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 Post subject: How do I rate an if transformer
PostPosted: Feb Tue 17, 2004 5:56 pm 
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Location: Austin, TX United States
I just realized that the 455 k.c. rating for my 2nd IF transformer on my Philco 41290 radio may not be 455 kc as my schematic states that value as that of the radio and not specifically for the IF transformer in question. How do I determine specifically what I have. Philco part#32-3483<P>Thanks David<P>------------------<BR>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Tue 17, 2004 6:06 pm 
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Location: Detroit, MI USA
Hi David, The easiest way would be if the frequency were stamped onto the metal can, which sometimes is the case. Or you could look in the parts list for that radio and see if the part number of the IF transformer matches what was original.<P>Otherwise, if you were trying to determine whether an unmarked IF transformer is useable at a specific frequency, you would need to connect an RF signal generator and a voltmeter to the set, and attempt to perform the IF alignment procedure following the manufacturer's directions. If the IF transformer in question peaks at 455KC when you do the alignment, then it is correct. <P>Since the IF transformer in there has the Philco part number on it, if it matches the parts list then it is a 455KC transformer.<P>If the schematic states the IF frequency for the radio is 455KC, then all the IF transformers in the set will be 455KC. <P>------------------<BR>Dennis


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 Post subject: How do I rate an if transformer
PostPosted: Feb Tue 17, 2004 6:31 pm 
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Thanks a bunch Dennis <BR>It is an original part that was ruined at least twenty years ago and the pieces were stuffed into its can so I didn't know it was a problem until attempting to restore the chasis during the recap stage. I am learning so all the help everyone is giving me is invaluable and incredible thanks again and I hope to learn enough to able to help someone else someday.<P>David<P>------------------<BR>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Tue 17, 2004 6:43 pm 
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Location: Detroit, MI USA
Keep asking questions, because we all had to start somewhere and the only way to find out what you need to know is to ask. This is by far the best place on the internet to get information about radio restoration.<P>Personally, I think it is a bad day when I cannot learn something new. <P>------------------<BR>Dennis


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 Post subject: How do I rate an if transformer
PostPosted: Feb Tue 17, 2004 9:21 pm 
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Hi David,<P>You should go by the frequency shown on the schematic unless you have a VERY good reason to change it.<P>You will occasionally encounter a radio which has been intentionally retuned to a different IF, for example 460 or 465 for a radio designed to operate at 455. The technique was documented in the Philco service literature.<P>This was done in the "good ole days" to avoid interference from the maritime service that operated very high power telegraph stations in the 400 - 500 kc range. The maritime service is long gone, and the stations torn down and turned into beach-front condos <IMG SRC="http://antiqueradios.com/forums/smile.gif">. So there's no reason to shift the IFs. The radio will only track properly across the entire dial if the IF is set to its nominal frequency.<P>As to your original question, the part number might not match even though it's still a 455 kc transformer. For example, they use different part numbers for universal replacements, and might change numbers due to changes of internal components, different mounting styles, or other factors which don't affect the performance.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR> <A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Wed 18, 2004 3:41 am 
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Thanks everyone I do need all the help I can get. I do have another question. On my schematic it looks as though I have a first, second and third IF transformers the first left coil, as shown on the schematic has a .5 ohm coil the right side coil reads 11.5 ohms with a 7B7 tube the second IF transf. has a 8.5 ohm coil on the left side and a 22 ohm coil on the right also with a 7B7 tube The third IF transf. has 13.5 ohm left coil and a 21 ohm right coil with 2nd detector tube 7A6 next to it. The question is with all the IF transformers having different coil resistances how can they have the same rating?<P>Thanks Again<P>David<P>------------------<BR>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Wed 18, 2004 4:02 am 
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Hi Dave,<P>A transformer is a complex device. If you look at its resonant frequency, or its DC resistance, or its bandwidth, or the Q of the coil, or the turns ratio between primary and secondary, you're only looking at one factor. It's like looking at one vegetable in a seven-course dinner.<P>DC resistances are given on the schematic for diagnostic purposes, so you can determine whether a particular coil is open, shorted, or normal. They also help distinguish between parts if you happen to have one with the part number rubbed off. Some manufacturers used colored dots on the bottom of the coil form for the same purpose.<P>The different resistances also tell you, by inference, that the transformers are not interchangeable. Those in some radios are, while others are not. It depends on the design of the particular radio.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR> <A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Thu 19, 2004 12:35 am 
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Thanks for the info Liegh. That adds to my IF transformer problem though. I guess the next step is to find the characteristics for the part # 323483 IF transformer any suggestions or rescources???<P>Thanks David<P>------------------<BR>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Thu 19, 2004 12:59 am 
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Hi David,<P>Your best bet would be to find an old chassis or an original Philco part. You might try Gary Schneider's Play Things of [the] Past site at <A HREF="http://www.oldradioparts.com" TARGET=_blank>http://www.oldradioparts.com</A> . He's been out recently with a death in the family, so it might take him a few days to get back to you.<P>There are also general-purpose replacement IF transformers which would likely work in your radio. I'll try to look up some part numbers tomorrow.<P>Also try the Links page on my site, and the Resource page here. This is falls into the category of parts that may require many emails to locate <IMG SRC="http://antiqueradios.com/forums/frown.gif"> Better than the old days, when you might send out a bunch of letters and wait many months for responses.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR> <A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Fri 20, 2004 3:06 am 
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it is not necessary to match perfectly the resistance or turns ratio on IF's. otherwise we would not have universal replacements, which were common. What is important is the resonace frequency, and all of them near 456 are probably about the same . also a 455 kc will usually tune quite a bit either way (it passes 10khz when tuned to 455, so that is 445 to 465, without moving slug.As you pass by resonance, the drop off you see in response is due to tuning at least 10 kc away or off orf 455, which tells you something of the range they have.) ; All if 's in a given radio are tuned to the same frequency.The perfect replacement will give the exact designed in gain and bandwidth, but being off on one of them will not be detectable in a real radio, in the real world. You can usually find a way to mount "modern" tube type replacement slug tuned IF's (from AES, for one)inside the old IF can(even still inside its smaller can ) as long as you can get the tool to tune it in, which may need a hole modification. This allows use of PC type 455-456 tube IF's ,by mounting with stiff wire from IF pins to tube sockets etc.,along with epoxied wood spacers etc be sure to ground the can, however.The variations in R in coil are due to matching differing plate loads on different feed tubes,and different gauge wires used. This is for achieving certain Q and bandwidth , but none of that is critical to getting a radio working again, and working well. Don't want to send you on a wild chase for the perfect IF when it won't make much difference...FYI, John PS transistor type IF's will not work, as they are for much lower impedance circuits.<P>------------------<BR>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Fri 20, 2004 3:51 am 
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Hi David, I was just up in the attic looking for something else and found a junk chassis for a 41-245. The IF section circuitry looks very similar to yours on the schematic, with an adjustable coil slug and a trimmer on the first IF transformer, and only one trimmer on each of the 2nd and 3rd IF transformers. <P>Email me and I will send you an IF transformer off this 41-245 chassis that should be close enough to your original to work and you will probably not be able to tell the difference. I need to know exactly which position in the circuit you need on your set. Is it the one between the XXL and the first 7B7, or the one between the two 7B7's? You can possibly even remove the coil and trimmer as a unit and install it into your original can and it will then look 100% authentic. <P>Please fix the email address first.<P>tv radio at volcano mail dot com<P>------------------<BR>Dennis


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 Post subject: How do I rate an if transformer
PostPosted: Feb Sun 22, 2004 6:11 am 
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Location: Austin, TX United States
Dennis, the second IF transformer is the one in question it is located between the two 7B7 tubes a Philco part # 32-3483. I sent you an email but am not sure they went through, mine should be viewable now. <P>Thanks again<P>David <P>------------------<BR>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Mon 23, 2004 2:13 am 
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Location: Cambridge MN USA
Leigh- you said to follow the frequency on the schematic unless there's good reason not to. I ran into a Coronado that had to be tuned to 447 to track the whole dial properly.<P>Scott Todd<BR><P>------------------<BR>


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 Post subject: How do I rate an if transformer
PostPosted: Feb Mon 23, 2004 4:07 am 
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Hi Scott,<P>Two possible causes: 1) The mechanical synchronization between the dial and the tuning capacitor was lost somehow... possibly a prior repair or rework. 2) The inductance of the oscillator coil may have changed due to aging.<P>Since tuning capacitors themselves are extremely stable items, and don't change capacitance unless damaged, you need to look elsewhere. The laws of physics still apply, even to old radios <IMG SRC="http://antiqueradios.com/forums/smile.gif"> If the oscillator is not tracking correctly, there's a physical reason for the error.<P>But if you're happy with the way the radio works, don't worry about it <IMG SRC="http://antiqueradios.com/forums/smile.gif"><P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR> <A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A>


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