Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Aug Tue 09, 2022 10:14 pm


All times are UTC





Post New Topic Post Reply  [ 9 posts ] 
Author Message
 Post subject: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoughts
PostPosted: May Sun 15, 2022 7:31 pm 
Member

Joined: Aug Sun 23, 2015 5:01 pm
Posts: 1387
Location: NJ 08090
Location: Deptford NJ
Customer brought in a 1966 Packard Bell stereo console....Model RPC72W...solid state. The phono circuit has me stumped. I put in a new ceramic cartridge to replace the old one....but I just get weak tiny sound. I tried a couple other cartridges, no change. I found I got 15vdc on the hot tip of the RCA jacks from the phono cable. Looking at the schematic I now see there is voltage applied to each side (L-gets 7v to the outside RCA plug/R-gets 7v to the tip thru a 2.2k resistor). Never saw this before...can't understand what they were doing. I'm guessing that voltage is killing my signal from the cartridge. See attached circuit....
Image


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Sun 15, 2022 7:56 pm 
Member
User avatar

Joined: Nov Sun 29, 2020 4:59 pm
Posts: 544
Location: Northeast Illinois
Location: Carol Stream, Illinois 60188
That's not the usual schematic symbol for a ceramic phono cartridge, and not something that I've ever encountered.
A phono pickup that produces a variable resistance?
Your schematic looks to be from a Sams Photofact. What does the parts list say about the original cartridge?

- Jim


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Sun 15, 2022 8:04 pm 
Moderator

Joined: Jan Thu 01, 1970 12:00 am
Posts: 29318
Location: Detroit, Michigan, USA
I agree it's likely that was a very special cartridge which required that applied voltage to work properly. Possibly along the lines of the old ultrasonic TV remote receivers that had a + voltage applied to the center pin of the RCA jack and wouldn't work if that voltage was not present at the microphone.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Sun 15, 2022 8:23 pm 
Member
User avatar

Joined: Nov Sun 29, 2020 4:59 pm
Posts: 544
Location: Northeast Illinois
Location: Carol Stream, Illinois 60188
To use a "normal" ceramic cartridge, I'd start by removing the 2200 ohm resistors R83 and R128 and the +7V connection to the left RCA jack.
Instead connect the jack shell to ground like the right channel.
Some additional tweeks may be necessary, as the output level (and perhaps the frequency response) of the new cartridge may be different than the original.

Also... If the original cartridge appears to be intact and functional, I notice that turntableneedles.com still has a replacement stylus available for it.

- Jim


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Sun 15, 2022 9:52 pm 
Member
User avatar

Joined: Jul Fri 18, 2008 9:02 am
Posts: 2611
Location: Alton IL 62002 Near ST. Louis
It is Condenser phono cartridge like a condenser mic , it was made by Panasonic or Sony .It has a high level output and a special EQ and will need a different preamp stage to make it sound correct with a different cartridge .

_________________
Mark
(Conti the brain damaged robot )
PG-18-23909


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Mon 16, 2022 2:08 am 
Member

Joined: Aug Sun 23, 2015 5:01 pm
Posts: 1387
Location: NJ 08090
Location: Deptford NJ
Thanks for the info guys!!....I went back and checked the old cartridge and got good ohm readings out of each channel..but the needle is busted. I just 'assumed' it was a ceramic that was old and dead..so much for assuming. If I brush the cartridge saddle with my finger I do get some sound...so it appears alive. I ordered a needleBTW...It has a Euphonics U15-2 cartridge.


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Mon 16, 2022 2:36 am 
Member

Joined: Jan Thu 01, 1970 12:00 am
Posts: 2443
Location: Mt. Airy, Maryland
Attachment:
Screenshot 2022-05-15 223513.jpg
Screenshot 2022-05-15 223513.jpg [ 439.43 KiB | Viewed 559 times ]


Not a condensor, it's solid state and needs the bias.


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Mon 16, 2022 8:35 pm 
Member

Joined: Sep Thu 20, 2007 2:16 am
Posts: 1102
Location: Winter Park, Florida
The top line Admiral consoles used the Euphonics Miniconic also.


Top
 Profile  
 
 Post subject: Re: Odd Phono Ceramic Cartridge Circuit--Need Opinions/Thoug
PostPosted: May Fri 20, 2022 2:56 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 12:00 am
Posts: 11783
Location: Beaver Falls, PA. USA
Admiral used a variable resistance cartridge back in the 1940s; the element was made of conductive rubber.

_________________
Tim KA3JRT


Top
 Profile  
 
Post New Topic Post Reply  [ 9 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB