Opened up this Philco, and what the.....??

[Kamakiri]

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?

[quaddriver]

a poor mans inrush resistor?

[Chip Chester]

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

[maxhifi]

Maybe the old caps shorted and took out the rectifier, so he decided to add some fuses to the new ones?

[old_coot88]

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.

[Findm-Keepm]

Originally Posted by old_coot88

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.

A #44 bulb has about a tenth of an ohm cold resistance, hardly a huge ESR value. I have a 1940's Coyne manual that details adding current limiting of B supplies with a dial lamp. Exceed the current rating of the bulb, and it blows, and in-between, it limits the current. It saved many a costly power tranny.

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,

[old_coot88]

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?

[Username1]

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....?

.

[Findm-Keepm]

Originally Posted by old_coot88

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?

Chicago miniature lamp catalog, dated 4/63, "measured at 25degrees C with millivolt bridge, to avoid heating effects." My L&N millivolt potentiometer has a setup card telling how to perform cold testing of tube filaments, all done with a few millivolts.

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....

[Kamakiri]

Actually, it's a 15X. Couldn't remember the model. Ended up just replacing the caps (sans bulbs), and it's working nicely......

[dieseljeep]

Originally Posted by Kamakiri

Actually, it's a 15X. Couldn't remember the model. Ended up just replacing the caps (sans bulbs), and it's working nicely......

I didn't think, Philco used that style chassis, that late. I seems to be, quite a set.. Eleven tubes, multi speakers. Must've been TOTL, that year.
Are you planning to re-stuff the bakelite block caps?

[DavGoodlin]

Originally Posted by dieseljeep

I didn't think, Philco used that style chassis, that late. I seems to be, quite a set.. Eleven tubes, multi speakers. Must've been TOTL, that year.
Are you planning to re-stuff the bakelite block caps?

There are lots of those condenser blocks in a model 15 from looking at the Riders. I never saw a set from that era with two speakers either.
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.

[Kamakiri]

Originally Posted by dieseljeep

I didn't think, Philco used that style chassis, that late. I seems to be, quite a set.. Eleven tubes, multi speakers. Must've been TOTL, that year.
Are you planning to re-stuff the bakelite block caps?

Oh HELL no!!!

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.

[Kamakiri]

Originally Posted by DavGoodlin

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.

No kidding, and Philcos are quite plentiful here as I'm sure they are there. They still used one or two in the early 40s consoles, but that 38-3 you had....I had one of those and I never restored the sucker.

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.

[dieseljeep]

Originally Posted by Kamakiri

Oh HELL no!!!

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.

A few years back, I was in an old radio TV shop. There was an earlier 30's Philco radio in for repair. I asked the owner if the bakelite block capacitors were replaced. He said no, they never go bad. I replied that, there would a lot of collectors that would disagree with you.
I read that those caps were vacuum impregnated. Having some experience with that process, I would almost have to agree.