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 Post subject: Slowly changing volume in Gonset Communicator IV
PostPosted: Oct Thu 11, 2018 3:43 am 
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Joined: May Thu 04, 2017 1:08 pm
Posts: 186
Location: Raleigh, NC area
My Gonset IV 6m has a volume issue. When it has warmed up for 10 min or so, the volume suddenly drops to perhaps half. I can then turn it up with the knob. Several minutes later, it might pop back up again. This up and down continues, thought somewhat randomly. Tubes seem to test ok on my Precision 912, but maybe not running them long enough on the tester? Could it be a cap issue? Resistor issue? Not sure where to start looking for this one.
Thanks, Dave


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 Post subject: Re: Slowly changing volume in Gonset Communicator IV
PostPosted: Oct Thu 11, 2018 8:10 am 
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Joined: Nov Sat 07, 2009 11:37 pm
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Location: Sayreville, NJ 08872
Volume is relative. Does the sensitivity get weak or is it the actual audio part of the receiver. If sensitivity gets weak, most likely it's before the diode detector. If it's actual audio (signal doesn't get weaker just the audio), most likely it's after the diode detector. A scope could define the area to look at. A scope is a very useful trouble shooting tool. Could be intermittent capacitor or sometimes even a resistor breaking down. Check the tube voltages on the pins before and after the problem.

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 Post subject: Re: Slowly changing volume in Gonset Communicator IV
PostPosted: Oct Thu 11, 2018 10:34 am 
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Joined: May Thu 04, 2017 1:08 pm
Posts: 186
Location: Raleigh, NC area
Thanks... Will probably have to inject a test signal. This is or 6m, and there's not a lot of activity. So hard to tell the reason a contact is lower or higher in volume. Easy to hear the static drop down and jump back up. Cooler weather is coming, so I won't mind having it out open on the bench in the garage to troubleshoot.

When I wrote in the title "slowly changing" it was probably misleading. I meant it changes volume after minutes at the same volume. Then, when it changes, it does so in a step. So almost seems like an intermittent connection, or voltage breakdown as you noted, rather than something which is related linearly to temperature.


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 Post subject: Re: Slowly changing volume in Gonset Communicator IV
PostPosted: Oct Fri 12, 2018 4:02 am 
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Joined: Sep Mon 16, 2013 2:42 am
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Location: Tucson, Arizona U.S.A.
Do you have an antenna connected? If so, how do you know that the problem is in the set and not something that it is receiving? Does the same thing happen without an antenna or with a signal generator connected?

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 Post subject: Re: Slowly changing volume in Gonset Communicator IV
PostPosted: Oct Fri 12, 2018 5:19 pm 
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Joined: May Thu 04, 2017 1:08 pm
Posts: 186
Location: Raleigh, NC area
Jim Mueller wrote:
Do you have an antenna connected? If so, how do you know that the problem is in the set and not something that it is receiving? Does the same thing happen without an antenna or with a signal generator connected?


Static changes volume even with a dummy load connected.


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 Post subject: Re: Slowly changing volume in Gonset Communicator IV
PostPosted: Oct Sun 14, 2018 10:05 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3520
Location: Monterey California USA
I have not worked on a IV but you already know the issue is internal to the set. If it were on my bench I would feed a signal in just upstream of the audio amp stage first and monitor the audio output, then use freeze spray to see if it affected the issue. Assuming you have tested the tubes and cleaned their sockets, the issue is probably a capacitor or a resistor that is internally cracked. Sometimes a chopstick poking around will reveal things (what useful radio tools come from eating any other ethnic food?)

I have had orange drop capacitors do this in the past even though they tested fine, and this was in a solid state receiver with 10 Volts on them!

AM receivers are hard to troubleshoot because everything from antenna to speaker affects the audio level at the speaker. FM sets not so.

Try to isolate the stage where this is happening. Then to the component itself. Don't forget things like bad rivet grounds (where applicable,) silver mica disease in IF transformers (where applicable) and even something as obscure as intermittent B+ fluctuations from a bad power transformer or a rectifier tube.

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 Post subject: Re: Slowly changing volume in Gonset Communicator IV
PostPosted: Oct Mon 15, 2018 1:33 am 
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Location: Tucson, Arizona U.S.A.
If you go with the previous suggestion, set the level of the audio/RF generator so that you can hear it and the static at the same time. Then you can tell when the problem occurs and if it also affects your test signal.

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