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Author Topic: Collins 30L-1 TUNING?  (Read 5679 times)
VK3BL
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« Reply #15 on: February 26, 2017, 10:55:11 PM »

 It took a while.....several really helpful hams willing to Elmer the uninformed.....and injury to a nice set of old tubes to overcome the newbie tendency to get every last bit of power from one's first amp--and tuning up too long without cooling down between attempts.  Over driving them didn't help either.
 
Four NOS RCA 811A's just arrived.  Tried them out at 500 watts and all was well.  Went back to the old ones....as they too are still putting out 500 with the 50 watts of drive.


Sincere thanx to all for the great advice.  Should be able to keep this old 30L-1 on the air for a while now.  Hope this thread will be as helpful to others as it was to me.  73's

Use the old ones up, the slight plate warping / silvering should have minimal if any bearing on life.  RCA states this in one of their early HAM Tips columns.
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J.D. Mitchell - VK3BL / XU7AGA - http://vk3bl.wordpress.com
N6QWP
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« Reply #16 on: February 27, 2017, 02:20:12 PM »

Okay....just pulled out the "over-tuned" tubes and under close inspection, notice that there are tiny-almost microscopic pinholes in each of them on the anodes.  Thought that they were blistered coating at first, but now see the beginnings of very small punctures.  

Wondering if I should still use them until they die.....or replace them before they can cause some cataclysmic event (like a blown transformer or ? Huh).  Any reason not to replace them before something happens.....or just use them and wait until I can see some major openings (or notice considerable drop in output or flattening of the tuning dips)?
« Last Edit: February 27, 2017, 02:40:10 PM by N6QWP » Logged
VK3BL
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« Reply #17 on: February 28, 2017, 02:55:30 AM »

Okay....just pulled out the "over-tuned" tubes and under close inspection, notice that there are tiny-almost microscopic pinholes in each of them on the anodes.  Thought that they were blistered coating at first, but now see the beginnings of very small punctures. 

Wondering if I should still use them until they die.....or replace them before they can cause some cataclysmic event (like a blown transformer or ? Huh).  Any reason not to replace them before something happens.....or just use them and wait until I can see some major openings (or notice considerable drop in output or flattening of the tuning dips)?

Pin holes are fine, and should not reduce useful life to any real degree; filament emission will most likely be lost first.  I had the same problem with a set of Chinese 811As that had their plates scratched during manufacturing.  The pin holes did not reduce output, and I used the tubes until they went soft.

The only time to replace an 811A with a damaged plate is if it is sagging inwards towards the grid, which can result in a plate <-> grid short if it gets bad enough.  This is mainly a problem with Russian & Chinese 811As.

Keep using them whilst you prefect the art of tuning Wink. That way, you'll be confident you'll get the most out of your new ones when it is time to put them in.
« Last Edit: February 28, 2017, 03:00:06 AM by VK3BL » Logged

J.D. Mitchell - VK3BL / XU7AGA - http://vk3bl.wordpress.com
N6QWP
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« Reply #18 on: February 28, 2017, 05:16:29 AM »

Thanx again Jarred....and if a grid to plate short were ever to occur, what could be the worst case scenario as far as the amp itself?  

I'll try to keep an eye out for any sagging, but the two bottom tubes are difficult to view unless actually removed-as are the other two also.I assume that before the sagging would occur, the holes would probably get more pronounced and be a harbinger of impending doom?

Any precursors that might give one a heads up?
« Last Edit: February 28, 2017, 05:31:38 AM by N6QWP » Logged
G3RZP
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« Reply #19 on: February 28, 2017, 07:20:55 AM »

Where 811s are used horizontally, there is a restriction in that the filament pins and the filaments should be in a vertical plane. I've got some Chinese 811As where, when the filament pins are in a vertical plane, the plate is at 45 degrees instead of vertical and also one where the plate is horizontal when the filament pins are in a vertical plane so the filament can sag into the grid!
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N6QWP
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« Reply #20 on: February 28, 2017, 08:05:58 AM »

I have all NOS RCA  or JAN 811A tubes...all are mounted vertical or very nearly so.  Am I to be concerned with both the plate to grid sagging as well as the filament to grid sagging?  Which element will be doing the sagging in each case?

Same questions as just asked regarding what to look for in performance or visually as warning signs of problems under way?

And.....what would be the worst case consequences to the amp as a result of either?

If I could get the answers to the above questions, I think I will have learned enough about these issues and hopefully can give everyone a break ;-)
« Last Edit: February 28, 2017, 08:26:11 AM by N6QWP » Logged
G3RZP
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« Reply #21 on: February 28, 2017, 01:01:36 PM »

It's only if the tubes are horizontal you need to worry. Genuine RCA tubes will then have the plates vertical i.e. looking down from the top of the amplifier, you are seeing the thin outline rather than the large outline looking broadside on.

If plates sag into grids, it really is running them too hard!
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KM1H
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« Reply #22 on: February 28, 2017, 03:33:20 PM »

Chinese versions will go soft long before holes appear. Anything much over a dark red will boil the coating off and good bye soon after.

The only thing they are good for here is as modulators in my Clegg Zeus where they are loafing at around 900V, in my USN ATC (Collins ARC-13) or as replacements for 809's in some rigs.
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N6QWP
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« Reply #23 on: February 28, 2017, 04:15:46 PM »

The questions still remain unanswered:

1) What will I look for where filaments and grids sag into one another?  Which one is like to do the sagging?

2) Are there any warning signs of the above getting ready to happen-short of pulling the tubes from time to time to inspect them?


3) What is the worst thing that can result from that or anode to grid sagging?  Is there a chance of doing any major harm to the amp?

Thanx again for any input....I am, and I'm sure many others are learning something from each reply.  From the number of views, there certainly seems to be a lot of interest in these old amps.
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KM1H
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« Reply #24 on: February 28, 2017, 04:31:24 PM »

Too many variables for a proper answer and if you are that worried either replace them or run at lower drive/output of say 400W.

Next step might be getting an amp with a more rugged tube(s)
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N6QWP
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« Reply #25 on: February 28, 2017, 07:30:12 PM »

OK.....not able to get the answers that I am looking for (so far)......so let's just try to get a consensus of what can be the worst case scenario that can happen to a 30L-1 if any of the 811A tubes suffers a meltdown, short, flashover or any other effect of a tube going bad?

Is there any reason not to continue to use the over-driven "injured" tubes until failure"?

I am willing to "drive them into the dirt"......as long as there can be no real risk of destroying any of the major parts of the amp.  I am trying to weigh the risk factor against using the over-driven tubes for the remainder of their useful lives vs taking a chance on causing some major and costly problem with the 30L-1.

If I can just get some pertinent answers to this question, it will alleviate my paranoia and let me enjoy the "learning curve" until I can feel safe in installing the new tubes.  

This is my first----and last amp.  Just trying to get to the point of being confident about it's proper use and care.  Trying to use up the tubes that I have already injured before installing a new set.

Sorry to be "beating a dead horse" here, but I am feeling like a fledgling bird getting ready to take my first flight.....and just want a nudge--in the right direction.  Thanx once again and 73

(Can I please get some experienced answers to this one question?Huh)
« Last Edit: February 28, 2017, 07:53:36 PM by N6QWP » Logged
G3RZP
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« Reply #26 on: March 01, 2017, 01:44:18 AM »

Provided the tubes are built like RCA ones (or ARE RCA ones) the chances of the filament sagging into the grid is remote - unless you run the amplifier on its side. (Don't laugh - the WW2 Halifax bomber had a very cramped area for the radio installation so the receiver was mounted on its side!) The plate sagging into the grid is even more remote provided you don't run the amplifier with the plates white hot. A plate to grid short will probably mean a major rebuild of the grid circuitry: it could also require replacing other components. But its unlikely. Tune up for quickly for 500 watts out, expect 300 to 350mA plate current on speech peaks, note the tune and load control readings so you can preset them before applying power and then you just need a quick 'tweak' on them.

You might find that changing tubes affects the input SWR: if so you need to trim the input inductors as per the handbook.
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VK3BL
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« Reply #27 on: March 01, 2017, 04:13:37 AM »

Chinese versions will go soft long before holes appear. Anything much over a dark red will boil the coating off and good bye soon after.


It depends.  I had a batch that were scratched during manufacturing.  The expansion / contraction cycle when used caused cracks to appear along the scratches. 

The tubes went soft before any serious problems occurred. 

Carl is spot on about them getting much more than a dark to medium red.  In some Chinese tubes, this will result in the zirconium getter boiling off the molybdenum plates and causing the glass to darken / go silver on the inside.

As far as what will happen to an 30L1 if there is a plate to grid short, I can't answer as I've never owned one.  Looking at a schematic it has tuned inputs, so exciter damage is very unlikely.

On the other hand, the grids are not directly grounded - they have a bypass capacitor to ground.  If you're keen, I would suggest removing these capacitors and directly grounding the grids. On the other hand, if you don't, a plate to grid short could take the capacitors out... its hard to say having never owned one.

Surely someone here has a 30L1 and has experienced a tube arc event?

Sorry I can't be of more help, but the tube damage you have described thus far doesn't suggest to me you are likely to have an arc.

73,

Jarrad

Looking
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J.D. Mitchell - VK3BL / XU7AGA - http://vk3bl.wordpress.com
N0RCN
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« Reply #28 on: May 17, 2017, 11:10:09 AM »

I appreciate all the info on the 30L. I just won one on eBay. Looks to be in very good condition. And the previous owner put all new tubes in, and allowed them to "settle" prior to selling. No, I'm not sure at this time what brand of tubes he put in.

I just got my General ticket, and have never had a linear before. So all this info should be quite helpful. I'm hoping to learn how to use it when interfaced with my new ICOM 7300 and my 3KW 7-Band OCF.

I'm not one of those power-hungry hams. So don't get me wrong. I actually work in an engineering lab at Rockwell Collins, and have been there for over 17 years. So I saw this 30L purchase as a way to own a piece of my own career history. But I do look forward to having a bit more output power available than my ICOM 7300's 100 watts, should I ever need it.
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K9MB
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« Reply #29 on: May 19, 2017, 01:17:52 PM »

I cloned this amplifier 36 years ago.
It uses 200pF grid bypass capacitors to raise grids above ground and introduce some negative feedback, which raises the drive requirements from about 65 watts for 4-811As to about 120 watts for my clone of the 30L1.
Putting 811As in super cathode driven mode means that apparent efficiency soars, but above 15mHz, the long electrode leads can cause lots of instabilities.
Neutralization can help, but these are audio tubes- in the end.

I got 700+ watts easily out of 4 of them all the way through 20 meters, though.
I have 1500 volts at 100-125mA quiescent and 1460 ot so at about 700mA
Grid current varies between 100-125mA at full output.
I can put a brick on the key for about 20 seconds before plates get about half dull orange.

The 30L1 should work about the same, though B+ is more like 1650 volts, I think.

I suspect that both instability and softness chatacterize Sino-811As
Get some NOS RCAs or Amperex. I have used both.

If you get arcing, it sounds like bad tubes or instabilities. There are no bargains in tubes, IMO, and some good NOS 811As will last for many years.
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