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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Mon 03, 2019 9:03 pm 
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Checking around, it seems that the 1N914, 1N916 and 1N4148 are all the same. Originally each step up had somewhat better specifications. But these days they just make one type of diode and sell them under all the different part numbers.

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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Mon 03, 2019 10:00 pm 
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Location: Bloomington, IN, 47401
Tom Schulz wrote:
What kind of parts store do you have? They may well have small signal diodes. They are also called high speed diodes or switching diodes. 1N4148 is a common type. It won't hurt anything to try 1N4007s, but if you end up with the horizontal locking in only over a narrow range of the horizontal hold control, try better diodes.


A very good one. They usually have everything I need.

I took the two untested tubes from the TV set to the store, where the owner had a Sencore Mighty Mite 7. The 6DQ6 tested as Bad, at about 25-30 on Emission, no shorts. The other tested good. I've ordered a replacement off eBay.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Tue 04, 2019 5:30 am 
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Tom,
I have a Predicta here that I used 1N4007 diodes and sure enough the H. Hold was pretty narrow. I replaced them with some 1N4148 and the H. Hold was much wider. Thanks.

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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Tue 04, 2019 3:59 pm 
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Location: Dallas, TX
Tom Schulz wrote:
Checking around, it seems that the 1N914, 1N916 and 1N4148 are all the same. Originally each step up had somewhat better specifications. But these days they just make one type of diode and sell them under all the different part numbers.

Sometimes the differences are small and don't matter much for a application.
1N914B 100 max reverse volts, 1 volt forward drop at 100 ma.
1N4148 75 max reverse volts, 1 volt forward drop at 10 ma. with a bit lower reverse leakage.
Both diodes have the same reverse recovery time.

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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Wed 05, 2019 1:56 pm 
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Crist Rigotti wrote:
Tom,
I have a Predicta here that I used 1N4007 diodes and sure enough the H. Hold was pretty narrow. I replaced them with some 1N4148 and the H. Hold was much wider. Thanks.

Good to know Crist but I am not surprised though. Signal diodes vs. "power" diodes.

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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Wed 05, 2019 11:18 pm 
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Not sure if it's been mentioned yet, but be sure to check *all* the socket contacts on the pcbs. The contacts on the sockets are notorious for developing a hairline crack right where the contact bends. All the Predictas I've worked on had at least a few hairline cracks. The cracks are small enough that it often creates an intermittant connection. Wiggling the tubes, flexing the pcb and heat can cause these cracks to open up intermittantly.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 3:13 am 
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Something else that I don't think has been mentioned yet is a quick way to see if the horizontal output and flyback are at least sort of working.
Bring a florescent lamp such as one of those spiral CFLs near the horizontal output tube. The lamp will glow if there is high voltage being generated. It should glow even brighter if you bring it near the 1B3.

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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 3:27 am 
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Location: Bloomington, IN, 47401
Tom Schulz wrote:
Something else that I don't think has been mentioned yet is a quick way to see if the horizontal output and flyback are at least sort of working.
Bring a florescent lamp such as one of those spiral CFLs near the horizontal output tube. The lamp will glow if there is high voltage being generated. It should glow even brighter if you bring it near the 1B3.


Got nothing. 1B3 tube has no filament glow.

Ugh.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 3:42 am 
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Looked inside and the flyback has a obvious crack on the surface. So, any sources for flybacks?


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 4:17 am 
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indy_kid wrote:
Looked inside and the flyback has a obvious crack on the surface. So, any sources for flybacks?


Guess I should pull it out first and check for a broken winding and some other issues.

There are some Thordason flybacks on eBay. Anyone know the proper replacement number if I need to go that route?


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 4:38 am 
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Location: Albion, CA, USA, 95410
You won't see a glow on the 1B3. It is a 1 volt tube and the filament isn't visible. The test mentioned above is to see if a neon bulb or CFL will light if held close to the flyback. If it glows even weakly there is HV present.

Most old flybacks have some cracks, don't panic yet. Carefully take resistance measurements, the SAM's should have the DC resistance listed. Look for any carbon or signs of overheating. Don't pull the flyback until you are sure it is cooked.

+1 on the above about the tube sockets being fragile. I had to replace several on the main PCB board of mine.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 5:02 am 
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indy_kid wrote:
indy_kid wrote:
Looked inside and the flyback has a obvious crack on the surface. So, any sources for flybacks?


Guess I should pull it out first and check for a broken winding and some other issues.

There are some Thordason flybacks on eBay. Anyone know the proper replacement number if I need to go that route?


Okay, I see the very fine wires (the wax coating is cracked, though). Does ~12 Ohms/~380 Ohms sound right? I'm not getting an open anywhere.

Thus, if those values are correct, it would seem the problem must lie upstream of the flyback.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 1:37 pm 
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I am assuming that you have tracked down the Sam's for your set. It should have the values for the flyback resistance test. It is important to be slow and methodical. There are multiple windings, make sure all of the values are in the ballpark. Find a CFL or neon bulb and do the test mentioned above to determine if you have HV present.

The cracking is quite common and after you get the set working and make sure the flyback is dry it is a good idea to coat it with an appropriate HV sealant.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 2:21 pm 
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According to SAMS, T3 is indeed 12 ohms, 385 ohms, so it sounds like you are OK there.
Dan


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Thu 06, 2019 3:28 pm 
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Here is what a CFL does near a flyback or horizontal output.
Attachment:
FluorHorzE01.jpg
FluorHorzE01.jpg [ 114.2 KiB | Viewed 434 times ]

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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Fri 07, 2019 3:11 am 
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Top cap of the flyback was detached. No contact, so no juice. One left on eBay, and I'm going to make sure it's well sealed and sturdy before anything else!

Would it be possible to use something like conductive epoxy to reattach the top? It was just metal-to-metal contact, held in place by the wax.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Fri 07, 2019 2:05 pm 
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I'm not sure what you mean by the top cap of the flyback. Can you post a picture? I have a different model Predicta but there is no cap on mine.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Fri 07, 2019 3:29 pm 
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I'd Hazzard a guess that the wire that does to the top cap connector of the HV rect snapped off the HV winding....if you can find the end of the magnet wire you can reattach it, but provisions to keep the wire affixed need to be made.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Sat 08, 2019 2:43 am 
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Location: Bloomington, IN, 47401
Image

Apparently, the structure (wax, cardboard, etc.) for the wire leading from the 1B3 tube to the flyback was in worse shape than I knew. It detached completely, breaking the magnet wire. I attempted a repair, but it's too fine for me, and sitting hunched over the set while trying to effect the repair was murder on my back (18 years since the last fusion; probably time for another).

I went ahead and ordered the single replacement on eBay, a Thordarson FLY 119, which looked identical in the pix. I couldn't find any info about equivalent flybacks online, but it was this one or nothing. I also ordered some silicone sealant and HV dope. The first thing I'll do with the replacement is fill the cracks with sealant (there are cracks in the replacement; the seller gave no guarantee that it will work), then give the outside several layers of HV dope to stabilize it for further handling.

"Crispy" doesn't begin to describe the state of these flybacks! What were they thinking with just a wax covering? Yeah, I know, they didn't expect folks to be messing around with it; once it place and not to be touched again. Still, simple thermal expansion would cause cracks in the wax, which could lead to arcing and other problems. A more robust covering seems like a no-brainer, especially if you want your stock of unsold parts to survive for years in some warehouse.


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 Post subject: Re: 1959 Philco Predicta Restoration Thread
PostPosted: Jun Sat 08, 2019 3:40 am 
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Flybacks are set specific, appearance means little as many of them look alike. FLY 119 is not for a Predicta as it's clearly marked 70 degrees on the box label and the Predicta is a 110 degree set.

Unfortunately the correct one is scarcer than hen's teeth since they haven't been made in decades and it's always been a high failure part and today if/when you find one for sale it will usually be priced accordingly.

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