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


It is currently Nov Thu 23, 2017 4:20 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 6 posts ] 
Author Message
 Post subject: Perdicta Barberpole 9L37 chassis
PostPosted: Oct Mon 09, 2017 12:37 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 976
Location: Coopersburg, PA USA
Sometimes life gets in the way and things sit. Such is the case with this Predicta. Last I posted I had issues with vertical hold locking - adjust vert hold knob, then it scrolls - lather, rinse repeat.

i ordered a K3 couplate from Bob Anderson (first-rate products) since that's what my other partner in crime George suggested.

I installed the K3 (pulling the master board again (arg). Now I get full audio but no raster on the screen. Also the 12DQ6 Horiz output is v-e-r-y hot to the touch.

Please help this TV newbie figure it out.

BTW, all paper and lytic caps replaced, resistors out of tolerance and couplates rebuilt by myself except K3. Set is pulling exact amperage per schematic.

Wiggling all tubes does nothing. I say this because in the past I had a loose 9BR7 tube.

_________________
Stan Saeger
Coopersburg, PA
http://www.saegerradio.com/


Top
 Profile  
 
 Post subject: Re: Perdicta Barberpole 9L37 chassis
PostPosted: Oct Mon 09, 2017 4:17 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 25721
Location: Detroit, MI USA
Sounds like the horizontal drive to the 12DQ6 is missing........ could be the oscillator is not running, most likely something happened while you had the board out to replace the couplate.

I'd start by carefully checking the resistance of the horizontal oscillator coil (don't ask me how I know this) followed by verifying that all the wires connecting to the circuit board are soldered to the correct stakes, and all the ground stakes are soldered to both the board and to the metal chassis.

_________________
Dennis

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


Top
 Profile  
 
 Post subject: Re: Perdicta Barberpole 9L37 chassis
PostPosted: Oct Mon 09, 2017 5:32 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 976
Location: Coopersburg, PA USA
I did voltage and resistance checks on the 12DQ6 tube:
Resistance
Pin1 - open as expected
Pin2 - 23ohms, should be 22 OK
Pin3 - open as expected
Pin4 - 7.5K ohms, should be 9K ohms OK
Pin5 - 1.1M ohms, should be 1M ohms OK
Pin6 - Not used
Pin7 - 20 ohms, should be 20 ohms OK
Pin8 - 0 ohms, should be 0 ohms OK
Cap - 14 ohms, should be 28 ohms OK

Voltage
Pin2 - 79vac, should be 93vac
Pin4 - 137vdc, should be 175vdc
Pin5 - 1vdc, should be -45vdc <<------
Pin7 - 68vac, should be 81vac
Have to try an figure out why Pin5 is so far off. Any ideas appreciated.i
Mr. Detrola - do you know the part number for the horiz osc coil (Ln where n is a number)? I don't see it on the parts list.

Again, 12DQ6 is H-O-T to the touch
s

_________________
Stan Saeger
Coopersburg, PA
http://www.saegerradio.com/


Top
 Profile  
 
 Post subject: Re: Perdicta Barberpole 9L37 chassis
PostPosted: Oct Mon 09, 2017 5:46 pm 
Member
User avatar

Joined: Nov Thu 11, 2010 6:03 pm
Posts: 629
Location: Pewaukee, WI
Pin 5 voltage indicates loss of signal from H osc.

The osc coil is L22 on this schematic: http://www.earlytelevision.org/pdf/Phil ... -439-1.pdf

Until you get the osc working I recommend removing the H output tube and connecting ONLY it's heater back into the set via clip leads....If you run the output tube without grid drive for more than ~20 seconds you risk damaging that somewhat pricey tube.


Top
 Profile  
 
 Post subject: Re: Perdicta Barberpole 9L37 chassis
PostPosted: Oct Mon 09, 2017 8:54 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 25721
Location: Detroit, MI USA
In addition to damaging the 12DQ6, which may already be ruined, drawing that excessive amount of current through the flyback for more than a few seconds can also ruin that nearly unobtainable part.

The horizontal oscillator is definitely not providing a drive signal to the output tube as evidenced by the missing negative grid voltage on pin 5, as Tom already pointed out.

_________________
Dennis

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


Top
 Profile  
 
 Post subject: Re: Perdicta Barberpole 9L37 chassis
PostPosted: Oct Mon 09, 2017 9:23 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 976
Location: Coopersburg, PA USA
Thanks for your help so far. I checked the resistance of L22 and it measures 147ohms, spec is 140 ohm, so L22 looks good.

_________________
Stan Saeger
Coopersburg, PA
http://www.saegerradio.com/


Top
 Profile  
 
Post New Topic Post Reply  [ 6 posts ]  Moderators: 7jp4-guy, Mr. Detrola

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 10 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB