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 hum and distortion on Oceanic H5000

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tubenut



Join date : 2016-08-03

PostSubject: hum and distortion on Oceanic H5000   2016-08-26, 7:06 am

I have worked on a lot of these, but this one got me puzzled.  This radio has great sensitivity, volume and I have checked all resistors,  caps and voltages.  However, when I use the 1L6 tube not only is there hum between tuned stations, but garbled audio when tuned in.  If I use a 1R5, all stations are crystal clear, but I still have the loud hum between tuned stations and sensitivity on shortwave goes down the dumper.
I believe there has got to be something I'm missing in the 1L6 circuit, but I can't seem to find it.   Perhaps someone can help.
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: hum and distortion on Oceanic H5000   2016-08-26, 7:45 pm

Can you use it in battery's only mode? Without problems?
If the 1L6 is the culprit then a substitution is needed with another 1L6. If that solves the issue, then it's possible the grid is shorted. The next thing to look for is a shorted wire around that socket. Or one of the pins isn't making solid contact inside the socket, if that's the case then use a scribe to very carefully bend the contact that is causing trouble. It could also be a dirty pin or contact.

If you have a signal tracer, start at the plate on the audio, and temporarily short out the speaker output terminals. Then test the grid next, Do this with each stage backward. 
Check the volume control for opens or shorts.

The biggest culprit is a floating grid. That is where the RF or IF transformer probably has an open winding.

An open AVC or screen bypass capacitor will cause Hum.

NOTE: whatever you do, DO NOT BYPASS ANY CAPACITOR WITH ANOTHER WHILE THE SET IS TURNED ON, YOU WILL BLOW OUT THE TUBE. ALSO DO NOT REMOVE OR REPLACE ANY TUBE WHILE THIS RADIO IS ON. YOU WLL BLOW OUT THE FILAMENTS. Make sure any capacitor you do a bridge with is shorted first to bleed off any stored voltage.

Hum usually doesn't start at the RF Section except for the antenna section, with one of its leads open or disconnected. That radio has a built in swing up antenna that is connected by hinges, they may need to be checked for intermittent contact. Also look at the whip antenna for the same condition.
Sometimes reversing the power plug will reduce the hum.

One thing would be to check is the tuner capacitor for shorts to ground.
Check the 117V bypass caps. If they are open, that could cause the hum.
Make sure you also check the D.C. PLATE Voltages meet specs. Sometimes the power is reversed and supplied from the input rather than the output filter which is wrong.

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Cliff Jones
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PostSubject: Re: hum and distortion on Oceanic H5000   2016-08-26, 7:52 pm

I have mentioned this before that the 1R5 does not have the frequency range that the 1L6 has, therefore your reception will get worse at higher frequencies.

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Cliff Jones
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PostSubject: Re: hum and distortion on Oceanic H5000   2016-08-30, 8:27 pm

By the way you can use the search "TUNABLE HUM" in a Google search.
Here's one of em I put my 2 cents worth in back in 2013.

[You must be registered and logged in to see this link.]

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ton10291

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Join date : 2016-08-15

PostSubject: Re: hum and distortion on Oceanic H5000   2016-09-04, 5:17 am

This probably has nothing to do with what you're seeing but...

Maybe 20 years ago I re-capped a pre-war Transoceanic but the audio was always distorted. When the radio was first turned on the audio was OK but it rapidly degraded as the set warmed up. I spent many, many hours trying to troubleshoot the issue but was never able to resolve it so the radio went on the shelf for display only.

For some reason about a month ago I decided to look into it again and this time with the aid of the internet was able to track it down to the candohm resistor "leaking" to the chassis .

[You must be registered and logged in to see this link.] .

When I physically disconnected the resistor from the chassis the radio played fine with no distortion.

I'm currently in the process of re-stuffing the candohm resistor tower and expect the radio to be a player again before the weekend is over.
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Cliff Jones
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PostSubject: Re: hum and distortion on Oceanic H5000   2016-09-04, 9:18 am

I edited your reference link, so people that are interested in it can click on it and go directly rather than copy it and type it in. I have saved the PDF file for my library. Thank you very much for your response and its follow up.

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