1. The radio was at some point...repaired. The reason was obvious, the electrolytic caps. Judging by the parts it was done long time ago.
The caps 126 and 127 (I extracted them) weigh very little and they are supposed to be heavy. Bone-dry inside. One of them foamed. And according to the sch they are 8uF each, but the real ones are 4uF each. And the guy replaced them with one old tubular 10uF cap (they are paralleled).
Surprisingly the replacement cap which is probably over 30 years old is still 9.7uF. It was paralleled to that cap that foamed; another one was cut off.
2. Big surprise: The Candohm 4K+1K is alive and is indeed 3.9K + 1.0K, nice!
3. The output tubes' wiring seems to be factory, the pins 1 and 8 (one is NC and 8 is Cathode) grounded. And the transformer filament windings (both) that are supposed to be grounded via centertapped 60 Ohm resistors are not. So I take it this is the version with 6A5 tubes and not 6B4.
4. Some tubular caps are there, some seem to be original and some are added to probably fix some backelites.
5. The backelites were not rebuilt.
6. The backelites have their rivets flooded with solder. Some look like they were touched up. But the internal wires (that I am supposed to cut when rebuilding) are all soldered to the rivets; will complicate the process somewhat.
Well, not all is bad.
In 2-3 weeks I will get those 5C4S rectifier tubes (5U4), new unused Soviet production, plus some 6S2S (6J5) - it's a gift and the one that comes handy at that.
The underbelly is clean and with exception of one small cobweb does not need cleaning at all.
Thanks Ron, great help.
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I am rebuilding the bakelites now and it is a major PIB as the guy flooded all the rivets and I cannot release the wires by cutting and insert the pin to push the block out - have to clean them first and while you do that the tar starts bubbling out of those rivets.....Not too bad but complicates it some.
Good thing is, as I go over them some tubular caps start to disappear as the guy threw them over the existing ones.
The guy was obviously a loyal Philco repair person as all the tubulars inside are Philcos.
But his judgement I do question as why would you throw a 0.006uF cap from one line to chassis when you already have 0.015uF there. And if those caps (which are death caps) are in question - why not remove them first (I take it Y-caps were not available back then).
I also question Philco's technique of mounting the filter caps across the line before the switch. This way they may be charged while the unit is Off and the plug is pulled out in an arbitrary moment of time and have no way to discharge so one could receive a little jolt by touching it. In todays line filters there is always a resistor across the line. Granted it is 7.5nF equivalent, won't kill ya....I still intend on soldering 1/2W 200K-300K resistor across.
The final answer to your post about the two bad 6J5s where you wondered if my tester is OK itself: today I received from the eBay 10 used "test good" 6J5GTs (could not resist 10 pcs for 19 bucks whereas the rest sells them for 10-12 bucks a piece) and tested them all; the "new" value is supposed to be 2600. All but one tubes test at least 2,200 and several 2,500 - 2,700. Only one happened to be 1,800 (between good and bad). At the end I put the original two in - you guessed it - same as they were, 100-150, that is dead. So, yes, it is the coincidence (whatever the reason is) and not the tester.
I never could understand why some manufacturers chose to connect a line capacitor ahead of the power switch, brand Z sets, even AC/DC ones, always seemed to do this. Whenever I run into a set like this, and it's feasible to do so, I move the line capacitor to the radio side of the switch so it isn't energized unless the set is turned on. RCA sets, and Canadian G.E ones, had an electrostatic shield built into the transformer so they didn't need line capacitors. Philco seemed to like connecting two line caps between either side of the power line and the chassis so while you could switch one of them you could not switch both.
Regards
Arran
Question: in the discriminator circuit there is a dual cap 110nF (110uuF) which is a backelite.
Are those micas or paper and do they need to be replaced?
I would think that they are mica, they used to put those in the Bakelite blocks too. If in doubt maybe take it out and put it on a resistance-capacitance bridge type tester. As far as I know they used molded micas, installed them in the block, and then potted them with the same tar as the paper caps.
Regards
Arran
I do suspect the same as making paper caps with low value of good stability and of high tolerance would be difficult.
But....who knows. I think I will leave those undisturbed and find out if the work. They don't present any danger as they are not exposed to a high voltage across them.
Those two caps are, indeed, paper types and can easily be replaced with a pair of 110pf. dipped silver mica's.
Dipped silver mica types are rated at 600 volts, by the way.
Older nomenclature of micro-microfarads (uuf.) equals today's picofarad (pf.) not nF or nano farads.
I've seen both mica and paper inside those bakelite blocks when it comes to the dual 110 pF caps. Usually paper, but sometimes mica. I feel it is best to just go ahead and restuff these, as well as all other bakelite block caps.
Oh...I meant "pF" of course (110nF would be that 0.1uF which I have plenty).....and I do have one (leftover) 600V 100pF cap from another Philco restoration prj (I think that was the 18)....but since those are expensive and I only had one....I thought that maybe those were micas and I would have one less block to restuff and 6 bucks less to pay (I remember they were about $3 each at 1% accuracy and #2 at 2%).
Oh...well.
I recently was thinking about the ripple current (I am about to write a thread about it) and I realized that in many radios we may be undersizing the ripple rating so I think I will be ordering some aluminum cans anyway, will order some of these also.
(BTW I found a great way to at least double the ripple rating for the DC filter caps).
PS. What tolerance were those originally?
(This post was last modified: 06-04-2013, 10:52 AM by morzh.)
It is a rectangular tin box riveted to the chassis. From the bottom it is covered by a backelite cap.
What's the best way to take it off an open, or should I disregard it, cut the wires and throw the new caps in using some old tubular caps' shells (which I have some).
The tubulars are gonna be a b..ch to replace in this one, so if it is too time-comsuming I could use avoiding some aggravation.
That will be one nice radio when you are done with it. Interesting the way your speaker is bolted to the board. My 38-1 is just the opposite...upside down. Actually there is no room to install it the way yours is because of the inclined chassis shelf. Those are heavy dudes aren't they?! Your grille cloth looks fairly good...going to keep it? I hope you can. Current replacement cloth is fairly $$$$$. Good luck.
I don't know what it is with this particular Philco's bakelite caps, but restuffing them was a pain.
First of the guy who repaired this radio ling time ago for unknown to me reason filled the rivets with solder and so the wires were stuck. And sucking out the solder starts the tar boiling.....
Except three caps out of seven the rest refused to jump out of the backelite shell; my blunt allen wrench I use to push the tarred caps out would just go through the tar. Different tar? The worst ones were the 110pF caps...oh my.
I am doing one a day. Yesterday I finished the last one.
Today started on tubular.
Once I did that I realized that some caps I ordered are radial not axial and they refuse to fit. Geezzzz!!!
Most resistors though are in a remarkably good shape. Few are about 20% off. Weird - same two resistors, 51K, one is 51K, another - 64K. WOnder why.
Maybe different temperature regimes where they are?
