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 Post subject: Re: Predicta restoration
PostPosted: Oct Tue 29, 2019 11:11 pm 
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Location: Grand Chute, Wisconsin
Tom Schulz wrote:
wiscojim wrote:
Which Sam's?
466 shows R76 as a fixed power resistor and R74 as a fusistor.
http://earlytelevision.org/tv_schematic ... hilco.html

Maybe R63? Where is that on the schematic?

Not relevant to the set being discussed, but R63 is in the yoke.


Thanks, Tom. Didn't spot it there.

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 Post subject: Re: Predicta restoration
PostPosted: Nov Sat 02, 2019 7:28 pm 
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Location: Hampton Roads, VA
Started going through and replacing caps and resistors. I've pulled the board up without disconnecting it. Another repairman actually cut out part of the chassis for service, It should definitely make things easier. Any thoughts on the reliability of the mica and ceramic caps in the set? I'll be placing in another bulk order soon and I don't really stock much of either.


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 Post subject: Re: Predicta restoration
PostPosted: Nov Sun 03, 2019 2:27 am 
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Location: Belrose, NSW, Australia
As a general rule, ceramics are OK. Mica caps will be OK if across coils, low value resistors etc. If in the circuit there is a DC voltage across a mica, silver migration will happen after 50 years or so. Some nasty long-term intermittent symptoms can result.

So the rule is, replace any mica that has 50 volts or more across it.

Examination of the circuit will tell you this. But if it's part of a tuned circuit (i.e. across a coil) it's best to leave it alone.

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 Post subject: Re: Predicta restoration
PostPosted: Nov Sun 03, 2019 5:20 am 
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I leave the ceramics alone. I do replace the 2 micas though.

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 Post subject: Re: Predicta restoration
PostPosted: Nov Mon 04, 2019 1:00 am 
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Location: Hampton Roads, VA
Do you happen to know what the values of the two mica are? The SAMS folder doesn't differentiate between ceramic and mica, at least not that I can tell based off of the parts list


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 Post subject: Re: Predicta restoration
PostPosted: Nov Tue 05, 2019 12:07 am 
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Most ceramic capacitors of that period are in the .0001 to .1 microfarad (uf) range, while most micas are in the 1-1000 micromicrofarad (uuf) range.
You might want to consider replacing the ceramic networks that Predictas used for sync and sound stages, since a number of folks have found them defective. There are a few threads on this forum about that, and someone makes replacements.

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 Post subject: Re: Predicta restoration
PostPosted: Nov Tue 05, 2019 5:04 am 
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Location: Waxahachie Texas
Zsuttle wrote:
Do you happen to know what the values of the two mica are? The SAMS folder doesn't differentiate between ceramic and mica, at least not that I can tell based off of the parts list


Riders 35, Sams 47 is a 47pf 500V Mica
Riders 36, Sams 48 is a 390pf 500V Mica

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 Post subject: Re: Predicta restoration
PostPosted: Nov Thu 07, 2019 9:29 pm 
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Thanks for those values, besides physically checking, is there a good way to determine what is what? I ordered a bunch of parts I was out of, and they should be here Saturday or so.

In the meantime, I pulled the flyback which needs to be recoated, I believe that I got all of the tar off without incident. Still checks out for continuity. Ordered some of the recommended sealant. Waiting on it to arrive. About halfway through the electronics. Slight differences between the 10L43 and the 11L43 schematics, but I've been directly replacing components as I pull them from the board. Just to confirm, there are 6 networks in the 11L43 and 7 in the 10L43 correct?


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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 08, 2019 4:14 am 
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Location: Waxahachie Texas
Zsuttle wrote:
Thanks for those values, besides physically checking, is there a good way to determine what is what? I ordered a bunch of parts I was out of, and they should be here Saturday or so.

In the meantime, I pulled the flyback which needs to be recoated, I believe that I got all of the tar off without incident. Still checks out for continuity. Ordered some of the recommended sealant. Waiting on it to arrive. About halfway through the electronics. Slight differences between the 10L43 and the 11L43 schematics, but I've been directly replacing components as I pull them from the board. Just to confirm, there are 6 networks in the 11L43 and 7 in the 10L43 correct?


The 390pf is bigger and closest to the tube. Also they are labeled on the PC board but there seems to be a disconnect on the labels. 390pf is C36 and the 47pf is C35. But in either case the 390pf is the one closest to the tube.
Yes, the 10L43 uses 7 Networks, while the 11L43 uses 6.

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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 08, 2019 6:10 am 
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Oh, sorry, to clarify, I was asking on the SAMS if there was a good way to differentiate from the mica and ceramics in the parts list. (Eg for next time) They group them together and the only way I actually know how to tell them apart is by physically looking at each one, which makes it a pain if I have to order anything.


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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 08, 2019 1:50 pm 
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Location: Grand Chute, Wisconsin
Zsuttle wrote:
Oh, sorry, to clarify, I was asking on the SAMS if there was a good way to differentiate from the mica and ceramics in the parts list. (Eg for next time) They group them together and the only way I actually know how to tell them apart is by physically looking at each one, which makes it a pain if I have to order anything.
All you would need is an old supplier catalog from Sprague, Centralab, Aerovox or one of the other substitute brands listed to look them up by part number to identify their characteristics. For example in the Cornell-Dubilier column shown below, once you find what designations such as BYA and CUB stand for you would be able to quickly know the types of capacitors they are.



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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 08, 2019 3:06 pm 
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Are there pictorial diagrams in your Sams?
Dan


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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 08, 2019 3:13 pm 
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Yarehobbiesso$ wrote:
Are there pictorial diagrams in your Sams?
Dan
Full Sams here: http://www.earlytelevision.org/pdf/phil ... _466-1.pdf

Even with the images, it's often hard to make out what is what.

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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 08, 2019 6:31 pm 
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The is one 390 pF mica cap on the main board in the Pedestal.

It's label as C5 390 SM (silver mica) in the Philco Factory service manual schematic. C43 in the Sams

I've circled it in red. They are maroon in color and shiny.

Image


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 Post subject: Re: Predicta restoration
PostPosted: Nov Sat 09, 2019 7:36 pm 
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Joined: Jun Wed 28, 2017 5:32 pm
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Location: Hampton Roads, VA
Thanks all,
I know where they are on my board. I was just asking mainly for future sets. I've started stocking a good amount of mica caps anyways, but it's always helpful to know what's what. I'll definitely have to pick up an older catalog for the parts. I'm surprised how few mica caps these predictas use, most of the late 40s ones use way more than two, and they always seem to cause me issues in the horizontal and vertical sections.


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 Post subject: Re: Predicta restoration
PostPosted: Nov Mon 11, 2019 7:25 pm 
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Location: Pewaukee, WI
By the mid 50's mica caps were usually made better and rarely fail...even on 40s sets I then to give micas the 'innocent till proven guilty' treatment....Not bad to order parts or stock spares for mr Justin Case (the most cautious of the case Bros :mrgreen: )....


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 Post subject: Re: Predicta restoration
PostPosted: Nov Tue 12, 2019 12:53 am 
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Location: Belrose, NSW, Australia
The main failure mechanism of mica caps is silver migration. This takes an applied DC voltage and a long time.
So yes, micas across a coil winding can be regarded as OK. A mica cap coupling the plate of a stage to something near ground potential, after 40 or 50 years will be suspect.

I know, I've been caught!! It was a very long term intermittent that I only found by scoping the circuit over a long period.

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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 15, 2019 7:18 pm 
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Location: Hampton Roads, VA
Got all of the resistors and capacitors replaced and reassembled the unit. I've got a full raster, though I'm not getting any audio or video. You can hear a crack out of the speaker when you change channels, but no audio, and I can't seem to get a lock on the vertical or horizontal. Tried adjusting both, and no luck. Probably a mistaken value put in somewhere. Possibly video stages?


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 Post subject: Re: Predicta restoration
PostPosted: Nov Fri 15, 2019 11:45 pm 
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Location: Hampton Roads, VA
Here's a few pictures of what's happening. I starting poking around, and almost have the vertical to a lock, but the vertical started collapsing when I did that. The frequency of the collapse increases along with the vertical adjustment. I skimmed the vertical section and found the vertical linearity pot is busted. Anyone have any ideas where to get another one?


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 Post subject: Re: Predicta restoration
PostPosted: Nov Sat 16, 2019 1:19 am 
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I have a NOS pot from a similar Philco chassis that can be made to work if nothing else shows up.

Your chassis calls for 33-5591-20 a 1.5K WW pot with 180 ohm stop or there is an alternate part listed with a 300 ohm stop. I have a NOS 33-5591-21 which is 3.3K WW with 340 ohm stop. If a 1.5k resistor is put in parallel, it becomes a 1.5K with 300 ohm stop. If you need the 180 ohm, the metal stop can be punched down with a punch and a 180 ohm resistor put in series.

PM if you are interested in this.

As a word of caution, do not run the set with that bright line, it can burn a line into the phosphor. Turn the brightness down to minimum when troubleshooting.

Regards,


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