Ranger Low power mod revisited

[KI4THX]

I have read a few opinions about various ways to lower the power out in the ranger. Im thinking that I would like to try the rear plug mod, are there any definite instructions for this ? I do have the manual with schematics, but am leary of pulling this off without advice or instruction from those who have become familiar with this idea.

Any help is appreciated !

Thanks.

[AB2EZ]

Here's one thing to keep in mind:

The way the "operate" switch on the Ranger is wired... if you select "CW", the high voltage B+ supply (600V) will be directly connected to the 6146 plate choke... regardless of whether you wire the 9 pin plug to operate on low power or not.

To prevent this causing the high voltage B+ supply feeding current into the low voltage B+ supply (via the 9 pin plug) you should include a 1N4007 (1kV PIV rated) diode in the connection (in the 9 pin plug) that runs from the low voltage B+ to the bottom of the modulation transformer's secondary. If the 9-pin socket is in the stock configuration, this is the connection between pin 4 (the low voltage B+) and pin 2 (the bottom of the modulation transformer's secondary) of the plug used for the low power operation.

This diode should have its cathode connected to pin 2 (bottom of the modulation transformer's secondary).

If you select "CW" on the "operate" switch, this diode will block current from flowing from the high voltage B+ supply into the low voltage B+ supply.

Stu

[WB5IRI]

Instead of trying to lower the output on some of these rigs, I just built an attenuator pad. First, find out what the fully loaded output is from your rig, then how much power it takes to drive your amplifier, then do the math to find out how many dB attenuation you need to get the right drive power to your amp. I use the online calculator at http://www.crownaudio.com/db-power.htm to get the figures. For instance, my Multi-Elmac AF68 puts out 38 watts on 75 and 40, and my Alpha 89 needs 12.5 watts to drive it to 375 watts carrier -- 100% modulation gets me 1500 watts PEP output, the legal limit. A 5 dB attenuator gives me 12 watts drive from my original 38 watts, close enough. Henryradio on eBay has hybrid attenuators in 100, 150, or 250 watt versions, ready to mount on a heatsink. These are 50 ohm impedance in and out and good to 2 gigs. Work like a charm. They come in several different attenuation levels. I took a 4 dB and a 1 dB, butted them together and put an SO239 at each each end of the pair, and there you have it -- nice, 5 dB, 250-watt attenuator. Plug your transmitter in one end, plug coax from your amp in the other, and you are good to go. No need to butcher your rig, and your modulator is happy working into a full load on the exciter side. The attenuators never even get warm at this level.

Doug, WB5IRI

[WQ9E]

Doug's approach is nice because you can easily move it from rig to rig as your vintage gear collection grows (and trust me it will).  In addition to the hybrid attenuators on ebay it is also easy to build an attenuator out of discrete metal oxide resistors and I have built several of these for use between various rigs and vintage amps and I also used them for both the grid loading and cathode resistors in my homebrew triple 4CX800 amp.  These resistors have sufficiently low inductance, particularly in parallel, to work perfectly at HF.  You can find construction information in several vintage amplifier manuals available on the edebris site (i.e. Johnson Thunderbolt, Hallicrafters HT-33 series, etc.) or online.  With careful construction practice you can also build a switch into the attenuator to bypass and provide selectable levels of attenuation as needed.

[W2VW]

How many of you guys turn down the volume on the stereo by placing an attenuator in line with the speakers?

[WQ9E]

How many of you guys turn down the volume on the stereo by placing an attenuator in line with the speakers?

Well in the days before remote control L pads were commonly used just for that purpose with remote speakers.

As to attenuating transmitter output I choose what I feel is the right tool for the job, others will have different preferences...

I just reduce the output via the drive and loading on the Ranger I use to drive my Desk KW since the modulation is accomplished in the Desk KW and I don't find an attenuator necessary for that task.

[WB5IRI]

Well, if you had to tear into the guts of your stereo every time you wanted to change the volume, you might. My AF68 does not like to be operated at anything except fully loaded. Loading it lightly reduces the output, sure, but then the modulation is squirrely, over driving like crazy and hard to tame. A swamping attenuator is a tried and true method for driving an amplifier with one of these old rigs that doesn't have a drive pot to simply lower the output, like modern rigs have. Brute force, true, inelegant, yes. Inefficient and turning much RF into heat, yep. But it works, and you can move it from rig to rig without having to do surgery or mistune each radio to get the power output down. Just one solution. I'd really welcome ideas on other ways to do it that don't involve making permanent changes to the rig.

Doug, WB5IRI

[KI4THX]

How many of you guys turn down the volume on the stereo by placing an attenuator in line with the speakers?

What would you recommend

[wa3dsp]

The way I did it in my complete Ranger overhaul was to replace the final grid bias resistor with a pot mounted behind the crystal socket and easily accessible from the front panel. This effectively reduces the screen voltage and thus the power out to any level you want. I have received good reports using it into an SB200 with about 150 Watts of carrier which is about 15-20 watts of drive. I made many other mods including regulating the entire LV supply and switching the HV and portions of the LV with a relay. I realize you don't want to get into a big overhaul but the pot is easy to try. It could be mounted rear panel also. 

http://www.crompton.com/hamradio/JohnsonRanger/RangerRestoration.html

[W2VW]

You probably already read this thread:

http://amfone.net/Amforum/index.php?topic=33527.0

If you desire simplicity and circuit evaluation is a dirty word, use an attenuator and amplify the distortion. It keeps other QSOs spaced away and gives AM haters something else to complain about.

If you wish the best performance from the existing equipment simply perform the low power mod.

Use a higher power exciter to load the amplifier for maximum peak power and do not retune.

Be sure to check out Stu's caveat post.

[WB5IRI]

Of course, if you have a dirty signal with distortion, then an attenuator or amplifier is not going to help that. An attenuator will simply give you a dirty little signal, and an amplifier will give you a big dirty signal. First make sure the signal from the original transmitter is free from distortion, then choose the scheme you want to lower the output to drive your amplifier properly so as not to overdrive the amplifier or exceed the legal limit. A clean signal free of distortion, no matter what the power level, is the goal. Some like to modify gear. Others like to keep their rigs in as close to original condition as possible for either esthetic reasons or for resale value later on. There is no good or bad, wrong or right way here, just differences in preference. If you do modify your rig, though, be sure to document, document, document. I cannot tell you the number of older rigs I have looked into and then scratched my head over undocumented changes that I have no clue about what they do or how to properly adjust them. If you do make changes, document them thoroughly so when you need to work on them later you won't be relying solely upon your memory or so the next owner will not be cussing you while he (or she) tries to figure out how to make the dang thing work.

As to the AM haters, they will be there no matter what. Ignore them. Put out a clean signal that is the best you can engineer, and you won't be causing anyone any legitimate reason to complain. I won't say any more about this matter here except to note that some AMers, like some sideband operators, tend to think certain frequencies are "their" frequencies and will come on the air even when there is another QSO on or near the frequency. Good operating practices, like good engineering practices, are the same for everyone.

Hope to work you all on any mode/frequency some day!

Doug, WB5IRI

[Steve - K4HX]

Keep in mind that many rigs in the original condition are not clean. So running an original rig that is dirty is the wrong way to do it, especially when dumping it into an amp.

Others like to keep their rigs in as close to original condition as possible for either esthetic reasons or for resale value later on. There is no good or bad, wrong or right way here, just differences in preference.

[WQ9E]

A properly adjusted stock Ranger does NOT create excessive distortion products and has long been viewed as one of the best sounding stock rigs.  I have looked  at my stock Ranger and Ranger II on my scope and spectrum analyzer when they were undergoing restoration and they were quite clean.  Certainly by not loading and/or exciting the final properly or over-driving the audio you can create issues but that isn't a rig fault.  Not every vintage AM rig is as clean but properly adjusted none of them I am aware of are horrible.  The worst crap I have been hearing on 80 meters lately is from a couple of  DYY rigs and that is more op than rig.  As far as interfering with other ops (including non-AM ops) in my experience the biggest offenders are the golden ear crowed shooting for hifi audio out of a ham rig.

[K1JJ]

For newcomers to AM experimentation and modifications:

There are many ways to modify a transmitter to achieve great results. (and linear amplifier combo) Experiment to your heart's desire!

The bottom line is we need effective standards to measure fidelity, distortion, bandwidth and determine the total harmonic distortion (THD) and intermodulation distortion. (IMD)    

In this day and age, AMers can afford to have an SDR spectrum analyzer, ($25 Softrock)  a clean audio sine wave generator and an audio triangle generator - and a good scope.   With these tools we can test the rig with precision and know exactly what is going on. Otherwise, we are at the mercy of on-air reports and other guesswork that can lead us down the wrong path.

Yes, it is one more PIA to master, but learning how to sweep a transmitter and knowing what is good or bad BEFORE putting it on the air is an AM skill worth pursuing.  Grab the bull by the horns!

There are several good threads on this BB addressing the subject.

T

[AB2EZ]

The advantages of using the 9-pin plug method to reduce the B+ on the plate of the Ranger's 6146... and therefore to reduce the Ranger's output power at carrier, are:

1. Keeps the modulation impedance, and the optimal pi-network settings the same as they are for full power operation.

Note:

Changing the screen voltage to reduce the average plate current, while keeping the unmodulated B+ the same, would increase the modulation impedance. This would have an unfavorable effect on the low (audio) frequency modulation performance of the Ranger... because of the magnetizing inductance of the modulation transformer (about 8H) that is in parallel with the modulation impedance of the RF output stage. For example: At 100Hz, the impedance of an 8H inductor is j5026 ohms. At 600V B+ and 125mA average current, the modulation impedance of a Ranger is 4800 ohms.

Reducing the average plate current while keeping the unmodulated B+ the same would also increase the required RF load impedance on the 6146, looking into the pi network. Achieving proper loading might not be possible with the existing pi network (not enough available loading capacitance).

2. Reduces the average current through the modulation transformer's secondary winding by a factor of two (2) ... which significantly reduces core saturation; and, therefore, significantly improves the linearity of the modulation transformer in response to input signals with large amounts of low frequency content.

3. Reduces the required modulator output power by a factor of four (4), which also significantly reduces modulation transformer core saturation associated with input signals with large amounts of low frequency content. This also avoids having to drive the modulator tubes into class AB2 (grid current on modulation peaks)... which avoids the associated distortion on modulation peaks.

4. Reduces internal heat generation (v. the use of an external attenuator)

5. The 9-pin connector approach can also be used with an external, variable voltage B+ supply (instead of using the low voltage B+ supply of the Ranger), to make the output power of the Ranger completely adjustable. Since the DC power required of that supply will be less than 125mA x 700V =87.5W, even with full RF output power, such an external B+ supply for the Ranger's 6146 RF output stage is easy to construct.

6. It is easy to do, and requires no changes to the Ranger itself... although it may be a good idea to install a solid state diode-based rectifier in place of the existing low voltage B+ supply's rectifier tube.

Eight pin octal plugs, and 1N4007 diodes are readily available to construct a solid state diode-based rectifier that will plug into the socket used by the stock low voltage B+ supply's rectifier tube. [To "solid state" the low voltage B+ supply, use two (2) 1N4007 diodes in series on each half of the full wave rectifier, in order to conservatively accommodate the peak inverse voltages]

7. Since the 9-pin socket provides access to: the top and the bottom of the secondary winding of the modulation transformer, the modulated B+ leading to the plate choke, chassis ground, the (unmodulated) HV B+, and the low voltage B+... you can do lot's of things that can improve the audio modulation fidelity of the Ranger. I have used the 9-pin plug to apply external modulation to the Ranger with adjustable B+ (bypassing the existing modulator and the existing modulation transformer). Separately, I have also used the 9-pin plug to convert the Ranger's modulation to modified Heising (adding an external Heising choke and an external Heising capacitor)... thus removing the DC plate current from the secondary of the stock modulation transformer.

Of note: with respect to modulation fidelity... the limiting aspects of a stock Ranger are: the transformer that drives the modulator tubes (which easily saturates) and the bypass capacitors (too much total bypass capacitance) from modulated B+ to ground (which roll of high frequencies). These, of course, require internal modifications if one wants to improve the audio fidelity of the Ranger.  

Stu

[W2VW]

A standard of measurement is a great idea.

An envelope display and reports from friends are not enough especially at QRO.

The no brainer is to look at peak power with a Ranger through an amplifier with an attenuator and then with the low power mod. The difference will jump right off the meter.

The Ranger was not intended as a stand-alone transmitter in the design and the modulator is not up to the task of low distortion at full power. Fine for 45 watts, not fine for legal limit.

Yes, they "sound good" but most experienced boatanchor operators can pick the grainy sounding audio out of a lineup.

Thanks Stu for taking the time to post.

An adjustable supply for the RF amp is nice as it allows any power level and high power is useful for proper adjustment of the linear amplifier to follow as mentioned in the original post.

[Steve - K4HX]

It's likely that a stock Ranger has THD in the 10% range at high modulation levels. That might have been acceptable in the 1950s, it is not today. I'd be happy to see some measurements that prove me wrong. Then I can put my stock Ranger on the air.   

[w1vtp]

It's likely that a stock Ranger has THD in the 10% range at high modulation levels. That might have been acceptable in the 1950s, it is not today. I'd be happy to see some measurements that prove me wrong. Then I can put my stock Ranger on the air.   

Steve

I did a THD simulation on my calculator assuming a frequency bandwidth 4 KC modulation and 10% distortion would be horrendous with stuff going well out to plus / minus 20 KC with levels somewhere around -20 dB from the modulation frequency amplitude levels.  Actually, I've seen something like that on the bands.

There have been some good points brought up on this thread that bears some good thought by all of us.  My 32V1 has been modified is a similar fashion as recommended by HLR, VW EZ etc and the BW is good / fidelity is great.  The method does work.  I wonder if we have anything published on this approach of marrying up Rangers etc to linears.

Al

[K1JJ]

The Ranger was not intended as a stand-alone transmitter in the design and the modulator is not up to the task of low distortion at full power. Fine for 45 watts, not fine for legal limit.

An adjustable supply for the RF amp is nice as it allows any power level and high power is useful for proper adjustment of the linear amplifier to follow as mentioned in the original post.

Yes.   In tests, I've found that decreasing the power of an amplifier stage by 1/2 can improve IMD by as much as -9dB 3rd order. This is significant and agrees with the idea to run a stage conservatively to get better linearity.

So, when using the Ranger as an exciter to a linear amp, it makes sense to drop the Ranger's plate voltage and power, if possible, thus running the exciter more linearly. This assumes that there are no new problems generated like mismatches, etc.  In addition, the modulators will not have to work as hard to hit 100% modulation and may even be able to run in AB1, no grid current, for even more pristine operation. By running more voltage on the modulators than the final, we may be able to do this.

The thang is... we need to run the IMD and THD tests ourselves to prove this out and find the sweet spots for our particular rig. This is usually an individual thing that can be optimized.

* I am a firm believer in using tubes that are TWICE the dissipation and emission required for the job. Run them at 1/2 power and we are almost guaranteed a clean signal.

T

[flintstone mop]

Here's a neat idea to reduce power to the 6146 final. Parts: 500k 2 WATT potentiometer,,,An NPN transistor...DTS-801...
Get a T0-3 case NPN transistor (Find an NTE sub for a DTS-801). Isolate the transistor case from ground.

Disconnect the 30k resistor or whatever that was connected to the screen of the 6146 and connect that to the collector.
A 500k 2 watt potentiometer is next. One end is connected to the collector/resistor that fed the screen. The WIPER of the potentiometer is connected to the base of the NPN transistor. The "other side" of the potentiometer goes to ground. The EMITTER of the transistor connects to the screen of the 6146 RF output tube.
That's it!!
Reduces the RF output without messing with the HV and loading.
Fred
Hope this made sense

[KI4THX]

WONDERFULL advice and technical discussions !

Thank you all very much, I appreciate every word and opinion that was given. I am currently in the process of converting the power supplies to solid state and a few other recommended mods.

[wa3dsp]

That last mod varies the screen voltage. If that is what you are going to do it is a lot easier to just put a pot in place of the grid bias resistor and use the clamp tube to vary the screen voltage as per my schematic. It works well for me. I also use the suggested screen voltage mixing circuit of modulated and unmodulated voltage.

http://www.crompton.com/hamradio/JohnsonRanger/RangerRestoration.html

[W3GMS]

A couple of things that have worked for me concerning the Ranger.  Like anything there are many ways to achieve a goal but this is what I choose to do.   

I power the final off the LV supply.  When I did this I put the current shunt in the cathode circuit of the tube and that keeps the HV off the meter and allows me to measure the cathode current.  When I powered the final off the LV supply, I noticed that the filter choke got pretty hot.  Since my Ranger has SS diodes instead of the tube rectifiers, I mounted a filter choke up top where the old rectifiers were located.  I found a style of choke that was the same style as the other transformers so it looks very good! 

To reduce heat, I use the HLR PTT scheme.  Basically 4 poles to control the screens of the modulators, screens of the final, keying the vfo and lastly providing the 120V to the rear apron for the external antenna relay.  I also got rid of the tapped resistor which tend to be very problematic.  The source of the screen voltage for the modulator is off the LV supply.  I do use a FET as a series regulator to  keep the screen voltage stiff.  To control the resting current, I used a shunt regulator to keep the tubes biased in AB-1.   

I also use a series FET as a source follower to make adjustments to the screen of the 6146.  Be careful when doing that to control the output power.  With a given plate voltage the screen voltage has a sweet spot for best scope pattern.  With the FET you can mix audio with the gate bias voltage in order to  control the amount of audio on the screen for a given screen voltage and optimize a trapezoidal pattern.  On the AM Window, Dean WA1KNX gives some time concerning optimizing the amount of audio applied to the screen of a DX-100.   

As others have said, the modulation transformer is much happier and you will get cleaner low end response when you reduce the secondary DC current.  For driving my pair of 3-500Z the cathode current is around 60 MA which the mod iron likes!

Since this thread concerns reducing the power of a Ranger, I will skip the extensive audio mod part. 

I modified my Ranger about 15 years ago and its been very trouble free.  Zero problems which is nice. 

Joe, GMS               

[AB2EZ]

Joe (W3GMS) wrote:

"I also use a series FET as a source follower to make adjustments to the screen of the 6146.  Be careful when doing that to control the output power.  With a given plate voltage the screen voltage has a sweet spot for best scope pattern.  With the FET you can mix audio with the gate bias voltage in order to  control the amount of audio on the screen for a given screen voltage and optimize a trapezoidal pattern.  On the AM Window, Dean WA1KNX gives some time concerning optimizing the amount of audio applied to the screen of a DX-100."  

This is a neat way of adding a separate, adjustable, modulated B+ supply for the screen of the 6146, while continuing to modulate the plate voltage... and continuing to make average power reductions (if desired) by reducing the HV B+ applied to the 6146 from 650V to a lower value .

Note: if you do this, and you wish to reduce the average power output of the Ranger... you will need to reduce the unmodulated value of the screen voltage and the level of the modulation of the output of the separate voltage screen modulator at the same time that you reduce the B+ on the plate of the 6146 and the level of the modulation of the reduced plate voltage.

The stock, 30k ohm, modulated B+ -to-screen resistor makes this adjustment happen automatically. One can think of ways to make this happen automatically when using the separate, modulated, screen voltage supply. For example, the DC input to the gate of the separate screen modulator could be obtained from a high impedance voltage divider connected to the HV B+. A total resistance (the sum of the two resistors in the voltage divider) of around 300k ohms would be a possible choice... to keep the total power dissipated by the two resistors in the voltage divider to less than 2 watts. The audio input to the gate of the separate screen modulator could be obtained from a stage in the Ranger's audio chain that is after the stock "audio" pot. The DC and the audio inputs to the gate of the separate screen modulator can be combined using a "modified Heising" approach, where the function of the Heising reactor is performed by the 2nd resistor in the 2-resistor DC voltage divider. E.g. if the two resistors in the voltage divider are approximately 200k ohms and 100k ohms, then the source impedance, looking into the (3:1) voltage divider will be around 67k ohms. Since the DC input resistance, looking into the gate of the FET, is essentially infinite... one can add an additional "modified Heising" resistor, in series, between the output of the voltage divider and the gate of the FET.

The fidelity of the modulation of the screen voltage is actually significantly more important than the fidelity of the modulation of the plate voltage in producing high fidelity modulation of the RF envelope. Since the change in screen current / the change in screen voltage is not a constant for all relevant values of the modulated screen voltage ... a low impedance source, like a source follower, is a good approach.

I may try this in the future on my Ranger, or another low-to-moderate power plate modulated transmitter.

Of note: the power delivered to the 6146 screen at carrier (when running the plate at full voltage in full power operation) is around 200V x 0.015A = 3W. The power dissipated in the FET depends on the drain voltage... which should be chosen to be at least 500V (to provide enough headroom for upward modulation of the screen voltage). So the FET, itself, will be dissipating around (500V-200V) x 0.015A at carrier = 4.5W. Therefore, one has to pick an FET that can handle 500V of drain voltage, and it needs to be attached to a suitable heat sink.

When thinking about all of the alternatives for operating a Ranger at reduced power, and modifying the audio circuitry to improve the modulation fidelity... I am reminded of a comment that a business colleague of mine (Jim Carpenter) made to me almost 30 years ago, when I was trying to figure out the best way to set the agenda for our monthly program review meeting with our principal customers. His comment was based on his experience in setting up the agenda, prior to my inheriting that responsibility when I was promoted:

"Stu: There are a thousand wrong ways to do this. So far, we have only tried ten of those"

Stu