Johnson Ranger Audio Mod

[n8fvj]

The Johnson Ranger and Ranger II is a very cool AM transmitter and manageable at 40lbs. A little low power, but an amp makes it a heavy hitter. High level modulation and a built-in VFO. There are a lot of audio mods for the Johnson Ranger, but do not address the real Johnson Ranger audio issue. It is the tiny modulation transformer. It looks about 25 watts of transformer. It is as small as I ever seen in a transmitter with carrier power of 40 watts and likely even a 25 watt carrier transmitter has larger mod iron.

Renown WA1HLR could not have said it better: 'The only factor limiting deep bass response is the undersized modulation transformer. A better transformer could be used but much relocating of components to be done. I recently picked up a Triad M-15 30 Watt modulation transformer for the Ranger which I was able to shoe-horn in place of the stock unit using removal of meter shield can and trimming the meter bolts. The M-15 fit like a glove. The performance was unbelievable. Frequency response from 50 - 10,000 Hz and the ability to modulate 180% positive using this transformer in a mild step-up mode.'

Anyways, Heyboer Transformer in MI makes a replacement upgraded mod transformer for the Ranger. It is HTS-13267. The forementioned Triad M-15 mod transformer is about unobtanium plus removing the meter shield and trimming the meter bolts is not wise. The new Heyboer mod transformer replaces the 10HY choke and the new choke is a Hammond 159S that goes where the original mod transformer is located. The new 4HY choke installs on an angle, but just fits. It is only 4HY thus increase the 10uF HV capacitor after that original choke to a minimum of 50uF. 100uF would be better. It will have a better AC ripple spec too.

The new mod transformer is the size of the original 10HY choke and is made with M6 audio laminations thus has plenty of low frequency audio for the size. The stock Johnson Ranger mod transformer can only provide a low frequency of 400 Hz audio at 95% modulation. The new mod transformer provides 100 Hz at 100% modulation (note I have .02uF 12AX7 plate capacitors installed). It cost $150 a few years ago. The old choke and mod transformer can be sold to lower overall cost. The new transformer has color coded wires for no fuss install.

Perform the usual audio mods with new audio coupling capacitors, change 12AU7 to 6CG7 with the filament wiring change, remove the feedback loop and install a lower gain 12AV7 for the 12AX7.
I doubt anyone has ever installed a better Mod transformer inside the Johnson Ranger.

While on the subject of modulation, the modulator tube replacement. The original 1614 tubes are rated at 585 volts plate and no one reported a tube arc. The Ranger uses per manual 500 volts on the modulator tube plates. Use either Sovtek 6L6WXT+ 500 volt tubes or 6550 600 volt tubes. The 1614 produce 45 watts or enough power for 100% modulation. Best 1614 tube price is Findatube in Ohio at $21 each. Don't forget changing 12AU7 to 6CG7 with filament wiring change for best audio and if removing feedback change 12AX7 to 12AV7 to lower gain.

The Johnson Ranger design. Unlike a Viking II, Johnson purposely designed the Ranger for 400Hz and higher audio. It is evident upon the tiny modulation transformer and capacitor C52 of 500pF in the audio chain. The reason was the Ranger lower power (vs the Viking II) with the high frequency audio would punch thru better on the air even if the low frequency response is missing. Using an amp on the Ranger makes the high frequency only response not required with full body audio in a Heyboer modified Ranger.

BTW- this modified Ranger is for use with a legal limit amp. To be heard operating barefoot you may want the 400Hz punchy audio due to the Rangers low power output.

[n8fvj]

New Heyboer mod transformer installed.

[n8fvj]

Tiny Johnson Mod transformer. Weight is 2 Lbs. I posted the mod two other forums and many either do not believe the 400Hz Ranger lowest frequency or some just attacked (guessing I am not well known). Every other 50 watt output class transmitter with high level modulation (Gonset G-76 for example) uses at least a 4 Lb mod transformer. Johnson used a .005 uF cap on first section of the 12AX7 audio tube plate for a low of 400Hz. Change to a .02uF for 100Hz response.
2 Lb Ranger mod transformer vs 6 Lb Heyboer mod transformer- errr, no brainer folks.

[n8fvj]

New Hammond choke installed. This is a 4 HY 225ma choke. The Ranger idles at 150ma when dead keyed and peaks with peak signal about 280ma that includes modulator peak current. The choke always maintained critical 'crit' keeping the voltage correct, but likely is providing only about a little over 3 HY at peak current. The resistance of this choke is 65 ohms or about same as the original 10 HY choke thus voltage is same. However, use at least 50uF capacitance on the HV capacitor (twoo 100uF 450 volt in series) vs the stock 10uF. It works well.

[n8fvj]

100Hz tone into Johnson Ranger with Heyboer mod transformer. A little over 100% modulation. Sorry for somewhat askew scope image.

[W3SLK]

N8FVJ said:

Sorry for somewhat askew scope image.

That's because you have your choke 'askew!'

[n8fvj]

N8FVJ said:

Sorry for somewhat askew scope image.

That's because you have your choke 'askew!'

New choke just barely fit.

[n8fvj]

BTW- you can achieve even better sounding audio beyond the Heyboer mod transformer in the Johnson Ranger. You have to have strong signal to hear the quality audio though. First, replace the 500pF cap on 12AX7 plate with .02uF polypropylene cap and keep the .02uF cap on 12AX7 output to the 12AU7 with polypropylene capacitors. Change 10uF on 12AX7 cathodes to 25uF.
 
Replace existing 12AX7 tube with a JJ E83CC (12AX7) frame grid tube. The JJ E83CC audio is of the best audiophile quality I heard in a stereo tube amp and NOS tubes do not sound better. Not even a $200 Mullard long plate 12AX7 outperforms the JJ E83CC. The Tubestore has best price.
 
Next, clip wire jumper on pins 4 & 5 on the 12AU7 tube socket driving the driver transformer in the modulator section. A 12AU7 is very poor sounding in any brand. Connect filament wire from pin 9 to pins 4 or 5 (whatever pin does not have a wire connected) on the 12AU7 tube socket. Install a Dumont 6CG7 (EIA 158 code) tube or rare if you can find one Raytheon 6CG7 black plate tube (EIA 280 code). A CBS/Hytron 6CG7 black plate or Hytron 6CG7 black plate is also almost as good. RCA 6CG7 top getter black plate are ok if the other tubes cannot be found. Again the Dumont and Raytheon tubes excel in a stereo audio amp. Other 6CG7 tubes are not as good sounding. A quality microphone is needed that performs to 100Hz.

Note- I am not a believer in removing the mod transformer feedback winding connection. If you disconnect the feedback winding, I read change the 12AX7 to a 12AV7. Change cathode resistor to 120 ohms each section, not sure of plate resistor change. Although mentioned by others I do not recommend the 12AV7. It would likely be better to use a lower gain 5751 tube that does not require any circuit changes. Additionally, there is a modulation feedback mod that is superior changing the feedback from the 12AU7 to the second section of the 12AX7 that is superior. It is shown in Technical forum under 'Best Mods for Johnson Ranger Upgrade' by me. I would not remove the feedback.

The Johnson Panger performs well enough with the stock mod transformer and was purposely designed to produce punchy audio of say 300 Hz (70% mod) to 4kHz. This modulation transformer mod is for AM broadcast like quality audio limited to about 6 KHz with the Ranger mods listed in the Technical forum under 'Best Mods for Johnson Ranger Upgrade'.

I Edit the 12AV7 paragraph.

[DMOD]

... If you disconnect the feedback winding, change the 12AX7 to a 12AV7. Any older 1950s black plate 12AV7 sounds ok.

What was your bias resistor value and cathode bias voltage when you changed to a 12AV7 with 320V on the plate?

Most tubes have black plates for a specific reason.

[n8fvj]

... If you disconnect the feedback winding, change the 12AX7 to a 12AV7. Any older 1950s black plate 12AV7 sounds ok.

What was your bias resistor value and cathode bias voltage when you changed to a 12AV7?

I read without the feedback loop the 12AX7 provides too much gain. The 12AV7 was recommended to replace the 12AV7. But did not specify grid or cathode resistor changes. However, the tube plate current draw is much higher in the 12AV7. At 100 volts plate a 120 ohm cathode resistor for each section is specified per tube datasheet. As for a bias resistor I do not understand what you are asking for. A grid to ground resistor should be 3.3 meg ohm in first section for a D-104 mic.

Read the 12AX7 to 12AV7 mod here: http://amfone.net/Amforum/index.php?topic=47674.0

[DMOD]

... If you disconnect the feedback winding, change the 12AX7 to a 12AV7. Any older 1950s black plate 12AV7 sounds ok.

What was your bias resistor value and cathode bias voltage when you changed to a 12AV7?

I read without the feedback loop the 12AX7 provides too much gain. The 12AV7 was recommended to replace the 12AV7. But did not specify grid or cathode resistor changes. However, the tube plate current draw is much higher in the 12AV7. At 100 volts plate a 120 ohm cathode resistor is specified per tube datasheet. As for a bias resistor I do not understand what you are asking for. A grid to ground resistor should be 3.3 meg ohm in first section for a D-104 mic and likely 470K in second grid position.

I have never heard of this mod. The mic gain control R21 gives the 12AU7A the correct amount of peak-to-peak audio voltage it needs to drive the interstage transformer T3.

SO you have never used or tested this mod?

Any time you change tube types you have to examine the tube curves and determine the operating points via the tube characteristic curves.

This means you have to change the cathode and plate resistors.

The cathode resistor determines the bias on a tube since a positive voltage at the cathode sets the respective control grid voltage bias point. For example, if the triode tube curves say you need a -1 volt grid bias at a tube current of 0.5 mA, then that cathode resistor value needs to be 2.0k or 2.2k for the closest standard value.

[n8fvj]

... If you disconnect the feedback winding, change the 12AX7 to a 12AV7. Any older 1950s black plate 12AV7 sounds ok.

What was your bias resistor value and cathode bias voltage when you changed to a 12AV7?

I read without the feedback loop the 12AX7 provides too much gain. The 12AV7 was recommended to replace the 12AV7. But did not specify grid or cathode resistor changes. However, the tube plate current draw is much higher in the 12AV7. At 100 volts plate a 120 ohm cathode resistor is specified per tube datasheet. As for a bias resistor I do not understand what you are asking for. A grid to ground resistor should be 3.3 meg ohm in first section for a D-104 mic and likely 470K in second grid position.

I have never heard of this mod. The mic gain control R21 gives the 12AU7A the correct amount of peak-to-peak audio voltage it needs to drive the interstage transformer T3.

SO you have never used or tested this mod?

Any time you change tube types you have to examine the tube curves and determine the operating points via the tube characteristic curves.

This means you have to change the cathode and plate resistors.

The cathode resistor determines the bias on a tube since a positive voltage at the cathode sets the control grid bias point. For example, if the triode tube curves say you need a -1 volt grid bias at a tube current of 0.5 mA, then that cathode resistor value needs to be 2.0k or 2.2k for the closest standard value.

No, I never did this mod, but thought worthy of mentioning it as others mentioned it. Rethinking this, I recommend a lower gain 5751 tube that needs no resistor changes.

[DMOD]

... If you disconnect the feedback winding, change the 12AX7 to a 12AV7. Any older 1950s black plate 12AV7 sounds ok.

What was your bias resistor value and cathode bias voltage when you changed to a 12AV7?

I read without the feedback loop the 12AX7 provides too much gain. The 12AV7 was recommended to replace the 12AV7. But did not specify grid or cathode resistor changes. However, the tube plate current draw is much higher in the 12AV7. At 100 volts plate a 120 ohm cathode resistor is specified per tube datasheet. As for a bias resistor I do not understand what you are asking for. A grid to ground resistor should be 3.3 meg ohm in first section for a D-104 mic and likely 470K in second grid position.

I have never heard of this mod. The mic gain control R21 gives the 12AU7A the correct amount of peak-to-peak audio voltage it needs to drive the interstage transformer T3.

SO you have never used or tested this mod?

Any time you change tube types you have to examine the tube curves and determine the operating points via the tube characteristic curves.

This means you have to change the cathode and plate resistors.

The cathode resistor determines the bias on a tube since a positive voltage at the cathode sets the control grid bias point. For example, if the triode tube curves say you need a -1 volt grid bias at a tube current of 0.5 mA, then that cathode resistor value needs to be 2.0k or 2.2k for the closest standard value.

No, I never did this mod, but thought worthy of mentioning it as others mentioned it. Rethinking this, I recommend a lower gain 5751 tube that needs no resistor changes.

To lower gain to about 1/2 (Av = 1700) for the Speech Amplifier stage with a 5751 you would need to make at least 5 component changes in order to place the 5751 in its linear range:

The original gain of the ranger Speech Amplifier stage was about 3300.

[n8fvj]

... If you disconnect the feedback winding, change the 12AX7 to a 12AV7. Any older 1950s black plate 12AV7 sounds ok.

What was your bias resistor value and cathode bias voltage when you changed to a 12AV7?

I read without the feedback loop the 12AX7 provides too much gain. The 12AV7 was recommended to replace the 12AV7. But did not specify grid or cathode resistor changes. However, the tube plate current draw is much higher in the 12AV7. At 100 volts plate a 120 ohm cathode resistor is specified per tube datasheet. As for a bias resistor I do not understand what you are asking for. A grid to ground resistor should be 3.3 meg ohm in first section for a D-104 mic and likely 470K in second grid position.

I have never heard of this mod. The mic gain control R21 gives the 12AU7A the correct amount of peak-to-peak audio voltage it needs to drive the interstage transformer T3.

SO you have never used or tested this mod?

Any time you change tube types you have to examine the tube curves and determine the operating points via the tube characteristic curves.

This means you have to change the cathode and plate resistors.

The cathode resistor determines the bias on a tube since a positive voltage at the cathode sets the control grid bias point. For example, if the triode tube curves say you need a -1 volt grid bias at a tube current of 0.5 mA, then that cathode resistor value needs to be 2.0k or 2.2k for the closest standard value.

No, I never did this mod, but thought worthy of mentioning it as others mentioned it. Rethinking this, I recommend a lower gain 5751 tube that needs no resistor changes.

To lower gain to about 1/2 (Av = 1700) for the Speech Amplifier stage with a 5751 you would need to make at least 5 component changes in order to place the 5751 in its linear range:

The original gain of the ranger Speech Amplifier stage was about 3300.

Here is a 5751 spec: Class A 100   Volt plate, -1.0 Grid, 0.8ma current, 58K plate resistance, 1.2 S.
Here is 12AX7  spec: Class A 100 volt plate, -1.0 grid, 0.5ma current, 80K plate resistance, 1.25 S.

I would lower gain 30% not 50% with the operating parameters above. IMO no component changes are required. In fact, looking at the plate curves does not suggest linearity is an issue. Tube gain and plate resistance:

 Tube   Gain Plate Resistance   
12AX7 100   62.5kΩ
5751     70      58kΩ

If one wants to calculate the best plate and cathode resistors I suggest this 19 pages of reading on this site: https://www.tubecad.com/articles_2003/Grounded_Cathode_Amplifier/page10.html

[DMOD]

Here is a 5751 spec: Class A 100   Volt plate, -1.0 Grid, 0.8ma current, 58K plate resistance, 1.2 S.
Here is 12AX7  spec: Class A 100 volt plate, -1.0 grid, 0.5ma current, 80K plate resistance, 1.25 S.

I would lower gain 30% not 50% with the operating parameters above. IMO no component changes are required. In fact, looking at the plate curves does not suggest linearity is an issue. Tube gain and plate resistance:

 Tube   Gain Plate Resistance   
12AX7 100   62.5kΩ
5751     70      58kΩ

If one wants to calculate the best plate and cathode resistors I suggest this 19 pages of reading on this site: https://www.tubecad.com/articles_2003/Grounded_Cathode_Amplifier/page10.html

Here were my values that were fed into the tube design/simulator program derived from the actual curves and curve intercepts. I think you are neglecting the curve data on page 5 of the 5751 Tube Specifications.

You only get a fraction of the gain of any tube when used in an actual circuit. The Mu figure DOES NOT equal the voltage gain you get from an actual circuit. The actual voltage gain for a common cathode triode stage is Av = (Mu*RL)/((Rp+RL) + (Mu+1)*Rk)).

Type 5751 Dual Triode Medium-High Mu Gain Stage 1
Mu = 65; % From Data Curves at Plate Current of 1.25 mA for Linear Operation
Vs = 300V % Source Voltage
Vp = 75V  % Voltage on Plate after Drop across RL; Vp = 75V from tube curves
IpandIk = 1.25 mA % From curves in Linear Region
Rp = 70e3; % Plate Resistance From Tube Curves for Ip
VKBIAS = 0.5V % From Curve Intersects
Computed Values
RL = 180k % Load Resistance from Plate to Vs
Rk = 390 ohms
Zo = 50.4k

AVG1StageUnBy = (Mu*RL)/((Rp+RL) + (Mu+1)*Rk)) = 42 unbypassed, ~ 50 Bypassed with 33uF


Type 5751 Dual Triode Medium-High Mu Gain Stage 2
Mu = 65; % From Data Curves at Plate Current of 1.25 mA for Linear Operation
Vs = 300V % Source Voltage
Vp = 100V  % Voltage on Plate after Drop across RL; Vp = 100V from tube curves
IpandIk = 1.25 mA % From curves in Linear Region
Rp = 70e3; % Plate Resistance From Tube Curves for Ip
VKBIAS = 0.75V % From Curve Intersects
Computed Values
RL = 150k % Load Resistance from Plate to Vs
Rk = 620 ohms
Zo = 49.5k

AVG1StageUnBy = (Mu*RL)/((Rp+RL) + (Mu+1)*Rk)) = 38 unbypassed,

What tube equations did you use, and how much actual gain reduction do you need? You haven't told us that via any equations or anything else.

What do you think is the primary purpose of the mic gain potentiometer R21 in the Ranger circuit?

I suggest you study, Hollow-State Design by Grayson Evans for a good introductory text on tube circuit design.

[n8fvj]

DMOD, I did not use any tube evaluations. It is generally accepted a 5751 can sub for a 12AX7. Fact is the 12AX7 in the Johnson Ranger is not set up in the most linear part of the 12AX7 itself. I may change the circuit values. I am using a 12AX7 as I do not believe disconnecting the feedback is a good idea and I am changing the feedback from the 12AU7 to the 12AX7 second section. One can use a 12AX7 with no feedback, but the mic gain control will never be past 9 o'clock on the potentiometer.

Frankly you are making the 12AX7 to 5751 tube swap a big deal and it is not.

BTW- back to the original 12AX7 to 12AV7 mod. I posted the 12AX7 to 12AV7 mod due to this post. However, the resistors must be changed for a 12AV7 and the post did not detail the necessary resistor change. Here:

'Re: WA1HLR "LITE audio mods" for the Ranger, 2022
« Reply #2 on: May 24, 2023, 09:28:59 AM »
Reply with quoteQuote
Unofficial UPDATE from WA1HLR.

Tim recently spent a month "doing up a Ranger" for Pedro AJ4OO and has made a few minor refinements to his "lite" mods. Per Tim 'The most significant refinement is substituting a 12AV7 for the 12AX7 speech amp tube. Tim found that the lower gain 12AV7 improved headroom and reduced the possibility of self oscillation in the modulator'.

Per Tim, 'I tried it (12AX7 to 12AV7) and can report markedly better performance. As a result, the 12AX7 simply had way too much gain, and often produced distortion on peaks unless the audio gain was throttled back to between "1" and "2". The 12AV7 cures all of that and lets the audio gain control operate within a more reasonable range'.

Entire topic here: http://amfone.net/Amforum/index.php?topic=47674.0

[DMOD]

Frankly you are making the 12AX7 to 5751 tube swap a big deal and it is not.

No, just trying to provide accurate technical information and at the same time linearizing the speech amp.

A very simple way to reduce gain is to reduce the "load" resistance on each gain stage.

In most transmitters the mic gain potentiometer is a 1 Meg or so pot. A 1 Meg pot load allows the stage gain to approach the ideal gain according to the gain equations.

In the schematic below, the first stage gain is reduced by placing a 390k to 470k (Rnew) across the 1 Meg pot R21 and increasing C52* to .01uF to retain low audio frequency components. No tube change is needed.

Also included in the schematic below page 2 is a Solid stated and regulated Modulator bias circuit.  

[n8fvj]

Frankly you are making the 12AX7 to 5751 tube swap a big deal and it is not.

No, just trying to provide accurate technical information and at the same time linearizing the speech amp.

A very simple way to reduce gain is to reduce the "load" resistance on each gain stage.

In most transmitters the mic gain potentiometer is a 1 Meg or so pot. A 1 Meg pot load allows the stage gain to approach the ideal gain according to the gain equations.

In the schematic below, the first stage gain is reduced by placing a 390k to 470k (Rnew) across the 1 Meg pot R21 and increasing C52* to .01uF to retain low audio frequency components. No tube change is needed.

Also included in the schematic below page 2 is a Solid stated and regulated Modulator bias circuit.  

Your skills are undeniable.

[n8fvj]

BTW DMOD, instead of stating the factory stock 12ax7 resistors for the 12AV7 are incorrect, why not post the 12AV7 resistors changes to help others with this mod. No doubt the 12AX7 resistors are way off for a 12AV7 to perform.

[DMOD]

BTW DMOD, instead of stating the factory stock 12ax7 resistors for the 12AV7 are incorrect, why not post the 12AV7 resistors changes to help others with this mod. No doubt the 12AX7 resistors are way off for a 12AV7 to perform.

The 12AV7 is NOT a good solution because it takes 10X the plate current of a 12AX7A to get it to operate linearly.

The solution I posted above is the simplest solution for reducing gain and not changing tubes.