Re: {Collins} Oscillation on 30L-1



Hi Carlos,

I am the guy that published that magazine and, first comment, I hope you will explore our CCA website for all the free resources including all the back issues of our Member magazine after two years has elapsed. 

You should particularly look at the RX for Your Collins section that you can access from our website home page by clicking that title on the tool bar.
http://www.collinsradio.org

Also, Don, Jackson, the author of that article is a good friend of mine. He is also the technical editor of the Signal Magazine and a professional EE that worked in Receiver and Transmitter design.  I have also fixed a lot of 30L-1s.... Don and I talked, and we agree that the 1 Amp kind of "run-away" plate current PA oscillation that you are seeing is not due to either of the causes that Don addressed in that article.   The oscillations he worked on are secondary parasitic kind of oscillations, one at lower broadcast band kind of frequencies and the other a more insidious one that occurs sometimes at about 21 MHz when in the 15 meter band.

Personally, I have never seen a 30L-1 that had all its correct parts and was maintained well take off like that on any frequency.

I think you are looking for damage somewhere else, a bad or wrong component, or as was pointed out, a bad ground like on that shaft.

I would focus there.  But, I sure am glad you have discovered the CCA and all that we offer in the way of support.

Best Regards,

Bill
Bill Carns, N7OTQ (Trustee K0CXX)
Past President, Collins Collectors Association
Founding Board, Collins Radio Heritage Group
Editor, Signal Magazine (Retired)
Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)





-----Original Message-----
From: Collins [mailto:collins-bounces+wcarns=austin.rr.com@xxxxxxxxxxxxx] On Behalf Of Leigh Sedgwick via Collins
Sent: Wednesday, October 18, 2017 12:43 PM
To: 'Carlos Pechiar' <ch@xxxxxxxxxxx>; collins@xxxxxxxxxxxxx
Subject: Re: {Collins} Oscillation on 30L-1

Carlos,

See the excellent article written by Don Jones on this subject and how to correct it in the Signal, Q4 2013.

Good Luck

de Mike
K7PI

-----Original Message-----
From: Collins [mailto:collins-bounces+bipi=comcast.net@xxxxxxxxxxxxx] On Behalf Of Carlos Pechiar via Collins
Sent: Wednesday, October 18, 2017 10:03
To: collins@xxxxxxxxxxxxx
Subject: {Collins} Oscillation on 30L-1

Hello everyone.

I am fixing a 30L-1 for the Club which was out of service and that we do not know the history behind it. It has 811 tubes that are mid-life but the four measure the same. I replaced the original power supply with the replacement kit found online. No problem with that. I also replaced the chokes on the plates of the tubes that were overheated and their resistors cracked.

First tests went fine but suddenly, in the 20m band, when keyed down, an oscillation was trigged drawing about 1 amp on the plate current and overheating the new chokes.

I have seen this behavior before in other units but they were repaired by other people. I also heard that there is some “fix” for that or, a reason for that to happen.

Al tests were performed on a dummy load.

I’ll appreciate help.

Thank you for your time,

Carlos
CX6BT.
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