Thanks for reply Steve

So it would seem to be held in a fairly common environment.. so ??one wonders if Halligan bought micas from other supplier for a while .. so who knows?..so far a mystery … is it possible that your tester is very sensitive ?in the mica range??

Don VA3DRL

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Another point of view -- I think we need to realize that Hallicrafters (or Hammarlund, or National, or whoever…) never intended or anticipated that their products would be in use 60+ years later.? Those crappy capacitors are creating problems for us now, but for the expected life of the receivers they were probably just fine.? IMO, we need to anticipate these headaches in the boat anchor community – and it’s only going to get worse as time passes.? It’s frustrating – for example, earlier this year I restored a HQ-180A that had problems in the 60 KHz IF section.? The challenge was that Hammarlund parked a switch array smack dab over the top of the entire 60 KHz IF section.? Fixing the problem was a surgical procedure that would have driven many people mad.?

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73 – Steve, KW4H

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Hi all,

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Three weeks ago I began restoring a SX-42 that was gave to me.

Cosmetically, it was very good: almost no rust on the chassis, only dust…

Manufacturing date: May 12, 1947.

Some previous owner already tried to “restore” the unit and changed the original PIO capacitors for some “Orange Drop” ones.

Except that this person seemingly never learned to solder properly: cold joints everywhere…

In a word, a real mess…

And nobody ever care to measure the resistors: I found many 1.2K ohms ones almost behaving as open-circuits, due to the former PIO caps leakage, surely…

The guy who gave me the set (my dentist, actually) tell me that is was “very deaf”.

You bet: I found many PIO still within (in the most impossible places) that needed to be changed, plus all the out-of-tolerance resistors, plus about the third of the mica caps within to be defective, including ones within the IF transformers…

So I slowly, carefully rebuilt it.

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Hey.. do you know how many “manufacturing” variants of the SX-42 exists ?

First schematic is labeled as 89D210 and production runs goes from X to XXXX then, to 1 with schematic 89D210K (June 1947).

From that, my unit was made from the production run XX…(after March 1947).

From the first to last, not less than 21 product modifications (call them “upgrades” if you want…)

Then the 89D257 schematic came (Oct. 3, 1947)

Revisions of this one went from A to G (Feb. 14, 1948)

I’ve done my best to “upgrade” my unit to the latest schematic/stocklist status (because it is supposed to be the best one, right ?).

But I finally ended with something compliant to the revision “E”, plus the R108 added to the 6H6 noise limiter filament (revision G)

More changes were impossible to implemented due to changes in the band switch sections.

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Then the time came to power it up.

Everything went well, except when I tried the “tapping” test.

The purpose was to “tap” on the chassis to detect any intermittent tube and/or bad connection(s).

Well, it failed the “tap” test badly, as every hit to the chassis triggered a very loud speaker “crash” noise, especially when I hit the tuning gears casing.

OK, what I had do wrong ?

I spent many hours checking every soldered connection, swapping the tubes and etc.

But the crash noise was still there, and even appeared randomly when I DO NOT hit the chassis…

Then suddenly, I seen some light intensity flickering near the tuning knob with some noise coming from the speaker at the same time.

What the …. ?

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There is three #44 pilot lamps to light the dials in a SX-42, plus one #47 in the meter.

When I hit the pilot lamp that was mounted closer to the tuning knob, I obtained a very loud crash in the speaker…

What ?

I changed this lamp for a NOS one: crashes were gone.

AARGH !

I re-done the soldering of the leads on the suspect one: still noisy, so it is inside !!!

Never met a noisy pilot light before…

But think about that if ever it happens to you !

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The S-38D was basically an all-American five with some extra coils added.? It didn’t have the looks of the Lowey versions preceding it.? It was a simple, very popular, and useful radio that found its way into a lot of homes and was the first receiver for many SWL’s.? It also has a hot chassis and can blow you across the room.? ?? I wasn’t alive during that time, but wonder what the context is when they try to call it a “typical wartime communication receiver”.? It was manufactured from 1954 – 57.? Which war are they referring to?

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73 – Steve, KW4H

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I guess? all other classes? got of Scott-free,? so you need to reclassify yourself to avoid the taxes.?? It seems that the number of classes is rising by the day.

Anominus ?don

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Hi all,

Three weeks ago I was restoring a SX-42.

Apart of the out-of-tolerance resistors and “leaky as hell” PIOs found within (that were not changed by the previous owner- more on this in another topic post) I also found about the third of mica caps that needed to be replaced.

Detection method ? A simple DMM on ohmmeter range.

A 180pF mica cap measuring like a 4M ohms resistor ?

Not normal, I believed….

More leakage tests on that same component proved that it was not behaving as a true capacitor anymore.

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I caught many cases like this one before.

I once had a big provision of NOS “mica” caps that I found ages ago in a “army surplus” store.

But last year, I decided to test them all, both for leakage and value.

Some of these units failed the leakage test miserably (about 20% of them).

When I “broke” them to see what was within, on some I found the internal construction to be like a winded PIO (Paper-In Oil) capacitor, and obviously, the slow oxygen penetration thru the molded phenolic casing have turned the “oil” into… well… something else.

But the real surprise was to find some units made of silvered mica, plus some oil remnants, within the phenolic casing !

I do not know if this was to help the casing molding process or what, but this “oil” presence was surely the cause of the component failure during it’s leakage test.

However, not all vintage mica dielectric capacitors are subjected to this kind of time degradation.

See for example the lozenge-shaped mica + copper foil capacitors made in-house by RCA during WWII, like the ones used in an AR-88 receiver: they still test perfect after 80 years of use.

But… no trace of any “oil” within their styrene plastic casing.

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At the end, I do not know if these old mica capacitors failures is due to the silver migration alone, or more to the presence of residual “oil” within their phenolic casing.

I believe that to trigger a silver migration phenomenon in a mica capacitor, some “contaminant” is also needed within.

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Some time back, I was watching a TV Documentary about the middle of WW2? and they spoke of communication receivers and showed an S-38D as a typical wartime communication receiver.

… WELL… ?maybe ….it was ?the first prototype of the S-38D .. way back then

Don VA3DRL

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I do know the history of this particular radio – it belongs to a lifelong friend, and it was originally purchased new by his grandfather and then passed on to his father and then to him.? It hasn’t been powered on for many years, but it’s been sitting in places like a closet shelf, or maybe an attic or a basement.? His father and grandfather have long since passed away, so no further details are available.? It has not been subjected to weather extremes to my knowledge.? I didn’t expect this quantity or severity of mica capacitor failure.

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73 – Steve, KW4H

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Out of interest for this and other radios, do you know the history of its environment .. as in temp and humidity ??

Don VA3DRL… ???catching up on emails

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Richard, I guess we are assuming that the “case“ has over time had inherent gradual “leakage in” , or has cracked in later years and eventually ?leaked ?…allowing the SMD to take place…? is that your guess ? or is it some other mechanism?.

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An aside…about “failures”

Long ago I found a transistor that normally worked .. and it was a critical component? … but at about minus 40 ?it would not function , some simple tests indicated that the base opened up..? we never did have an answer but I assumed that slight thermal “shrinkage” opened the connection to the base. I worked again and again when warmed up a bit.

Don ?VA3DRL

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Your comment is intriguing; ?you seem to have detected and classified ?failure modes ??shorted, out of tolerance,? and unstable.

When you say shorted , I guess you mean effectively dead short [ making it deadly to the circuit it is in], not just high leakage??

When you say ?unstable , I guess you mean you have detected changes in the capacitance ? not leakage and in a short time [few seconds]?

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Would be interesting and helpful to catalogue failure modes detected on ?60, 70, 80, even 90 year old components

I wonder if some of the reasons these faults are now being found and? spoken about is that we [more people] now have testers that can detect these faults,, and that is a suggestion and question to everyone. ?

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I had/have an S-47 where the FM sub-chassis ?had a sudden bad short , and think it was a mica. Luckily, the chassis was upside down for inspection and “some” fault was detected by my nose , but it was not easy to locate ..

Don VA3DRL

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Out of interest for this and other radios, do you know the history of its environment .. as in temp and humidity ??

Don VA3DRL… ???catching up on emails

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I am late going thru mail? but… this off topic thread is still active so..

You seem to think that big governments in the world? cannot ?make new laws to put you in jail for using bitcoin etc? [or some places it will be worse than jail.]

I know nothing about bitcoin but govts have their ways of doing things

73?? don VA3DRL ??

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