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Extensive Ranger Mods from WA1HLR

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Author Topic: Extensive Ranger Mods from WA1HLR  (Read 4613 times)
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Steve - K4HX

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« on: December 15, 2012, 11:28:43 AM »

The Competition Class Stock Eliminator Ranger


Timothy M. Smith
WA1HnyLR, The TimTron

See the attached Modified Modulator Schematic

See the attached New PTT Schematic

WELL, WELL, WELL! Its about time I sat down and did up an article on total dehyellification and other related modifications to the Johnson Ranger transmitter. Before one intends to modify this rig one must read and understand this article as well as have some skill in homebrewing and working with tools. If you decide to go all the way with these modifications you will wind up with a transmitter with performance far beyond other typical modifications that one may do. When complete the revitalized Ranger will run MUCH cooler, a for real T/R system and high fidelity audio.

There are actually three different Ranger transmitters rather than two as most people think. The early models used cathode keying of low level RF stages and cathode bias for the modulator. Both later models of the so-called Ranger I and Ranger II had a bias supply for a grid-blocked keying system and fixed bias for the modulator. The model with the bias supply is more desirable but if you happen to have an older model a bias supply can easily be added. This will be covered later.

Now, let's look at a stock Ranger transmitter and see what we really have.

AUDIO: The audio in the Ranger was considered to be good. It was assumed that if you had a Ranger and a D-104 microphonium that you had good audio. In reality there are a number of restrictions in the path of good audio - restrictions caused by undersized coupling capacitors to chop the low end and plenty of capacitors to kill the high end audio frequencies. Poor power supply regulation, especially the method that the screen voltage for the modulator tubes is derived caused distortion, and the modulator would 'bottom out' under heavy modulation conditions.

The Ranger power supplies leave a lot to be desired. The overworked 5R4 rectifier can barely handle the load placed on it by the final and modulator. The plate voltage sags to a low 450 Volts under full load whereas the voltage will remain fairly constant at 550 - 600 Volts with solid state rectifiers. The 10mF 700 Volt capacitor is barely adequate for the job and also is a cause of low audio frequency distortion due to its capacitive reactance.

The same things could be said for the low voltage power supply. The 6AX5 is a weak link and 30 mF is insufficient for our needs, as well. Solid- stating this supply also helps out with regulation along with an increase in power supply voltage. The bias supply is not as bad off as the other supplies but the cardboard tubular electrolytic by now has long lost its capacitance. Solid stating this supply also helps performance and is also one less tube to worry about.

The factory push-to-talk T/R relay system was an afterthought thrown in at the factory. Its coil received its voltage from a reststive divider in the low voltage power supply - more heat being generated inside the rig. The factory PTT did the following:

In the standby mode excitation is removed from the final causing the clamp tube to pull the resting current down to 50 or 60 mills on the final. This represents 25 - 30 Watts of energy being dissipated in the final. The modulator remains on at all times relying on the microphonium switch in the base of the trusty D-104 G-Stand to kill incoming audio during standby operation. With 50 - 70 mils of idle current another 30 - 40 Watts of heat energy is released inside the cabinet baking away the components.

The DRIVE control pot (25K 4 Watt wirewound) behaves as a bleeder for the low voltage power supply. In much used and tired Rangers this control craps out and is a pain in the scrot to replace.

The VFO uses an 18K 2 Watt carbon resistor as a voltage dropper for the VR tube in the VFO compartment. This resistor does become a source of trouble - it is barely able to do the job. The same resistor is used in the Valiant and Johnson 500 as well. Over a period of time this resistor's value will decrease causing more energy to be dissipated within itself and the VR tube. Eventually a runaway situation develops like that of a miniature Chernobyl in the VFO compartment.

OH YES! I forgot to mention the famous 20K 50 Watt bleeder in the HV supply. This device functioned as an adjustable source of modulator screen voltage, clamp tube screen voltage and space heater to keep the rig warm on those cold winter nights. This device gets the axe!

As you can see, the Ranger transmitter could stand much improvement. The modifications presented herein are all inter- related. In other words they ALL have to be done or problems WILL crop up during operation. These modifications have been performed on many Ranger transmitters with changes and improvements over the years. As can be seen from the high fidelity modulator, to the properly solid-stated and filtered power supplies, to the smooth heat saving T/R control system, everything is inter-related and as a system works well. LET'S DIG IN!

Let's take a look at this high performance modulator circuit. Notice that it is ALL resistive coupled eliminating the problems associated with the original driver transformer circuit. Earlier past modifications have used the stock driver transformer but with the core gap spacing eliminated and cross-laminating of the core. Also a 6DR7 dissimilar dual triode was used as a driver as well as an additional stage of speech amplification. The secondary of the driver transformer was resistively loaded for stability and smoothness of response.

In spite if all this there is one problem, the driver transformer. It was found that the modulator tubes operate in AB1 with the increase of screen voltage on modulators. This eliminated the need for the driver transformer and use of resistive coupling with the 12AU7 tube as phase inverter. The phase inverter circuit is very simple and straightforward. The component values should be strictly adhered to for proper circuit operation. Notice that the same tubes are used in this circuit that are used in the stock modulator.

The stock modulator tubes, 1614 in the first two models and 7027 used in the Ranger II are nothing more than the famous 6L6 but rated for higher voltage. These are tubes with better electrical characteristics than the 6L6 type tubes used. I have used the 6550 with excellent results. These husky tubes can deliver as much as 100 Watts of audio with the plate voltage supply of the Ranger, but the impedance presented to the tubes by the stock modulation transformer will yield enough audio to modulate 120% positive. The large reserve power capabilities of the 6550 will reduce bass distortion caused by the small stock mod transformer.

There are tubes other than the 6550 that can be used with good results such as the 6CA7/EL34 and the 8417. These tubes have a similar pin connection to the 6550 which has the same pin connections as the 6L6.

The low level speech amp stages are similar to original circuit but the component value have been changed to preserve the fidelity. The input resistor on the grid is very high value (10 meg). This is to work well with crystal and ceramic microphoniums. A small 50-100pF disc ceramic cap serves as an RF bypass on grid of first stages. Lead dress in this area is very critical. Leads of component length shall be kept very short to prevent hum pickup. There is also a closed circuit type phone jack for a high level input for use of external preamps or processed audio or tape deck playback.

One very important step is the reiwring of filament ground returns. The Ranger as well as many other commercial transmitters used the chassis as a return for one side of the filament line. This practise caused hum to be induced into low level audio stages. The filament ground returns on the two speech amp tubes and modulator tubes MUST be removed from chassis ground and a separate return buss wire (insulated) run from past grounded filament pin the the buss wire is connected to chassis on the other side of the chassis where the filament winding is tied off to ground. A second ground buss is run of #10 or #12 bare copper wire from microphonium plug ground to all audio ground points in the speech amp. These grounding procedures are mandatory or you may wind up with a carload of hummmmmmmmmmmm.

Negative feedback around modulator is retained, but fed into the cathode of the 3rd audio stage. Modulator resting current should be set for 65 - 70 mA for 6L6 tube types, 80 - 90 mA for 6CA7 and 90 - 100 mA for the 6550 and 8417.

Once the modulator has been reworked and properly set up with all modifications in place you will get good clean audio and resonance from 80 - 15,000 WITH THE STOCK IRON! The only factor limiting deep bass response is the undersized modulation transformer. A better trasformer could be used but much relocating of components to be done - to be covered later.

The T/R control circuit is much more sophisticated than the original Johnson abortion! TWO relays will be needed. I used 24 volt units due to their availability. A typical 4-pole double-throw unit and a larger 3-pole double-throw KCP 11 type 11-pin plug-in type. The 3 pole must have good voltage rating as it performs the following:

1. applies 117VAC to antenna changeover socket.

2. applies screen voltage to the final amp tube or grounds screen during standby.

3. applies low voltage B+ to screens of the modulator tubes, clamp tube screen and drive control pot.

The 4-pole miniature plug-in relay is used for the following:

1. to key the transmitter as done in the original PTT circuit.

2. applies 6.3 volts AC to the red pilot light on the front panel (VFO escutcheon) to let you and any visitors to your shack know that you are ON THE AIR!

The remaining two sets of contacts are brought out to a 6-pin Jones connector or other socket for the control of other devices such as receiver muting or keying up another transmitter when using the Ranger as an exciter. If one wishes to cut corners you can get by with a total of 4 poles of double-throw contacts.

The solid state power supplies are simple and straightforward. Being that choke input filters are used, a suffucient PIV rating of the diodes shall be observed - a minimum of 4 kV PIV per leg LV power supply and 6kV per leg HV supply and 1kV per leg PIV for the bias supply. Capacitors are connected across both filter reactors in supplies to help limit peak transient voltages. Both rectifier tube sockers are removed in order to mount the 2 can electrolytics used in HV supply - an additional hole may be drilled or punched where serial number used to be in order to mount LV power supply cap.

A number of different values of electrolytics may be used when doing up the power supply. A minimum value of 80 mF to be used in the LV supply and same for the HV supply. The caps used in the HV supply can be rated as low as 350 VDC being that they are in series.

The LV filter cap must carry a 450 VDC rating. In the particular RANGER that this article is patterned after I used a pair of 250 mF per-section dual caps in series in the HV supply for a total of 250 mF! A 200 mF can was used in the LV supply - total overkill I admit, but what the Hell, it can't hurt!

The bias supply has also been solid-stated as well, therefore eliminating the 6AL5 tube. In place of the 6AL5 one of the control relays was mounted. The other relay was mounted beside it. Both relays are socketed for the ease of relacement should it become necessary. Bias supply filter capacitor MUST be replaced. The piece of #b%$&8@ that EF Johnson put in there has long dried up and lost all of its' capacity. An 80 - 200Mf 100VDC device should suffice.

In the stock Ranger, the modulator bias is taken from a divider consisting of two 4.7K resistors in series. The bias must be made adjustable. Do the following:

Connect a 2.7 - 3.3K 1 Watt resistor from bias supply outpoot to a 40 - 45 Volt zener diode string to ground.

Feed the zener regulated voltage to a 10K 1 Watt pot on one end. The other end of the pot is grounded and the wiper arm goes to the modulator grid resistor.

Oh yes, remove the pair of 4.7K resistors that were in the original circuit. If you happen to have one of the very early RANGERS that does not have the fixed bias supply do the following:

After solid-stating the low and high voltage power supplies, series up the unused filament winding as shown in the relay control schematic and make up a voltage TRIPLER as opposed to a doubler.

MAKE SURE that polarities of diode amd capacitors are reversed in order to obtain NEGATIVE bias for the modulator.

If 24 vdc relays are used it would be a good idea to place the proper value series resistor in line to relays being that the outpoot from the bias tripler is in the order of -38 to -45 Volts. Use a 10K pot across supply to obtain the proper bias.

(Note: in the printed form, Part One ended here. Ed.)

Over the period of time it has taken me to write this article (on and off for four years) there have been a few more improvements made. It has been found that a much better modulation transformer can be shoe-horned into the spot that the stock mod transformer occupied. If you remove the meter shield can and carefully cut the bolts to as short a length as necessary to mount terminal lugs. The largest transformer stuffed in there was a Stancor A3893 60W unit. The end bells had to be removed and hacksawed down to about 1/8" in from the mounting frame. The entire transformer was used, full primary to full secondary in the mild step-down mode. The unused leads were carefully clipped at the windings.

When disassembling the transformer MAKE SURE that you are certain with your hookup. Stancor has a wierd way of numbering their terminals. The primary uses 7 & 10 to mod plates. Tie 9 & 12 together use as center tap SEC use 1 & 4 tie 3 & 6 together as center tap. This center tap is needed when driving Johnson Kilowatt or other modulator.

Being that there are no negative feedback winding one must get their feedback from other places such as from one of the modulator plates. Use a 0.1mF 1kV cap from the appropriate modulator plate (the wrong one will cause positive feedback and much squealing) with a 150K 2 Watt resistor to the cathode of the first section of the 12AU7 tube (voltage amplifier ahead of phase splitter - the same point where the negative feedback is applied from the stock transformer). This worked very well.

A Stancor A 3892 30 Watt unit worked well in another RANGER but had to limit final plate current too 100mA being that, that is the maximum rating for that transfrmer.

This article was written after a particular RANGER that I modified for a friend, who many years later did not have a use for it and gave it to me, the story continues.....

I recently picked up a Triad M-15 30 Watt modulation trabsformer which I was able to shoe-horn in place of the stock unit using removal of meter shield can and triming the meter bolts. The M-15 fit like a glove. The Triad series of multitap mod transformers is different in concept being that the secondary winding is one winding with a bunch of taps. No center tap is available so a center-tapped transformer will have to be used when using as an audio driver only.

The performance was unbelievable. Frequency response from 50 - 10,000 Hz and the ability to modulate 180% positive using this yransformer in a mild step-up mode!

Lead hookup info: Tie red leads to B-plus Sec. is blk/red and grn/wht.

I have even stuffed a 125 Watt Triad M-12A in an earlier RANGER that I did up but much rearrangement of the rocks had to be done.

Why am I relating all of this to you, you may ask? Well, it is to provide some incentive to take it into the full fidelity dimension. The stock transformer is okay but a marked improvement is noticed with one more cut out to do the job. There are other mods dome by such individuals as Pete W1VZR and John K1DEU in the RF end of things. Various neutralization schemes and improvements in VFO stability by putting the 150 Volt regulated line to the VFO plate and using a 22K resistor from the 150 Volt source to the 6AU6 screen.

Hopefully this gives many RANGER owners incentive to take it to the limit! There is one more modification that I shall deal with in an upcoming article - the low power mod for using the RANGER as a high-performance exciter for a linear amplifier. I realize the complete works here will take time to do from start to finish but it will be very rewarding with the reports you will received from your de-hnyellaphied RANGER.

Component Values For High Performance Ranger Modulator

C1 .005 mF (original value)

C2 50 - 100 pF disc ceramic

C3 20 - 50 mF 6 - 25 V electrolytic

C4,C6,C8 10 - 40 mF 450VDC electrolytic

C5,C7 0.02 - .1 mF 600VDC

C9 0.001 mF 100V minimum

C10 .047 mF 100V minimum

Negative feedback freq correction C11,C12 .068 - .15mF - all must have 1000 Volt rating. C12 may have as low as 400 Volt rating.

Resistors all 1/2 Watt unless noted otherwise.

R1 4.7K (original value)

R2 4.7 - 10M grid resistor

R3 1.8K - 2.2K cathode resistor

R4 470K (original value) plate resistor

R5,R7 33K - 68K decoupling resistor

R6 220K plate load

R8 2.7K cathode resistor

R9 1M pot (original value)

R10 470K - 1M grid resistor

R11 15K decoupling

R12 220K plate load *critical value*

R13 4.7K cathode resistor

R14 1K part of neg feedback correction

R15 30 - 33K negative feedback resistor

R16,R17 68K 2 Watt 5% tolerance plate & cathode high-level phase inverter. *Value critical*

R18,R19 150K - 220K modulator grid resistor - pair must be matched

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