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Opened up this Philco, and what the.....??
Okay, I've seen my share of bad repairs and unusual repairs, but this one takes the cake.
Opened up the bottom of this early 30s Philco console radio I'm redoing for a friend. For filtering, it's got a pair of 8 uF caps as you'd expect, but underneath the chassis plate I find this, once the ancient cloth black tape is unraveled. A pair of 10 uF 450V caps with pilot lights wired into them on the + side. I'm assuming this is for some kind of isolation, but why??? The only thing that I can think of is a possible short in the power transformer? I have no idea. Anyone ever seen something like this?
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#2
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a poor mans inrush resistor?
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QuadDriver Pioneer Silver-face Collector |
#3
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Perhaps the original tech was not the brightest bulb in the chandelier.
-or- Sometimes the dim bulb tester is a person, not a thing. Either works. But current limiting is a possibility. Chip |
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Maybe the old caps shorted and took out the rectifier, so he decided to add some fuses to the new ones?
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#5
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If the bulbs are directly in series with the caps, they would add a huge "ESR" value, diminishing the caps' effectiveness.
'Specially the one coming directly off the rectifier. |
Audiokarma |
#6
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You've got an old-timer's following of the Coyne Radio repair manual. I have only a couple of volumes - it was 8 in all. Cheers,
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Brian USN RET (Avionics / Cal) CET- Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit! |
#7
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I was guessing they were #47 bulbs. Just tested a couple of #47s. Each shows 7 ohms cold, rising to 10 ohms (due to heating from the VOM's 1.5V battery).
I don't have a #44 to test, but it would probably be around 4.2 ohms cold (due to higher current rating, .25A vs .15A). Though maybe not "huge" but still a signifigant ESR figure if the bulb's in series with a 10 mf cap. But then you gotta figger in filament heating due to ripple, which will further increase resistance. In any case, it seems like the more rational place to put a limiter/fuse would be directly in the B+ line coming off the rectifier. Or two bulbs, one in each leg of the HV winding going to the rectifier plates. Or, one bulb in the center-tap lead of the HV winding. Just curious - where did you get the 1/10 ohm figure for the #44 bulb? |
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I don't think it would really be ESR value with the bulb....
It would be an odd animal.... Slight change in resistance as the current goes up.... Capacitors acting as current leads voltage.... the ripple would cause current fluctuation which for the most part would cause a voltage to appear across the bulb..... I almost think ESR would go down as the bulb would kinda filter out, so to speak, the current spikes that the cap would be absorbing.... What you guys think....? I agree 100% the effectiveness of the cap would be reduced..... Higher ESR with bulb and series resistor in parallel with cap....? .
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Yes you can call me "Squirrel boy" Last edited by Username1; 04-01-2015 at 07:00 PM. |
#9
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What do you figure for the ESR? 10 @450 is worst case 28 or so ohms......for that vintage...... I wonder why two bulbs, perhaps taps of the B supply, or a straight splitting to reduce the current out each leg through the bulbs? Looks a lot like my Philco 86 chassis....
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Brian USN RET (Avionics / Cal) CET- Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit! Last edited by Findm-Keepm; 04-01-2015 at 11:32 PM. |
#10
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Actually, it's a 15X. Couldn't remember the model. Ended up just replacing the caps (sans bulbs), and it's working nicely......
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
Audiokarma |
#11
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Are you planning to re-stuff the bakelite block caps? |
#12
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I recently restored a Philco 38-3 that had 8 blocks, 27 wax caps, 4 electrolytics, more than a few way-off resistors, yet only one 6K7 of the 9 tubes was weak. Restoring a Philco radio is a ton of work, so I wonder what we should be charging for it too little $$$ and the customer thinks that's all its worth, too much and you unknowingly sold a service agreement so everytime something is not quite right, you're put on the spot.
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"When resistors increase in value, they're worthless" -Dave G |
#13
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This one was a freebie for a friend. I don't think I'd un-tar one of those caps if you paid me. At worst, I'd just use the terminals on the block to mount components externally. Done it before and even managed to make it look really good. In this case it didn't seem to be needed. Just did the filters and sorted out a few wiring issues. Slow power up and ran it at around 80V for an hour before amping the voltage up. Played fine at full voltage for an hour and everything ran cool, so it went home. I'll take it step at a time....if it needs the blocks done I'll do them, but I really don't want to.
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#14
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It was probably 15-20 years ago when I had it....back before I got heavy into TVs I had a basement packed with Philco consoles. Sold them all in one lot to Radio Daze, and shifted to TVs after that.
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#15
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I read that those caps were vacuum impregnated. Having some experience with that process, I would almost have to agree. |
Audiokarma |
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