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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Wed 04, 2017 5:37 am 
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Here's a 6.2k, 5 watt. I kind of doubt the individual candohm sections were rated for 10 watt, but I guess we'd have to take a look at the specific circuit.

http://www.mouser.com/ProductDetail/Vis ... 8vL0lk8%3d


Here's an 8 watt.

http://www.electronicsurplus.com/ward-l ... ckage-of-2


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Wed 04, 2017 5:45 am 
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sdyer wrote:
I can find 820 ohm and 1500 ohm 10-watt resistors, but I can't find a 6200 ohm. Does anyone know where I could get one in that particular value? If I can't find it, I can put in series 5k, 1k, 200 ohms to make it, right?

Yes. And you would be within 5% of the correct value without the 200 ohm resistor. Also given the way the power would be shared, the 1K would only have to be a 2 watt resistor if the 5K is a 10 watt resistor.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Wed 04, 2017 7:00 am 
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Why not disconnect the wires from that candohm and measure the resistance across the 3 individual sections? Also measure the resistance from each terminal to ground. Personally I like to get a handle on what's gone wrong before just willy-nilly replacing the whole thing. Knowing those resistance readings should give one a little better sense of direction, just in case things don't turn out the way you'd expect them to.

Basically your B+ is coming in from L1 and splits at the node between the 820 and 1500 ohm sections. The 1500 ohm section is the one feeding the audio amp, audio output and video output plates. The 820 section feeds the horz sync amp, video and sound IF's, detector, video amp, agc, etc. The 6200 ohm section is in series with the 820 section and supplies a lower B+ to the tuner.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Thu 05, 2017 12:53 am 
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I'm not sure any of the current R100 is salvageable. It sizzles along its whole length, wax bubbles out and drips - it doesn't look good.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Thu 05, 2017 2:32 am 
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cant hurt to check it with an ohm meter but it does sound like a short. the only way to tell is check each terminal to the case an if you get a reading you know that it is shorted to the case. also check each wire from the resistor incase one has a break in the insulation that is shorting to something.

where the individual sections of the r100 is used you should get away with a five watt replacement. i dont think that their is a particularly high current flow through them..

do you have a kill a watt or variac?

if you want to replace the canned ohm resistor with another canned ohm resistor you may be able to get one at play things of the past. they also may have the modern resistors in the values you need.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Thu 05, 2017 4:30 pm 
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I checked R100 with the MM and the second lug is shorted to the chassis. I get a beep on the MM on that lug, not on the others.

I ordered 10 watt resistors. The 820 and 1500 ohm ones from Antique Electronic Supply, and the 6200 one from Surplus Sales of Nebraska of all places. That's the only place I found 6200 ohm online. It's NOS, I ordered two. Here are the details of what I ordered - let me know if they look good to y'all.


Attachments:
File comment: From Surplus Sales of Nebraska - http://www.surplussales.com
6200ohm-10watt.jpg
6200ohm-10watt.jpg [ 18.75 KiB | Viewed 1656 times ]
File comment: From Antique Electronic Supply - https://www.tubesandmore.com
AntiqueElectronicSupply-10watt.jpg
AntiqueElectronicSupply-10watt.jpg [ 15.02 KiB | Viewed 1656 times ]
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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Thu 05, 2017 6:09 pm 
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Those should work fine. The 6.2K Dalohm is one nice looking resistor.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 06, 2017 1:34 am 
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as i recall ohmite made some good quality resistors and they are made here in the usa. at least they used to be. great choice.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Tue 10, 2017 4:01 am 
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I got the resistors today, to replace R100. I clipped the 4 lugs off of R100, jumpered in the new resistors, ramped up the variac, got no picture or sound or horizontal frequency whine, started to smell smoke, and turned off the variac before I started a fire. :(
The new 820 ohm resistor for R100A had gotten VERY hot very fast, charred the schematic on which it was setting (and the wood underneath), then melted a terminal strip I set it on to get it off the paper. I set it on top of an open jar to cool. It stayed very hot, so I put it out on the driveway. It's 14 degrees out there, that should cool it off.

It looks like it may not have been R100 after all, but rather something delivering vastly too much current through R100A. Of course R100 is now destroyed so I must replace it. But I'm concerned with finding what the heck is wrong.

What could have failed to thereby deliver such 10-watt-resistor-frying current? A tube? Nothing in the new resistor circuitry goes to ground, so it's not a short to the chassis. A short somewhere else?

I need help guys. This is getting me down. It was working well, now I may just be doing damage.


Attachments:
File comment: All the new resistors jumpered in (I'd already disconnected a jumper from R100A in the foreground, but it was jumpered when I powered it up.)
Replacing R100A - jumpered.jpg
Replacing R100A - jumpered.jpg [ 99.45 KiB | Viewed 1590 times ]
File comment: This shows the cut lugs on the original R100 - RIP.
Replacing R100.jpg
Replacing R100.jpg [ 96.67 KiB | Viewed 1590 times ]
File comment: This is the text on the 10W 820 ohm resistor I got. Is it salvageable when it cools off? Or should I get another one for permanent repairs?
Replacement R100A.jpg
Replacement R100A.jpg [ 38.93 KiB | Viewed 1590 times ]
File comment: Shows the scorching from the heat of R10A.
Fried R100A.jpg
Fried R100A.jpg [ 98.03 KiB | Viewed 1590 times ]
File comment: Close-up of scorched replacement 10W 820 ohm R100A.
Fried R100A Underside.jpg
Fried R100A Underside.jpg [ 38.48 KiB | Viewed 1590 times ]
File comment: It got hot enough to nearly set the paper on fire.
Fried R100A - Damage.jpg
Fried R100A - Damage.jpg [ 53.71 KiB | Viewed 1590 times ]
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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Tue 10, 2017 6:07 am 
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Unfortunately that resistor feeds a buss that goes all over the place. But most of the things that are fed off it get their power fed through other resistors. So most of the places where there could be a short would cause another resistor to burn up too. One thing that is directly connected to that line and to ground is C105B. You might take your ohmmeter and measure across that cap and see if you get a very low reading. If You do try disconnecting C105B and see if the short goes away.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Wed 11, 2017 7:52 pm 
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It sounds like you didn't leave the set on very long, so the black residue is likely from the paper fire and not the resistor burning up. As long as it still measures close to 820 it should be fine.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Thu 12, 2017 11:40 pm 
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I just looked at the schematic and looked at the voltages at each end of R100a. 340 at one end and 245 at the other. According to my calculations, if everything is working correctly, it would dissipate 11 watts. So to give a little margin you should have a 15 or 20 watt resistor. BUT, 11 watts in a 10 watt resistor would not get that hot that quickly. I think that you will find that the 245 volt line is shorted to ground.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 13, 2017 12:06 am 
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Tom Schulz wrote:
Well, the parts list does not show any power ratings. See if there are enough voltages shown on the schematic to find the voltage at each connection to that resistor, or at least a few places. Then subtract the readings to get the voltage across each section. The power will be the voltage squared divided by the resistance in ohms.
That resistor is called a Candohm, that being a registered product name from a particular manufacturer.
Other companies made similar products.

The method that Tom explained is the right way to calculate the actual power dissipation in each section.
Those values can vary widely, from a hundredth of a watt up to 2 or 3 watts, usually not higher.

The replacement resistor should be rated 3 to 5 times the calculated value.
The Candohm used the chassis apron as a heat sink. The replacement has no such ability.

ALWAYS replace all sections of the Candohm, not just sections that are currently open.
Completely disconnect all wires from the Candohm. Mount the wires and new parts on terminal strips.

- Leigh

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 13, 2017 12:20 am 
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Thanks Leigh. I have disconnected everything from R100 and will be rewiring it. I'm using 10W resistors for two sections, and I just ordered a 20-watt 820 ohm resistor. Are these wattages too low?


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 13, 2017 12:23 am 
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sdyer wrote:
Are these wattages too low?
I can't answer the question since I don't know the voltages involved.

The power rating of the new part should be at least four times the calculated power dissipation.
If the air circulation around the new part is quite poor, a higher factor may be appropriate.

- Leigh

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 13, 2017 2:09 am 
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I found the rest of the voltages. For R218, 1500 ohms, the actual power dissipated is 3.3 watts. For R405, 6200 ohms, the actual power dissipated is 2.8 watts. It looks like you can mount them with plenty of air around them, so 10 watts should be good enough. For power resistors, which are wire wound resistors, resistors at 1.5 the actual power should work but double the actual power would be better. If they are crammed into a small space with no air around them then you should over rate them more.

Now the carbon comp resistors have a tendency to deteriorate if they are run close to their power rating. But wire wound resistors are tougher.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 13, 2017 2:19 am 
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Hi Tom,

Yes, 10 watts should be fine for both.

- Leigh

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 13, 2017 2:27 am 
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I should add that the 820 ohm resistor should be OK for testing. 11 watts is only just slightly over the rating and wire wound resistors can be run at their rating for short times. Just keep it away from anything that can burn. It is very likely that your meter will show that the 245 volt line is shorted to ground.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Fri 13, 2017 6:36 am 
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These aluminum housed resistors work well to replace Candohm sections, but it's not always possible to find the values at the wattage needed. http://www.mouser.com/ProductDetail/ARC ... pxtQ%3d%3d


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Jan Sun 15, 2017 1:14 am 
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GOOD NEWS: I found the short. It was near R200. I'd used a short piece of white wire because its leads were too short to be resoldered, and the solder joint was left bumped up against the adjacent ground lug. To find it I connected one end of the MM to the chassis and probed the bus before and after each component. See the schematic - I noted red where it beeped and blue/X where it did not. I probed all along from R100A all through the bus, to all 19 components on it. None were shorted. Then I just jumpered the other end of the MM to the end of R100A generating a constant beep, and jiggled wires. That's how I found it - jiggling wires. When the beep stopped, I discovered the joint up against the lug. The pictures below show the source of the short:
Attachment:
File comment: The short is circled in green. The small white loop extends the lead from the (still original) R200. It was too short to resolder recently - likely I'd snipped that end to test it out of circuit. You can just see R200 in the picture, the bit of orange/orange/red resistor lurking behind the terminal strip. While I used a bit of spaghetti tubing to prevent a short to the capacitor leads, I left the solder joint itself exposed. That joint had been accidentally nudged into contact with the ground lug very near it, causing the short.
Top of Loop Shorted to Lug-1.jpg
Top of Loop Shorted to Lug-1.jpg [ 86.61 KiB | Viewed 1433 times ]

Attachment:
File comment: This shows the path I probed along the bus, starting from the end of R100A. The shorted wire is noted at the top by R200.
Short on the Schematic.jpg
Short on the Schematic.jpg [ 77.04 KiB | Viewed 1433 times ]


When I pulled the joint away the beep stopped. I powered up the set and it is in much better shape. The speaker makes noise and the picture tube displays a raster. The quality is much worse than before however - no picture, sound is vanishingly faint behind a deep buzz.
Attachment:
File comment: Raster but no image. Sound is very, very faint - mostly a deep buzz.
State 1-14-17.jpg
State 1-14-17.jpg [ 77.57 KiB | Viewed 1433 times ]


Due to this simple mistake I've now destroyed R100. That is sad - it was a unique original component. But it's done. I don't suppose I could get another one online somewhere? Do you guys know if there are NOS of these out there? Do the lugs need to be moved to get the proper resistances, even if I did find one? Should I try to solder the lugs back together? (doesn't sound like a good idea.)

After running for just a minute or so, the 10W/820ohm cement resistor I have got VERY hot. The other two did not get hot. I have a 20W/820ohm coming - we'll see how much heat it gives off.

I'm concerned now about overheating. These resistors will be dissipating a lot of heat into the underside of the chassis, which is an enclosed space. The original dumped the heat into the chassis, using it as a heat sink, but that's gone now. Do I run the risk of overheating here? Could it cause a fire?

Finally, the picture and sound now need more diagnosing and fixing. Sigh.


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