Viking Valiant and the 6146 series

[WB2WIK]

As the owner of many Valiants and Rangers, I can assure you 100% any stuff about certain 6146's not neutralizing or not working is nonsense.

The ONLY time a 6146 will not sub is if the tube you bought is defective, or the equipment you are plugging it into is hypersensitive to impedances of the tube at very high frequencies. If you have unstable gear, like some Collins rigs that wrap feedback around multiple stages, or certain VHF transmitters, you might have to be brand specific.

My Ranger II's are just fine, even on six meters, as are my other Valiants and Rangers across HF all the way to ten meters with 6146B's or W's or any other flavor. I have never once had an issue.

73 Tom

I only had one Ranger and one Valiant so can't speak about those, much. But the KWM-2 seemed picky.

[W8JI]

I only had one Ranger and one Valiant so can't speak about those, much. But the KWM-2 seemed picky.

The KWM2 is picky, because Collins wrapped feedback around two stages. Anyone who understands tuned circuits and feedback probably scratches their head about the wisdom of that. While the intention was to add negative feedback, the problem comes in as circuits are off resonance. Now the tuned circuits add phase shift that is largely unpredictable.

Good designs that operate the system well within stability limits, like a Valiant, Ranger, or a dozen other rigs, have no problems at all.

[WB5WPA]

"Bandwidth has nothing to do with whether or not there's a clipper and low pass filter in the circuit. "

Ouch! That's going to leave a mark ... I'm not sure what the above means, however, in light of reality.

Here's some off-air video, and I think it tells the story by itself:




Jim de WB5WPA

[WB5WPA]

Let's see if this video will work ... not sure this one will work here:


http://www.ustream.tv/recorded/19103052

http://www.ustream.tv/recorded/19103052

Jim de WB5WPA

[K1ZJH]

Tom also said this:

And the bandwidth you refer to there definitely sounds like overmodulation.

Looks like over 100% negative modulation to me.

Pete

[W1GUH]

Tom also said this:

And the bandwidth you refer to there definitely sounds like overmodulation.

Looks like over 100% negative modulation to me.

Pete

I said that, too. Or are you referring to me? I'm Paul.

[WB5WPA]

Bandwidth has nothing to do with whether or not there's a clipper and low pass filter in the circuit. It has everything to do with the bandwidth with which the carrier is modulated and whether or not the transmitter is adjusted properly or not. I grant that there ARE some AM'ers who think HiFi is everything and modulate with audio up into the ultra-sonic region. Not a good thing. But there are AM'ers who keep he bandwidth of their modulation audio to something more appropriate to the AM window. And, the fact is, the audio from a stock Valient is just play thin and lousy. Good in the days of wall to wall signals on the band, for sure, but with today's conditions, there's no real need for that "full war mode" audio. It's so much more pleasant listening to an AM station like the op is in the shack with you. An AM signal with a bandwidth of 6 or 8 kc. that's not distorted, and eq'ed properly is a joy to listen to. And the bandwidth you refer to there definitely sounds like overmodulation. Don't you wish that all AM'ers would use a 'scope to adjust there modulation level? I sure do. There's a good chance that if someone is that over-the-top he'll be gently educated about adjusting his transmitter. Most of the AM'ers stick to very high standards, and that is just unacceptable in the window.

As far as I'm concerned, whenever I've heard, "Man you soon good with the BW set at 15 kc", I've thought what that really means is, OM, you sound good but there's no need for all that bandwidth. Might consider cutting back on it to something more appropriate for the AM window.

Cheers!

This might be what you are alluding to (the example in the video below) ... despite the use of an "Inovonics Audio Processor" ...

I have seen mention in more than one place that the Gates BC-1G et al series can be 'unstable' converted to a band as high as 75 meters without physical changes internally for the reason of 'extraneous coupling' leading to instability (self-generation of spurious RF products) ...

So, without further adieu, directly below is an example showing energy +-50 kHz (~ 100 kHz wide) from an AM transmitter ... it really gets broad with S's coming thru ... brief 'pulses' (like buckshot splatter) can be heard as low as 3.6 MHz (about 300 kHz lower) on 80 meters too ... this would be like a station on AM broadcast band at 820 kHz bothering stations on the dial up to 1120 kHz (very near the equivalent of WBAP at 820 affecting reception of KRLD at 1080 in the DFW area!):





By contrast this is how clean a broadcast station looks on the very same Icom radio (during the EAS test couple months back)!




Jim de WB5WPA

[K1ZJH]

I said that, too. Or are you referring to me? I'm Paul.

Hi Paul,

I was responding to Jim's post, not yours.

73

Pete

[W8JI]

Bandwidth is determined by multiple things, but the carrier can go to zero without splatter. It is a common myth that reaching zero causes splatter.

It is the slope of the waveform at any point that controls bandwidth, not if it reaches zero. I can have an amplitude-varying signal 100kHz wide that never reaches zero, and a signal 5 Hz wide that reaches and holds at zero.

There are two problems with old rigs causing wide bandwidth:

1.) The PA tube does not respond linearly to modulated voltage changes. This is a big problem with tetrodes.

2.) The audio stages have too much bandwidth.

Most old Ham rigs get really wide long before they reach zero on negative peaks for those reasons.

Leaving the filter in helps with number 2.

Optimizing screen voltage, loading, and audio level applied to the screen can help number 1 a great deal. It requires a fixed power level for the PA stage though, because the optimum screen to plate only occurs around one set of tuning conditions.

One thing that always bothered me is the claim a negative peak limiting diode would prevent splatter by removing or limiting negative peaks on the modulated voltage to the tube. It does no such thing, because going negative never was the cause of splatter. I can drive an anode negative during modulation peaks and not have any splatter at all, or stay well above zero and have terrible splatter.

The slope of the RF envelope as the tube cuts off is what causes the splatter, and that cutoff can occur while the anode is well into the positive range with tetrodes. Actually, it is the slope of the RF envelope at any point that determines bandwidth. People are seriously kidding themselves if they think a scope not reaching zero means they are not splattering, or that reaching zero means splatter.

73 Tom

[WB5WPA]

About a year ago I drove the bejeebers out of a signal generator just to get some AM 'distortion' and display it on a radio and on a lab spectrum analyzer ... the result is the quick video below.

Starting out, the carrier is on the far right hand side of the Icom display ... the carrier on the actual spectrum analyzer shown at about the 50 sec. point is in the center ... I widened out the span (250 kHz) on the spec and to give one an idea just how far out some of these products can be when SG is driven hard ... now, this is a signal generator used in this demo, not a rig, so the amount of 'splatter' aways from the carrier may be greater than any radio could produce ...

Things to note are how the sidebands 'grow' as modulation increases, and MANY sidebands are created at multiples of the modulating frequency (referred to as 3rd, 5th, 7th etc order IMD products on account of how 'mixing' in the PA plate stage mathematically 'relates' them)


http://www.youtube.com/watch?v=8pN9JI-lWps



I would LOVE to do the same demo using a real, live tube rig ... but I have nothing capable of high-level plate modulation like a Johnson Viking etc ...


Jim de WB5WPA

Caveats, again: This is not a rig, this was a signal generator and this was for captive, lab *demo* purposes into a dummy load only.

Merry Christmas all!