Johnson Viking Ranger odd behavior

[W6MQI]

 When I tune up my Ranger into dummy load I see 50 + watts with flat SWR. When I try to load into an antenna directly like my 13-30 Mhz log periodic or into a center fed dipole, with 450 ohm  ladder line coupled through an antenna coupler things go crazy. I'm seeing roughly 50 watts output but, the SWR is like 3 or 4:1 and no matter what adjustment is made to the antenna coupler SWR will not come down, same with the log periodic and I know the SWR is good on it. Geez I'am I having a brain fart here or what? I've never seen this before my Drakes perform just fine into the same loads, same antenna coupler.

Dave.

[W2VW]

Could you be loading up on a harmonic?

[KA2DZT]

Recheck all your connections and cables, one of them is probably bad or not making proper contact.  When you have problems like this it's not a mystery.  Look over everything you're doing and I'm sure you'll find the problem.

Fred

[WQ9E]

As W2VW noted, you may be tuned up on a harmonic.  Check that the exciter and final tuning knobs are indexed properly to their respective capacitors and that the settings you have on are reasonably close to those suggested in the tune up data table in the manual.

Several years ago I noticed odd behavior from one of my Johnson Valiant transmitters.  I have a few pieces of vintage gear in the "contest radio" room and I used my FT-1000MP to adjust my homebrew tuner on 160 for 1 to 1 SWR before switching over to the Valiant.  I noticed with the Valiant the SWR was higher than 1 to 1 and increased as I decreased the Valiant power output.  I looked at the output on my Tektronix spectrum analyzer and found this Valiant was developing close to 5 watts output on 170 Khz.  I traced it to a damaged grid choke which apparently was setting up some odd oscillation in the final, a new choke cured the problem.

[W6MQI]

W2VW Could you be loading up on a harmonic?

 Could be.. If I tune up on 40m using the VFO I see the oscillation, If I switch to crystal mode no more oscillation. Also checked other bands 160 ok, 80m ok, 40m osc. w/crystal ok, 20m osc, 15m osc on this band I can hear a high pitched tone come and go from what I think is the final PA while I tune "FINAL"  for a dip in plate current. The final tube is a 6146B I heard some where that 6146B's can cause oscillations and a 6146A would be the better choice is this true? Also did the Range originally come with the 6146A? One more thing on 15m if I dip the plate current in CW mode for a full dip then let up on the key I get power out just a few watts even though the key isn't depressed. Then if I de-tune using "FINAL"  power output stops until key is depressed as normal.

Dave

[W6MQI]

As W2VW noted, you may be tuned up on a harmonic.  Check that the exciter and final tuning knobs are indexed properly to their respective capacitors and that the settings you have on are reasonably close to those suggested in the tune up data table in the manual.

Several years ago I noticed odd behavior from one of my Johnson Valiant transmitters.  I have a few pieces of vintage gear in the "contest radio" room and I used my FT-1000MP to adjust my homebrew tuner on 160 for 1 to 1 SWR before switching over to the Valiant.  I noticed with the Valiant the SWR was higher than 1 to 1 and increased as I decreased the Valiant power output.  I looked at the output on my Tektronix spectrum analyzer and found this Valiant was developing close to 5 watts output on 170 Khz.  I traced it to a damaged grid choke which apparently was setting up some odd oscillation in the final, a new choke cured the problem.

Thanks I'll check the settings a little closer maybe I'm missing something.

Dave

[WQ9E]

Also did the Range originally come with the 6146A? One more thing on 15m if I dip the plate current in CW mode for a full dip then let up on the key I get power out just a few watts even though the key isn't depressed. Then if I de-tune using "FINAL"  power output stops until key is depressed as normal.

Dave

That output with the key up indicates you probably need to properly neutralize the final as per manual instructions.  As a quick check, maximum output should coincide with plate current dip.

Any of the 6146 family works fine in a Ranger.  My Ranger 1 is running a W and my Ranger 2 has a B installed.   The only place I have seen a problem with later version 6146 units is in some early Collins KWM-2 units and that was due to a marginal neutralizing circuit which was later corrected.  Heathkit/Johnson/B&W/etc. 6146 rigs work fine with any of the versions.  I don't mix various types in a final with parallel tubes and the only other caution is not to use an earlier version in a rig designed for the B version (like a lot of the later SSB transceivers) where the additional plate dissipation is needed based upon rated input and idle current.

[W6MQI]

Ok I went back and made sure that "BUFFER", and "FINAL" knobs and caps were set correctly. Next followed the tune up procedures checked BUFFER, and FINAL caps positions per manual. 160,80,40,20 went ok no oscillations SWR and PWR indications on meter were normal. 15,10 caused oscillation couldn't tune, dip in plate current didn't coincide with max power out which tells me neutralization but, maybe I'm missing something here the Ranger doesn't have a trimmer cap to neutralize the final how would I complete a neutralization? sorry for my ignorance on this I'm new the Ranger.

Dave

[WQ9E]

Dave,

I forgot Johnson considers the Ranger to be stable without neutralization.  One thing to check is if the final socket is riveted and depends on this for grounding (or if it was kit built but the screws/nuts for the final socket are loose).  With rivets you probably need to drill them out and replace with screws, nuts, and star washers.  Also check that the parasitic suppressor L8 is intact and the resistor is OK.

[W2VW]

Many people including myself have been able to use any variety of 6146 in a Ranger without any issues. Changing to an A may help expose the real problem though. Depends if it has different interelectrode capacitance than your existing tube.

The socket ground is one trouble point as reported.

[W6MQI]

 This was a kit built Ranger all sockets are screwed down along with everything else inside. I do see a little rust on one side of the 6146 tube socket mounting flange. Tonight when I get home from work I'll lift the socket and clean the area, also check the parasitic choke for value change or cracks. Output power on 15, 10 meters is real low especially on 10 never did check operation on 11 meters :-) If I do come across a 6146A tube just to be sure there are a group of three letters below 6146 some end with B, W, A I assume I should be looking for a group ending with an A to signify an A model 6146?
 
                  6146  6146
                  GWB   TFA

Dave

[KM1H]

While I have heard that some brand B's are problematic Ive not experienced it in any rig.

Your problem appears to be a parasitic that may or may not be enhanced by neutralization.

Since the Ranger is a kit Id check all grounds right back to the VFO and also see if beating a bit on the VFO and chassis generates any strange signals.

A 33 Ohm 1W carbon is fine for the suppressor and I would also suggest a 10 Ohm right at the socket grid pin and a 100 Ohm at the screen pin. Use a .01 disc with short leads right at both ends of the 100 Ohm.

The 6146 was designed to have the metal base grounded for stability. I do this with some hamfest surplus finger stock at both socket screws, regular spring brass or even galvanized steel should suffice as well.

Sloppy wiring will almost always cause stability problems. Short leads to grounds and RF connections, good soldering and non RF wiring dressed close to the chassis are important. Space RF leads as far from others as you can to minimize coupling while not lengthening.

Im about a week away from getting into a 3 pack of Rangers for customers should you still need assistance.

Then, if the 6146 still needs neutralization there are ways to do it but Id first try another tube.

Carl

[Pete, WA2CWA]

 If I do come across a 6146A tube just to be sure there are a group of three letters below 6146 some end with B, W, A I assume I should be looking for a group ending with an A to signify an A model 6146?
 
                  6146  6146
                  GWB   TFA

Dave

The tube would be labeled 6146A, 6146B, 6146W. etc. Don't worry about any "group lettering"

[W6MQI]

 Well I seem to have the Ranger working now. I went through the wiring around the 6146 tube socket did some rearranging, changed a bypass .005 cap, re-flowed all the solder joints, pulled the socket out and cleaned the chassis, socket, and all ground tabs. Ranger is putting out around 25+ watts CW on 15m, and 25+ watts CW on 10m I have no idea of the condition of the final tube being I purchased it at a garage sale. With a good tube what would be some good numbers to see for final power output in CW mode?

Carl wrote:
 A 33 Ohm 1W carbon is fine for the suppressor and I would also suggest a 10 Ohm right at the socket grid pin and a 100 Ohm at the screen pin. Use a .01 disc with short leads right at both ends of the 100 Ohm.

I assume the 10 ohm on the grid is in series with the 56 ohm choke that's on there now?

The 100 ohm is in series with the screen lead coming from the clamper plate, with bypass caps to ground? Also what would be the purpose of these mods?

 73,Dave

[AB2EZ]

"A 33 Ohm 1W carbon is fine for the suppressor and I would also suggest a 10 Ohm right at the socket grid pin and a 100 Ohm at the screen pin. Use a .01 disc with short leads right at both ends of the 100 Ohm."

Each 0.01uF capacitor has an impedance at 5000Hz (audio frequency) of -j3183 ohms. Two (essentially) in parallel will have an impedance at 5000 Hz of only -j1592 ohms.


Such a low impedance from screen to ground will attenuate the modulation of the screen voltage at higher audio frequencies of interest... and therefore limit the modulation frequency bandwidth of the Ranger.

I would suggest that the total screen bypass capacitance be limited to .002uF

Stu

[KM1H]

Hopefully nobody will be running a Ranger at 10kc total BW.

At 3kc the reactance of a pair of .01's is 2653 Ohms and if the response isnt what is wanted a pair of .005's should suffice with a total of 5305 Ohms. Even at 4kc it is still a relatively high 3979 Ohms.

While that rig uses a total of .004 uF in the B+ it wouldnt hurt to increase those a bit when the audio stages arent limiting the high end rolloff.

Carl

[W2VW]

And the screen's impedance this propose reactance appears in parallel with is ??

[AB2EZ]

Carl

In the example I gave... 5kHz is the audio modulation frequency. If the highest audio modulation frequency is 5kHz, then, for DSB AM, the total RF bandwidth (ignoring non-linear distortion products) is 10 kHz.

If you wanted to limit the total DSB AM RF bandwidth to 4kHz, as per your example... then the highest allowed audio frequency in the modulation would be 2kHz.

I don't think most Ranger users would be happy limiting their audio (modulation) bandwidth to 2 kHz.

Dave

The screen modulation resistance at carrier is approximately: (the screen voltage at carrier/the screen current at carrier). I.e. the change in screen voltage resulting from a change in screen current, that would occur at carrier, is approximately (but not exactly) equal to the screen voltage at carrier / the screen current at carrier.

For a 6146, as used in the Ranger, the screen voltage at carrier is approximately 150V, and the screen current at carrier is approximately 0.008A (as obtained from the 6146A specification sheet for class C plate modulated ICAS operation). Therefore the modulation resistance looking into the screen of the 6146 (at carrier) is approximately 18,750 ohms.

To calculate the modulation bandwidth, one has to consider the parallel combination of the modulation resistance (18,750 ohms), and the resistor between the plate supply and the screen (30,000 ohms). The parallel combination is 11,538 ohms

If one uses two (2) 0.01uF screen RF bypass capacitors in parallel, then the modulation bandwidth (3dB down) would be the audio frequency where the reactance of those capacitors is equal to -j11538 0hms.

The corresponding frequency is 690 Hz.

Therefore using a pair of 0.01uF capacitors to bypass the screen of the 6146 in the Ranger, would result in a 3dB modulation rolloff at 690Hz.
If the total screen bypass capacitance is .002uF, then the 3dB modulation bandwidth is 6900 Hz.

Stu