Hallicrafters T-67 HV corona ring
 

Thirty years ago I bought a Hallicrafters T-67 at a junk store in Washington DC. The seller warned me "careful, its a sparker!" Its been sitting in my attic ever since. After coming across the videos from bandersentv, I got motivated, pulled it down and looked it over. Yes there is significant carbon build up at the terminal atop the 1B3GT HV rectifier tube, but the flyback is pretty clean. However I noticed that there is no corona ring on the socket underneath the 1B3GT. Shouldn't there be one? Also looking at the SAMS picture, it looks like there is a cover over the 1B3GT top terminal - is this true? - mine's missing.

I looked through the old photos of my T-67 restoration, and I don't have one that shows the underside of the 1B3GT socket. I might be wrong, but I believe I have seen those sockets with and without corona rings. It's hard to imagine someone removing that part, so my guess is that yours never had a ring.

The following photo shows my 1B3GT from above, with a roll of something like fish paper covering the top cap.

The T-67 is a decent performer when restored, so I'd encourage you to get yours running. Here are some restoration notes about mine:

https://antiqueradio.org/hallit-67.htm

Regards,

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

https://antiqueradio.org/art/Hallicr...werChassis.jpg

OOPs! Double post. Dumb, dumb.:o

Seems like corona rings were gradually phased out, as they're not really needed as long as solder joints are made smooth and ball-shaped with no pointy ends sticking out.

Phil and Old_coot88, thanks for the info! The socket looks to be a substantial one, made out of ceramic, and there is no scorching around the terminal lugs at the bottom. It looks like the lack of that fish paper at the top of the 1B3GT might have caused the arcing in mine. I've just repaired the curling veneer on the top where someone must have doused it with water when it was sparking. I'm definitely itching to get to the electronics, and will as soon as I finish with a Hammarlund 129x I'm struggling to align (the IF curves look as they should but the sensitivity is poor).

m-m-m-m-my corona!

Well I've been slowly working on the restoration of this TV and learning the electronic theory along the way. However I've discovered that the 4.5 MHz sound trap coil is open. It looks like someone has broken the wire in the center of the coil by mashing several turns at the top. I'll try to repair it, but I don't think I can. Since the likelihood of finding an exact replacement (Hallicrafters part #51A1037) is pretty slim, can I replace this with any 4.5 MHz sound trap coil? I see a few available on ebay.

You need a coil that will resonate with the connected capacitance, consisting of C53 (1.5 pf) plus whatever the input capacitance of the 6AU6 sound IF tube is. So, guessing total C is between 1.5 pf and 5 pf, that would be somewhere in the range of 25 to 83 microhenries (and probably toward the lower side, depending on the 6AU6 capacitance) if I did the math correctly.

Many thanks for the info. Does the 100 pf capacitor C54 need to be included into the calculation? or because it is in parallel with the 150K resistor, not a factor here? Can I alter the capacitor C53 to match whatever coil I can find? I have a Miller coil 1470 which ranges from 38-100 uH.

The 100 pF does not need to be in the calculation because it's in series with the grid capacitance. 100 pf is so much larger than the grid capacitance that the series combination is only a tiny bit smaller than the grid capacitance itself.

C53 is already very small, plus you will always have the grid capacitance loading the coil, so adjusting C53 smaller for a higher value coil will not work. However, if you get a lower value coil, you could try increasing C53 to tune to 4.5 Mhz if necessary.

If you can find an aluminum core that fits the Miller coil, you might try that to reduce the inductance, but beware that it will also reduce the Q, possibly too much.

Any chance of removing some windings from the Miller coil without breaking it? If so, you could measure the resonant frequency in circuit before removing windings to get an estimate of how much to remove, and then proceed cautiously.

Bulletin!!!!

I skipped a decimal point - required inductance is in range 250 to 830 microhenries.

Go ahead and try your Miller coil as-is!

Ah great, excellent. I was wondering about the calculation - I was getting 250-833 uH myself. I won't be able to power this thing up until I finish recapping and checking the remaining resistors. Then I'm going to go over this thing point by point, checking it again with the schematic - I've already found a few instances where the wiring was changed from what it was originally. When that is done, I'll try the Miller coil as is (although I expect I'll have to increase C53 10x because the Miller coil I have is only 38-100 uH). Again, many thanks for your help.

Well I'm having bad luck with coils on this set. As I've been recapping this set, working from one side of the chassis to the other, I've been checking resistors with an ohmmeter. I came to a peaking coil (L23 in the Sams) which is a coil wrapped around a 39Kohm resistor and it reads 39 kohms! With the coil in parallel it should read 10 ohms. This is a peaking coil from the video detector V8 and is coupled through a 0.05 microfarad capacitor to the grid of the video amp and looks like it also forms part of the AGC. Looking at it through a magnifying glass, I can see many shiny broken ends of copper wire poking through where the wax has been scraped away - this is royally busted. It looks like whoever worked on this set before me recklessly smashed this coil into the sharp edge of the tube tie point of pin 1 on V8. I have no idea as to the inductance of this coil or how to go about replacing this. Does anyone have any info?

This assumes you never find a cross reference.

The first thing to do is see if you can find the connected end by removing the broken parts. If so, try measuring the remaining inductance (not connected across resistor).

If not, rewind the rest of the coil and count the turns. Then rewind with roughly the same size wire with an estimate of the number that got ruined.

Lacking anything else, try inductors in the range 70 to 390 uH across 39K,
and use whatever you think looks good. These things are noncritical
and are often tuned by eye by the designers. Ideally you look at the horizontal
sync pulse waveforms on a scope.

100 to 150 uH probably will work fine.

Hi dtvmcdonald and thanks. I'm afraid there are too many breaks for salvaging this coil. Under the glass, I see shiny broken bits of wire not just on the end of the doughnut, but also along the face indicating that the coil of wire is cut all along its length. I did just order a Miller 6179-TV peaking coil which is 180 uH/39K ohm off ebay. This is within the inductance range you mention and has a shunt resistor of 39K. I'm hoping this will work out.

http://www.videokarma.org/picture.ph...pictureid=3858
http://www.videokarma.org/picture.ph...pictureid=3860
http://www.videokarma.org/picture.ph...pictureid=3859

Well, I had to change all the electrolytics and the paper caps (I tested them as I removed them, they were all leaky). I checked all the resistors and replaced those that were out of spec (one was burnt and broken in half!). I checked and rechecked node by node against the schematic (I had to do some rewiring around the horizontal output tube to put it back to spec). So for the 4th I decided to fire up the T-67 for the first time. No fireworks! But as you can see from the pictures, I have a few problems.

1) When I'm injecting the cross-hair pattern from the VA62 into any channel, I see two vertical lines, not one (I believe the vertical line in the center is the correct one from the test pattern, and the one on the left is an artifact). I see this left hand vertical line on all channels even when no signal is being applied and there is just snow. With the cross hatch pattern the situation is the same. I've adjusted the horizontal and vertical hold as best as I can, and it seems to lock. However the horizontal width and horizontal linearity controls do nothing. I haven't done any alignment or adjustment of the sound trap yet. Does anyone have suggestions as to what might be causing this vertical line?

2) In the cross hair test pattern, I see faint vertical bands on the right half of the screen. Is this 4.5 MHz sound bleeding through?

3) There seems to be black lines between each horizontal scan line-the vertical resolution is bad. Is this normal for this set?

4) The vertical lines seem to be fainter than the horizontal ones. What might be causing this?

I would be grateful for any suggestions you have.:scratch2:

How about putting a regular picture in instead of a test pattern. Some of the stuff you see could be occurring during retrace, or due to wrong sweep frequencies; hard to identify with a cross-hatch test pattern but easy to see with a normal image, as you could identify part of it folding over.

Vertical lines fainter than horizontal could just be poor frequency response, could be as simple as fine tuning. Should not worry about this until you are sure you have a stable picture with correct sweep frequencies.

http://www.videokarma.org/picture.ph...pictureid=3862
http://www.videokarma.org/picture.ph...pictureid=3861
Fantastic! a real picture is better. Still a bright vertical line though.:scratch2:

Note the parts of the picture to the left and right of the bright line don't match. this would indicate the horizontal scan is stopping there for a short time. So, you need to look at the horizontal drive and the damper circuit.

Not sure, but I would try adjustment (B1, B4) or replace damper tube.

i noticed the same thing, it's a bit weird.

Hi guys,

I swapped the damper with another NOS tube I had - unfortunately it made no difference. Turning B1 (horizontal drive) crowds the image to the right (as it should) but does nothing with the bright vertical line. Turning B4 (horizontal linearity) does nothing when it is turned (neither does B3, the width).

I poked around with a scope looking first at the control grid of the horizontal output tube V19. Not the best saw-tooth pattern with bumps at the beginning. The pp voltage there is actually 111 volts (I had the wrong probe setting on that one).
http://www.videokarma.org/picture.ph...pictureid=3863

Next I looked at pin 2 of the horizontal oscillator V18B which feeds the control grid of V19.
http://www.videokarma.org/picture.ph...pictureid=3864

However pin 5 of the horizontal oscillator V18A was difficult to get the scope to trigger on. Ultimately with tweaking of the contrast control I got a stable trace. This section feeds the horizontal linearity and width controls.
http://www.videokarma.org/picture.ph...pictureid=3866

Finally looking at the control grid of V18A (pin 4) which collects signal from one side of the horizontal sync discriminator V17 (6AL5). This seems weak with a peak height of only 306 mV. Sams or Riders don't give sample scope images for this set. Do these images seem reasonable?????
http://www.videokarma.org/picture.ph...pictureid=3865

As I was rechecking around the horizontal sweep section I noticed something funny. The components wired to pins 2 and 7 on the Horizontal sync discriminator V17 (6AL5) are swapped from what is pictured in the SAMS. However the wiring as found is consistent with what is pictured in Riders. Does this matter? or should K1 be paired with P1 and K2 with P2 for correct function of the tube?

V18A pin 4 should be mostly DC, with most of the pulses filtered out, so that's OK. When the horizontal is out of sync, you would expect to see a beat note in this filtered discriminator voltage.

The 6AL5 must be wired correctly, or the horizontal wouldn't sync, so SAMS is wrong.

It's troublesome that the width and lin coils have no effect. Maybe you should check if either of them are open or if the connection to pin 5 or 6 of the flyback is open.

Success! :banana: At least with regard to the bright white vertical line. Turns out it was the horizontal drive set too high. According to Grob (page 393 in Basic Televison: Principles & Servicing 1954), you adjust the drive control until the white line or wrinkle appears, then back off enough to eliminate the distortion - it works!....But still no response out of the width or horizontal linearity control. I've checked the resistance from pin 6 to pin 4 of the flyback and I get 9.8 ohms; the horizontal linearity control is 24 ohms. I'll have to disconnect the wire from pin 5 to check the width control. However, I can live with it as is...

One thing I'm wondering about is the slight vertical wavy distortion just to the right of center.

http://www.videokarma.org/picture.ph...pictureid=3867

You checked the flyback winding resistance and the linearity coil resistance, OK. But did you check from the width coil to the flyback to make sure there is a connection?

I disconnected the lead from pin 5 of the flyback and I'm reading 0.4 ohm from pin 6 to the lead I disconnected from pin 5. When I reconnect the lead to pin 5 and measure from pin 5 to pin 6, I read 0.2 ohms (Both the width coil and a portion of the flyback from pin 5 to 6 are in parallel - for this measurement all the other plugs are disconnected from the power unit to the rest of the TV). It sure seems like I've got continuity through the coils. I've also checked from pins 4,5 and 6 of the flyback to ground and see no shorts. One thing I've noticed is that someone has tried to solder the clip that holds the width coil to the chassis and that solder blob is broken and the coil wiggles in the hole. Does the ferrite (?) core of the coil need to have a good ground for the coil to work properly? I've also checked the back end of the core to see that it rotates and it moves as I rotate the adjustment screw. The same holds for the linearity coil.

I can't think of a reason that the core would have to be grounded.

Still very strange that adjusting the coils has no effect.
Have you checked the SAMS resistance readings from the pins of V20 and V21?

I've measured the resistances of V20, starting at pin 1 and relative to chassis: inf, 0, (from pin 8 of V20), inf, 8 kohm, inf, 8 kohm, inf and 0. Interesting that pins 4 and 6 have much greater resistance than specified in SAMS (65 ohm). All pins of V21 read infinity relative to ground. Also one thing I've noticed is that if I back off even more on the horizontal drive a little more, the faint vertical bands just to the right of center disappear. Unfortunately if I back off to the limit of the drive capacitor I still don't get any response from the width or horizontal linearity control. I'm wondering what should the peak to peak voltage of the drive signal to pin 5 of the horizontal output tube be?

I've run out of ideas for now.

I'd look at those lin and width coils and see if you have any of the mods shown in the Sams. And check those resistors.

I'm also going to toss this out:

Are the yoke and flyback the original ones? I've seen cases where folks sub them and all hell breaks loose...

I've checked the wiring against SAMS and only have the thing configured for T-67. I can't see a part number on the yoke, but it looks like the one pictured in SAMS. The number on the flyback is 55H11S which is different than the one specified in SAMS (55C113)! Hmmm, would continuous use of this flyback damage anything?

I looked up both flyback numbers in my Thordarson cross reference and while 55C113 crosses to a Fly 1, there is no listing for a 55H11S? Does your flyback even resemble the one pictured in Phil's restoration pictures? I'm a little suspicious that that number could be a much later part, possibly not a direct replacement. On the other hand if it looks like a typical Fly 1 it probably an OK sub. My newest cross reference no longer included Hallicrafters so I have no way to verify when a 55H11S may have come into existence. :scratch2:

Whoops! I made a mistake-what I get for just looking through the grill. Its actually 55H113!

http://www.videokarma.org/picture.ph...pictureid=3868

Here is the best photo I can get of the yoke.....

http://www.videokarma.org/picture.ph...pictureid=3869

And one showing the horizontal linearity control (left), drive (center) and width control (right). They look original to me.

http://www.videokarma.org/picture.ph...pictureid=3870

Currently I have to back the drive control off to its counterclockwise limit to remove the vertical wrinkles at the right side of the picture. Is there any risk of damage of the flyback or horizontal output tube if I do this?

They have been mentioned before on this site (that's how I found them), but I just want to add what a fantastic source Moyer electronics is for hard to get parts. Bill was able to find for me a sound trap, an assortment of peaking coils (from which to experimentally determine the best one) and a correct field coil speaker (the one that came with the set was a smaller substitute and was eaten by mice anyway). This is much better (and cheaper!) than bird-dogging Ebay for needed parts.

Just an update-success with the width problem. I replaced the mica (or micamold) capacitor C77 and the 1 M resistor R84 in the circuit providing drive signal to grid 5 of the Horizontal output tube V19. I was able to get the picture within the screen by backing width control almost completely out and adjusting the drive control until it crowded the right side of the screen and couldn't be compensated for by adjusting the width control and the horizontal centering control.

Then an interesting problem arose after I turned it on a few times. The final time I turned it on, a crackling sound, then no picture, no sound, and just a grey raster that couldn't be brightened or darkened with the brightness control. The resistor R94 was getting unusually hot for the TV being just switched on. I pulled all the insides out, back on the bench and found that the new capacitor C4B 30uF 250 Volts was a dead short. I replaced it with one rated for 500 volts, and while it was on the bench, measured the surge voltage when switched on, it surged to 333 volts across that capacitor then relaxed to 180 volts. Its interesting that both the Riders and Sams parts lists call for a capacitor rated for 250 volts. But I've used it a few times since and no problems yet.