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Author Topic: Johnson Ranger Output Power  (Read 25380 times)
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WA1QHQ
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« on: April 15, 2007, 03:52:48 PM »

I am going through the Ranger that I have owned for about 10 years and making sure everything is working properly. While I was in there I added WA1HLR's PTT mods. The rectifiers have been solid stated and new beefier filter caps added. This is one of the first Ranger 1s the model without fixed bias and grid block keying.

When I load the Ranger up to full output in CW mode I have measured the full load B+ on the final as 540VDC and the PA is drawing 150mA. So input power is 81W and I am getting 40W of output power. This seems kind of low, I would expect more like 50 to 55W of output. I have checked these numbers very carefully and am sure my plate current meter is accurate as well as the plate voltage. I calibrated the plate current meter by disconnecting the plate cap from the PA and substituting in a fixed load power resistor of the same value as the PA impedance about 3.4K and then making sure the panel meter agreed with the calculated value, luckily the Ranger measures plate current rather than cathode current. The screen voltage is 180VDC. I get the same output power on all bands, at least 160 thru 20 meters. I have varied the drive level and this doesn't make much of a difference, I have even increase the screen voltage and increased the grid leak bias to see if I could get better efficiency with no real improvement. I pulled out the clamp tube to see if this would make any difference and it did not. I went thru all the input and output tank components and resoldered all connections, no difference. I have also tried 3 different 6146As with no difference.

The first power meter I used was a Bird 43 with a 100W slug. I then confirmed the Bird was accurate by using an HP435 with 8481A detector running through a 40dB power pad that I calibrated on a network analyzer that I trust, the HP and Bird meters agreed with each other so I am confident in my output power measurement.

I also fired up the spectrum analyzer and ran the output of the TX through the power attenuator into the analyzer and the worst spur was 40dB down so the low power is not due to spurious emissions.

 I  also checked to see if any of the tank components were warming up and they were all running cool so all the wasted power is being disipated in the tube as best as I can tell, however the plate of the 6146 is not showing any color.

Am I trying to do the impossible is 50% efficiency normal for these rigs. If any of you have gone through this exercise and used an accurate power meter to make the measurement I would be interested in what you got and any suggestions for improving the PA efficiency.

Thanks,

Mark WA1QHQ
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w3jn
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« Reply #1 on: April 15, 2007, 04:01:18 PM »

 The shunts are notorious for going band and giving erroneous readings.  Too low drive might be a problem if the grid current shunt is bad.
 
Other than that, didjya check for harmonics?  You did mention spurs, but look further out.
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WA1QHQ
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« Reply #2 on: April 15, 2007, 05:07:29 PM »

The shunts are notorious for going band and giving erroneous readings.  Too low drive might be a problem if the grid current shunt is bad.
 
Other than that, didjya check for harmonics?  You did mention spurs, but look further out.

All shunts have been replaced and are right on the money and like I said I did play around with the grid drive level with no noticeable improvement.

I lumped harmonics in under the banner spurious emmisions although I guess that isn't really the true meaning, turns out the strongest non-fundamental output is the VFO fundamental leak thru. The Johnson has a pretty ugly waveform out of the VFO that is cleaned up into a sinewave by the two buffer stages otherwise it would be even worse.

Mark WA1QHQ
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WQ9E
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« Reply #3 on: April 15, 2007, 06:30:52 PM »

Mark,

Another possibility is the loading is too heavy, try reducing the loading somewhat and see if you can still reach the desired plate current at resonance with reasonable drive.  Some power is certainly being lost in the Pi network; I have read several articles noting the lowered output from the convenience of bandswitching a tapped coil versus using plug in coils for each range.  Class C efficiencies/output ratings sort of like car horsepower ratings in that the typical value stated is net at the "power producer" and ignores drivetrain (or in this case output network) losses.

Generally, I imagine very few rigs approach the theoretical class C output efficiencies and I vaguely recall an article I read years ago that compared the output of several contemporary class C rigs that were running about the same input but had very different power outputs.  As I recall, the "winner" was a WRL/Globe rig that used plug-in coils and the author calculated an output efficiency of under 70% as being the best of the bunch. 

73, Rodger WQ9E
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Rodger WQ9E
Steve - WB3HUZ
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« Reply #4 on: April 15, 2007, 06:39:39 PM »

True. But the efficiciency should be significantly more than 50%. In using a similar transmitter, an Eico 720, with a single 6146, I saw 40 watts output with no more than about 60 watts input.

Mark,

Another possibility is the loading is too heavy, try reducing the loading somewhat and see if you can still reach the desired plate current at resonance with reasonable drive.  Some power is certainly being lost in the Pi network; I have read several articles noting the lowered output from the convenience of bandswitching a tapped coil versus using plug in coils for each range.  Class C efficiencies/output ratings sort of like car horsepower ratings in that the typical value stated is net at the "power producer" and ignores drivetrain (or in this case output network) losses.

Generally, I imagine very few rigs approach the theoretical class C output efficiencies and I vaguely recall an article I read years ago that compared the output of several contemporary class C rigs that were running about the same input but had very different power outputs.  As I recall, the "winner" was a WRL/Globe rig that used plug-in coils and the author calculated an output efficiency of under 70% as being the best of the bunch. 

73, Rodger WQ9E
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The Slab Bacon
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« Reply #5 on: April 15, 2007, 08:24:38 PM »

Mark,
         It soundz like you have covered all of the bases except possibly one. What are you for a load?? Remember that a Bird 43 slug is calibrated for a 50 ohm load. If your dummy load has drifted in value, or you are checking it into the antenna, the bird wattmeter could not be reading accurately due to the differences in the load impedance. Especially if you are checking it into the antenns and it has a large reactive or reflective component.

If a 6146 was dissipating 41w, I would sure think that plate would be lookin kinda hot and uncomfortable. 

another thing to check is, what does the plate current do when you swing it out of resonance?? this will tell you a lot of what is going on. If you do not notice a large upswing when you swing out of resonance, you may not have enuff drive or some other problems.

Just my $.02 worth.
 
                                                                                 The Slab Bacon
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WA1GFZ
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« Reply #6 on: April 15, 2007, 10:42:00 PM »

Mark,
Try shorting a turn on the pi network coil and increase the Q. Another trick is tune up at the low end of the band then the high end to see if there is a difference in efficiency
Check your efficiency at lower power. I would think you have too much L if the efficiency goes up at lower power.  Try a meter in the plate lead to verify plate current.
Remember Screen current will be high if it is lightly loaded.
600 volts 125 ma with 250V on the screen should give you 52 watts out by my book.
540 should be a bit less efficiency.
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Steve - WB3HUZ
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« Reply #7 on: April 16, 2007, 09:29:04 AM »

Or you are tuned up on a harmonic.
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WA1QHQ
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« Reply #8 on: April 16, 2007, 01:04:55 PM »

Thanks for all your suggestions, I had some time this morning to play around with this a little more. I tried alot of combinations of grid drive and loading as per Rodgers suggestion and saw some gain doing this. I also raised the plate voltage to 580VDC loaded. I can now get 50W out with 144mA of plate current measured with my DVM inserted in line well before the plate chokes so no RF is getting in to it to mess up the readings. I also played around with the screen voltage raising it from 180 to 240VDC with no improvement in efficiency. So by my calculations I am getting about 60% efficiency. I am absolutely sure of my power meter accuracy and that my load is 50 Ohms since I was able to compare these with lab standards. I also am positive I'm not tuned up on a harmonic which is all but impossible to do with a ranger due to the limited range of the tuning controls and the fact that I checked the output on a spectrum analyzer.

I havn't heard from any other Ranger drivers out there as to what they typically are seeing for output power vs input power. The Ranger does have it's output tank widely spread about on the chassis with some fairly long interconnecting leads so maybe it is just an inherently poor design with higher than usual losses. I would be interested in comments from other Ranger drivers that may have gone down the same road I'm traveling on right now.

Mark  WA1QHQ
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Tom WA3KLR
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« Reply #9 on: April 16, 2007, 01:57:10 PM »

No Ranger here, but this is the RCA TT-5 Manual data for the 6146 plate-modulated:

ICAS typical operation
Plate voltage 600
Screen v. 150, from a series resistor of 56 k.
Grid 1 bias v. -87, from a resistor of 27 k.
Grid 1 current approx 3.4 ma.
Plate current 112 ma.
Power out approx. 52 Watts.

Mark, that is 77 % plate efficiency.

I would put the screen voltage back where it belongs.

What I am thinking of:

1.  I wonder about the quality of the screen bypass capacitor.
2.  PA grid circuit efficiency down (conduction angle too high?) - quality of the chokes, coupling caps, and resistor values there.  Gassy 6AQ5 clamp tube?  It hangs on the same grid bias node.

GL and 73 de Tom
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WU2D
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« Reply #10 on: April 18, 2007, 08:51:47 PM »

Mark,

Are you using a 6146 straight, 6146A, W or a B?

With the Ascratchy, I found that tuning for peak, was not as effective as the old DIP the plate, Decrease the Loading, Recheck the grid drive and repeat method. I actually could squeeze a good 20 more Watts out than using the tune for max smoke method. (with two 6146B's that is) 

Mike WU2D
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WA1GFZ
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« Reply #11 on: April 18, 2007, 09:00:22 PM »

I seem to remember if the dip and peak power are at different settings the tank LC ratio is off.
144 ma of palte current sounds a bit high.
Check the efficiency at each ends of the band for a clue.
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AB2EZ
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« Reply #12 on: April 19, 2007, 06:59:02 AM »

Hi Mark et. al.

I have what appears to be low effiency with my Ranger as well. I measured the usual things and tried various hypotheses based on the schematic... but no luck yet.

A few observations:

1. If the screen voltage is around 200 volts and the plate voltage is around 500 volts, then that means that the current flowing through R15 (screen current + clamper plate current) is around 10 ma. The "plate current" reading on the Ranger includes this additional current. So, the actual plate current is about 8% lower than the meter reading when the meter is reading 125 ma.

2. One thing I have been meaning to do, but have never actually done is to look at the signal on the grid of the clamp tube with a scope. The top of the 20 ohm shunt should be a good place. I wonder if RFC L7 is doing a good job of keeping RF off of the grid of the clamp tube... and if not, what the impact of a bypass capacitor might be.

3. It would also be interesting to put a small value resistor between the cathode of the 6146 and ground... and look at the plate current waveform with a scope. To achieve high efficiency, the plate current should be very low except during a small portion of the cycle when the grid voltage is near its peak. I.e., is the tube really running in Class C.

Best regards... if you find something, I'll be very interested.

Stu

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WA1QHQ
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« Reply #13 on: April 19, 2007, 10:35:09 AM »

I havn't had time to play with the ranger for the last couple of days but where I left it I am now up to 55W out with about 82W input power which gives me about 67% efficiency. Stu I did factor in the screen current when doing my plate current readings but good call on pointing this out, I would like to know what kind of efficiency your Ranger is giving you. Mike I have tried 6146, 6146B with same output for both. Frank the efficiency is the same high and low end of band and all bands from 160 to 20 and the point of max output does occur at the dip so that is working OK. My next test will be to run at lower input power and measure efficency to see if there is an improvement. My biggest improvement was to go easy on grid drive, 2.5mA is optimal, and then set loading for desired output, this seem to optimize the match into 50 Ohms and achieve best efficiency which is probably how the Johnson engineers had designed the plate tank to begin with. I did mess around with screen voltage but did not see any difference, I also pulled the clamp tube just in case it was influencing things but no difference there either. I am going to start to look into the actual plate tank components, RF choke and bypasses to see if they may be eating up some of the power, a Watt here and there begins to add up. I'll let you guys know what I find
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WA1GFZ
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« Reply #14 on: April 19, 2007, 10:46:14 AM »

Mark,
Look at the mechanical connections in the two pi network caps to see if they are making good contact. (rotor to case)
I'm running 215 screen volts with 760 plate volts V2 CDC. I plan to drop it about 50 volts though because the plate current at dip is a bit high at full loading C. Maybe the higher grid drive was reducing the conduction angle too much and the tank Q couldn't fill in the gap.
It would be interesting to look at the output waveform with higher grid current.
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WA1QHQ
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« Reply #15 on: April 19, 2007, 04:01:33 PM »

Mark,
Look at the mechanical connections in the two pi network caps to see if they are making good contact. (rotor to case)
I'm running 215 screen volts with 760 plate volts V2 CDC. I plan to drop it about 50 volts though because the plate current at dip is a bit high at full loading C. Maybe the higher grid drive was reducing the conduction angle too much and the tank Q couldn't fill in the gap.
It would be interesting to look at the output waveform with higher grid current.
Hi Frank,

I shot deoxit on all the wipers on the variables and they have always acted like they have good contact, no intermittent action when tuning. On your V2 you are really running those 6146s at a plate voltage where they sart to get real efficient, unfortunately the plate spacing on the Ranger tuning cap is a little tighter and I would be afraid of flashing it over on audio peaks, other wise a cap input filter on the high voltage supply would be the way to go. Also increasing grid drive should lower the plate current somewhat and allow you to load'er up a little more. It must be nice to have those roller inductors in there and big variable caps so that you can get the PA dialed right in.
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WA1GFZ
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« Reply #16 on: April 19, 2007, 04:15:54 PM »

Yes the tubes really like that voltage but the screen is a bit high. I want to get them back to about 160v. At full loading C I still get over 210 ma of plate current at dip. No color on the plates. I'm slowly moving stuff around to clean up the layout.
I'll have your problem when I start on the PDM V2 with an 813 stuffed into it.
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WU2D
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« Reply #17 on: April 19, 2007, 10:32:59 PM »

OK Mark,

Take the tube and squeeze it until you get every milliwatt out.

Mike


* MARKQHQ .jpg (271.18 KB, 1808x1676 - viewed 1069 times.)
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WA1GFZ
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« Reply #18 on: April 20, 2007, 09:28:58 AM »

Hey,
That's Mark behind the pickled egg plant hauler....
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WU2D
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CW is just a narrower version of AM


« Reply #19 on: April 20, 2007, 12:32:24 PM »

Frank,

If we could just get Mark to eat the magic pickeled Eggplant, he would not have to warm up by over dissipating 6146's! For some reason he thinks that a warm Dr. Pepper and a couple of cherry frosted pop tarts at 8:00 AM is normal. I have watched him put crazy things into his stomach over the past 3 years - why not the Eggplant?

Mark also called me and said that the picture made him look pudgy and I need to be more sensitive. Actually Mark is so cold that all of the blood from his lower extremities are pooled in his head, trying to keep his brain comfortable.

The Swiss hat sets off the picture. This of course is an subliminal plea for neutralization, which I don't think Johnson was too big on.

Mike WU2D
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« Reply #20 on: April 20, 2007, 07:58:19 PM »

Hey Q, my unmodified Ranger puts out 40 watts as measured by my low tech test equipment here. This De-Ranger is an old one also, no bias supply or grid block keying circuit. I don't even remember where I got this transmitter from. May have been from mini-qix some time ago. In any case, get the thing on the air for God's sake...............Larry
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WA1GFZ
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« Reply #21 on: April 20, 2007, 08:12:44 PM »

Yea mark fire up and yack with us losers.
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