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 Post subject: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Thu 24, 2019 1:21 pm 
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I have a 1953 tabletop Zenith Cobramatic phonograph. It plays very well, but, for no obvious reason breaks into a very loud crackling screech that sounds like it with blow the speaker! It doesn't seem to happen because of volume or a loud point on the record. It's made the unit basically unusable. A friend said to tap the tubes when it's playing and see what happens. It has a new multi-use green/red needle and what I believe is the original cartridge. Thanks all for any information or ideas.


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 Post subject: Re: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Thu 24, 2019 2:02 pm 
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Location: Long Island NY
Easy...
First spray the tube sockets with Deoxit. Then try the 6J5 or 12J5, whatever it uses as the phono preamp tube.
The issue is somewhat common.

:)

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 Post subject: Re: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Thu 24, 2019 2:48 pm 
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OldRestorer wrote:
Easy...
First spray the tube sockets with Deoxit. Then try the 6J5 or 12J5, whatever it uses as the phono preamp tube.
The issue is somewhat common.

:)

Many thanks Kirk!! Mine's the 12J5. The phono is too nice to not be enjoyed.


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1953 Zenith Cobra-matic S-9010.JPG
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 Post subject: Re: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Thu 24, 2019 9:45 pm 
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Awwww,
I sold mine last year to get the S-9011. I sold mine with the 45 adapter stupidly...

:(

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 Post subject: Re: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Thu 24, 2019 11:02 pm 
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Location: Long Island, N.Y.
OldRestorer wrote:
Awwww,
I sold mine last year to get the S-9011. I sold mine with the 45 adapter stupidly...

:(

I found the adapter on eBay and jumped at the opportunity. I got this one from Terry several years ago, and although it plays fine with a very good double cone replacement speaker, it has a low thumping sound that drowns out when the record is playing. I ordered a good tested replacement tube and am looking forward to hearing this unit play without screaming at me! LOL. It is a beautiful Cobramatic that you don't see or hear about much. I honestly thought it was from the late '40's. Kinda of deco for '53.


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 Post subject: Re: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Fri 25, 2019 2:24 pm 
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Thumping is the idler. It wont go away unless you get it redone. I have the same low bump but I dont mind it since I also cant hear it when the player is active.

:)

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 Post subject: Re: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Sun 27, 2019 2:36 pm 
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OldRestorer wrote:
Thumping is the idler. It wont go away unless you get it redone. I have the same low bump but I dont mind it since I also cant hear it when the player is active.

:)

Thanks Kirk. When the set is running for about 15 minutes the thump gets much quieter. I'll probably leave it as is. I got the new tube, but probably the worst choice (I was later learn) which is a glass Tung-Sol. It turned out to be 100% better though. It slightly goes into a short low microphonic buzz if you push the volume on certain recordings, but it doesn't go into the ripping screech like the original tube.


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 Post subject: Re: Microphonic sounding screech - '53 Cobramatic
PostPosted: Oct Sun 27, 2019 4:42 pm 
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Ya know,
I could have easily sent you the tube. If the problem is solved then great. If you want me to send you another tube to try let me know.

Kirk

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