46-200 audio distortion SOLVED
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Joined: Oct 2018
City: Silver Spring
State, Province, Country: Maryland
I have just re-capped and "re-resistored" my "new" 46-200. It's one of the later iterations with a PM speaker, resistors in place of the field and a few other part substitutions from the earlier production runs.
All is well EXCEPT for the audio. It's distorted at any volume level above low -- as if the AVC isn't working properly. All components in the circuit are new except for the tube.
A several-year-old thread notes a potential cause related to the built-in loop antenna. The loop exhibits continuity just fine and appears to have just two connections -- one to the antenna coil and the other to the RF section of the the tuning capacitor. Do these need to be in any particular order with regard to front and back of the loop? I can't see that it would make any difference, but I'm surprised that the antenna has anything to do with audio distortion at all, so...
Oh -- here's another new post-restoration symptom that may be related: when I remove the external antenna lead from the chassis, reception is improved, even without an antenna wire connected. (The distortion remains, though). In other words, a two inch long chunk of wire outperforms the loop!
Any ideas?
Many thanks,
Craig
Silver Spring, MD
(This post was last modified: 10-25-2018, 09:47 AM by crgrbrts.)
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Welcome to the Phorum!
There's a Philco Service Bulletin for that model available on the audiophool site. (you need a djvu plug in or reader that is available for download on one of his pages, if you have trouble seeing the schematic let me know and I can covert it to pdf for you).
The Nostalgiaair Riders link is HERE for those with troubleshooting skills. (I'll let other more skilled folks try to sort out your problem)
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City: Roslyn Pa
Hi Craig and welcome,
1st off the loop has two connections one to the rf side of the tuning cap and the other to the avc line. If the avc side isn't connected that could give the problem you describe.
I'd check the spkr to be sure the voice coil isn't rubbing on the pole.
Check voltage @ pin 5 of the 50L6 should see abt - 7vdc.
Would think that the avc line would be abt - 4 or -5v when tuned to a strong station.
Grew up near Silver Spring (Sandy Spring) but have been up in Pa (near Philly) for the last
30 yrs.
de N3GTE
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
(This post was last modified: 10-24-2018, 09:43 PM by Radioroslyn.)
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Thank you Bob and Terry -- terrific advice. This morning I turned my attention to the 46-200's apparently touchy loop antenna circuit by asking myself "what have I done to change this?" Hmmm. Well, I did replace that old, original wax paper Philco branded antenna coupling cap up top with a shiny new yellow poly number. The waxy brown one was marked .0015 MFD, so I substituted a new one of the same value (or did I?).
At any rate, I dug the old Philco cap out of my trash bin and re-inserted it. Bingo! No more audio distortion! (Okay, there's one exception and that's a 50KW clear channel AMer at 1500 KHz whose transmitter is precisely one mile from my house. None of my receivers, including my fancy Kenwood and ITT Mackay Marine jobs, can handle WTOP Radio very well, so I'll forgive my $20.00 Philco). Anywho -- the 46-200's playing nicely now.
BTW, my most rewarding Philco project was the rebuild of a PT-25. I found the cute little number in a New Hampshire antique shop. It was in cosmetically decent and definitely worth sprucing-up condition. When I pulled the chassis out, however, I was shocked to note that an apparent 'lytic unwellness had blown to smithereens all power supply components and most of the radio's wiring. Melted insulation, charred resistor remains, boiled wax and scorch marks littered the bowels of the little Philco.
I was about to toss the thing in the trash (it had cost $10.00) when I drew myself up to full height (5'6") and vowed to bring this abused little wireless set back to life. And I did -- working from a schematic and replacing every single cap, resistor and hookup wire in the thing. About the only original components left intact were the IF cans, inductors and tuning capacitor. After a long round of TLC, it played, naturally, just as new.
Thanks again, fellas!
Craig
W3CRR
Silver Spring (near Sandy Spring) Merry-Land
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State, Province, Country: OR
Posts: 7,215
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Hey Craig we are HAM's we can fix ANYTHING! [Image: http://philcoradio.com/phorum/images/smi...wisted.gif]
>WTOP
Oh the old WJSV. You might enjoy this: https://archive.org/details/OTRR_WJSV_Co...ay_Singles Some of your old sets
may have played this when broadcasted
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
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City: Boston
State, Province, Country: Massachusetts
Great news Craig, WTOP sounds good up here in Beantown, and I like 1500 Federal Radio, do they still play the Capitals games?
Paul
Tubetalk1
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State, Province, Country: Maryland
Hey Paul!
Beantown, eh? Well, I moved down here from Gloucester about 20 years ago (and still get mighty homesick). WTOP sounded good up there, f'sure, and I listened regularly. Now, considering my proximity to it, it sounds good on my microwave, bed springs and electric toothbrush.
Yup, the Caps games are still broadcast by the station down the street. (I'm looking at their towers now).
Craig
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Well at least the seafood is still good and fresh!
Paul
Tubetalk1
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