry it will feel "crunchy".  Old/contaminated grease will wear out the shaft and ball bearings in the drive.

It is easy to clean and lubricate and will restore smooth VFO action while avoiding excess wear to the mechanism which can only be replaced by finding one from a parts unit.  The front escutcheon (but not the entire panel) needs to be removed. After the exciter, final, and VFO knobs are removed you will find nuts holding the bottom of the escutcheon in place while the pilot lamp assemblies hold the top.  One set of set screws for the VFO coupler is accessed via a hole in the chassis.  Once the ball reduction drive is out it disassembles into two halves by unscrewing, I use rubber jaws in my bench vise to hold the thread half while turning the other with a wrench.  Once it begins to loosen remove it from the vise or other holding fixture and finish disassembly over a container to catch any of the ball bearings that may fall out.  Most will have 4 ball bearings, 3 that mount in the sides with a 4th that forms a thrust bearing at the end of the shaft but I did repair one that had the thrust bearing cast as part of the shaft.  I have yet to find worn bearings but if they are (or you lose one) they are standard size individual balls that can be found at any bearing supply house. Thoroughly remove the old lube (WD-40 actually works pretty well as a degreaser), dry the parts, and then reassemble using fresh lube.  I use the same synthetic grease I use for the grease fittings on my truck and tractor but any good quality lube will be fine (do NOT use lubriplate).  The only somewhat tricky part is determining the proper pre-load to apply to this bearing assembly which is set by how tightly the case halves are screwed together.  Too loose and you will have slippage, too tight results in stiff tuning and excess wear.  There is a pretty broad range of settings that will work so just go by feel and it should be fine.

[W6MQI]

Alan
 I second what N8ETQ suggest I also put a cap across the meter as well.
Never could get the vfo to be stable enough for CW on the high bands nothing but grief complaining I was drifting. So I ended up using a DDS for CW op's and never looked back.

73,Dave

[AB2EZ]

I suggest the following additional precautions:

Keep the AC between 110VAC and 115VAC... using a small variac or (if you don't have a variac to dedicate to this purpose), a "bucking" transformer configuration.

Do not "solid state" the HV B+ and/or the LV B+ power supplies

The above precautions will avoid the stress on the components that would result from higher HV B+, and/or higher LV B+ (particularly, but not limited to, the stress on R3 (the 18k ohm 2W "Chernobyl" resistor) and the 0A2 regulator tube in the regulated voltage supply of the VFO)

Place a small "muffin" fan on top of the cabinet, above the power transformer... to pull out warm air. The power transformer gets pretty hot, as do some of the other components.

If you are only going to operate in CW mode, you should remove the 6L6's and the low level audio tubes... in order to reduce heat production, and to reduce stress on the power transformer.

With respect to the meter:

I agree that you should put a .002uF or a .001uF capacitor across the meter terminals, and you should put a pair of 1N4007 diodes (one in each direction) across the meter. A full scale reading on the meter occurs when 200mA passes through a 0.5 ohm metering shunt. Therefore, full scale is 0.1V across the meter. The 1N4007s will have little effect, provided the voltage across the meter remains below 0.1V.

I would also strongly suggest that you remove the existing capacitors that go from either side of the meter to ground (C64 and C65). You can reuse these for the capacitor to be added across the meter terminals. The reason for removing these is as follows:

Both of these capacitors charge up to the full HV B+ when the meter switch is moved to the plate current position. When the switch is then moved to another position, these capacitors will rapidly discharge... causing a spark at the meter switch. Furthermore, this will result in a current surge through the meter.

If either capacitor shorts out (or becomes unusually conductive) the meter will be toast.

These capacitors are there to bypass RF to ground... for TVI reduction. They are not needed, for that purpose, any more.

Stu

[W4AMV]

Rodger, Stu, Dan and Dave. Thanks!

All great inputs. Any others, please. I want to preserve this rig in a reasonable manner and was glad to receive inputs that are doable and hence get accomplished.

Alan

[AB2EZ]

Alan
et al.

Just a clarification on the efficacy (or lack thereof) of using a pair of 1n4007 didoes (one in each direction) across the meter of the Ranger ... in order to add some over-current protection for the meter movement:

The characteristics of a Ranger meter are as follows:

Terminal-to-terminal voltage for full scale: 0.1V
Terminal-to-terminal resistance: 20 ohms
Current through the meter to produce a full scale reading (follows from the above): 0.1V / 20 ohms = 5 mA.

From the specification sheet for a 1N4007, the forward voltage required to produce 10mA of current through the diode is 0.6V. The forward voltage required to produce 200mA of forward current in 0.8V

http://www.fairchildsemi.com/ds/1N/1N4007.pdf (figure 2)

Therefore, the current through the diode will only begin to exceed the current through the meter at around 0.7V across the meter || diode combination.

At 0.7V across its terminals, the meter will have 35 mA of current flowing through it ... i.e. 7x the current required to produce a full scale reading. The heating of the wires inside the meter will be 49x the heating that occurs with a full scale reading.

Therefore, while the diodes will offer some protection against a very brief over-current events... by diverting current around the meter... they will not protect the meter against a long duration over-current condition. See the comments below regarding the .002uF RF bypass capacitors.

Separately: 0.002uF x 20 ohms = .04 microseconds. So an added .002uF capacitor, from terminal-to-terminal is only going to protect the meter (by diverting current around it) against very short duration over-current transients. If one increases the value of the added terminal-to-terminal capacitor to 0.1uF (non-polarized), then the time constant will increase to 0.1uF x 20 ohms = 2 microseconds.   See the comments below regarding the .002uF RF bypass capacitors.


Such over-current transients would occur (for example) if one does not remove the .002uF RF bypass capacitors from each side of the meter, to ground. With these capacitors left in place, an over-current transient would arise (for example) if the meter switch position is changed from "modulator current" to "plate current", and if one switch contact takes place (one side of the meter is connected to HV B+) before the other switch contact takes place. Likewise, when the meter switch position is changed from "plate current" to "modulator current"... and one side of the meter is connected to ground before the other side of the meter is connected to the top of the 0.51 ohm resistor (or vice-versa).

Using germanium diodes, instead of silicon diodes, does not appear to be of much help in this application

http://www.mtmscientific.com/1n34a.html

Stu

[W4AMV]

Thanks Stu for the clarification. Why not add a meter shunt and scale the meter reading accordingly. There is an issue of course in reading grid, oscillator and other lower current values when the meter switch is in those positions. However, a log of cap load, drive and tune values could bypass that step and the plate dip and load still useful. 

[AB2EZ]

I think that several problems would have been avoided if the Johnson engineers had put the 0.51 ohm "plate current" shunt between the 6146 cathode and ground:

1. It would be safer to not bring the HV B+ out to the meter switch and meter terminals

2. The sparking at the contacts of the meter switch, that occurs if the 0.002uf RF meter shunt capacitors are in place, would be eliminated

3. The meter would work (still read the current) in the "plate current" position when using an alternative B+ (or modulated B+) supply for the 6146

4. The main hazards to the meter, itself, (things that can cause large amounts of current to flow through the meter) would be eliminated if the HV B+ was not present at its terminals in the "plate current" position of the meter switch.

Since, in the stock configuration, the meter is reading plate current + screen current, when the meter switch is in the "plate current" position, the addition of the grid current (2.5 mA)... if the shunt is moved to the cathode of the 6146... seems like a good tradeoff to obtain the above benefits.

The next time I take my Ranger out of its cabinet, I am going to add a 0.5 ohm, 1% tolerance, "non inductive" resistor (with a 0.1uF capacitor, a .01uF capacitor, and a 0.001uF capacitor in parallel with it), between the cathode of the 6146 and ground.... and use that shunt for measuring  the "plate current".

Note: in class C operation, the peak cathode current on each RF cycle will be more than pi x the average cathode current. That is, the peak cathode current in the Ranger (at carrier) will be more than 400ma, on each RF cycle, if the average cathode current (at carrier) is 127.5 mA. It is important to have a low RF impedance between the cathode and ground at the fundamental RF frequency, and at higher frequencies. The lead lengths on the RF bypass capacitors, between the 6146 cathode socket pins and ground, need to be kept short.

Stu