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Author Topic: Collins 30l-1 help  (Read 3273 times)
AD9DX
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Posts: 1481




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« on: March 21, 2012, 05:33:03 PM »

So I bought a Collins 30l-1 at a hamfest on Sunday. It has a few issues that I am not completely sure about.  For one, it only seems to work on 20m.  On every other band it passes DC to the antenna.  It isn't a huge deal to me because I only paid $200 for it.  I changed the tubes to a matched quad set of Chicom 811's.  And am starting to think the best course of action would be for me to take the thing down to the chasis and start over cleaning the nicotine and corrosion off each part. Does anyone have a service manual for this amp?  I have taken a part a few amps before, but this Collins is a different bird.  Thanks in advance.
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EX, KC9TRM, KB9IRZ
W1QJ
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« Reply #1 on: March 22, 2012, 12:37:02 AM »

Can you explain what you mean by the amp passing DC on all the other bands.  I am not grasping what you are trying to say.
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AD9DX
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« Reply #2 on: March 22, 2012, 03:39:16 AM »

The amp will peg my bird watt meter on other bands. BTW I have a 2500w slug in the meter
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EX, KC9TRM, KB9IRZ
K2DC
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« Reply #3 on: March 22, 2012, 03:58:09 AM »

The US Army Depot Maintenance Manual is available on Bama:

http://bama.edebris.com/manuals/collins/30l1/

BTW, the Bird meters use a coupling sampler that should not pass DC, followed by a detector that cannot pass DC.  Maybe something's up with the meter.  Have you tried a different meter?

73,

Don, K2DC
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W1QJ
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« Reply #4 on: March 22, 2012, 04:22:36 AM »

ok, that tells me something, you cannot peg a Bird 2500 watts slug with a 30l1.  If you really mean DC is coming out then you have a bad blocking cap.  This is a dangerous situation.  CHANGE that blocking cap before you even turn that amp on again.  You have DC plate voltage present on the antenna output.  That's what I thought was wrong and since you say the meter is pegging makes alot of sense.  Normal RF antenna voltage is 300vac  you have about 1500vdc there now.  Also you must change the safety choke it is either missing or blown open!!!!!!!!!!  Be careful!!!!!!!!





!
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AD9DX
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Posts: 1481




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« Reply #5 on: March 22, 2012, 04:53:35 AM »

ok, that tells me something, you cannot peg a Bird 2500 watts slug with a 30l1.  If you really mean DC is coming out then you have a bad blocking cap.  This is a dangerous situation.  CHANGE that blocking cap before you even turn that amp on again.  You have DC plate voltage present on the antenna output.  That's what I thought was wrong and since you say the meter is pegging makes alot of sense.  Normal RF antenna voltage is 300vac  you have about 1500vdc there now.  Also you must change the safety choke it is either missing or blown open!!!!!!!!!!  Be careful!!!!!!!!





!

Thanks for the help... I have the Amp almost completely disassembled right now. I am not going to renergize the thing until I check out the components you listed above and replace the scary power cord. This amp is going o be a challenge for me, but I am fairly sure I am not over my head. I am also planning on doing the Harbach power supply update. Those old components need sent down the river Smiley. Thanks again, Jon KC9TRM/ae
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W1QJ
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« Reply #6 on: March 22, 2012, 04:59:48 AM »

the blocking cap if bad should look bad (maybe)  Please get back to the group and let us know how you make out in the end.  Good Luck and be careful!
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AD9DX
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« Reply #7 on: March 22, 2012, 05:05:38 AM »

the blocking cap if bad should look bad (maybe)  Please get back to the group and let us know how you make out in the end.  Good Luck and be careful!

This project will take me a while, I have a 40+ hour a week job and three young kids. So spare time is limited. I have been taking pictures as I take it apart. So hopefully when I am all done I can give everyone before and after pics.

My first priority has been rebuilding the meter. It is stuck and someone used some nasty glue to reattach the glass. That glue is now yellow and everywhere. This thing is rough and it is going to take a lot of TLC. I think I have a good summer project a head of me.

Jon
KC9TRM
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EX, KC9TRM, KB9IRZ
G3RZP
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Posts: 4589




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« Reply #8 on: March 22, 2012, 05:41:09 AM »

There is a 2.5mH RF choke across the laoding cap: if that is  burnt, check the couling cap. There should be practically almost zero ohms DC across the loading cap.

The wiring for 230 volts in the manual is dangerous, becasue it attempts to balance the two 115 volt supplies using the transformer winding, which is a good way to burn up the transformer.

If you look back in the archives here, you'll find a thread on this amp from a few months ago, which may help you.
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K4FMX
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Posts: 17




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« Reply #9 on: March 22, 2012, 07:54:23 PM »

The amp will peg my bird watt meter on other bands. BTW I have a 2500w slug in the meter

DC passing to the antenna will not cause the bird meter to peg, only RF will.
I would bet that you have an open or short circuit on the antenna connection and or an extremely high swr on the bands  that you are seeing the problem on. That is the only thing that will allow the bird meter to read that high. Self oscillation could cause it also if it is taking off on a frequency other than what the antenna is resonant on. That would cause an extreme swr at the oscillating frequency.

Try the amp on a dummy load.

73
Gary  K4FMX
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G3RZP
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Posts: 4589




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« Reply #10 on: March 23, 2012, 03:28:34 PM »

Note as well that once you get above about 20m, the stability of the 30L1 is more than a little suspect. See W8JI's webpages. I don't always agree with Tom, but I sure do on this subject!
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WA0ZZG
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Posts: 158




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« Reply #11 on: March 26, 2012, 09:48:17 AM »

OK;   The 30L-1 is a trusty old grounded grid amplifier.  The big problem with grounded grid is that it places the input in series with the output.  That's why some of the input power shows up in the output.  The catch is chassis ground needs to be nearly perfect.  Make sure that ALL chassis hardware is clean and tight.  Recommend these upgrades be done:
1. Primary transformer rewire as mentioned before.
2. High voltage diode and filter stack upgrade.
3. Bias supply upgrade.
4. Clean and lube small cooling fan.
5. Realign input Pi networks.
6. Wire amp to power, put 50 ohm loads on input and output. Power up. Verify high voltage and zero current.  Let run for a couple hours.
7. Key with shorting plug. Verify idle current. Verify no change in current in each band position and all tune and load positions. Any current spike is a problem.
8. Align meter tune position with two-tone generator.
9Amp is designed to run hot but many add anothe small fan to the top.
Dave WA0ZZG
Cedar Rapids...
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