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 IF transformer - fixable or not?
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 Return to top of page · Post #: 1 · Written at 5:27:11 PM on 19 May 2013.
Maven's Gravatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

By a lot of cautious prodding with a wooden stick, I think I have isolated the erratic volume-fade problem that has been bugging me for years on my Philips Radioplayer 123. It has recently got worse.

The IF transformer is L5,L6 on the schematic - 12ohms, with capacititive shunts across both coils, inside the can.

I have found that pushing sideways on lug 3, on the primary coil L5, progressively increases output volume, proportionate to the pressure applied.

This makes me wonder if the capacitor inside the can on that side is failing, and reacts to pressure. I would think that if there were a loose connection, it would not have that progressive change with pressure.

Question is - is it possible/practical to open up the can and fix the problem? If not, how do I find an appropriate replacement IF transformer? The can has no markings and there are no specifications other than the 12ohm rating on both coils.

Maven


 
 Return to top of page · Post #: 2 · Written at 7:47:31 PM on 19 May 2013.
Redxm's avatar
 Location: Tamworth, NSW
 Member since 6 April 2012
 Member #: 1126
 Postcount: 466

Maven
Can't picture the model 123. Can you post a couple of pics.
1) The radio
2) The IF transformer

I have a few junked philips chassies here I could possibly have one for you to experiment/replace

cheers
ben


 
 Return to top of page · Post #: 3 · Written at 8:34:26 PM on 19 May 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

It is quite possible to get wire breaks when changing caps & components on IF transformers & coils, often excerbated by the application of too much heat, or force

My 132L shows it to have the small type IF's. I would have to slip the chassis to see how the can itself is actually assembled. I have only ever had one IF in forty + years (not that type) break a cap internally.

Just make sure that it is not a component like a resistor connected to it, that is the issue. There is a type of resistor in the fifties that causes me to shudder when I see them, their reliability is shoking & I have had to replace everyone of them in some radios. I did have an Astor RK fixer, where that happened for one.

Marc


 
 Return to top of page · Post #: 4 · Written at 9:52:17 PM on 19 May 2013.
Maven's Gravatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

.Marc

Not sure what "small type" is. The can in my 123 is slightly smaller diameter than the standard octal valves, but definitely larger than the mini valves. It seems to be held in place by three integral clips that could be bent to release it through the top of the chassis. The can has six lugs, of which 1&3 are L5, 4&6 are L6. The composition base of the unit seems to be held in place by the folded-in aluminium rim of the cylinder, which could be bent back with pliers, I imagine.

I'll post a photo of the base in the next day or so. Maybe a wide enough shot to identify suspect resistors.

.Ben

The front of the 123 radio cabinet is my avatar pic. It's out of the cabinet at the moment, so I'll post top and bottom pics of the chassis when I get them done.

Maven


 
 Return to top of page · Post #: 5 · Written at 9:52:18 AM on 20 May 2013.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 830

In America, the "K-tran" IF transformer was very popular, and they used a silver mica wafer that tends to fail. See my page of repair tips, scroll halfway down http://www.wa2ise.com/radios/repair.htm.





If your IF transformer looks something like this, you could try taking it apart. Be careful of the fine wire. And if you have to, you should be able to sub another IF transformer if it would physically fit.


 
 Return to top of page · Post #: 6 · Written at 10:23:35 AM on 20 May 2013.
Maven's Gravatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

.Wa2ise - thanks for the link. Very informative for me. My Philips uses different, cylindrical can IFs, but perhaps the principles might be the same? Maybe failing internal caps to be replaced by external ones?

Philips RadioPlayer 132 valve radio
Philips RadioPlayer 132 valve radio


Maven


 
 Return to top of page · Post #: 7 · Written at 7:48:13 PM on 20 May 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

My Philips 132L is the one Brad had as radio of the week a few weeks back.

Philips Radioplayer 132L


I have the Philips data which says IFT1 is CZ.320.421: IFT2 CZ.320.420. This is not what yours has.

One is oblong with two adjusters top. They are shorter than the valves & held down by a spring clip similar in concept to those used to hold down valves.

Yours have been swaged. You can likely fold the rim back to dismantle. Make sure all is marked (position of green dot) before dismanteling anything.

Take a good look at the power transformer, thats the type that often have have wires exiting from the sides of the wrap.

Marc


 
 Return to top of page · Post #: 8 · Written at 9:06:28 AM on 21 May 2013.
Scraps's Gravatar
 Location: Blue Mountains, NSW
 Member since 10 March 2013
 Member #: 1312
 Postcount: 401

It may make no difference but I'd try the simple things first. The solder joint doesn't look so good, clean it up with soldering braid, clean the resistor lead and wire so they're shiny and resolder the joint. As I say, it mightn't fix it but at least eliminates the joint.

Cheers,

Warren


 
 Return to top of page · Post #: 9 · Written at 10:40:38 AM on 21 May 2013.
Maven's Gravatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

I have redone the joint at lug 3. There's a bit of flux left on the base, which I can clean up later. I think the joint is firm, because there is no effect if I push down or sideways on the resistor, only if I push sideways on the lug itself, to the left.

I checked the part numbers written on the IF cans and they are consistent with the AORSM list :

IF1 = CZ 320-421.
IF2 = CZ 320-420.

Perhaps the later parts with same number used a different construction, but same specs.

The trimmers are external, and there are threaded holes in the centre of top and bottom of the cans. I guess these may anchor the iron cores of primary and secondar coils? If so, I would be concerned about spoiling the alignment by taking apart.

If I were to open IF1 and find no loose connections, should I look to replace the capacitors, as described by Wa2ise in his linked article?

I'd be concerned not to mess with alignment if I can avoid it. So say I bypass the internal ones and put replacements across the external lugs 1-3 and 4-6. How do I work out correct values for those caps?

Maven


 
 Return to top of page · Post #: 10 · Written at 4:41:57 PM on 21 May 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

I have as said only found a broken cap once. There is the possibility (more common) that there is a wire break. Do make sure the resistor is OK.

As an aside make sure that white bodied one is ok. I see quite a few of them out of tolerance.

If you replaced parts in the RF it is recommend, by HMV, for one that you re-calibrate.

They are not wrong

Marc


 
 Return to top of page · Post #: 11 · Written at 7:21:21 PM on 21 May 2013.
Redxm's avatar
 Location: Tamworth, NSW
 Member since 6 April 2012
 Member #: 1126
 Postcount: 466

Maven.

You might be interested in this.

http://www.ebay.com.au/sch/alans7413/m.html?item=290919468696.

I've had a bit of a dig, ran out of time today, but I'll keep looking.

Marc's suggestion about a broken wire is probably on the money.

Cheers
Ben


 
 Return to top of page · Post #: 12 · Written at 9:09:29 AM on 22 May 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

Under the heading "Seen it":

Dismantle that solder joint: That sort of plastic sleeving can be melted into the solder joint at which place it can insulate, totally, or partially, the wire it is sleeving.

A pair of Haemostats make a good heatsink for the benefit of stopping the heat melting some of the plastic formers, or the connection on the other side.

A really hot iron used quickly can be better than a colder one on joints like this.

If the former melts, the pin can move & break wires. Wire breaks on formers, due to repairs, are more common than one may think.

Bakelite, Ceramic & Wood formers are tending to be the more resilient. Several of the plastic ones are now suffering irretrievable decomposition. And that also applies to plastic cabinets.

Marc


 
 Return to top of page · Post #: 13 · Written at 5:19:32 PM on 22 May 2013.
Maven's Gravatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

OK, I've gone to the next stage on this. I removed the IF-1 can and opened it by working around the swaged rim just enough to release the base. In side I found the whole assembly was slathered in what looks like beeswax.

The internal capacitors are micas of the same type as the rest of the circuit, smothered in wax that I would have to remove to read any ratings on them.

Philips Radioplayer 132 IF transformer


When I carefully touched the wire leading from lug 3 to the coil, it parted. The wax has several obvious cracks in some places, I believe likely due to changes in temperature over. The wax layer over the tiny 5-strand copper wire has probably reduced the flexibility and created a point that concentrated all the normal flexing and eventually broke, as copper flexes can do at plug entries, for example.

It was quite difficult to repair. I took about 2cm of similar fine stranded copper wire and tinned the whole length of it with solder, then soldered it to the base lug. I carefully wiped the end of the wire leading to the coil with a soldering iron and a flux pen, trying to get rid of as much as possible of the wax and varnish insulation. The wire is very fragile and I didn't want to lose any more of it. Eventually I got a bond between the loose end and the end of the new tinned section.

Philips Radioplayer 132 IF transformer


I checked that there was continuity on both coils. The repaired primary showed the rise and fall in resistance consistent with a capacitor in parallel circuit, and settled at 20ohm. The secondary settled at 12ohm, which is the specified rating for both coils. So the repaired coil has gained 8ohm through the repair joints - I don't know if that is significant or not.

I set up the IF TX with double-ended test leads to put it back in circuit, out of the chassis. In the photo, you can see the leads at the chassis top left, and you can just see the tinned section of repair wire bottom right.

The radio functions exactly as before, with fluctuating volume affected by duration of service and by spikes in the power circuit - eg switch on/off - but I'm wondering if this might be a secondary effect of those spikes sending a RF pulse through the RF circuit.

Many questions now:

1. Is there a safe way to remove the wax to read those mica cap values, and should the wax be replaced in some way?

2. Should I proceed to replace the internal mica caps?

3. The resistor R3 between lug 3 and V1 is specified as 30kR, but reads 40kR - does that matter?

4. Should I be just replacing a whole lot more components while the chassis is on the bench? So far, only the higher-value capacitors have been replaced.

Maven


 
 Return to top of page · Post #: 14 · Written at 6:00:19 PM on 22 May 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

Do remember that the wire on those coils is insulated and that needs to be scraped off.

Any resistor labled one thing and is 10% out is, as I fix commercially, is replaced. If the Monkey has been in there, it is not at all unusual for the wrong part to be in there.

The A.G.E. (Radiola 31) on the bench had all but one cap replaced with 0.1mfd and the filters were wrong as well.

The IF caps are often specific to the coils, the primary has the highest volts on the caps but not across them.

The fault has the hallmarks of a bad connection (dry joint) however, that is also the footprint of a bad Mica cap. They also have a habit of hissing & crackling.

Does the radio go off frequency when it faults?

The most likely Mica to fail is one with High voltage DC on it.

C11 (30pF) & 12 (100pF) would be high on my suspicion list

Marc


 
 Return to top of page · Post #: 15 · Written at 8:33:29 PM on 22 May 2013.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6678

A thump sound at switch off can be attributed to bad IF caps (particularly in Philips sets according to a mate of mine).


 
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