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Author Topic: Troubleshooting Collins 30L-1. Clean unit but way high swr reading  (Read 8224 times)
AA4PB
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« Reply #15 on: July 16, 2013, 03:55:07 PM »

The 30L1 manual says 20.5 but I've never tried it.
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W1QJ
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« Reply #16 on: July 16, 2013, 05:29:51 PM »

you can't use a G5RV without a tuner.  You will need a tuner after the amp and before the G5RV or else the antenna will have a high swr on all bands.  You need a tuner that  can handle a KW,  Whoever told  you that you don't need a tuner is wrong.  Your set up is flawed at this point.
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AA4PB
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« Reply #17 on: July 16, 2013, 05:38:50 PM »

Yes, according to the manual the output impedance is 50 Ohms and the SWR cannot exceed 2:1. You can use the 30L1 without a tuner with a 1/2 wave dipole or a trapped dipole but it won't work all bands with a G5RV.

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G3RZP
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« Reply #18 on: July 16, 2013, 10:12:09 PM »

The 30L1 is reputedly said to be on the verge of unstable on the upper bands; although the 20.5 foot length of RG58 was in the original handbook, later on that got changed. The instructions for operation on 230 volts in the handbook are basically dangerous even in the US, and on mains supply systems in Europe, will either trip breakers, blow fuses or burn up the transformer.

Is the amplifier oscillating?
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KC4MOP
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« Reply #19 on: July 17, 2013, 03:54:18 AM »

You're gonna beat yourself to death without a Dummy load. When we visited the Philippines, I had wire and insulators and 100 feet of coax to make something for 40 or 20M. I brought my MFJ 259 and a little 100W dummy load, soldering gun and solder.
Vacations are not supposed to be frustrating.
Fred
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KD7KTV
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« Reply #20 on: July 17, 2013, 08:53:49 AM »

Ok so I need a tuner after the amp to work w the g5rv.

Back home I have also the ldg at-600 auto tuner.
I Believe that is rated at 600 W. Is that good enough margin for the Collins 30 L1 500 W output?

Really appreciate all this feedback.

Jim
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K0IZ
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Posts: 737




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« Reply #21 on: July 17, 2013, 09:23:24 AM »

Don't worry about the 20.5 length of coax between 706 and amp.  That is not causing your problem.  Most, including me, just use a short length of coax.

The In/Out (ANT) transfer relay is an open contact type relay at back.  Possible that contacts are dirty (mine was).  Hard to get to the relay, take a look at the manual.  My preferred method for cleaning open contacts is to cut a strip from a business card, saturate with contact cleaner, then place strip between contacts and push/pull several times.  For the open circuit contacts, manually close relay while doing this.

The input circuits are pi networks between input and 811 filaments.  These are switched by two wafers on the bandswitch.  Possible that the contacts are also dirty.  Use contact solution (don't overdo it), and turn the bandswitch back and forth several times.  Since the problem occurs on several bands, I doubt that all of the networks are mistuned or defective.

If cleaning doesn't help, trace out the connections between in/out relay, into pi network bandswitch, and into 811, looking for something unusual.  Input SWR on 30L1 should be 2:1 or less when everything is ok.

Re AC power, I recommend using 230/240 circuit rather than 120.  Most do, I do.

And as others have said, you need an antenna tuner with a G5RV, except perhaps on 20 meters.  Tuner between amp and feedline.
« Last Edit: July 17, 2013, 09:26:18 AM by K0IZ » Logged
KA5N
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« Reply #22 on: July 17, 2013, 09:40:26 AM »

While the 30L1 is a handsome amplifier and does a nice job for those folk familar with it and
have it working properly, it can be a handful  for a newbie. 
If possible get someone familar with the amp to go over it with you (and make sure all is
okay inside). 
Also get a dummy load!  it is next to imposible to get amps and antennas working together
without a dummy load.

Good Luck and persevere!!

Allen KA5N
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W1QJ
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« Reply #23 on: July 17, 2013, 01:15:48 PM »

It seems that this Collins amp is new to the owner.  I assume he has little knowledge of its history.  On TWO occasions I had the task of repairing a Collins 30S1 and 30L1 which had no histories known to the owners.  The first amp I was  called upon to repair was the 30S1.  It was bought by a relative of mine represented in "not working" condition.  He knows quite  a bit about fixing amps and figured he could repair it, then sell it at a profit.  The previous owner attempted to repair it but was never successful.  My relative tried to fix it,  after considerable time spent  he gave up.   He spoke to me about the problem and it sounded like a real challenge for me.  I decided to take a weekend and spent it with him and look at the amp.  He briefed me on the problem and his attempt to troubleshoot it.  Since the 30S1 is a console amp I decided to get in there and have a look.  His problem was exactly the same as this one mentioned here with the 30L1.  There was a high swr looking into the amp when keyed up.  Armed with an ohm meter and flashlight I got on my back and examined the circuitry.  I looked  and looked over an over again and did not see anything "obviously" wrong.   I was looking for any signs of "repair work" that could have been botched.  All connections had the obvious military coating on the solder connections.  OH....did I mention this was a military surplus Collins 30S1?  Yeah, it was a surplus unit bought at auction.  After a few hours of inspection and testing I went on my back for another look.  This time it hit me.  The amp had been tampered with.  Someone (for some unknown reason) surgically switched the ground and the center conductor on the coax from the input circuit to the antenna relay.  When the relay was engaged and RF was applied, the signal was being grounded and (naturally) the swr went sky high.  Upon noticing that I switched the wires and the amp came alive and worked perfectly.  All the tampered connections were switched with surgical precision and connections had the red sealant applied as to disguise its tampering.  Go figure...  Now to the 30L1.... I bought a beautiful 30L1 at a hamfest one year shortly after the past event.  The seller (an old man of 80+ years) whom I have seen many times at hamfests in the area was selling it.  I procrastinated  about buying it all day and when he was packing up to leave we cut a deal.  He assured me he had just used it the other day and it worked perfectly.  I believed him because he reminded me of my beloved grandfather so I unidentified with him.   Eagerly I hurried home to plug it in to use it.  When I got home I set it up to try it out.  My first attempt to key the amp produced no results.  The amp would not key up.  It was like the antenna relay was dead.  I checked my ground on transmit signal with an ohm meter and it was fine.  Have I been had by my grandfather look alike?   I tried grounding the relay at the connection, still nothing.  Looks like I been had.  No way that amp was keying up just the other day.  SO now I dig into the amp.  Pull it out of the case and check voltage at the relay.  it's there.  SO the idea of no voltage at the relay is not the problem.  I grounded the minus side of the relay at the relay and it kicked in.  hmmmm.....  Relay works fine.  Something wrong from the antenna relay jack to the minus of the relay.  Started to trace the wire back to the relay jack.  Ah-oh can't see behind the jack it is hidden.  I have to remove a small sub chassis to gain access to the back of the relay jack.  Looking at the schematic showed there should be a 39 ohm 2 watt resistor in series with the relay jack positive terminal with the wire to the minus of the relay.  OK, I removed the sub chassis so I can see the back of the antenna jack.  I looked for that 39 ohm resistor thinking it could be opened.  Well, I did see a resistor connected to the jack and then to the wire going to the relay.  Fortunately when I was a novice back in 66 I made it a point to learn my resistor color code. Wink  Immediately I read the code on the resistor.  It was not 39 ohms, it was 4000 ohms.  Hmmmmmm......  Looking at the resistor it looked like it was factory installed.  No visible sign that it had ever been tampered with.  Still had the military red coating on the solder joints.  OH.... Did I mention this was a military surplus 30L1?  Anyhow, I changed the 4K resistor to a 39 ohm resistor and the amp cam alive and worked flawlessly.  I can assure you grandpa never got that amp working as he said he did.  Wonder how long he spent trying to get it to work?  So to my surprise this is the second Collins amp I encountered that was a military unit that had seemed to be "surgically" sabotaged.   Further investigation with Collins collectors revealed that many military Collins units are "decommissioned".  For some reason the government goes through great pains to surgically decommission these units before they go to auction.  Looking for obvious signs of tampering is undetectable.  Again, go figure.  Could this amp be a decommissioned unit?
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G3RZP
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« Reply #24 on: July 18, 2013, 08:01:41 AM »

My 30L1 handbook has a wiring diagram for 230 which is dangerous. It shows the two 115 volt primaries in series across the 230 volts line - fine. BUT it connects the junction of the two primaries to ground. So if there's an imbalance between the 230 volt lines, the transformer will attempt to fix it.........hopefully blowing the fuse first. If there's GFI, that will keep tripping. It does say to not ground the junction if it's a two wire 230 volt system.
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K1DA
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« Reply #25 on: July 18, 2013, 02:01:36 PM »

I suspect the two Collins amps which "never worked" probably got shuffeled around because of that, carried on a MARS station TO&E, for example,  until the Harris stuff came along.  The military had such a vast collection of gear that a dead amp may not been critical  to ANY mission  and thus not fixed.   When the IG inspectors came through  they were interested in seeing things darkening the shelves in correct numbers, but whether they worked or not was another matter.  I was once at a MARS station where the S Lines were replaced every SIX months, and the slightly used one shuffeled off to "property disposal" where friends of the guy in charge of the station got them at "by the pound" prices.  MY understanding of the "red stuff" is that it was a "QA marker" put on at the factory by inspectors who, being human, may have made a mistake.  It's far more likely the units shipped that way than that someone carefully switched wires and  then found some "glyptol" to cover their traces for any particular reason, except, perhaps, hoping to grab the"non-functioning" unit at "property disposal" when it got written off.   
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KD7KTV
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« Reply #26 on: July 18, 2013, 03:08:15 PM »

To K0IZ.
the unit was wired really weird for 230.
Unfortunately at the beach shack the circuit breaker is maxed out
and adding an outside junction box would probably cause the brothers-in-law
concern.
So I had the dealer re-wire it for 115 Volts.
I understand I may have issues with tripped circuit breakers.

Any experience with that?

I will take my dummy load down to the beach next trip.
I talked to the LDG factory yesterday about their 1000 watt auto tuner.

Thank you for the info on cleaning up the contacts on the band switch selector.

All the best,
jim
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N0NZG
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Posts: 122




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« Reply #27 on: July 20, 2013, 07:09:23 PM »

I thought I might ask the obvious question. Is there any chance that the OP’s amp shows a good swr on 28 MHz because it was re-engineered to be a 27Mhz / 11 meter amplifier?


You might open it up and see if it has the large tank coil and it all looks like it is wired to a band switch correctly. One could also poke around to see if the tuned input /s  are still present and accounted for on the other bands as well. Does the amp have tubes in it?
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W1QJ
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Posts: 1446




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« Reply #28 on: July 21, 2013, 04:58:39 AM »


I decided to put my auto tuner back in line before the Collins. 
It will do its number on the 20 meter band and get a match.
But when I key up to talk the tuner goes back into auto tune mode.

When you use any radio with an amp you should not have an active tuner in between the radio and the amp like you stated above.  Your whole set up is wrong and I am not surprised you having trouble.  You don't mention anything about loading up the amp.  You are not telling us what type of kilowatt rated tuner you have after the amp and before the G5RV.  You do know you need some sort of KW rated tuner after the amp don't you?  You would not need a tuner after the amp if you are going into a dummy load though.  One could use a tuner inside the radio sometimes to help improve the match to the amp but in your case you need to find out how the amp is really working without a tuner in line.  Your proper test set up should be the radio, amp, dummy load.  How are you keying the amplifier?  The 706 does not provide an easy way to key amps and you should have a proper interface between the radio and amp.  Although a certain length jumper is called for any jumper should give you some decent swr to work with so that you can attempt to load up the amp.  Sometimes the input match gets better as the amp is loaded up and the tank circuit resonates on the band in operation.  Since you have no even verified if the amp will put out any power it is possible that bad tubes will present an improper match to the input.  At this point you do not know anything about the health of this amp and there could be issues with the antenna relay who knows what?  When you key the amp with no drive intended is the ZSAC correct?  And please tell us what KW rated tuner you intend to use between the amp and before the G5RV?
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KE3WD
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« Reply #29 on: July 21, 2013, 03:00:35 PM »

When the amp is in standby mode, the relay makes a straight thru connect to the antenna and your Autpotuner is getting a match for the antenna only. 

But once the amp is keyed, the amp's input circuit is now seen by the radio and autotuner and the tuner is retuning to that. 

You should be finding out why the amp does not work. 


73
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