I'm working on a 17" tabletop Predicta, model H3412L, chassis 10L43. After recapping and replacing a number of off-tolerance resistors, the HV has disappeared. The set had some minor repair sometime in the last 30 years and it did make a picture of sorts when I got it.

I temporarily placed the service manual at this link:

http://antiqueradio.org/art/temp/Philco_H3410-Predicta-Princess-Sams-466-1.pdf

All tubes test OK. B+ voltages are reasonable (except boost; see below.) I checked the resistances on all tube pins using the Sams chart and found nothing remarkable. All resistances look reasonable on the flyback transformer and related coils (L17, L18). All ground stakes on the board are making good contact.

At present, the voltages look bad on the 6DQ6A horizontal output tube. I measure around zero at the grid (pin 5) where it should be -45V. I also measure 296V on pin 4 where it should be around 175V. (The 400V boost voltage is also deficient, measuring around 235V where it should be 400V, but perhaps that's no surprise if the HOT isn't working.)

Below is a piece of the schematic showing the HV section. As you can see, I have replaced everything around the HOT except C51 and R69. (Items with a red check have been replaced.)

http://antiqueradio.org/art/temp/PhilcoH3412LHOTDamperSchematic.jpg

The waveform on pin 5 of the HOT is not what you'd expect (W14). It looks more like the W13 waveform observable on the upstream side of the K7 couplate:

http://antiqueradio.org/art/temp/PhilcoH3412L_HOT_Pin5_W14.jpg

Given all that, I'm inclined to suspect the K7 couplate that provides input to the HOT at pin 5.

Any other ideas? I'm not eager to pull the main PC board again to replace the K7 couplate if that's a wild goose chase.

Thanks!

Phil Nelson

what does W13 look like?, and what does Pin 6 of the 6CG7 show for voltage and wave form?

Phil,
I would check to verify that the 6DQ6 cathode (pin 8) is making contact to ground, by measuring to the tube pin itself. The readings you're getting suggest the cathode might be 'floating'.

Carefully check for bad connections on the PC board at the 6CG7 and 6DQ6 tube socket pins.

Thanks, I will check those things. Waveform W13 looked like this:

http://antiqueradio.org/art/temp/W13.jpg

I think the scope was not locking well on the signal, but you get the idea. Much the same as what appears at pin 5 of the HOT.

Phil Nelson

what does Pin 6 of the 6CG7 show for voltage and wave form?Pin 6 measures 188V (schematic says 195V). Here's the waveform:

http://antiqueradio.org/art/temp/Pin_6_6CG7.jpg

Phil Nelson

I would rebuild the couplate. I do have a fly if needed.

with the screen voltage that high (no current draw) and no negative on the control grid, the HOT should be screaming to get out of the TV. I would have to guess the HOT is dead or as mentioned earlier, the cathode is not on ground. I would be careful if the tube is dead as a new one may overcurrent violently without drive.

Before rebuilding the couplate, i would verify that the cathode>ground connection is good on the HO tube. If still no go, sub with a known good tube (a 'BQ6 would do for the test).
Once the tube is conducting, the G1 drive `might` assume the correct waveform.

The 6DQ6 is making good ground contact on pin 8. I wrapped a thin wire around that pin and reinserted the tube. My ohmmeter shows it's connecting to ground. I grounded that little wire to the chassis and briefly powered up the set, and got the same old symptom.

I borrowed another 6DQ6 from my Philco Miss America and briefly tried it out. Same symptom: no HV.

Before attacking the couplate, I'll take out the chassis and re-clean the holes in the 6DQ6 and 6CG7 sockets and verify that they are connecting to the right spots.

If I do rebuild the couplate, what about voltage rating for those little caps? I have 500V dipped mica caps in the right values. I have some 1KV and 2KV rated caps, but they are ceramic and much larger.

I'm tempted to try replacing the couplate from above, since every time you pull and reinstall that board, you increase the chance of creating new problems.

Phil Nelson

do you have a analyst? would be a good set to try it out on, although it sure seems like it must be the couplate. I had ground issues, but it was the damper tube filament IIRC.

I do have a 1077B TV Analyst. Do you mean using it to provide a horizontal grid drive signal? I haven't tried using it that way. Would you pull the 6CG7 and connect the signal lead to the 6DQ6 HOT grid?

Phil Nelson

There is also a plate drive on that unit that you can connect to the plate cap of the HO Tube which can confirm the fly and other circuits downstream of it. without the need to worry about properly connecting the grid test signal.

I pulled the 6CG7 multivibrator tube and connected the TV Analyst's grid drive to the HOT grid, and got a bright raster.

The Analyst makes a nice clean signal:

http://antiqueradio.org/art/temp/BKTVAnalystHorizDriveSignal.jpg

A label on the PC board points to the HOT grid:

http://antiqueradio.org/art/temp/HorizOutputGridLabel.jpg

The HV is back, yay!

http://antiqueradio.org/art/temp/RasterBack.jpg

The raster is nice and bright with full horizontal deflection. The vertical locks, but the maximum height is what you see in the photo.

Perhaps replacing the K7 couplate will fix the HV problem, after all. Not sure what to think about the height problem. When I played it before recapping, the height was lacking somewhat, but not as much as now. I would have expected recapping to improve the height, if anything. With my luck, the vertical integrator (K4 couplate -- ugh) is also flaky.

Phil Nelson

The height might not be a "real" problem. The vertical circuit relies on the +400V boost voltage, which might not be where it needs to be using a substituted horizontal drive signal.

Check the boost voltage before ripping into the vertical circuit. It is quite possible that you will not get proper boost until you fix the HOT drive problem.

Thanks, I'll reserve judgment on the vertical until I replace the K7 couplate.

I discovered that there's (barely) enough room to sneak a soldering iron under the board and unsolder the couplate leads without pulling the board. Tomorrow, I'll make the replacement and give it a whirl.

Regards,

Phil Nelson

If you have to deal with tough bugs in both deflection circuits, and if they are both on the same (tough to remove) board then it might be a good idea to mod it so all the wires going to the board are numbered quick connects to facilitate checks during trouble shooting.

on mine I was able to get at a lot of the caps with a soldering GUN with the tip bent 90 degrees. The problems I had with the predictas were the bent wires (not through hole plated) so its easy to mess up the traces if you are not very careful. I used a lot of solder wick (coated with flux) to get everything cleaned out. Also low power on the dual heat gun. I dont recall if there was enough opening near the couplates for the bent gun tip trick.

I always thought the output from the plate of the horz osc was a sine wave, that was modified by a RC network (the couplate in this case) that made it look like the correct Hor output tube grid drive. Guess what I am getting at is to make sure you are getting the correct wave from from the horz osc. of course if the couplate is goofed up maybe that is not possible. It sure seems like the couplate has to be the problem if all the voltages are correct at the horz osc tube.

Well, I removed the couplate last night and I had to cut it up to remove it, since the access is very tight and a couple of the leads were bent. It's hard enough to remove one of those long, multiple-lead jobbies all in one piece when you have normal access.

As I recall, voltages on the 6CG7 were normal except the negative voltage on its grid was deficient or absent, similar to the HOT. Yesterday I did check that 6CG7 socket carefully, confirming that the resistance is normal on each pin and that every pin actually connects to the right spots. I also pushed things around and didn't see any evidence of an intermittent pin or broken trace.

I'm not confident that I can install a new couplate in this cramped space without messing up a trace underneath. Whether the TV will need further work at this stage is unknown. Adding quick disconnects on all of the board leads seems worth a try. Then I can swap the board in and out faster and less destructively. This local place has small Molex connectors:

http://shop.vetcosurplus.com/catalog/product_info.php?cPath=72_226&products_id=6845

I already connected three of the six ground stakes with a bus. If I complete the bus to connect all six of them, then I can use one Molex to connect the bus to a ground outside the board and perhaps reduce problems with bad board grounds.

Some of the leads from the board will need lengthening. I'm going to leave the existing wrapped/soldered connections alone and cut each lead an inch or so from the board to install the disconnect.

This will take a while. My hand-drawn diagram lists about three dozen leads, plus the six ground connections. After drawing that diagram, I got a copy of the Philco service manual, which has a nice diagram labeling everything on the board. I'll use their numbering scheme this time around.

Phil Nelson

I like the idea of leaving the WW alone and cutting about 1" away, then attaching the connectors, doing 1 at a time and if possible some way to color code or number. If I ever work on another predicta that requires any kind of tough dog work (like a busted socket) then that is how I would go. I like sermos connectors (aka anderson power poles) because I have used them in the past for RC airplane use (my other hobby).

Thanks for the connector suggestion :yes: I'm about to dive into my first predicta and have been searching around for connectors. I had no idea what they were called though and was coming up empty.

The Molex connectors are bigger than I expected, once I got one installed:

http://antiqueradio.org/art/temp/MolexConnector.jpg

I bought 10 of those today, all the store had in stock. Maybe I'll go back there (or a hobby store) tomorrow and look for power pole connectors. I built an RC plane some years ago and do remember those connectors being smaller.

The Philco manual has a diagram that labels the connection points and tells what they connect to. This snippet shows WW connectors L38 and L46, etc., as well as ground connector G16:

http://antiqueradio.org/art/temp/BoardDiagram.jpg

I'm a little concerned about creating a mess of wires & connectors hanging over the board. The factory installation tucks the leads along and under the board edges. Things may get weird by the time you have three dozen connectors up above, leaving enough slack to unplug & plug things without accidentally snapping leads off the WW pins.

Edit: The powerpole connectors look about the same size as the Molex, 1-2/3 inch long when complete. They also appear to be the crimp-on type, which I like less than soldered connectors.

http://www.mouser.com/catalog/specsheets/1327G16-Anderson-Power-datasheet-42848.pdf

Phil Nelson

Well, I came home with a sack of powerpole connectors, which are even thicker than the Molex type.

http://antiqueradio.org/art/temp/PowerpoleConnectors.jpg

The parts store had nothing smaller. The only alternative was spade-type connectors, which are just too danged ugly.

I'm starting to wonder if this is a bad idea . . . .

Phil Nelson

maybe stagger cutting so they dont line up, I can see how its going to get kinda messy with a lot of connectors, considering the space limits. You need to do a lot of planning before making the 1st cut.

Yah, I'll stagger them for sure. For some of the WW pins, I may remove the old lead and install a new one made of more flexible multi-stranded wire. That will be the short pigtail to which the other long end connects.

Maybe I'll sit down and draw a diagram, as a way of thinking through the whole layout wire by wire.

Phil Nelson

yep. maybe even just tape them in place to see how its all going to work out. This looks like one of those deals where you really want it all figured out before starting. Of course if it does work out, I am sure there will be a lot of predicta owners that would follow your approach.

Would something like Molex female terminals pressed right onto the ends of each board pin work?

I just tried out a Molex female terminal, and the answer is yes. The size is right and it fits pretty securely.

The Molex terminal doesn't go down the full length of the pin, but I compared it to the factory video lead, which plugs onto the board the same way, and that connector only covers about half the pin, too. The video connector is simply a female terminal about the same size with a bit of shrink wrap around it.

The question is whether you would want to trust all three dozen leads to that sort of junction. Philco used that type for the video lead, so it's not completely loony. On the other hand, this board is dodgy under the best of circumstances.

You'd need to extend a number of the leads a bit, to accomodate this kind of connector. That would be less work than installing two-piece connectors all around, though.

If you did use push-on connectors all around, there would be some risk of accidentally dislodging one when replacing a tube, etc.

Phil Nelson

I'm starting to wonder if this is a bad idea . . . .
Ugh. The powerpole connectors look too big. I laid out several next to the terminals where they'll connect:

http://antiqueradio.org/art/temp/PowerpoleTrial.jpg

Picture each one of those with a 1-2 inch pigtail to the board and a longer lead trailing above or alongside. Seems like a real mess to me.

By loosening the ground stakes and dismounting the rear pots and range switch, I was able to lift the board a bit, perhaps enough to install the couplate. If that works, I'll reconnect the grounds and see what happens.

Phil Nelson

yep that would get messy oh well maybe someday somebody will find a micro connector that is no larger than the wire itself. Too bad, it would be nice to be able to easily separate the pcb for easy access.

Well, the Molex female terminals are about as small as anything can get and still allow you to solder onto it. A few of the board's WW pins would be easy, since the old leads have enough slack to simply attach a Molex terminal on the end. A number of leads are tight and would need lengthening. There are at least three WW pins with two wires attached.

Meanwhile, the new K7 couplate works fine, but the height is still deficient.

http://antiqueradio.org/art/temp/K7Replaced.jpg

The 400V boost voltage measures 400V on the money. On the 6DR7 vertical tube, the voltage at the oscillator grid is low (-.03V rather than -3.5V) and the plate is somewhat high (155V rather than 115V).

As with the horizontal section, caps & resistors around that tube have already been replaced, which leaves couplates K4 and K5, I guess.

Phil Nelson

I've been puttering around with the height problem, still seeking a solution. Height is 1/3 of the screen at most, and linearity is poor.

I wonder if the vertical output transformer could be funky?

I have subbed known-good 6DR7 vertical tubes, replaced the K4 and K5 vertical couplates, checked or replaced Rs and Cs around that tube. The pots for hold, height, and linearity are working and have the right resistance. The 400V boost voltage is normal. Here's a piece of the Sams schematic:

http://antiqueradio.org/art/PhilcoH3412LVerticalSchematic.jpg

Voltages are close except that pin 7 (grid) is only -0.5 volts rather than -3.5. Resistance of the vertical windings on the yoke looks normal.

On the vertical output transformer, the secondary measures 2.6 ohms (expected 2.5) but the primary measures 410 ohms where it should be 425 (or 430 in the Philco schematic).

Could a few shorted turns in the output transformer account for the lack of height? I feel like I've eliminated just about everything else. This problem existed before I did any restoration.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Some things to try:

Bridge the 100 mfd cathode bypass.
Rotate v lin while measuring cathode, pin 9. It should go to 0 at extreme end
Bridge electrolytic on the 275 volt source
Recheck cap values that were replaced. C 40 will have most effect on height.
Height and lin pots and the .0015 (C43) were common failure points.
The small pix accounts for the low neg voltage on pin 7 since the source is the output plate.
Make sure pin 7 measures 68 k to ground.

Thanks for the ideas. Here's what I found.

Bridge the 100 mfd cathode bypass.

Tried, no change.

Rotate v lin while measuring cathode, pin 9. It should go to 0 at extreme end.

If you mean going to zero volts, it never goes below about 20 volts. Resistance of the v lin pot varies from about 10 to 770 ohms. I wonder if this is a replacement? The manual calls for a 1500-ohm pot with a stop at 180 ohms. This looks like a (roughly) 750-ohm pot and someone added a 950-ohm/1W resistor in series to make a max of about 1700 ohms. So, with the resistor the pot is varying between about 960-1700 ohms. Shorting that resistor didn't change the height noticeably.

Bridge electrolytic on the 275 volt source.

Tried, no change. The 275V source measures 273V.

Recheck cap values that were replaced. C 40 will have most effect on height.

Rechecked, all caps look OK. I replaced C43 (.0015/1KV) by wiring two .0033/630V in series. In Sams, C44 is listed as .033, with .022 as an alternate value. I temporarily subbed a .022; no change.

I noticed one difference: R55 (between pin 8 and vert hold pot) should be 33K and I installed 39K for some reason. (Perhaps 39K is what I found there.) Not sure how important that is. I measure 8.6V on that pin; Sams calls for 7.5V and the Philco manual calls for 10V.

Make sure pin 7 measures 68 k to ground.

It measures 67.5 K.

Regards,

Phil Nelson

Phil:

Agree that nothing seems out of range. 33K vs 39K will only affect vert hold range. It locks OK.

The vertical output transformer could have some shorted primary. Check resistance with a DC meter, not a digital one. Some digital meters are fooled by high inductances because they use an AC voltage for resistance.

Make sure the 100K 1W is not burned. It may be necessary to sub a VOT for test. You can try driving the output stage with about 20 VAC, 60Hz to see if it will sweep at all. It will be distorted, but it will give an indication.

I hauled out my trusty old analog Triplett meter. The primary measures lower, if anything -- 400 ohms, give or take a couple. This is measuring from pin 1 of the VOT to test point 33 (275V source) in Sams.

The 100K/1W resistor (R60) is new and it measures 100K.

I just remembered that my BK 1077B Analyst can provide a vertical plate drive signal. (I need to use that thing more often!) Tomorrow, I'll pull the VOT and see what happens with that signal.

Regards,

Phil Nelson

...I just remembered that my BK 1077B Analyst can provide a vertical plate drive signal.
Dang, i had forgotten that too, having last used an Analyst many aeons ago.:nerd: I was fixing to suggest what Don L just suggested.. drive the output stage with AC.

OK, the vertical plate drive signal from the 1077B looks like this:

http://antiqueradio.org/art/BK1077BVertPlateDriveSignal.jpg

I removed the 6DR7 vertical output tube and injected the Analyst's vertical plate drive signal on pin 1. Here, the 1077B's Amplitude control is set about midway:

http://antiqueradio.org/art/PhilcoH3412LVertPlateSub1.jpg

The height's about the same as before, with linearity very compressed toward the bottom.

Cranking up the Amplitude control nearly fills the screen:

http://antiqueradio.org/art/PhilcoH3412LVertPlateSub2.jpg

Phil Nelson

Phil, can your Analyst generate a signal to inject on the grid of the vertical output tube? Reason I ask, is that you still could have shorted turns on the vertical output transformer, and turing up the Analyst output would cover it up, sort of speak. The sam's says "do not Measure" so you don't know what the amplitude of the plate waveform should be. But the grid drive is shown. But it's inverted compared to the plate's, as you'd expect. If your analyist can make a grid waveform, dial in the amplitude, and disconnect the coupling cap C42 from the vert osc circuit and inject it via that cap to the output triode grid there. And see if the height is good.

just a long shot, what about a defect in R53 (thermistor in yoke).

I would look for a better match to the lin pot as well. the 950 in series sound like it could be a prob.

resistance chart shows 450 at pin 9 of the 6Dr2 (granted it varies but are you in the ball park?)

It also looks like it is borrowing some neg bias from the horz out grid circuit. I would check R58 and R59 which makes up a voltage divider for the bias and also scope the grid of the 6DR7 pin 2-3. sometimes the neg voltages at the pins can be misleading esp if that bias supply is goofed up due to a faulty divider network (R58/R59). oh and check C50 the .22 cap that looks like it filters that bias supply.

Test the bias divider:
1. Turn down brightness
2. Remove 6DR7
3. Measure grid, pin 3

It should be roughly half of the 6DQ6 grid bias or about 22 volts. That saves unsoldering some parts.

one more thing, if the lin pot has been hacked up, make sure the cathode bypass cap (100uf electro) is NOT being cut of of the circuit when the lin pot is turned to min, esp since that 950 fixed resistor is in there. Worst case you have a 950 unbypassed cathode resistor with the lin pot turned in such a way as to take the cap completely out of the circuit. IIRC there is something different between how the schmatic is drawn and how the lin pot and cap are actually done, but I may just be remembering that wrong. If it was me I would for grins just put a 500 ohm fixed resistor and the cap in there and see how that works (disconnecting the hacked up lin pot/resistor combo), as is sure seem like its a gain issue on that tube, assuming of course the grid bias and drive are correct.

With the 6DR7 removed, I measure about 0V on pin 3. (It starts out higher when the set is cold and then sinks to zero, never going negative.) I will slide out the chassis and inspect that voltage divider.

Phil Nelson

If there is high voltage, then there is -45 volts on the 6DQ6 grid. That goes through the 470K-560K divider to lug 21, looped to lug 40 to the 1.5 meg bias resistor and the .22 uf bias filter. If all those components are good, then the .1 coupling cap or .22 uf bias filter is leaky or the tube is very gassy.

The 100 ohm isolation resistor is not critical as long as it is somewhere in range.

All this assumes there are no wiring errors. I am using the Philco service notes for things that do not show on the attached Sams print so some component designations may not match.

Thanks, we may be getting somewhere. I traced the negative voltage from the 6DQ6 grid, along the path you described, and it all looks reasonable until I get to the junction of the 100-ohm resistor and pin 3, so possibly something is funky there -- a bad solder joint, cracked trace, or bad socket . . . . I'll investigate tomorrow when I'm feeling fresher.

I recently got the Philco service manual, which is better than Sams in some ways. For instance, it has a wonderful diagram of the main circuit board, with a list of what all of the perimeter connecting wires are connected to -- something I had laboriously drawn by hand in the past.

I scanned the Philco schematic (in two parts) in case anyone might find that helpful:

http://antiqueradio.org/art/Philco10L4xSchematic1.jpg
http://antiqueradio.org/art/Philco10L4xSchematic2.jpg

An advantage of using the Philco docs is that the part numbers (and other IDs) match those printed on the circuit board.

Regards,

Phil Nelson

I checked the voltage divider components, 6DR7 socket, and relevant connections. All seem fine. While looking at some other voltages, the height started to bounce irregularly, and eventually I realized that the 6DR7 tube (a new one!) was failing in front of my eyes.

With a fresh 6DR7 in place, I'm getting some bias voltage on pin 3, although still weak, only about -7 volts. Currently, I have -43V on the 6DG6 grid (pin 5), -17V at the junction of divider resistors R58/R59, and -7 volts on pin 3 of the 6DR7. The picture is very nice apart from the height problem, only with a very slight bright foldover at top or bottom depending on how you adjust vertical hold, but that doesn't seem remarkable considering how compressed it is.

I temporarily bridged different resistors across the 1.5-meg (R57) to see what would happen with greater bias on the 6DR7 pin 3. Even when that voltage increased to around -17V, there was no significant change in height or the operation of the height and v lin controls.

I disconnected the vertical linearity pot for rechecking and it measures nearly 800 ohms max and operates smoothly. The schematic calls for a 1.5K pot (disregarding stops). I got rid of the old series resistor and installed a 750-ohm/2W resistor, making its total resistance close to 1.5K. It doesn't have a stop, but I'll just avoid turning it all the way to minimum, and meanwhile it should operate within the needed range.

My 1077B Analyst does provide a vertical grid drive signal, so tomorrow I can try wa2ise's suggestion about lifting C42 and injecting the signal there.

I contacted Moyers and they have the vertical output transformer in stock if I need one.

Phil Nelson

Phil:

With the 6DR7 removed, nothing should load the bias at pin 3 assuming you're using a high impedance meter. It could be dirt on the PC or a leaky cap.

That is probably not the cause, but it should be fixed eventually.

Don

I clipped the lead between C42 and C40 and injected the 1077B's vertical grid drive signal to C42. With the 1077B Amplitude control set about midway, the height is the same as always. Cranking up Amplitude farther distorts the picture but doesn't noticeably increase the height.

Maybe it's time to order a new vertical out transformer and see if that changes anything.

Regards,

Phil Nelson

I am still leaning toward a problem with the vert lin and 100uf cap area.

I would try a 500ohm resistor bypassed with a 100uf cap in place of the whole pot/resistor/cap.

I tried bypassing that pot with resistors of various sizes, and finally just shorting out the pot/resistor combination. Shorting it all out increased the height, but not enough to fill the screen. Bridging in an additional 100uf cap had no effect on any of those combinations.

Phil Nelson

In the interest of thoroughness, I disconnected C3C (the 100uf vert lin pot cap) and C3A (10uf, connected to height control) and checked 'em. Both are good, correct values, not wired backwards.

I left C3C disconnected and wired a fixed resistor and new 100uf electrolytic in place of the old vert lin pot/cap combination. Here's the best height I can get:

http://antiqueradio.org/art/PhilcoH3412LVertLinPotSubbed.jpg

Changing the resistor's value affects the height somewhat, with smaller values giving more height. Never more than seen in the photo, however.

The Height potentiometer (R7B) tests in the range of about a few K min to 2.7 megohms maximum (3 meg is specified). I tried bridging some resistors in parallel with it, just out of curiosity. I can get the height to decrease by lowering the resistance, but not increase. That pot would be an ordeal to remove for replacement or further testing. It's part of a two-pot control soldered directly to the board with eight lugs.

Phil Nelson

Fold over at the pix bottom indicates over drive. Back off until the fold over disappears, then measure the 6DR7 grid for proper wave form amplitude. If OK, then the output transformer and yoke are all that are left.

I measured the VOT primary on a working test chassis using three different meters. They all indicate 415 ohms within a few ohms. That is no guarantee yours is good.

You can temporarily clip yoke lugs Y5 and Y6 together to eliminate the thermistor.

Here's a waveform from pin 3 of the 6DR7.

http://antiqueradio.org/art/PhilcoH3412LPin3GridVertOut.jpg

I didn't see any vertical foldover when that was taken. The height control was fully CW, giving maximum height.

A while back I measured resistance of the vertical yoke windings from the plug. Sams says each winding should measure 18 ohms and the thermistor 4 ohms cold. I measured 18 ohms between pins 10-11, and 25.2 ohms between pins 9-10 which includes the thermistor. So my thermistor measures 7.2 ohms cold, I guess. No idea what it measures when hot, but at least it doesn't look shorted or open.

I see lugs Y-5 and Y-6 on the Philco schematic. I assume you pull the yoke to get access to them.

Phil Nelson

cant tell the PP from that scope pic. can you check the cathode current on the vert out, per sams 30ma.

I replaced the most recent scope pic with one that's easier to read. Refresh this page in your browser to make sure it shows up. The vertical volts/cm control is set to 5 volts/cm and the horizontal sweep time/cm control is set to 2 ms. The probe is at 1x.

I got out my HP 428B milliammeter to measure the current on the cathode (pin 9). Looks like about 38-39 ma. (The meter's set to 100 ma scale and the needle points to about .38-.39.)

http://antiqueradio.org/art/PhilcoH3412LPin9CathodeCurrent.jpg

I also tried measuring the old fashioned way by bridging a .1 mfd cap on the cathode connection and putting my probes across the cap leads. With my old Triplett analog meter, the reading looked like 36-38 ma, in the same ballpark.

If I interpret any of this correctly, it seems that cranking the Height control all the way up sends both the grid voltage and the cathode current too high, yet I'm still not getting full vertical deflection.

While doing all this, a couple of times I heard a distinct snap from the yoke area. Maybe it's time to remove the yoke and look at that thermistor.

Phil Nelson

if I read that right then the PP is only 30v on pin 3 sams shows 140v. Unless I am just reading it wrong, is the 5v for each square or each division inside each square in which case it 150v

so now you need to scope pin 6, should be 140v pp same shape.

According to my scope manual, that vertical setting is 5 volts per square, so 6 squares in the previous photo would equal 30 volts, but I don't use a scope to measure voltage, so don't count on me having it set up correctly for that.

I turned down the Height control to reduce the pin 3 grid voltage to around -20V as given in the manuals and connected my DMM as well as the scope. This photo shows the voltage reading and waveform at pin 3 (compare to waveform W8 in the Sams manual):

http://antiqueradio.org/art/PhilcoH3412LPin3GridVoltsW8.jpg

Without changing the Height control or scope settings, I switched the probes to the pin 6 plate (compare to waveform W7 in Sams):

http://antiqueradio.org/art/PhilcoH3412LPin6PlateVoltsW7.jpg

Pin 3 voltage is about -21V (Sams says -20V) and Pin 6 voltage is about 131V (Sams says 115V). The Philco manual calls for 130V on pin 6, so the measured 131V is good enough for me.

Executive summary: on that plate and grid, the waveforms match the models and the voltages look OK, but the height is still badly deficient -- about 2 inches high. Great picture, otherwise.

Phil Nelson

the neg voltage readings don't tell the whole story since its derived from the neg bias of the HOT via the voltage divider. in this case I would try to figure out why the PP is not correct.

you should be able to calibrate the scope if it has a test point on the scope, generally a .5v square wave. then you adj the center of the voltage knob to make if fill one square when its set to 500mv. OR your can just use a 9v battery, set the scope to DC and see if you get apporx 2 squares of rise when set to 5v

can you confirm the resistance readings on the 6DR7 esp the pin 7

Here are the 6DR7 resistance readings.

1: 406 ohms (measured from 275V B+ source)
2: 1.97 megohms
3: 1.97 megohms
4: .1 ohm
5: zero
6: 1.68 megohms (measured from 275V B+ source)
7: 67.3 K ohms
8: 51 K ohms
9: 217 ohms

The resistance on 6, 8 and 9 varies with control settings.

The R63 thermistor is behind the yoke. I shorted it out with a jumper and tried the set. No change in height.

Phil Nelson

http://antiqueradio.org/art/PhilcoH3412LThermistorR63.jpg

http://antiqueradio.org/art/PhilcoH3412LThermistorR63Disabled.jpg

I checked the scope's vertical calibration using its native signal (jack at upper right), a 0.5V square wave. With the Chan B vertical control set to 0.1V/cm, the trace is about 5 squares high, so 5 x 0.1V = 0.5V. Things add up.

http://antiqueradio.org/art/BK1474Calibration.jpg

Then I changed the Chan B control to 5V/cm and checked pin 3 of the 6DR7 with a couple of meters (an old Voltohmyst VTVM and a new Fluke DMM). I left the photos full size so you can read the dials & meter settings. The meters show -20V to -21V, and the scope seems to agree (4 squares x 5V = 20V). Things still add up.

http://antiqueradio.org/art/6DR7Pin3VoltohmystVoltage.jpg
http://antiqueradio.org/art/6DR7Pin3FlukeVoltage.jpg

I left the vertical control unchanged -- still at 5V/cm -- and then checked pin 6. The meters agree, both showing around 130V. The waveform has the right shape, but if you count the squares, they don't add up to 130.

http://antiqueradio.org/art/6DR7Pin6VoltohmystVoltage.jpg
http://antiqueradio.org/art/6DR7Pin6FlukeVoltage.jpg

So, my VTVM gives the same readings as my DMM, for what that's worth. And my scope can give sensible voltage readings for some test points, but not pin 6 for some reason. I'm using a plain vanilla scope probe, 1x. Possibly I'm overlooking something obvious, or I don't have the right equipment to learn much more from measuring these points.

Phil Nelson

Wunner if there could be a carbon track in the tube socket itself lugging down pin 6. :saywhat:

don't try to use the scope to check DC voltages to sams when wave forms are present, the wave forms are avged out in a meter and the sams takes that into account.

Use the 10x probe setting, it's likely throwing off your readings.

to further illustrate the point of scope reading for voltage compared to meters, read the test point with you meter, should be 2.5v not 5v PP as on the scope. the square wave duty cycle will avg out on the meter between 0 and 5v pp. since its duty cycle is the same on and off, the meter will just avg and give you 2.5. Sine waves are different scope PP will be 1.41 IIRC more than the meter. This is why you get 165 vdc out of a 120vac supply, the PP of the 120vac is actually higher, and when rectified and filtered it shows up.

when reading odd shape waves it gets really wacky. So sams gives both the meter voltage AND the PP to make it easy to see whats going on. I dont know the input impedence of modern DMMs prob as high as a VTVM, but I still prefer the VTVM again due to how odd shaped waved may effect the DMM.

I do use the scope for reading DC voltages, like B+, you can use the DC setting to check voltage, and then look at the line for ripple. IF the DC is correct you can switch to AC and take a closer look at the ripple.

If the meters are to be trusted on pins 3 and 6, then I'll quit fretting about them, since the meter readings match the specs and the waveforms are shaped correctly.

The final question concerns pin 7, the other grid, where the waveform looks correct (per Philco manual) but the voltage looks low, less than -1V where the manuals call for -3.2V to -3.5V.

http://antiqueradio.org/art/6DR7Pin7VoltohmystVoltage.jpg
http://antiqueradio.org/art/6DR7Pin7FlukeVoltage.jpg

As I understand it, the pin 7 grid returns feedback from the pin 1 plate. I have replaced the K5 couplate, which does the returning.

I also replaced capacitor C43 (.0015/1KV) by wiring two .00033/630V caps in series to make one .00165/1260V. Since then, I got a ceramic .0015/1KV cap which I could substitute for C43 if the difference between .0015 and .00165 seems that critical. (Only a 10% difference, right?)

On that part of the tube, the plate voltage on pin 6 is correct and the cathode voltage on pin 8 is in the ballpark (actual 6.5V; Sams 7.5V).

Beyond that, I'm back my original question whether the output transformer is bad. I ordered a replacement from Moyer, so I'll soon be able to test that by substitution.

Regards,

Phil Nelson

I also replaced capacitor C43 (.0015/1KV) by wiring two .00033/630V caps in series to make one .00165/1260V. Since then, I got a ceramic .0015/1KV cap which I could substitute for C43 if the difference between .0015 and .00165 seems that critical. (Only a 10% difference, right?)


Phil Nelson[/QUOTE]

2 .00033 in series would be .000165 not .00165 off by a factor of 10x that would certainly cause problems. if that is the case it point to the reason why I alway check what comes out to what goes in on my old cap tester. even leaky caps will generally give a good enough value check to compare to new caps going in.

oh and would not trust the series 630's as a replacement for a 1000 anyway, that cap has a tough job dealing with all kinds of spikes etc... not sure if the voltage would evenly distribute across a series connection.

Dang, I will go back and look at those caps to see if I really installed the wrong values or just mistyped the value now from bad memory.

Thanks,

Phil "I was told there would be no math" Nelson

if you do need to replace it, I would pop for the film cap, the disc cap will prob be work fine, but may drift causing changes in vert height as it heats up (clearly if this is the problem).

I replaced that cap with the .0015/1KV ceramic that I had on hand, just to see what happened:

http://antiqueradio.org/art/PhilcoH3412LC43ReplacementCeramic.jpg

No magical improvement in the height, unfortunately. And you're right, it changes value when heating up. After a few minutes of play, the vertical becomes unstable and then collapses.

Mouser has 1KV micas of the right value. I presume those would be a better choice.

Phil Nelson

I would stick with a reg film cap. After you get the correct cap in, try reading the PP on pin 6. You need to find out why the PP is only 30v and not 140v.

I am sure you have checked, but I presume you are seeing the 275v on the red lead of the vert out.

check for the 400v boost on the one side of the height (if not checked already). did not see a check mark by C3A 10uf 450v

OK, justradios has orange drops of that value. I'll order those.

Incidentally, the series-d caps I removed were .0033, not .00033, so I'm not as crazy as I thought. They were film caps and also stable, unlike the ceramic. I'll put a pair of them back in so that I can play the set for more than 2 minutes at a time while waiting for more parts to arrive.

Edit: the 275V source is at 273V, like before. The 400V source was 400V when I checked before, now it is somewhat high at 430V (don't ask me why).

Regards,

Phil Nelson

Here is a Mouser .0015/1600V film capacitor:

http://www.mouser.com/ProductDetail/Cornell-Dubilier/DPPM16D15K-F/?qs=ddUFzNrI4yV6ks7NkOt8TsokMMuCAn9471iJrRleNpY%3d

I used that one or a similar value just now in my CT-100.

Ah, under the mysterious "snubber" category. When I searched in the usual categories, everything of that value was unstocked, with 20+ week lead times. Or maybe I was too restrictive in the voltage rating. Searching their website is kind of a black art.

Phil Nelson

shoot, I was really hoping you had .000165 in there. I doubt the new cap will solve the problem. I know you have tried a new tube as well...

I am about out of suggestions, other than just going over your work with a fine tooth comb. Yes the snubbers are the place to find HV caps.

You have tried adjusting the lin and height as they interact.

Searching their website is kind of a black art.
You summed it up well there, Phil. I only knew how to find those easily this time from all the tinkering a couple of weeks ago when I first needed to find one or more over-1000-volt capacitors. I think I clicked "capacitors", then "film" (which has sub-categories as you mentioned but I ignored them), then the value, then different voltages until I found some in stock. At that point I removed the value filter and found they stock a bunch of those CDE caps in different values. They fit right in with other orange, red, and brown dipped capacitors.

hmmmm, I search on predicta K5 and found a construction article, a 150k resistor is used where the sams (and you) have a 68k now. Do you have the old K5 around to check the pin 3 and 4 for resistance.

just checked mine, 150k pin 7 to ground of the 6DR7

Phil what did you use on the Holiday resto? I cant see anything but the two caps and the 33k resistor, no signs of a 68k or 150k? I am assuming the same K5 is used on both models (maybe a bad assumption, dont have the sams for the holiday to compare).

The 9L37 chassis used in the Holiday and barberpole Predicta has a different vertical tube (10DE7 vs. 6DR7) and the value of that resistor in the vertical feedback couplate is different.

In that chassis, the couplate is named K4 (Sams) and the resistor is 150K.

In the 10L43 chassis in this 17-inch Siesta, the couplate is K5 (Sams) and the resistor is 68K.

The Sams and Philco manuals for chassis 10L43 agree on 68K for this resistor. Here's a snip of the Philco schematic, where the feedback couplate is named N2:

http://antiqueradio.org/art/PhilcoH3412LN2N3CouplateSchematic.jpg

I've read competing theories on how to build the R3/C2 resistor/capacitor part of the vertical integrator couplate (N3 in this Philco schematic). One school says to put a .002-mfd cap on either side of a 90K resistor. That's what I did. Another school says to use two resistors equaling 90K and three capacitors equaling .004 mfd, one on each end and one in the middle, so the circuit looks more like your traditional vertical integrator.

Both schools claim that their version works, so I wonder if the difference is really important.

In all of the couplates that I've made, I put components on both sides of the perf board, so you won't see them all in a single photo.

Regards,

Phil Nelson

well I guess its not that critical a value since my princess read 150k (which is why I thought they used the same couplate) guess it has just drifted.

did you replace the C16 from that last schematic?

did you replace the C16 from that last schematic?Yes, and on checking, I see that I installed a 683 (.068) instead of 682 (.0068).

Sigh. Nobody to blame but myself. I will try to find time to change it later today. I suspect this will cure the height problem.

Now I see the value of testing new components when they go in. I wouldn't expect a high failure rate, but it would help prevent errors like this.

Thanks,

Phil Nelson

yea I know, I sure I have said it before but for folks that may have missed, this is where the value of an old school cap tester really shows up, take out the old, test its value (the null may not fully open but generally show some action), leave the settings alone, get the replacement ready and test, the eye should open without changing the settings much. Even badly shorted caps will generally still null enough to check. I sure hope this is it for you, I know its been a PITA trying to chase it down. good luck :thmbsp:

Bingo.

http://antiqueradio.org/art/PhilcoH3412LHeightFixed.jpg

The height is actually a little excessive now -- that's as small as I can make it -- and the linearity's not great, but we're back in the running.

Thanks again for the patient advice. This was a long detour, but on the way I learned how to use my BK TV Analyst to substitute drive signals, a trick that may come in handy in future projects.

Phil Nelson

:thmbsp:

looking good!

:thmbsp:

Good on 'ya Mate!

:banana: I'm glad your perseverance payed off.

Super-techs! Congratulations on overcoming vertical challenges!

BOO-YAH!! Houston we have vertical!
:sing::rockon::yippy:

In the couplates I made, On the one shown, I divided the resistance by 2. Then, I divided the capacitance by three. That value came out to about 0.0012. I found that using 0.001 caps worked fine. I found the values aren't that critical. Then again, Predictas are weird. Anything goes. Nice work, Phil.

It's sweeping the whole screen, but I don't consider the vertical fixed. It's not very stable, and when the sync is far off, it occasionally blinks to a horizontal line as if something (a shorted turn in the output transformer?) was arcing.

By clipping another cap in parallel with C16 (raising its value a bit), I can reduce the height to nearly fit the whole image on the screen, but still with poor linearity.

The best compromise between height & linearity doesn't seem too awful at first:

http://antiqueradio.org/art/PhilcoH3412LLinearity1.jpg

Until you look at a pattern:

http://antiqueradio.org/art/PhilcoH3412LLinearity2.jpg

I could live with that degree of non-linearity, but the instability really ain't acceptable. I'll keep pokin' around.

Phil Nelson

I am happy to hear that the "non-logical" vertical problem had a non-logical cause (the wrong value part); it can happen to any of us. Now you need to re-check the rest of that area because your vertical should definitely have better linearity than in your B&K picture.

Yes, in further puttering, I returned R55 and C44 (Sams numbers) back to the values given in the Philco docs. I had tried different values for them at various times, including an alternate Sams value. I also swapped amongst my three 6DR7 tubes until I found which one my set likes best. Linearity and vertical lock are both improved.

http://antiqueradio.org/art/PhilcoH3412LCrosshatch.jpg

http://antiqueradio.org/art/PhilcoH3412LLinearityGood.jpg

Then I ran through the horizontal & audio alignment procedures and played the set for a few hours. Nice and stable.

Those pics are from a DVD player, which has a strong signal and tends to swamp some sets. When I switched to the built-in rod antenna, it worked very nicely, receiving the relatively weak signal from my Blonder Tongue modulator on the opposite side of the house.

Not perfect, but I can see light at the end of the tunnel.

Phil Nelson

Excellent progress!

After a few more tweaks, I'm declaring this one finished.

http://antiqueradio.org/art/PhilcoH3412LRestored.jpg

Part of the difficulty I had with vertical linearity is that someone had adjusted the vertical centering as far off as it could go (perhaps to compensate for some aging component in the past). With that back in a sensible range, it was a piece of cake to make the vertical correct using the other controls. I always feel better when controls are somewhere in the middlin' range rather than maxed out.

There's an article, too:

http://antiqueradio.org/PhilcoH3412LPredictaTelevision.htm

In researching, I found Philco's original patent drawing for the tabletop cabinet:

http://antiqueradio.org/art/PhilcoPatentDrawing183779.jpg

Interesting that the original concept had more knobs on the front, and a slanted control panel.

On to the next project! Thanks again for the advice.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

P.S. I'm missing an end cap for one of the support arms. If anyone has a spare, contact me at http://antiqueradio.org/contact.htm .

Nice job, Phil.

And so concludes another neat resto adventure and accompanying write-up. Great job, Phil (as per usual). :)

Thanks, Phil for the invaluable contributions you make to the vintage TV/radio community. Now, if I ever trap a Predicta in the wild I'll know what I'm getting into :)

-Clark