Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Tue 12, 2017 12:11 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 10 posts ] 
Author Message
 Post subject: Cobramatic question
PostPosted: Nov Thu 30, 2017 1:21 am 
Member

Joined: Feb Thu 08, 2007 2:23 am
Posts: 737
Location: central Ohio 43062
Hi all, got a question regarding the phono function.When its on phono should i hear station noise (without the phono actually playing? I restored this unit a long time ago and fired it up the other day.I'm not hearing stations just off station noise.The function switch is excellent.Thanks for any info.


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Nov Thu 30, 2017 4:48 am 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 534
Location: Dallas, TX
I'm not sure what you are asking. You shouldn't hear radio stations when the switch is set to phono.
Are you talking about "hiss" sound that is similar to between radio station noise? You might hear that when no record is playing.

_________________
Tim
"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Nov Thu 30, 2017 5:18 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3990
Location: Boston, MA USA
You might have to touch up the tuning of the Cobramatic oscillator.

-David


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Nov Thu 30, 2017 12:08 pm 
Member

Joined: Feb Thu 08, 2007 2:23 am
Posts: 737
Location: central Ohio 43062
Yes, I'm talking about the hiss off- station noise when it's switched to phono. Don't remember hearing that ,but maybe it is normal?


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Nov Thu 30, 2017 6:08 pm 
Member

Joined: Jun Sun 15, 2014 11:04 pm
Posts: 757
Location: Coos Bay, Oregon
There should be little noise on the phono mode. The radionics pick up depends a lot on a good connection between the pins on the cartridge and the input to the oscillator. Make sure the contacts are clean and solid! Then, be sure the oscillator is peaked to its optimum. There may be other components that can cause hiss, such as leaky capacitors, or weak resistors, or even a noisy vacuum tube, especially the ones in the oscillator discriminator circuit.


Last edited by startgroove on Dec Fri 01, 2017 5:16 pm, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Nov Thu 30, 2017 6:47 pm 
Member

Joined: Feb Thu 08, 2007 2:23 am
Posts: 737
Location: central Ohio 43062
Yes, the oscillator is peaked. All the old caps were replaced. I'll check he resistors in the circuit. I did check the tubes in the oscillator circuit. thanks....


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Dec Fri 01, 2017 7:27 am 
Member
User avatar

Joined: Apr Wed 09, 2008 3:37 am
Posts: 14253
Location: Little Rock, Arkansas
I had static in one Cobra-matic that turned out to be a bad phono plug. I replaced the entire phono cable with a new one, and the player is now quiet as a mouse when no records are playing.


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Dec Fri 01, 2017 12:07 pm 
Member

Joined: Feb Thu 08, 2007 2:23 am
Posts: 737
Location: central Ohio 43062
Larry, was just thinking of that! I'll replace it and see. Thanks


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Dec Sun 03, 2017 5:49 pm 
Member

Joined: Feb Thu 08, 2007 2:23 am
Posts: 737
Location: central Ohio 43062
Replaced the phono cable,no change


Top
 Profile  
 
 Post subject: Re: Cobramatic question
PostPosted: Dec Sun 03, 2017 11:52 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 534
Location: Dallas, TX
Like startgroove said, noise can come from capacitors, resistors or tubes. Unfortunately the noise isn't detected on most tester. (Some tube testers do have a place to plug in earphones.) The noise you are talking about (hiss) is like a quiet 'bacon sizzle' isn't it? That's a random type of signal. You might try substituting tubes, or replacing resistors. Another possibility is that you just don't remember how noisy it was the last time you played it, it may never of been as quiet as modern players.

_________________
Tim
"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


Top
 Profile  
 
Post New Topic Post Reply  [ 10 posts ]  Moderator: Alan Voorhees

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 9 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB