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Author Topic: Collins 30L-1 tube flashover resulting in T-R relay inoperative?  (Read 17840 times)
HAMHOCK75
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« Reply #15 on: September 18, 2017, 01:11:14 PM »

Quote
The 1N458 has significantly less leakage than the 1N458A.

The datasheets from the Mouser web site for the 1N458 and 458A show exactly the same maximum leakage specification.

0.025 uA at 125 Vr at 25 degrees C and 5 uA at 125 Vr at 150 degrees C.
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K9AXN
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« Reply #16 on: September 18, 2017, 01:55:22 PM »

Quote
The 1N458 has significantly less leakage than the 1N458A.

The datasheets from the Mouser web site for the 1N458 and 458A show exactly the same maximum leakage specification.

0.025 uA at 125 Vr at 25 degrees C and 5 uA at 125 Vr at 150 degrees C.

Your correct.  I was looking at vintage data sheets --- one had the various temp parameters the other no.

FWIW you can buy 100 for $5.00 on ebay.  They used to sell 500 1n459A's for a few dollars.

Thanks for the heads up

Regards Jim
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N6QWP
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« Reply #17 on: September 18, 2017, 07:44:01 PM »

Thanx for all that info......have a question regarding L3.  My amp is from a SK so I cannot ask him questions.  It has a different coil from the original-and also has a 1k resistor across it to the "star" junction of the four grid resistors.  Am trying to figure out why the resistor.

R28 was composed of two 80 ohm resistors in parallel and were blown.  I have two different sources of recommrndations on the new resistor value.....56 to 39 or 39 to 56?Huh

Will continue to troubleshoot after I replace R28---which choice of value?  39 or 56?  

I still have 2000 vdc B+ on the meter, so that part of the power supply seems to still be intact.  Keeping my fingers crossed with the bias winding.
« Last Edit: September 18, 2017, 08:04:58 PM by N6QWP » Logged
VK6HP
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« Reply #18 on: September 19, 2017, 12:38:22 AM »

There is a slightly complex story behind some of the 30L-1 mods, which are in general pretty minor changes.  That's why a number of us keep referring you to the articles in the CCA database, especially those in the "rx for your Collins" section.  You need to understand the background.

The R28 value is not that critical: the IR drop across it sets the idle bias on the tubes, which is recommended to be 110 mA in the last service bulletin if my memory is correct.  The value has changed several times over the years but 39 ohms is shown on the schematic accompanying my round-emblem amplifier and it works out pretty well.

You should also read the article on the medium frequency oscillation tendency as this details the thinking behind final changes to L3 and the inclusion of a swamping resistor. Again, a variety of combinations can work in a troublesome amplifier but, again from memory, an extensive investigation showed that a value of 56 uH and 3k ohm was about optimum, but it's important to get the right choke with a self-resonant frequency well above the HF bands and a non-inductive resistor. I daresay a number of empirical combinations work OK and were included prior to the excellent analysis in the CCA "Signal" article.

Collins radio is not for the plug and play jockey..it's a religion and you have to be familiar with the bible Wink
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N6QWP
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« Reply #19 on: September 19, 2017, 07:23:24 AM »

Amen......this is where I come to for my expository sermons and answers to my "bible study" questions.  Glad to have found this site and blessings to all those that share their knowledge.....and teach The Word to those of us seeking the way.
« Last Edit: September 19, 2017, 07:40:12 AM by N6QWP » Logged
K9AXN
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« Reply #20 on: September 21, 2017, 05:29:11 PM »

Thanx for all that info......have a question regarding L3.  My amp is from a SK so I cannot ask him questions.  It has a different coil from the original-and also has a 1k resistor across it to the "star" junction of the four grid resistors.  Am trying to figure out why the resistor.

R28 was composed of two 80 ohm resistors in parallel and were blown.  I have two different sources of recommrndations on the new resistor value.....56 to 39 or 39 to 56?Huh

Will continue to troubleshoot after I replace R28---which choice of value?  39 or 56?  

I still have 2000 vdc B+ on the meter, so that part of the power supply seems to still be intact.  Keeping my fingers crossed with the bias winding.

R28 --- 56 ohms --- they want the idle at 100ma

Regards Jim
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VK6HP
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« Reply #21 on: September 21, 2017, 08:53:33 PM »

Jim, I'd be interested for documentation tracking purposes only to locate any Collins sources that recommend 100 mA and R28=56 ohms.  The latest I can find is SB3, which recommends 110 mA with R28=39 ohms, and R9=47 ohms.  Both these changes are of course incorporated in later model 30L-1s, including mine (which I think is probably c. 1968-69).  I also noticed these values seem to pervade the CCA 30L-1 articles, until recently at least.

It is no doubt a bit academic since line voltages have changed over the years and I could believe that, if the voltages have increased as they have in many parts of the US, a little more negative bias (bigger R28) will keep the idle closer to 110 mA.  Here in Australia we are supposed to have "harmonized" downwards towards 230V but I don't think that's happened anywhere.  My line voltages are often 245v (sometimes more) which, when combined with a Harbach replacement HV supply, are unnecessarily hard on a 30L-1 (especially the filaments).  I run the amplifier from a bucked supply of around 220V, at which it's a lot happier and cooler, while still making plenty of RF power. I was prepared to tweak the bias a little but, with R28 and R9 as per SB3, the indicated and independently-measured standing current is right on 110 mA (10 mA being only a needle width, of course). I run a mix of Chinese and classic tubes, as noted earlier.

Regards,
Peter.

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N6QWP
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« Reply #22 on: September 21, 2017, 09:07:44 PM »

Hi Jim--I am befuddled by your posts about R28, since my June 1961 30L-1 manual shows R28 as 56 ohms and idle resting current at 130 ma.

The service builetin of April 1962 recommends changing R28 to 39 ohms. along with R12 changed to 2000 ohms and R9 to 47 ohms.....all to achieve 110 ma of resting current in order to lower the temperature of the tubes and amp.

I appreciate all the other notes about sources at CCA where I found so much needed information.  I thought that I had it all sorted out.....but your advise of changing from 39 back to 56 ohms for R28 seems to disagree with all the changes from the original 30L-1 that I read about.

I remain confused on this one point.....but indebted to you and all the others who have shared their expertise and advise.

PS--I guess I was posting this at the same time as Peter.  It appears that we are both confused at this assertion.  I am about to replace R28 which was blown up when the 811 flashed over.....and want to use the correct value.
« Last Edit: September 21, 2017, 09:24:07 PM by N6QWP » Logged
K9AXN
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« Reply #23 on: September 22, 2017, 10:43:06 AM »

Hi Jim--I am befuddled by your posts about R28, since my June 1961 30L-1 manual shows R28 as 56 ohms and idle resting current at 130 ma.

The service builetin of April 1962 recommends changing R28 to 39 ohms. along with R12 changed to 2000 ohms and R9 to 47 ohms.....all to achieve 110 ma of resting current in order to lower the temperature of the tubes and amp.

I appreciate all the other notes about sources at CCA where I found so much needed information.  I thought that I had it all sorted out.....but your advise of changing from 39 back to 56 ohms for R28 seems to disagree with all the changes from the original 30L-1 that I read about.

I remain confused on this one point.....but indebted to you and all the others who have shared their expertise and advise.

PS--I guess I was posting this at the same time as Peter.  It appears that we are both confused at this assertion.  I am about to replace R28 which was blown up when the 811 flashed over.....and want to use the correct value.

Good morning Frank, Pete,

The Addendum in the 30L1 8th edition has the changes made to R28 and the 10 and 15 meter input circuits.  The write up was in the Signal magazine years ago --- I'll check my archives.  The change from 39uh to 22uh for the grid choke was in Information letter #26 of 7/70.  As you see they didn't make public all of the info letters.  The Collins site is absurd to navigate and they were incredibly silent about their design notes.

I believe there is but one Collins engineer today DR Gerald Johnson that understands the eloquence of 30L1 design. 

Regards Jim

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N6QWP
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« Reply #24 on: September 22, 2017, 05:47:35 PM »

Still confused.  My 30l-1 manual is the 4th edition from 15 November 1961.  Can anyone who has an 8th edition of the manual please check the date of it and let us know when it was issued and exactly what it said?

I have a copy of the article from the Signal (date unknown) titled The Care and Feeding of Your 30L-1.  It quotes from Service Bulletin #3 (4-2-62) recommending changing R28 to 39 ohms.  

Does anyone have the published date of the above article?

Need to clarify if Jim's quoted source=8th edition of the 30L-1 manual is later or earlier than that date.  It is hard to imagine that the manual went through 4 editions before the publication of that bulletin #3 which was still in 1962.  

So, the question, once again, is whether to follow the publish article and use 39 ohms.....or follow Jim's recommendation and go back to 56 ohms?Huh  Any help from others familiar with this amp?

The mystery is whether the 8th edition of the manual was published before or after the often quoted article The Care and Feeding of Your 30L-1.....and why the value of R28 would be changed back to 56 ohms if publish later???
« Last Edit: September 22, 2017, 05:52:04 PM by N6QWP » Logged
N6QWP
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« Reply #25 on: September 22, 2017, 07:58:23 PM »

BY GEORGE, I THINK I'VE FINALLY GOT IT!  

The 8th edition of the 30L-1 is dated 7-15-66.  The schematic shows the value of R28 to be 39 ohms.

The addendum included with it in the archives is dated 1-9-61=OUTDATED AND MISFILED!!!

So Jim, I think that this explains the discrepancy of your advice on the value of the R28 update to lower the temp of tubes and amp.  Not your fault.

UNLESS I AM WRONG?,  the value of R28 should be changed to 39 ohms +/-, along with the other suggested replacement values......if not already done so.

the updates in The Care and Feeding of Your 30L-1 article are valid.

This has been a very informative endeavor to research and get right the proper updates for me.  I hope that all of those who have followed along have also learned from this thread.

Thanx to all that have helped.  I will proceed to install the parts and troubleshoot the rest of the amp.  Will come back when done to advise of the success of my efforts.....or not?  Wish me luck in my hopes that the problem has not gone all the way to the transformer winding.  I already purchased another relay, in case it was hit in the flashover.  73 all.
« Last Edit: September 22, 2017, 08:19:33 PM by N6QWP » Logged
VK6HP
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« Reply #26 on: September 22, 2017, 08:00:07 PM »

Frank, I would not tie myself in knots over this.  As I mentioned in the previous posts, it's not that critical and extraneous factors - like line voltage and tube brand/condition - all enter into the final choice.  My own approach would be to try what values you have on hand and check the standing current.  If it's in the region of 100-110 mA, leave well enough alone.  I note that your amp came to you with 40 ohms (nominal) for R28, so perhaps start with 39 ohms and see where it takes you. Do you recall if the quiescent current looked OK prior to your "event" ?

I'm interested in Jim's references just for completeness of my files.

PS: just noted your previous post, which crossed with mine.   My manual is a 9th edition, 1 Feb 1968 and has R28=39 ohm, as I mentioned.

« Last Edit: September 22, 2017, 08:03:12 PM by VK6HP » Logged
K9AXN
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« Reply #27 on: September 22, 2017, 08:16:41 PM »

BY GEORGE, I THINK I'VE GOT IT!  

The 8th edition of the 30L-1 is dated 7-15-66.  The schematic shows the value of R28 to be 39 ohms.

The addendum included with it in the archives is dated 1-9-61=OUTDATED AND MISFILED!!!

So Jim, I think that this explains the discrepancy of your advice on the value of the R28 update to lower the temp of tubes and amp.  Not your fault.

UNLESS I AM WRONG?,  the value of R28 should be changed to 39 ohms +/-, along with the other suggested replacement values......if not already done so.

Most, if not all of the updates in The Care and Feeding of Your 30L-1 article are valid.

This has been a very informative endeavor to research and get right the proper updates for me.  I hope that all of those who have followed along have also learned from this thread.

Thanx to all that have helped.  I will proceed to install the parts and troubleshoot the rest of the amp.  Will come back when done to advise of the success of my efforts.....or not?  Wish me luck in my hopes that the problem has not gone all the way to the transformer winding.  I already purchased another relay, in case it was hit in the flashover.  73 all.


Very good Frank,

Your correct, The 8th edition that is on the Collins site has an addendum on the second page that is dated 1-9-61 and the manual is dated 1966, Slipped by me.

Good job.  I also agree with Pete, go with the 39 and see where it takes you.

Regards Jim
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K9AXN
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« Reply #28 on: September 22, 2017, 08:27:20 PM »

Frank, I would not tie myself in knots over this.  As I mentioned in the previous posts, it's not that critical and extraneous factors - like line voltage and tube brand/condition - all enter into the final choice.  My own approach would be to try what values you have on hand and check the standing current.  If it's in the region of 100-110 mA, leave well enough alone.  I note that your amp came to you with 40 ohms (nominal) for R28, so perhaps start with 39 ohms and see where it takes you. Do you recall if the quiescent current looked OK prior to your "event" ?

I'm interested in Jim's references just for completeness of my files.

PS: just noted your previous post, which crossed with mine.   My manual is a 9th edition, 1 Feb 1968 and has R28=39 ohm, as I mentioned.



Pete,

The most current manual on the Collins site is the 8th.  Do you have a pdf file of the 9th edition or any of the remaining information papers?

A good source of technical information for the 30S1 and 30L1 is "Single Sideband Principals And Circuits"  Pappenfus, Bruene, Schoenike all Collins engineers. 

Thanks regards Jim 

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N6QWP
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« Reply #29 on: September 22, 2017, 08:36:17 PM »

With the 40 ohms (two 80 ohm resistors in parallel) the idling current was right around 110 with the original RCA 811A tubes.  I purchased several 39 ohm resistors today along with duplicates of all of the other suggested parts that might need replacing. Figure I might as well be ready in case of a repeat.

Just had to resolve the puzzling question of R28 before I installed the 39 ohm one.....in case I should have to get and try others.  Again, thanx all, for leading me by the hand in getting into the innards of my first amp.
« Last Edit: September 22, 2017, 08:50:50 PM by N6QWP » Logged
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