Resistors for Predicta
 

Hello All, I normally do radios, and not tv's. So I'm going to start on pulling this 10L43 mainboard and replace everything (well caps, resistors, and couplates) Anyway, are carbon comp resistors preferred over metal film? (if so,..why) or is it ok to use metal film throughout this set ? Does it have anything to do with frequency stability, drift ? Other factors, than just replacing all the caps and maybe just out of spec resistors. I really want to do this right. Being in Canada, we just have to jump through more hoops than you guys in the U.S. and we end up paying more than twice for everything ( parts, shipping and duty hassles). I normally deal with Dave at JustRadios, but he doesn't have all the different resistor values and the one supply place in town leaves a lot to be desired.
Thanks !
Tony

Metal film are superior to carbon comp. Virtually no temperature drift and widely available in all values and wattages. I've had no problems using them in Predictas or any other set. Metal oxide are pretty good to.

Thanks Bob, I appreciate your expertise. I have gone through the set and checked every resistor and matched it up with the ones on the schematic. Most match, but not all. There are maybe 6 or 8 that seem to be way off in value. I don't mean the resistor changing value over time, but the color code not even matching the schematic. I take it, these were probably production changes and I should be replacing these with the value that is in there and not with the one shown on the schematic ? There are quite a few that have drifted as well. One thing I did notice is a small crack and what looks like carbon tracking on the damper tube socket (6DA4) between pins 5 and 6. That is looking down at the tube socket (from the top of the board) and counting clockwise from the first pin right of the keyway.
As far as I can tell, everything is original except for R54 (390 ohm) and cap C20 (.022 @400). They have been tacked on above board.
I like your idea of putting the electrolytics on top of the board rather than restuffing the cans.
Tony

Trust what is in the set unless you see evidence that it was previously replaced or that the resistors got overheated (which can discolor the color code paint). Might not be bad to order both possible values for parts that don't match the print. If the set don't work right and troubleshooting don't help changing the set from one rev of prod changes to another sometimes helps.

Yes, they did make production changes. Here is a two page Philco service bulletin describing some of them.

https://drive.google.com/file/d/0B37...ew?usp=sharing

Better: :D:D:D:D

So is it recommended to make all of these changes? I'm not where I can look but I think my set has some but not all of these changes.

I wouldn't unless your set is experiencing the problem the change addresses.

Would you happen to know where this "DOT" is located that signifies the various production runs ? It says Run 2 is RED dot, Run 3 is ORANGE and Run 4 is YELLOW. I know this has the 3 watt R15A resistor. I will check for some of the other changes. I don't see any painted dots on any sheet metal. Thanks Bob,.. this is good info.
Tony

Well I don't know about all that - just passing along my experience as a EE and tinkerer ;)

Sorry, I don't know. I reviewed pictures of several VOS boards but didn't see any colored dots.

Only thing I have seen is a stripe on the main circuit boards. One of mine has a yellow stripe and one has a green stripe, IIRC. Don't know if that has anything to do with the "dots" however.

Personal observations on carbon comps vs metal film resistors.

In small signal circuits where current is not an issue I have never had any problems with metal film resistors.

HOWEVER: I can't say the same is true in B+ power supply circuits. In old sets I have seen situations where 2W and 1W carbon comps were being pushed to their wattage limits. I have had more than one metal film self destruct under circumstances where the original ckt design was probably using a resistor that was under powered. In my experience metal film resistors will not tolerate overheating as well as a carbon comp.

As a result I have been using high quality NOS carbon comps in everything I rebuild. You never know when the original design might have been using a resistor that was under rated, and my experience is that carbon comps seem to tolerate abuse better.

Most high quality carbon comps have pretty good value tolerance and in old tube ckts the added accuracy you gain with metal film doesn't affect circuit function to any appreciable degree.

And besides, carbon comps are period correct, if you are into that sort of thing.

I should have mentioned I generally double the wattage when I replace resistors. 1W for 1/2W, 2W for 1W etc.

I use the PR01. PR02 and PR03 series from Vishay. They are a reddish brown rather than bright blue and the color bands are bright and clear. The 2W are similar is size to the old 1/2 watters.

Also very reasonably priced. Often as little as $0.02 each on sale. Available at Allied Electronics, Mouser and Digi-Key, Newark etc.

http://www.alliedelec.com/search/results.aspx?term=pr01

http://www.sm-elektronik.pl/galerie/...baec412385.jpg

You forgot author / preservationist-custodian......:D:D

Hey! Where can I get a copy? Just looked and don't see one for sale.

I should get me a copy and leave it on my bench for people that ask me if I learned how to work on TVs and radios by watching Youtube videos :whip:

Hey, where can I get a copy!

Hmm. Apparently cabin fever is setting in a little early this year. ;)

IIRC that cover was someone's photoshop gag creation.

I figured that much. It's the motivation that concerns me. Must be just a pick on Phil and Bob day. ;)

What! I was really looking forward to getting a copy and having Phil and Bob sign it. Just think a signed copy.....sigh.

Ancient post of mine, I just like to praise Bob's restoration efforts when I can. All in jest.

http://www.videokarma.org/showthread.php?t=249404

My comment on resistor types:

First, I always try to replace carbon comp resistors with modern film ones
that are the same physical size, not smaller. Modern film ones always smaller for the same rated wattage , which means at rated power they will get hotter: not good!
And this looks more authentic, even if they are bright blue.

Second ... some modern film types in fact have spirals of resistor element.
This won't cause a problem at audio or NTSC video frequencies ....
but most certainly can and will in VHF/UHF tuners. At 41 MHz IF frequencies,
I have no experience so can't make a statement.

I do have experience at 1.03 and 1.09 GHz, and at the IF Frequency of 60MHz. Film types from Dale/Vishay (RLR05/07 series) work fine if the lead length is short. Yeah, hard to find and pricey for civilian/non industrial use, but usable nevertheless.

Same here. I always replace with a higher wattage modern film resistor.

I have a question about the main "fuse" in this set. It is open and has been by-passed with (2) 4.5 ohm 10 watt in parallel (making 2.5 ohms). I have removed all the "kludges". All I can find in my area is a 5 ohm 10 watt resistor. Is this ok ?, the next step up is 6.8 ohms.
Tony

Yes, that's fine. The original was 5.6 ohms. Note that a regular power resistor is not the same as the original fusistor. A fusistor is designed to blow open like a fuse if current is excessive. A regular resistor will get hotter and hotter but not open up until it's really roasting.

I suggest adding a fuse in series with it. 1 or 2 amp slo blow should do it.

I am wondering how critical the small cylindrical capacitor is on the top of the tuner (labeled L2, C204) that has the 6.3 volt brown wire running through it to the heater of the 6X8 tube is. The reason I ask is while I was replacing the .22 mfd paper cap on the top of the tuner, I had noticed that someone in the past had removed the wire for the pilot lamp. It is missing totally, and only the 6.3 volt brown wire is there. There was a solder blob and what was left of the pilot lamp wire broken off down in this 5 pf cap. I was using a needle with my solder sucker and soldering iron to extract the remaining wire. I managed to crack the cap down the side. I see that the remaining half is ok inside the sheet metal of the tuner, the top half is still there (it cracked, but did not break off completely) When I put my ECG capacitance meter on it I don't get anything compared to the others on the tuner. My goal was to install a pilot lamp wire with lamp and holder. Is this cap there just to extract any remaining "junk" from the 6.3 volt line before it hits the tuner circuit ? I guess the only way I will know is when I finally fire up the set I don't get anything through the tuner. I guess the only place to get one would be out of a scrap tuner ? It is listed as #30-1268-1 :tears:
Tony

This might be a different chassis from yours but is shows that cap as C222 and is 1000mmf

http://www.earlytelevision.org/pdf/P...Sams-466-1.pdf

Hi, On the link to the Sams you posted, the capacitor I'm referring to is C204 (it is shown in the photo of the top of the tuner). It has the 2 wires running through it. In my case there was only one wire. I was trying to add the 2nd wire for the lamp when it cracked. It is a 10L43 chassis. It comes up on page 5 of the pdf document. Also, the Philco service data seems to show it better on the schematic in regards to the 6.3 volt line than the Sams does.
Thanks !
Tony

Mrjukebox160, you are correct. It is indeed a 1000 pf cap. Although the one listed is not the one shown in the picture ! Obviously an error on Sams part. The schematic does not match the photo part number. Sorry, I was scratching my head.
I had another question regarding the networks. I've watched a lot of Bob's videos on the Predicta's. Is K2, the only network (vertical section) you have to use 1000 volt caps on ? I know the one cap on the chassis board C14 .0015 mfd is the only one rated at 1000 volts, and the cap on the network (1500 pf) is directly connected to this cap. Will a 2200 pf @630 Volt poly on K2 go "poof !" ? Can you get away with 630 volt caps for the other networks ? I ordered 1000 volt mica caps from JustRadios, but his micas stop at 1000 pf. You then half to use the poly series. I ordered 3 -1300 pf @ 630 Volt 1% for using with the 2 - 47K resistors on the K3 network (also vertical section). I know his "regular" micas are only rated for 500 volts.
Tony

Oddly, on the Sams that network is shown as K5. I don't know how much A/C is getting through C14. The spikes might be too high for a 630 volt cap.

I now see there is a "second" K5 listed. Must be another misprint. It looks like 630 volt caps would work for the other caps. in the networks.

There seems to be some confusion regarding the Sams. The cap in question is C222 in the Sams, not C204. They mislabeled it on page 5.

It's a 1,000 pF ceramic feed-through cap. That's a type of cap commonly used to feed signals and power into a shielded box like a tuner.

Something like this may work if you need to replace it.
http://www.digikey.com/product-detai...043-ND/2079617

Some confusion between the Philco service info and Sams.

The networks are labeled N1-N7 by Philco and K1-K7 by Sams and the numbers do not refer to the same parts.

N2 is the same as K5 and is the vertical feedback. Yes, it is the only network that sees a voltage spike needing a higher voltage cap. 630 is more than enough for all the others.

Hello Bob, Thank-you for clearing that up ! I have a .0015 @ 1600 for that network. What about the 2200mfd that is used in the same network ? I have a 630 volt, but don't have anything at 1000V ? I will have to special order one if it is required. Also, I have replaced all resistors 1/2 watt with 1 watt, 1 watt with 2 watt. The only ones I'm questioning are the 3, 2 watt resistors R19, R40 and R45. These , I replaced with 2 watt ECG metal film, even though they are half the size of the original carbon comp ones. Nobody has any 3 watt metal film resistors in this area. I have left the WR4 (4100 ohm) and the R15A (5.6k 3 watt) one alone. I've pulled all 3 of the Can electrolyics and they all test good. Most are 20 to 30 mfd higher than the rating on the cans. I've pulled the solder from the traces on the board that cover up the holes where you added the 3 radial electrolyics to the board. Looks like I have to drill 1 or 2 holes (and run a small wire, like you did) to mount them. Also, did you mention that you used 1N5408 diodes to replace the original (34-8048-2) diodes ? It seems to be slowly coming together. I just wish the last person in this set didn't hack it up so much.
Thanks again for your valuable input.
Tony

Take a look at the Philco service info. You can see there is 3.2 VDC and a 60 Vp-p signal on that 2200 pF cap. 630 volt is more than enough. 150 would even be fine. I did the same analysis on all the couplate caps and determined that 250 was fine for almost all. 500 covered the rest. Use 630 if you really want to play it safe.

I also use C0G ceramic caps. That's the type thats the most stable type of ceramic. Mica is fine too, but rather pricey for the larger sizes. I've dissected some couplates and they appear to be tubular ceramic caps except for the vertical integrator. That's some type of thick film hybrid module bult on a ceramic substrate.

I use the Vishay VR01, VR02 and VR03 series of 1, 2,and 3 watt resistors. I get them mail order from any of the major vendors. Dirt cheap, great quality and look sort of like the old carbon comps.

Yes, I use 1N5408 diodes exclusively for all my projects now. Rated for 3A and 1,000 PIV.

All good info, I know you touch on these various things in your videos. I'll guess I'll have to re-watch anything having to do with the Predicta line and pause to take note. I have a cosmetic question. Has anyone had to replace the grill cloth in any of the Predicta line that uses cloth on the front ? If so have you found a close (suitable) match and where did you find it. This one is totally destroyed. I've been searching E-bay and locally and haven't found anything close.
Thanks !
Tony

Has anyone run into this problem and is there an easy fix ? The 4 plastic "lugs" that are molded into the back of the picture tube cover are stripped. They must have had quite a workout in their lifetime. 3 are completely stripped, one is almost. I've thought of drilling them out slightly and epoxying some 8/32" nuts on the backside and using a couple of longer machine screws instead of the metal plastic thread screws, or are plastic "heli coils" available ? or maybe a plastic insert ?
Tony

How about those plastic thingies they sell for putting screws in sheet rock and what not? I think they used to be called "mollies"? Just cut the flange end off. I was lucky, only one of mine was completely stripped so I just left it. I'ts not like they are likely to come flying off anyway, except maybe when moving the set.