While slowly powering up a Philco 112 (above 174001)on my isolation Power Supply there was a nice loud firecracker sound at about 80 or 100 volts applied, that made me jump about a foot off my stool. I was certain that I had correctly reconnected the two filter caps with the correct polarity. I usually check this several times. Only one (part #68) of the two replaced 450 Volt, 10 UF caps blew up like a fire cracker, blowing off the cover of the cap as well as the contents so you could no longer see the covering with polarity markings... After inspecting the wire that was connected to the negative cap side it had a tear in the cloth wire exposing the bare wire... Could this have caused the fireworks if it touched something?..perhaps the chassis? I have replaced the filter cap but I am waiting for an answer before trying to power it up again. Could there be other damage caused to the tubes or other parts? I see no visible damage to the other parts. I think I have cleared all the capacitor fodder from the chassis.
Bob
Strange . . . . that you didn't get the typical auditory precursor of the hiss before the eponential pressure build for the created BANG!, it being much akin to a cherry bomb firecracker. Enough from either, to see if you made a polarity of installation . . boo-boo. Being even further hindered from that, by their reduced filament level up to that time. Now, what say ye . . .on what you further found . . . after nosing ever more closely into the remnants . . .
Sir Bob E. . . . . .
Plus . . certainly there is probably enough of the end caps remnants to differentiate between the negative electrolytic having its wire lead remnant spot welded into the aluminum casing, versus the positive lead still connected into its surrounding insulative disc remnant ?
Normally, I would have expected the item #65 filter with its higher level raw DC to have been the unit to go.
HOWEVER, on this set there is the item #69 tandem series 70 +70 ohm wirewound (Candohm ?) which could be open or HAVE opened up OR had a connectivity problem on some connection to it, to create an open circuit equivalency.
That would then result in FULL unbridled rising of the B+ since, at that instance, there would be no shunting load between the center tap and ground.
The capacitors would then take it all, if the tubes filaments are still in their warm up stage before conduction.
Additionally, there is item #27 which sez it is a #3489 unit, of which I can not IMMEDIATELY find any specs for that units, sections, capacitance values.
Currently unknown to me . . . .But IF you have to / had ? / rebuilt it, and the capacitance section which connects between 5 and 6 is NOW having an electrolytic type of capacitor being used.
Do note, that if being an electrolytic, it would need its - lead going to #5 terminal while its + lead goes to #6 which then would get connected to ground.
An electrolytics positive lead going to ground ! ! ! ? ? ? . . . . certainly contrary to the norm . . .but inspect the circuitry and note that the centre tap (oops, I just slipped into my olde Ainglish mowde ) of the HV secondary of the power transformer is being held above ground by that dual item #69 power resistor.
That, being in order to then have a negative voltage develop across that load resistor.
The two levels of negative biasing are then feeding up to supply the 1st grid circuitry of 2 audio stages.
along with that now dissipated, distinctively acrid , aroma that an exploded cap leaves.
( But . . . not to worry . . . you should still be able to get some deposited electrolyte mist by doing a touchy-feely of the surrounding components.)
Pee Ess . . . is 'ole dawg still around . . . or had that caper "deceived" him so bad, that he is still cowering under the next rooms "Lavatory"?
73's de Edd
:http://www.nostalgiaair.org/PagesByModel/118/M0013118.pdf
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:While slowly powering up a Philco 112 (above 174001)on my isolation Power Supply there was a nice loud firecracker sound at about 80 or 100 volts applied, that made me jump about a foot off my stool. I was certain that I had correctly reconnected the two filter caps with the correct polarity. I usually check this several times. Only one (part #68) of the two replaced 450 Volt, 10 UF caps blew up like a fire cracker, blowing off the cover of the cap as well as the contents so you could no longer see the covering with polarity markings... After inspecting the wire that was connected to the negative cap side it had a tear in the cloth wire exposing the bare wire... Could this have caused the fireworks if it touched something?..perhaps the chassis? I have replaced the filter cap but I am waiting for an answer before trying to power it up again. Could there be other damage caused to the tubes or other parts? I see no visible damage to the other parts. I think I have cleared all the capacitor fodder from the chassis.
:Bob
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:Sir Bob E. . . . . .
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:Strange . . . . that you didn't get the typical auditory precursor of the hiss before the eponential pressure build for the created BANG!, it being much akin to a cherry bomb firecracker.
There WAS smoke...but I was not quick enough :o0
:Plus . . certainly there is probably enough of the end caps remnants to differentiate between the negative electrolytic having its wire lead remnant spot welded into the aluminum casing, versus the positive lead still connected into its surrounding insulative disc remnant ?
It shot the wad! nothing left inside the now all metal looking cylinder (no label covering) ...just little plate like things connecting to the wires dangling loose inside on one end...
one side blown clear out. No chance of telling how I had it connected after the fact... But I have made this boo-boo so many times that I usually check myself several times during restoration projects... (but I would not bet money on it tho...:O)
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:Enough from either, to see if you made a polarity of installation . . boo-boo.
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:Normally, I would have expected the item #65 filter with its higher level raw DC to have been the unit to go.
I double checked the wiring to my "Before" under chassis photo and verified that it is #68 that went bang (probably preceded with a hiss and definitely there was smoke.
:HOWEVER, on this set there is the item #69 tandem series 70 +70 ohm wirewound (Candohm ?) which could be open or HAVE opened up OR had a connectivity problem on some connection to it, to create an open circuit equivalency.
Resistors #69 has been replaced by two 68 ohm 5 watt "ceramic?" resistors in series that still check good. Connection points seem to look all ok. I use shrink tubing on everything. But the previous original wirewound resistor looked to have had some toasting in the past that took out half of it.
:That would then result in FULL unbridled rising of the B+ since, at that instance, there would be no shunting load between the center tap and ground.
:The capacitors would then take it all, if the tubes filaments are still in their warm up stage before conduction.
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: Being even further hindered from that, by their reduced filament level up to that time.
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:Additionally, there is item #27 which sez it is a #3489 unit, of which I can not IMMEDIATELY find any specs for that units, sections, capacitance values.
I have rebuilt this block. according to Philco info: #1 .5, #2 .5, #3 1.0, #4 .5, #5 .015, #6 Chassis Ground for 1-5 But I have not double checked to verify all of those actual connections are correct yet.
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:Currently unknown to me . . . .But IF you have to / had ? / rebuilt it, and the capacitance section which connects between 5 and 6 is NOW having an electrolytic type of capacitor being used.
It is only a .015 cap...but...
The negative ends of the two filter caps 65 and 68 ARE also tied to lug 5 of Filter block 3754 (#27).
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:Do note, that if being an electrolytic, it would need its - lead going to #5 terminal while its + lead goes to #6 which then would get connected to ground.
Not following you here...are you referring to #65 or #68??
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:An electrolytics positive lead going to ground ! ! ! ? ? ? . . . . certainly contrary to the norm . . .but inspect the circuitry and note that the centre tap (oops, I just slipped into my olde Ainglish mowde ) of the HV secondary of the power transformer is being held above ground by that dual item #69 power resistor. There is a wire between the two #69 resistors that goes to Resistor #47 which is a 13K (sub for a 14K) resistor. One end of the series goes to chassis ground. The other end goes to lug 11 (CT of TX)
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:That, being in order to then have a negative voltage develop across that load resistor.
:
:
:The two levels of negative biasing are then feeding up to supply the 1st grid circuitry of 2 audio stages.
:
:
:
:Now, what say ye . . .on what you further found . . . after nosing ever more closely into the remnants . . .
:along with that now dissipated, distinctively acrid , aroma that an exploded cap leaves.
:
:
:( But . . . not to worry . . . you should still be able to get some deposited electrolyte mist by doing a touchy-feely of the surrounding components.)
:
:
:Pee Ess . . . is 'ole dawg still around . . . or had that caper "deceived" him so bad, that he is still cowering under the next rooms "Lavatory"?
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:73's de Edd
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