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Author Topic: 30L-1 RF INPUT CABLE  (Read 27864 times)
K9AXN
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« Reply #45 on: July 29, 2016, 03:35:48 PM »

One other point Tom,

I stated explicitly that over neutralizing a grounded grid amp could provide negative feedback and under neutralizing for grid driven amps.  You will note that some grounded grid amps don't even use a variable neutralizing cap with the transformer.  That must tell you about the phase issue.

Heavily over or under neutralizing at some point will obviously cause instability in either amplified but for different reasons.  

Careful how you read things.

Kindest regards Jim
« Last Edit: August 07, 2016, 06:40:07 PM by K9AXN » Logged
WA1RNE
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« Reply #46 on: August 02, 2016, 09:42:47 AM »

Not sure if anyone has considered a couple other potential design factors which could influence stability of the 30L1.


 Good design of a grounded grid amplifier requires good shielding from between the input and output circuits - without which will certainly exacerbate neutralization requirements.

 Looking at Figure 6-1 of the 7th edition of the manual you will note the following:

 -  All 4 tubes are recessed about 1 inch into the chassis, creating a significant clearance between the input and output sections of the chassis. (there has to be a gap to allow clearance for the tube base and envelope)

 - The input/output changeover relay K1 is mounted approximately 1 to 1.5 inches from tube XV2

 - The output connector J4 has to be less than 1 inch from the grid connection for tube XV3


 From what I'm seeing, the layout of this amplifier is far from "ultimate" in terms of input/output isolation, but unfortunately changes to the mechanical design would not be an easy task as the amplifier is very compact and has no bottom chassis area to utilize.

 Thoughts?


...WA1RNE


 
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W9NVN
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« Reply #47 on: August 05, 2016, 11:29:37 PM »

I believe N6QWP got his answer with in a post or two.
My point is I feel Mr. Bruene and the Collins radio company were being disingenuous in sending out a 20.5 ft cable to work on all bands plus mars frequencies! When I first corresponded with Mr Bruene he was not forth coming with his design error, however, after a few good banters he sent me a letter with his signature stating more than one cable would be required! So what does this all mean? Well it is axiomatic, anyone using a Collins S-line/KWM-2/30L1, 30S-1 had phase distortion, except for the band the cable was cut for. And Jim, do not try to complicate this, in fact remember what you said to Pete, (How does that cable length work out for all bands??? )You new the answer!!!!
  Jim, for a short time you were humble and contrite, after your banter with Tom, I respectfully conclude you are unrepentant and incorrigible...
Now let us look at this comment you made, Jim;Regarding Tom: ( He is a far better writer than I and can convey information far more clearly than I can.  He also has the courage to write what he knows will be scrutinized and possibly be torn to pieces.  I believe him to be technically competent and his mantra (Personalities have nothing to do with technical accuracy or correctness, or being worthless in all areas because they make a few mistakes) is as philosophically good as it gets.  He simply does not listen well and tends to say ( you just don't understand).  There are times when he simply does not understand and I have those moments as well). The answer is in your first sentence!! In a nice way you need to look in the mirror. And why don't you tell I am a good writer too!? You over complicate most of the time..
 WA1RNE;( From what I'm seeing, the layout of this amplifier is far from "ultimate" in terms of input/output isolation, but unfortunately changes to the mechanical design would not be an easy task as the amplifier is very compact and has no bottom chassis area to utilize.) My comment is I agree there are design faults, I traded my 30L-1 long ago so I cannot comment on input/output isolation, I do not have the diagram. One problem I notice is the horizontal mounting of the 4- 811A tubes, as the  modern 811A are not the same as the old tubes relative to the way the plates are located.
I believe that was the only amp with horizontal mounting, the rest of the 811A amps used vertical mounting.
The best designed 811A amp IMHO is the Ameritron 811H..As I see it, they are using a modern design, nice layout, nice meters, and not over priced!
Plus no cable issue and lack of phase distortion...VY 73 W9NVN
« Last Edit: August 06, 2016, 12:36:57 AM by W9NVN » Logged
G3RZP
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« Reply #48 on: August 06, 2016, 01:30:27 AM »

In fairness to the designer way back when, the original 811 and 811A data sheets from Amperex and RCA do state that for horizontal mounting, pins 1 and 4 should be in the vertical plane. If modern 811s don't meet that, it's because strictly speaking, they don't meet the total 811 specification.

To my mind, the big design faults are the lack of neutralising and a plate feed choke which is far too small - it has the best part of an amp of RF in it on 80m.
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W9NVN
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« Reply #49 on: August 06, 2016, 02:37:15 AM »

In fairness to the designer way back when, the original 811 and 811A data sheets from Amperex and RCA do state that for horizontal mounting, pins 1 and 4 should be in the vertical plane. If modern 811s don't meet that, it's because strictly speaking, they don't meet the total 811 specification.

G3RZP, Thank you for making my point for me, quite eloquently I might add. Yes you correct the designers of the current 811A did indeed miss that
specification. I believe some of the Russian 811A did meet that spec, however a moot point since they are no longer made there. VY 73 W9NVN
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K9AXN
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« Reply #50 on: August 06, 2016, 12:08:14 PM »

 Jim, for a short time you were humble and contrite, after your banter with Tom, I respectfully conclude you are unrepentant and incorrigible...

Mike,

Can't ever remember anyone saying I was Humble or contrite.

Time or two was called dashingly handsome and modest but that came from a neighbor lady that wanted to borrow my car.  She also said that I was
incorrigible because I wouldn't chase the raccoons out of her attic.  You ever see one of those things up close when they're PO'd?

Don't believe I've ever seen a 76 year old fellow looking dashingly handsome --- including this guy. 

Keep your powder dry , have a super day, and cheer up pal.

Kindest regards Jim
« Last Edit: October 11, 2016, 08:53:18 AM by K9AXN » Logged
W9NVN
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« Reply #51 on: August 06, 2016, 01:35:37 PM »


Mike,

Can't ever remember anyone saying I was Humble or contrite.

Jim, what can I say, there is a first time for everything. HI HI !!!  Have a nice weekend in 9 land, I wish you the best old timer.
 
                             VY 73 W9NVN
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G3RZP
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« Reply #52 on: August 06, 2016, 03:40:49 PM »

Jim,

There's a possibly applicable rhyme....

I love me and I love me
And only me do I adore
And the knowledge that I love me
Only makes me love me more.

To which I add RZP's law; "If you disagree with me, you are wrong"


73

Peter G3RZP
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K9AXN
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« Reply #53 on: August 06, 2016, 05:02:24 PM »

Easy does it Pete was totally in Jest.

Some folks are simply humor challenged.  Living in a dark linen closet with a worn out keyboard isn't a good emotional environment.  I would encourage you to get out and about with people who embrace and live life to the extent that it brings purpose, happiness, understanding, and maybe a bit of humor.

Try not to take yourself too seriously.

Cheers Jim


« Last Edit: October 11, 2016, 11:35:37 AM by K9AXN » Logged
W8JI
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« Reply #54 on: August 07, 2016, 12:12:20 PM »

Not sure if anyone has considered a couple other potential design factors which could influence stability of the 30L1.


 Good design of a grounded grid amplifier requires good shielding from between the input and output circuits - without which will certainly exacerbate neutralization requirements.

 Looking at Figure 6-1 of the 7th edition of the manual you will note the following:

 -  All 4 tubes are recessed about 1 inch into the chassis, creating a significant clearance between the input and output sections of the chassis. (there has to be a gap to allow clearance for the tube base and envelope)

 - The input/output changeover relay K1 is mounted approximately 1 to 1.5 inches from tube XV2

 - The output connector J4 has to be less than 1 inch from the grid connection for tube XV3


 From what I'm seeing, the layout of this amplifier is far from "ultimate" in terms of input/output isolation, but unfortunately changes to the mechanical design would not be an easy task as the amplifier is very compact and has no bottom chassis area to utilize.

 Thoughts?


...WA1RNE


 

The overwhelming issue is the very high feed through capacitance of the 811 style tube structure. There is a very clear path inside the tube between anode and filament.

We have to set aside the ~100 MHz parasitic issue, which is caused by the grid's single thin wire that is relatively long. That's a totally different issue unrelated to the HF stability issue, so I'll set the 100MHz or higher stuff aside and focus on the HF stability that affects IMD and near-frequency spurious.   

Although I have not measured a 30L1 layout in detail, I have measured dozens of other layouts in detail. Intuitively, I would say any effects from the layout are meaningless. Much poorer shielding is meaningless, so we can logically assume the 30L1 layout is fine. 

I have run stability tests on the 30L1 and it is not good. It is very similar to the Dentron 4x 811 and 4x 572B series as far as results. It can be stable with a proper input impedance and heavy enough loading. 

The problem comes back to the tubes. In a perfect test fixture, two 811's are almost 100% unconditionally stable. The plate load impedance has to be very high and the input impedance as seen at the cathode high to have oscillation. Common operation is far from the point of instability or increases in IMD.

Three tubes is getting close to problem.

Four are just no good. They are too close to the edge.

Contrary to what someone keeps saying, the feed through capacitance has to be nulled out. It cannot be "over compensated". The issue is the high tank Q dominates the anode current. Energy in the tank is 10-20 times energy contributed by the "tug" of the tube on the tank. Consequentially, tank settings shift feedback phase significantly. The only way to eliminate the tank's effect on the drive signal is to ***cancel*** all capacitive feedback.

"Over neutralizing" is some sort of creative nonsense.

Neutralization cannot be perfect. The long thin grid wire and high grid capacitance causes the effective feed through to change with frequency, but nulling feed through on or just above 15 meters results in "good enough". 8 tubes are impossible to compensate, 6 can be acceptable, 4 are pretty well behaved when done correctly.

All of this aside, it is pretty clear Collins was just doing a political obfuscation of a problem caused by lack of neutralization. The only possible explainations are:

1.) The engineers did not understand transmission lines and simple networks

2.) Someone found a "patch" that seemed to help, and intentionally obscured the real problem with a bunch of technically indefensible mubo-jumbo. (As politicians of all genders very routinely do, and like our automakers do with things like air bag recalls.)

Logically, the second explanation makes the most sense. It is better than saying "without neutralization, adding loss between the highest Q part of the input system and the amplifier tank will make the system less critical for tuning adjustments".  It is, unfortunately, a very typical way of handling uncomfortable things.

Smiley

73 Tom   

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W9IQ
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« Reply #55 on: August 07, 2016, 01:09:02 PM »

Tom,

I just want to take the opportunity to congratulate you on the Yasme Excellence award. Very well deserved!

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
G3RZP
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« Reply #56 on: August 08, 2016, 01:05:26 AM »

Tom,

Some 30 years ago on a visit to Cedar Rapids, I was told by some amateurs working at Collins that the original 30L1 approach was done by one of the amateurs as a home brew item, and when seen, the commercial possibilities were recognised and so the 30L1 appeared. How true this is, I don't know. It is interesting that somewhat unusually for those days, it had input tuned circuits - if you remember the amplifiers using four modified 1625s in parallel in gg, that was never done.

I also find it interesting that the RCA application, done about the same time, of four 811As in a gg amplifier used neutralising - so why didn't Collins? Was it a case of the very common 'used a 50 ohm dummy load in the lab and it was OK' and real antennas were another matter?

We will never know....


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K9AXN
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« Reply #57 on: August 08, 2016, 01:50:52 PM »

Tom,

I would like to extend my congratulations for your receiving the Yasme Excellence award.  It's obvious, your heart is in your work.

The following is a quote from my earlier comment in this thread.

"Regarding Tom:  He is a far better writer than I and can convey information far more clearly than most.  He also has the courage to write what he knows will be scrutinized and possibly be torn to pieces.  I believe him to be technically competent and his mantra (Personalities have nothing to do with technical accuracy or correctness, or being worthless in all areas because they make a few mistakes) is as philosophically good as it gets". 

Yep --- meant every word of it.  I have the highest regard for those who have the courage to put to pen technical documentation knowing the risk of censure is imminent.  I have always enjoyed reading the experiences of people who take the time to write; there are so few.

Now Tom and I have had some spirited conversations which can be expected when differing opinions clash; that comes naturally with strong personalities.  Nonetheless, I have read most of his writing and enjoyed most even though I don't agree with some concepts.

Again Tom, congratulations! 

A great day to you and Kindest regards Jim
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K9AXN
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« Reply #58 on: August 08, 2016, 01:53:45 PM »

Pete,

A detailed description of the origin of the 30L1 is available in the Collins archives.
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K7KBN
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« Reply #59 on: August 08, 2016, 03:22:21 PM »

Indeed, congratulations on the Yasme Excellence Award, Tom!

I'm surprised, though, that nobody as yet has pointed out that they've never seen "Yeasue" spelled that way.  Grin
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73
Pat K7KBN
CWO4 USNR Ret.
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