Sparton 16A211 Width Problem
 

OK, my turn with a 15 inch color set issue. I've been trying to find a width problem with this set with no luck. It lacks about an inch on each side. Width and Hor. Linearity work properly. I've checked all the tubes (by substitution) and all caps are new.

I have the proper waveforms and p-p voltages at W17 and W18 (see the schematic). Power supply busses are within 5 volts. On the 6BG6s, screen voltage is right, but the cathode voltage is 12 vs 18 on the schematic. Grid voltage is -25, but I noticed that setting of the hor. drive changes it from about -15 to -30. I can just barely get 20 kv on the CRT with the HV control full up. Boost is 550 vs 620 on the schematic. Damper plate voltage is right.

I have checked all the resistors and capacitors in the H. out, flyback and damper areas. I've even changed the yoke. Like all 15 inch sets, the major components are RCA.

This thing is driving me crazy. Anyone have any ideas?

Schematic is here (better to download the pdf so you can zoom in):

http://www.earlytelevision.org/image...ton_16a211.pdf

Since the boost is developed during the first third of the sweep when the horizontal output tube is off and the damper is conducting current generated by the collapsing magnetic field and the boost is low, and the magnetic field generated by both yokes you tried is inadequate, I'm going to take a wild stab and wonder if the fly isn't the cause. Maybe something easy to rule out like conductive crap of some kind across the gap in the core.

I had a recent problem trying to get adequate width with a set using a 6BG6. I use an AVO Mark III transconductance tube tester and a bad tube will give only just adequate transconductance. The checker showed that the plate current was a bit low indicating cathode emission was down. Keep an eye that the plate current under test is correct and not low. I would try a few 6BG6's by substitution.

I suspect the Sparton's 6BG6 emission is low since the cathode voltage you indicated is low.

Question: Why did Sparton use a 6BG6 which such an old design tube in a color TV? I would consider substituting a 6CD6 as I believe it has a beefier cathode? (My guess after only just visually comparing tubes).

This set uses parallel 6BG6s, probably the only tube available in 1953 when the set was designed. I've tried a bunch of NOS tubes with no luck.

What about using a capacitor sub box and dial in some different values for c133.

Is that the one from G. in Orange County, CA? If so, he might have some input on that problem. I remember him having that set all apart and chasing a yoke-related problem, if I remember correctly. He may have swapped the yoke, but I'm sure if he did, he'd have kept records and the original. Again, I might be off on that, but it's worth asking (assuming this is the Sparton from him).

Charles

The 6BG6 was a carry over to the tube base octalization process in the mid thirties. It started out as a UY (5 pin) based 807. By about 1951-52, the transition was on to newer and better power tubes. Your Sparton from 1954 is the latest set I can recall using a 6BG6! (I will research this further and would appreciate feedback from everyone on this). Incidently, it is one of my favorite tubes: see my avatar!

Nevertheless, the 6BG6 cathode current appears low and the voltage drive to the grid appears adequate. To get the cathode current up a bit, you may try increasing the screen voltage slightly by reducing the screen feed resistor value. If you increase the screen voltage slightly to raise the cathode current, I would expect you will get the width you require.

The low width may be inherent in the design and it seems with the considerable effort that has expended elsewhere to fix this problem, I would see this solution as a good bet.

Terry

The proto set had a 6CD6 dated the 17th week of 1951, parallel 6BG6's must be design preference. Much the same way my split chassis Philco used parallel 6BQ6GT's, when it could have used a single tube.

Yes, this set is from G in Orange County. There was evidence of experimentation in the horizontal section.

However, I've tried a new yoke (no change). Also tried increasing the screen grid voltage with minimal change in width.

As for the low width being an inherent problem with this set, that isn't the case. All 15 inch color sets use RCA components, and the sweep sections are very similar. Width has never been a problem with these sets.

I'm leaning toward the flyback as the culprit. When I get back in Ohio in a couple of weeks I'll try swapping it.

The first Westinghouse color set also used two 6BG6's in parallel. I thought it was strange, as the 6CD6 was out at that time.

I think both the Westinghouse and Sparton were designed earlier, since both had prototypes in 1953.

Steve,
Any update on this? Did you manage to get the correct cathode current on the HO Tube(s)? What about the flyback transformer?

Just got back in town. Ill get back to it this week.

I messed around with it some more today. I rechecked all the components in the horizontal section and tried new tubes again. Everything is normal. I experimented with changing the screen grid resistor in the hor. output section and found that with the resistor shorted out I got about 16 v. on the cathode, indicating close to normal current, and width that is about 1/4 inch short on each side. Boost is still low at abut 560 volts, and actually dropped a couple of volts when I shorted the screen reisistor. Something is still wrong, but I'm sure I can get the small amount of additional width needed somehow.

http://www.earlytelevision.org/spart...storation.html

I don't have a suitable replacement flyback to try.

Any ideas?

Check the boost cap, if boost is low scanning width might be low as a result. I think it's loosing power from the horizontal section somewhere, even if the caps are new check them again. Make sure the cap doing boost duty is rated at least 1000 VDC.

I wonder if both 6BG6's are working.. You might try (very briefly) running the set with one, than the other. Possibly something goofy, bad solder or contact on one..
All the symptoms point to low power into the flyback, rather than an overload.
Weak damper, or poor boost filtering could be a problem.. May be worth scoping the boost supply. Also worth scoping the B+ that feeds the damper, although I'd expect other problems if the filtering here was poor..

Both 6BG6s are working. Removing either one results in much lower width. Filtering is fine. Very little hum on the B+, plus I've tried paralleling another 40 mfd cap on that line. Replaced the .082 boost cap, no change. I still suspect the flyback.

Before tearing into the HOT, I am still curious about the Horiz Output tube current. You say that with the screen grd feed resistor shorted, is the cathode voltage, hence current correct? With the screen resistor shorted, was the screen voltage correct? (eg high enough?)

Could be the HOT has a shorted winding. But then again there may be a problem in the boost circuit.

What makes me think it may not be the HOT is that the horizontal output tubes are running cool.

Shorting the screen grid resistor brings the screen up to the supply voltage, well above what the schematic shows as proper. Cathode voltage comes close to what it should be (17 vs 18 v relative to the the -135v buss).

Every part in the damper and boost sections has been changed. As you can see, there is very little connected to the boost (hor. osc and CRT screen grid pots). All those components have been checked too.

I see no other possibility other than the flyback.

Before you replace the flyback have you checked the sine wave coil? I have seen the sine wave coil cause lack of width in rca set's many times. Are you sure that that you have proper p-p wave form on test point w 18. Re Check c124,r 147 and c 127. You may be right about the fly but I would re check the sine coil just to make sure it is not your problem. Does the screen fill out when you turn the horz hold control? I forget which way you would turn it but try both directions and see if the screen fills out and see if you get some kind of increase in the hi voltage and boost voltage.

Hmmm. Did the set work correctly at one point, or has it always been thus? (Wondering if it's a failure, or some other influence) I'd take a hard look at C131, the 1uF in the cathode circuit. You're dealing with a pretty hefty pulse current here, and an aluminum electrolytic may have a high enough ESR to not work very well.. The sch seems to indicate it's not an electrolytic. Also R20 and R156 100 Ohm and 180 Ohm basically in parallel, (hard to keep jumping from one page to another) Scoping the -130V line may tell something too.

The waveform on the sine wave coil is correct. Turning the hold control to either extreme makes no difference in the width. c124, r147 and c127 have been checked.

I've owned the set for a couple of years but am just getting around to restoring it. There is evidence that the previous owner had the same problem, since many parts in the horizontal circuit have been changed and a few were partially removed. C131 is not an electrolytic, and I've changed it. The cathode resistors and the pot have been checked. The -130 v line is clean, with little hum. I've also tried adding additional filtering on all supply lines with no effect.

I don't have a spare flyback, and they are impossible to find, so I'll probably end up with no screen resistor and live with it.

There is a problem with the RF HV power supplies in some 7 inch black and white sets that seems to be related to accumulated moisture in the RF transformer. I've never heard of such a thing with flybacks, but could that be a possibility? I mention it because this set has probably not been operated since the mid 50s.

It will be a couple of weeks before I get back to this.

Steve,
It seems to me there used to be a width boosting product on the market which plugged into the damper tube socket and the damper tube plugged in turn into it. The result was boosted width. If I recollect correctly, this gizmo had a capacitor inside that connected between the damper tube's plate and cathode. I don't believe that I ever knew the value or voltage rating of the device's internal capacitor.
Maybe this memory of mine will jog the memory of someone who can recollect some more details.
If I had a set with such a rare flyback and stubbornly persistent width problem, I wouldn't be afraid to experiment with an added capacitor's capacitance using temporary capacitors that have a relatively high breakdown voltage.
Incidentally, I think your Sparton was once offered for sale to me as a source for a 15GP22 for a CT-100 that I once had. I couldn't see destroying one historically important TV to fix another historic set, so I passed on it. I just found my 20 year old note where I thought it might be - it says "15GP22 Dan (847) 823-2379." It's a very cold trail I'm sure but white pages.com reverse lookup say it belongs to Daniel L Gustafson of Chicago, Illinois.
I now see your set came from California, so the one once offered to me is probably a different Sparton. Someone might try calling Dan to inquire about the set. Not much to lose.

You don't know how wrong you are... :tears:


Dan G has been dead for a while, sorry to be the one. I won his 21CT55 at the ETF auction this year, no one will be getting in contact with him anytime soon lest they join him. Let's pray that's not the case.

I'm sorry to learn the bad news. I only talked to him once and he was a nice guy and willing to please.
I'm a little confused by your response. Are you saying that Steve's Sparton is the same set that Dan and I discussed years ago?

That would be my prognosis as well (assuming the fly itself is running cool and emitting no telltale whiffs of internal arcing).
Now that you've got near-normal width, I was gonna suggest the old damper shunt cap trick, but see another poster has already mentioned it. The cap should be disc ceramic, rated at 6KV minimum. Value can be anywhere from 68 to 150 mmf (pf). We used to keep several values on hand for this very purpose (higher value gives more width). The cap goes directly between cathode and plate of the damper tube.
But there's a trade-off as in the old saying "there is no free lunch". The HV drops a bit with each increase in width, as does the HO tube current. So the mod is only useful as a last resort in cases of intransigent marginal width such as this set appears to have.

The same trick can be used on B&W sets with the cap rated at 4KV minimum.

Thank you old coot88 for providing "the rest of the story." Does the Sparton use a shunt regulator for HV regulation? If it does, would the "damper cap" have any real effect on 2nd anode voltage?
Dropping the two horizontal output tubes' current can't be a bad thing.

The Sparton I have didn't come from Danny.

Yes, it uses a shunt regulator. I now have just about 21 kv max. The question is whether the capacitor trick reduces it to below 20.

Steve, I would try adjusting the value of the cathode resistor in the horizontal output tube(s), to see if this could result in a bit more width. Check the amplitude and shape of the parabolic waveform before you change the resistor value so you know what waveform is needed to drive the convergence circuit. But I would think there is some margin available for the convergence circuit.

I suspect that with a shunt regulator system there will be no reduction in delivered HV.

From your earlier, you had stated that the drive waveform (W18) was per the schematic (120V p/p) If so, it would be worth scoping the cathodes of the 6BG6's. (Just to confirm that C131 is doing it's job.) Also, it's interesting that the schematic is showing these freq's as 7875 cps, rather than 15,750. Maybe that's a ref to showing 2 cycles on the scope? Yes, the "capacitor across the damper" trick will increase width some, BUT will result in lower HV, boost, etc.

If there is a "surplus" of high voltage, presently being regulated by the shunt regulator, there may be no decrease in voltage at the 2nd anode with the addition of a capacitor across the damper.

Any progress Steve?

Steve,

I assume that you have done all these, sometimes, fresh eyes looking at a circuit might spot a possibility. From a schematic analysis, here are some simple checks that could have been easily overlooked:

Is the optional R158 which is parallel with R157 present? (This circuit should be either a single or a pair of resistors. The set should have either two 11000 ohm two watt resistors in parallel or one 5600 ohm five watt resistor. (It us easy to misread the schematic here if one missed the check-parts-list symbol! These resistors provide screen voltage for the 6BG6's.)

Check R178 for value. It is off the high side of the R-G-B balance controls. (It is not shown on your schematic, so I've added a complete schematic to this post.)

If your CRT is weak, has someone set the R-G-B balance controls excessively high to compensate? Are the three .022 caps off the wipers of R-G-B balance controls leaking?

Since a prior owner had extensively worked on the set:
Is the yoke a Sparton XD-2071-J or RCA 223D1?
Is the flyback Sparton XD-2166-J or RCA 240 T1?
Since that flyback has so many unused terminals and may be a replacement, did you check to see of the correct terminals were used?

Have you verified that the voltage on the on the HV regulator grid is within the specified range?

Verify the replacement component values and wiring connections of all the work done by the former owner of the set, preferably by someone who has not previously worked on this set.

James.

James, here is what I've found in reply to your excellent suggestions.

Is the optional R158 which is parallel with R157 present? (This circuit should be either a single or a pair of resistors. The set should have either two 11000 ohm two watt resistors in parallel or one 5600 ohm five watt resistor. (It us easy to misread the schematic here if one missed the check-parts-list symbol! These resistors provide screen voltage for the 6BG6's.) --- Yes, both resistors are there. I've removed one (lower width) and shorted out both (B+ directly on the screen grid, greater width, cathode current close to normal).


Check R178 for value. It is off the high side of the R-G-B balance controls. (It is not shown on your schematic, so I've added a complete schematic to this post.) --- I've checked it.

If your CRT is weak, has someone set the R-G-B balance controls excessively high to compensate? Are the three .022 caps off the wipers of R-G-B balance controls leaking? --- The CRT is excellent. There is no difference in width in any position of the R-G-B balance controls, so I think that rules out leaky .022s.

Since a prior owner had extensively worked on the set:
Is the yoke a Sparton XD-2071-J or RCA 223D1?
Is the flyback Sparton XD-2166-J or RCA 240 T1?
Since that flyback has so many unused terminals and may be a replacement, did you check to see of the correct terminals were used? --- The yoke that came with the set is a Sparton, but I've tried a RCA replacement, with identical results. I think the flyback is the original Sparton - there is no evidence of it ever being removed. I don't have a spare, so I can't replace it. I've checked the connections.

Have you verified that the voltage on the on the HV regulator grid is within the specified range? --- Yes, and I've removed the cap to the regulator tube to isolate any problems in might cause. Voltage is just 20kv with the regulator out of the circuit.

This week I will take a fresh look at it, after having been away for a few weeks.

You must have done this but I re read the thread and did not see if you checked the horiz centering control?

It's not centering, it's width. Shorth on both sides will not be cured by the centering pot.

Steve,

This is a longshot, I would try subbing out C137 through C141. I have had doorknob caps go soft. If you're only getting 20kv without the regulator, one or more of these may be the culprit.

Steve,

I was looking at the pictures you have on ETF of this set and spotted what to me looks like an old-stock molded wax paper capacitor in sweep chassis, that looks from your picture like a unit that historically was prone to moisture penetration due to poor seals on the leads. (It also could be a new type that I'm not familiar with.)

I can tell from your picture that it goes near or to the horizontal output, but can't see tell how it connects, however, the fattest condenser near that tube is C130, a .22 at 400 v, that filters stray damper hash out of the horizontal output screen voltage. This capacitor normally has 320 volts across it, plus whatever spike comes from the damper and centering circuit.

I think that a minor leakage in this capacitor would not cause the problem that you are having, unless it dropped the screen voltage, which you said was normal. It is a long shot, but it might be worth a test or a substitute.

James.

I spent several hours working on it today, rechecking everything. I could find nothing wrong.

John, I experimented with cathode resistor values and found that the original 180 ohm worked best.

So, I experimented with capacitors across the damper. I don't have a good selection of high voltage low value caps, but I tried 40pf, with a small increase in width, and 1000pf, with a very large increase (too much, probably 2 inch overscan on each side). With the 1000pf I still had 20kv, so I'm sure a smaller cap will give me the width I need with plently of HV. I'll order some smaller values.

So, it is still a mystery, but at least I have an operational set. Everything works well now, including the color circuits, and I have the RACS 15G in it (still working fine).