ANTIQUE-RADIO-LAB

Antique Radio Forum for Collectors antique-radio-lab.forumotion.com
 
HomeHome  RegisterRegister  FAQFAQ  SearchSearch  Log inLog in  

Share | 
 

 Problem with my Concert Grand

View previous topic View next topic Go down 
AuthorMessage
wildcat445

avatar

Join date : 2014-08-16

PostSubject: Problem with my Concert Grand   2017-05-15, 5:47 pm

This is not technically a radio, but it has a radio in it and the problem is evident with the radio in operation, so here goes.

I am using my Magnavox Concert Grand as a flat panel stand.  TEMPORARILY!  (Long story)  This fact is pertinent.

When I fired it up after sitting unused all winter, it suffered from the typical scratchy function switch.  I pretty much worked thru that, then a new problem developed.  There is a hissy, scratchy noise in the Channel 2 treble speaker that started out intermittent, but is now pretty much constant.  I am blaming the now inaccessible external speaker switch as being the problem.  I say inaccessible because I have to remove a 55" flat panel before I can open the changer compartment and mess with that switch.  I am also experiencing more hum than I would like on an intermittent basis.  I have problems with getting the function switches and speaker switches clean enough in the Magnavox "bi-amped" instruments to keep from having weird issues like that.  This stereo has been thoroughly gone thru, caps and most resistors replaced, tubes tested, the usual routine.  If it isn't that switch, I need to look at the tubes in that treble amp, P-P 6V6's.  There is no squealing or oscillation, so I'd believe that would pretty much rule out a cap opening up somewhere.  I have never seen a tube really cause an issue like this.  No smoke or anything running hotter than normal.  I don't see any flashing in the tubes like might be seen with a short somewhere.  The noise gets somewhat less when the set has run a couple hours, but it is always there.  There is no distortion or lower output.  My next step is to remove the TV and see if I can remove and clean the speaker switch.  I have some other tinkering I'm doing on this stereo.  I'm designing and making a new back for the cabinet that will allow for better cabinet ventilation, but that will be for another thread.  And I finally found a "short cable" Multiplex adapter that will eliminate some of the wiring mess in the cabinet.

Don't tell the Magnavox boys, but I'm beginning to believe a Concert Grand is more trouble than it is worth.  Mine fills a spot at the top of my Magnavox collection, I'm thrilled to have it and it gives me bragging rights, but that's about all it's good for.  Magnavox made better performing stereos than a Concert Grand, that I can tell you for sure.  There is always something wrong with mine.  Never serious, just enough to be annoying.  These things cost the price of a cheap Chevrolet when they were new.  But I have to remember the thing is over 50 years old and was never intended to be around this long.  I'm overlooking something here.

_________________
Often in error, seldom in doubt.
Back to top Go down
Cliff Jones
Site Administrator
Site Administrator
avatar

Join date : 2010-11-22

PostSubject: Re: Problem with my Concert Grand   2017-05-15, 6:08 pm

it's possible that a tube has an internal short. Reseat all the tubes, a unsoldered joint comes to mind also. Check the audio ground to the audio jacks. also if it has a phone jack (unlikely) some were hard wired into the speakers and when you inserted the Jack it disconnected the speakers. so when not in use the speaker reconnected, and the contacts became weaker by no longer making solid contact just like transistor pocket radios.

Heat will change things, if you have a resistor going bad it will cause noise, try tapping the components with wood or plastic stick. Not all new components are up to snuff.

_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!
Back to top Go down
Cliff Jones
Site Administrator
Site Administrator
avatar

Join date : 2010-11-22

PostSubject: Re: Problem with my Concert Grand   2017-05-15, 6:20 pm

http://www.antiqueradio.com/Apr08_Jones_Magnavox.html

Same problem on this link.

Note I may have to change the forum again there is no function for editing posts.

_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!
Back to top Go down
wildcat445

avatar

Join date : 2014-08-16

PostSubject: Re: Problem with my Concert Grand   2017-05-15, 7:22 pm

The instrument in the article you linked was for a 1ST665, that I call the "little" Imperial.  Although the amplifier is radically different than the Concert Grand's twin split-frequency amplifiers, he certainly offered food for thought.  Tube sockets, eh? 

This brings up an interesting thought.  When I redid my CG, I found it literally infected with white corrosion on most of the tube pins.  The 6EA8 in the MPX adapter to this day has issues with corroded tube pins.  With a split-frequency amplifier, the 12AX7 pre-amps work with the PPP 6V6 bass amp, and the 12AT7 works with the P-P 6V6 treble amp.  So, according to this article, I need to take a look at the tubes in the treble amp, IN TOTAL, in the Channel 2 treble amp.  Since the noise appears in all positions of the function switch, the issue should be confined to at least the Channel 2 amp, and likely the treble amp.  Interesting.  I can check this without removing the TV......

Thanks Cliff.  This gives me a place to start.

_________________
Often in error, seldom in doubt.
Back to top Go down
wildcat445

avatar

Join date : 2014-08-16

PostSubject: Re: Problem with my Concert Grand   2017-05-15, 7:24 pm

I see you have fixed the editing.

_________________
Often in error, seldom in doubt.
Back to top Go down
Cliff Jones
Site Administrator
Site Administrator
avatar

Join date : 2010-11-22

PostSubject: Re: Problem with my Concert Grand   2017-05-15, 7:30 pm

I just received a call that my brother in law was working in the garage close by and somehow gas caught on fire and he was burned over 75%, He was too heavy to transport by Evac and they don't expect Him to Survive. He Had A Previous Stroke Paralyzing Him on one Side.

Makes one Think about many things.

_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!
Back to top Go down
wildcat445

avatar

Join date : 2014-08-16

PostSubject: Re: Problem with my Concert Grand   2017-05-15, 7:32 pm

Here is the a picture of one of the CG amplifiers, top and bottom views.  This is just for one channel.  There is an amplifier like this for each channel.






_________________
Often in error, seldom in doubt.
Back to top Go down
wildcat445

avatar

Join date : 2014-08-16

PostSubject: Re: Problem with my Concert Grand   2017-05-15, 7:34 pm

Cliff, I'm sorry to hear about a tragedy like that.  My thoughts and prayers go out for him and his family.

_________________
Often in error, seldom in doubt.
Back to top Go down
wildcat445

avatar

Join date : 2014-08-16

PostSubject: Re: Problem with my Concert Grand   2017-05-21, 7:45 am

The problem with my CG appears to have originated in the external speaker switch.  I removed the TV set and got to the switch.  I manipulated the switch and changed, then eliminated the noise.  Instead of putting it in the recommended "D" setting on the switch, I put it in "E", which is all the speakers, instead of just the console speakers.  While I was there, I checked tube sockets and actually found that wiggling the 12AT7 pre-amp tube for the treble channel, there was some noise.  I subbed those tubes and the 6V6's with really no change one way or the other.  The speaker switch is housed in the speaker compartment of the Channel one speakers and is a total pain to mess with.  It was fairly dirty.  I cleaned it with a pencil eraser, contact cleaner and WD40.  We'll see.

_________________
Often in error, seldom in doubt.
Back to top Go down
Cliff Jones
Site Administrator
Site Administrator
avatar

Join date : 2010-11-22

PostSubject: Re: Problem with my Concert Grand   2017-05-21, 8:06 am

With all that white corrosion, you have a job ahead of you. But on the other hand, with so many tubes, switches and speakers, I guess in some quarters it's considered Creme-Della-Creme. The time spent cleaning may bring rewards.

_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!
Back to top Go down
wildcat445

avatar

Join date : 2014-08-16

PostSubject: Re: Problem with my Concert Grand   2017-05-22, 5:18 am

I would hate to be without my Concert Grand, but am also not in the market for another one!

I find the smaller, less complicated Magnavox instruments better performers without all the complication.  44 tubes in a console stereo is overkill to say the least.  There is lots of stuff to go wrong.  I am fortunate that I can make this statement with some basis in fact, since I own both the larger ones and smaller ones and can compare them side to side.  I have gotten the white corrosion situation under control.  My  CG is not used a lot, mostly on Sundays to play CD's.  The rest of the time we use the smaller ones.  I need to develop a method of cleaning switches that is more effective and more permanent.

_________________
Often in error, seldom in doubt.
Back to top Go down
19&41

avatar

Join date : 2014-08-19

PostSubject: Re: Problem with my Concert Grand   2017-05-22, 2:16 pm

For cleaning tube sockets, there are small brushes available at the drugstore that are made in various sizes for cleaning small spaces between teeth.  They would work nicely to pass through the pin sockets soaked in 91% iso alcohol.  Look where the dental tools and flossers are.

_________________
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke
Back to top Go down
Sponsored content




PostSubject: Re: Problem with my Concert Grand   

Back to top Go down
 
Problem with my Concert Grand
View previous topic View next topic Back to top 
Page 1 of 1
 Similar topics
-
» Grand Ayatollah Khomeini (1900-1989) - political & spiritual leader of Iran
» mardi 23 mars: Un grand restaurant de gastronomie....
» Silverfish problem....
» mardi 5 avril : Le grand ménage!
» Greek Company Wins 200m-Euro Grand Faw Contract

Permissions in this forum:You cannot reply to topics in this forum
ANTIQUE-RADIO-LAB :: Radio Repair Bench :: Radios -Tube type-
Jump to: