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/PhilcoH3...nPotSubbed.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/PhilcoH3...ridVertOut.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/PhilcoH3...odeCurrent.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/PhilcoH3...ridVoltsW8.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/PhilcoH3...ateVoltsW7.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/PhilcoH3...rmistorR63.jpg

http://antiqueradio.org/art/PhilcoH3...63Disabled.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/6DR7Pin3...ystVoltage.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/6DR7Pin6...ystVoltage.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/6DR7Pin7...ystVoltage.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/PhilcoH3...entCeramic.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/...71iJrRleNpY%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