49-905 IF Transformer disassembly question - Printable Version
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49-905 IF Transformer disassembly question - OZ4 - 10-03-2014
This should be a simple one. I have a 49-905 and I want to check out the caps and clean inside the IF transformers.
What is the trick to removing the can from the IF transformers without destroying them?
They are held on to the chassis by clips which I can release but the guts are stuck inside. These are some of the smaller ones. Part # are 32-4240,4310,4257-1,4258
Thanks
Chris
P.S. I did find some info in the archives. http://philcoradio.com/phorum/archive/index.php?thread-2807.html
It looks like it just pushes out the bottom of the can. Mine must be stuck. I will try some more force.
RE: 49-905 IF Transformer disassembly question - Arran - 10-03-2014
If it's like the last Philco IF can I took apart you will have to remove the can from the chassis first to get the cover back on once it's removed. There is a clip that is near the base of the IF can, and this clip fits through a pair of matching slots on opposite sides, this clip must be removed to get the cover off and be re-inserted to hold the coil form in place, both are much easier to do with the can removed from the chassis.
Regards
Arran
RE: 49-905 IF Transformer disassembly question - Joeztech - 10-05-2014
There is usually also a set of bent inward indentations or tabs of aluminum from the side of the can that help secure the can to the internal coil assembly. These can be straightened and flattened out to allow the internal parts to be removed gently. Be careful as the internal plastic has become brittle with age. If in doubt, post pictures here and ask questions.
Joe
RE: 49-905 IF Transformer disassembly question - OZ4 - 10-10-2014
Yes I found the tabs on the base of the can. Thanks. The xformer I have checked seems to tune pretty well on the scope so now I am nit picking the small caps that this thing has all through the oscillator and rf section along with the resistors.
My problem now is the Riders schematic seems to have some discrepancies in it. I found the 12AU6 pinout has a mis print. And the radio some extra parts. My radio must have revisions in it.
Any place I can find a more accurate one? I seem to remember some saying that one could be ordered that is a much better copy.
This thing is a 49-905 121
Thanks
Chris
RE: 49-905 IF Transformer disassembly question - klondike98 - 10-10-2014
You are probably thinking of the schematics Chuck offers at http://www.philcorepairbench.com/schematics.htm but those only go as late as 1947.
RE: 49-905 IF Transformer disassembly question - Joeztech - 10-10-2014
Take a look at similar chassis in the 1949 offerings and also look at some from 1950. Sometimes you will find modifications in the next year model that is similar or in a same model year unit that has similar circuitry. I notice that Philco used 9.1mHz FM IF frequency. This may make parts for their FM IF specific to Philco. At least they did show the value of the capacitors inside their IF and detector transformer circuits. Many manufacturers later just bought parts that already were assembled from various suppliers and never bothered to show the values of parts inside. The thinking was that repair would involve complete replacement of the IF or Detector transformer. The IF and Detector transformers were readily available back then at reasonable prices. Now they are unobtanium, except from another parts chassis or some old stock that may have survived on a shelf somewhere.
Joe
RE: 49-905 IF Transformer disassembly question (Now with new pics.) - OZ4 - 10-18-2014
I finally got back to working on this one again. It has a pretty nasty hum in it that is affected by moving the 35C5. I have cleaned the pins and tightened the socket. I already replaced the weak rectifier tube and of cource the electrolytics. Also I have re-stuffed all the paper caps. The voltage is good now. I think I need a 35C5 tube. Any recommendations? I looked on ebay but I thought I would ask here first before buying one.
Oh and here's my first time capacitor cooker seen below. It's about 75 watts and only takes about 5-6 minutes. And does it stink! It's an outdoor activity only.
Thanks
Chris
RE: 49-905 IF Transformer disassembly question - morzh - 10-19-2014
Unless a necessity, I'd leave IF transformers alone save the alignment.
RE: 49-905 IF Transformer disassembly question - OZ4 - 10-19-2014
Morzh
Yes so far I have only looked at one of them for the AM section. I was worried about the silver mica caps inside but stopped short of taking them apart.
Out of the circuit it seems to tune OK. So after reassembly I have tried to align the AM section only. It does align but still sounds bad.
I am not sure if I should put the part about the bad audio/hum and the 35C5 tube in a new thread, I think it's lost here because of the title.
Chris
RE: 49-905 IF Transformer disassembly question - morzh - 10-19-2014
A faster way with tubular caps: simply heat one end at a time with a heatgun until it sweats (5-10 sec) and pull the wire with needlenose pliers.
Turn, repeat.
RE: 49-905 IF Transformer disassembly question - OZ4 - 11-03-2014
Back to this one again. So I have done the basics and replaced bad tubes no more hum. Now the radio works kinda. Even the fm works with poor sensitivity.
The question I have is on IF transformer Z302. The signal level is dropping from 4vpp to .04vpp through it yet it seems to tune OK. (measured with a X10 scope probe) From the drawings Z302 looks like it is a step up transformer.
The other IF transformer has a drop from 4vpp to .5vpp.
Am I missing something here?
http://www.nostalgiaair.org/PagesByModel/674/M0013674.pdf
Upon further inspection and a different method of measuring I found that Z302 the input side has 4vpp and the output also has 4vpp.
I am still stumped as why there is such poor am reception. It seem there is not enough gain. and I don't know what is normal for this thing. I am tired of it for now I will work on it some more later.
Thats all for now.
Chris