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


It is currently Oct Thu 23, 2014 2:38 am


All times are UTC [ DST ]



Post New Topic Post Reply  [ 3 posts ] 
Author Message
 Post subject: Philco 48-482
PostPosted: Mar Thu 01, 2012 4:54 am 
New Member

Joined: Oct Sun 30, 2011 7:40 pm
Posts: 2
I've replaced just about all the paper/wax capacitors in this radio as well as all the electrolytics. I've gone through the AM alignment procedures and get the local station 1350 KHZ loud and clear - as I proceed tuning toward the lower frequencies signal drops off dramatically to nothing. This was also obvious during alignment procedure - 580 khz signal generator tone came in weak. Does anyone have a silver bullet for finding the problem?

Also, the first step in the alignment procedure calls for the signal generator to be set at 455 khz and the radio dial to 1700 khz and then for certain trimmer adjustments to be made. That makes no sense to me. I think that has to be an error: the rest of the alignment procedures have signal generator and radio dial set at same frequencies. Am I missing a point here?

And, when I turn down the volume I get strong positive feedback in the form of a squeal. Help! Help!

And I get zero signals on SW and FM - very unrewarding endeavor this.
I would very much appreciate some constructive ideas from some kind, generous and knowledgeable soul out there.
Andy


Top
 Profile  
 
 Post subject: Re: Philco 48-482
PostPosted: Mar Thu 01, 2012 5:10 am 
Member

Joined: Mar Sat 06, 2010 11:34 pm
Posts: 253
Location: Las Vegas, NV
Step 1 aligns the 455 KHz IF, there wont be any interfering signals with the dial set at 1700. Thats the theory anyway. This has to be right or the dial tracking in steps 4,5, and 6 wont work correctly.

step 4, 5, and 6 interact. you adjust C502B for max at 1700, then C502A for max at 1500, then C508 for max at 580.

then repeat 4, 5, and 6 as many times as required until no further gain is detected at step 6 then redo step 4


Top
 Profile  
 
 Post subject: Re: Philco 48-482
PostPosted: Mar Thu 01, 2012 1:40 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4390
Location: St. Louis, MO, USA
Very nice radio!
You've probably already found it, but there's a very legible service bulletin on this model available at:
http://www.audiophool.cjb.net/Misc/philco_48-482.djvu
You need to install the special djvu browser plugin to view it.

Some of the comments from past posts on this radio say that the ferrite cores in the I.F. transformers are fragile and easy to break. Hope that hasn't happened to yours. :cry:

Regarding the squeal at minimum volume: check out the 4.2 ohm resistor to ground at the end terminal of the volume control. If it has gone high in value, or opened, a feedback squeal might result on account of the connection there from the output transformer.

Also ensure that the built-in low impedance antenna is connected to the correct terminals, 1 and 2 it looks like. There is a 3rd terminal that goes to the output transformer. It's there for convenience in hooking up a meter during alignment. If the antenna got connected there, well weird things might happen.

_________________
Terry Davidson


Top
 Profile  
 
Post New Topic Post Reply  [ 3 posts ]  Moderators: Marcc, Norm Leal

All times are UTC [ DST ]


Who is online

Users browsing this forum: badwaxcaps, tbirdremembered and 11 guests



Search for:
Jump to:  




















Privacy Policy :: Powered by phpBB