Signal Injection Question
Posts: 41
Threads: 3
Joined: Jan 2017
City: East Brunswick, NJ
My model 46-200 has no sound at all. When I inject a modulated 455 Khz tone at the antenna the 1 khz tone is clearly heard at the speaker. What could be the cause of this disparity? I've replaced most of the caps and the voltages on the tubes seem to be within range of the schematic. The filaments and pilot lamp both are working although I really can't see the 7A8, 7B7 or the 7C6 filaments and don't have a tester for the Loktals. Can someone explain this signal vs. no sound "problem" ?
Welder
Posts: 2,118
Threads: 112
Joined: Jun 2010
City: Medford OR (OR what?)
Easy. Your IF section works and your RF and or first detector do not. I haven't looked at your schematic.
The long and short of it is to look for a problem prior to the IF with one caveat - the oscillator may also be defective so actually look for your problem prior to the last IF transformer.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
Posts: 41
Threads: 3
Joined: Jan 2017
City: East Brunswick, NJ
Thanks Phlogiston. Sounds like a plan. I just replaced the 7C6 converter but no change. I've never replaced an oscillator but could be in my future. Keep you posted.
Thanks!
Happy Holidays !
Posts: 2,118
Threads: 112
Joined: Jun 2010
City: Medford OR (OR what?)
OK, I got un-lazy and looked at the schematic. The 7A8 does all of those jobs - as a converter. So look at everything prior to and including the 14A7.
Your 455 signal is being rectified by the 2nd detector just as it would be in normal operation. There is also the remote chance that it could be the 2nd IF trans. The closer the failure is to the detector the less volume you will get with your injected signal. You can use this to trace the failure - if you have the right probes and knowledge- so be careful.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
(This post was last modified: 12-24-2017, 12:04 PM by Phlogiston.)
Posts: 16,582
Threads: 574
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
I am not sure what to think.
You are injecting the IF signal in the Antenna screw? And it passes?
What exactly does "no sound at all" mean? No reception?
Have you tried the 550kHz to 1600kHz signal injected in the antenna?
Or are you trying to receive stations?
Is your Antenna screw Grounded by chance?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 7,305
Threads: 270
Joined: Dec 2009
City: Roslyn Pa
>My model 46-200 has no sound at all.
It would seem that the audio, det, and IF stages are working as you would have no sound when injecting a 455kc signal. Are you experiencing sound but no broadcast stations heard??
Inject a 455kc signal at the ant connection. Turn the generator so you can barely hear it from the spkr. Peak the IF trimmer for maximum signal heard.
One thing to check is the 46-200 has a loop ant that is glued to the inside back edge of the cabinet. Sometimes they are missing. It needs to be there and connected to the tuning cap.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 41
Threads: 3
Joined: Jan 2017
City: East Brunswick, NJ
Yikes! Thanks for the responses: My unit uses a 7C6, 2nd. detector and first audio, 7B7, 7A8 instead of the 14's. I also have a scope to use for this signal path. By no sound I mean no reception at all, zilch. I am injecting the signal where the antenna is connected to the oscillator. I have not tried injecting 550 & 1600. The green wire is grounded to the chassis with a screw. The antenna is still in place around the inside the cabinet. One wire goes to the osc. the other to the tuning plate capacitor nearest the back of the chassis. I will try and check the IF cans as you suggested. Thanks so much for all your help. The holidays will put a delay in my future testing but I will keep you guys posted.
Posts: 16,582
Threads: 574
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Is your loop antenna ok? Check it for the open. Or unsoldered. Or maybe your chassis is out and it is disconnected.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 41
Threads: 3
Joined: Jan 2017
City: East Brunswick, NJ
Morzh;
Good point! I can't seem to get continuity but I tried another cabinet and that antenna does have continuity so I tried it but still no reception. Thanks for your post..
Welder
Posts: 1,269
Threads: 32
Joined: Jan 2014
City: Wellborn Florida
Looking at the sch on Nos. air going left to right 7A8, then a 7B7 as a sub for the 14A7, third 7C6 as a sub for the 14B6.Fourth tube 50L6. Then a 35Y4 Rect, I would look to see if some one has added a resistor in the filiment string to handle the extra 12 volts. and see if it is correctly installed and not dropping the B plus voltage.
http://www.nostalgiaair.org/pagesbymodel...013591.pdf
Posts: 1,269
Threads: 32
Joined: Jan 2014
City: Wellborn Florida
Will try and load info on the 7B7 and 7C6
Posts: 16,582
Threads: 574
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
So, when you moved between the cabinets, you unsoldered/resoldered the loop antenna, both wires?
AND you grounded the Antenna screw?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 41
Threads: 3
Joined: Jan 2017
City: East Brunswick, NJ
Morzh:
Yes, I did solder (tack) the wires for the other cabinet.
David: Thank you, I'll check out the tubes and possible resistor add. Thanks for the links.
Thanks Guys.
Welder
Posts: 41
Threads: 3
Joined: Jan 2017
City: East Brunswick, NJ
Morzh:
I forgot to post the antenna screw was grounded also.
You're referring to the green wire I presume.
Welder
Posts: 16,582
Threads: 574
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
How bout your tuning cap connection?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Users browsing this thread: 1 Guest(s)
|
|
Recent Posts
|
|
Philco Model 38-7: what caps & resistors do fail typically?
|
| Since you stated earlier, you have a console 38-7XX. They also had a 38-7T (table), and 38-7CS (chairside). A very nic...GarySP — 01:18 PM |
|
Part numbers to model cross
|
| That I wouldn't know, but sometimes the radio document itself shows one, same as the capacitor cans' etc pinouts.morzh — 12:46 PM |
|
Part numbers to model cross
|
| Thank you morzh, that is exactly what I was looking for. Now , is there some where that shows pinouts for Philco power ...Jim Dutridge — 11:37 AM |
|
Restoration of the Canadian General Electric A-87
|
| Thanks for your help Michael. In fact, this video is only an intermediate result. Later I had to apply another tinting l...RadioSvit — 09:01 AM |
|
Restoration of the Canadian General Electric A-87
|
| Great job on the cabinet.
PS. In the US notation, "kenotron" refers to specific type of tubes; we call re...morzh — 08:24 AM |
|
Part numbers to model cross
|
|
This document has at least some tables of models and parts used.
Example: Choke 32-7572, used in 604 radio.
Search f...morzh — 08:19 AM |
|
Restoration of the Canadian General Electric A-87
|
| I also checked all the radio tubes on my Hickok 530 tube tester. The 5Z3 kenotron turned out to be faulty, all the other...RadioSvit — 08:02 AM |
|
Restoration of the Canadian General Electric A-87
|
|
Well... While the varnish is drying up, I started repairing the chassis...
Of course I started by replacing the pa...RadioSvit — 07:12 AM |
|
Philco Model 38-7: what caps & resistors do fail typically?
|
| Hello Martin,
Welcome aboard our little community what great Model 38-7
Sincerely Richardradiorich — 12:30 AM |
|
Philco Model 38-7: what caps & resistors do fail typically?
|
| Welcome to the Phorum Martin.
I count about 9 paper caps, the 3 electrolytic caps and 2-Y2 safety caps to replace th...RodB — 09:44 PM |
|
Who's Online
|
| There are currently no members online. |
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
