7” electrostatic set deflection shortcomings
 

Has anyone else experienced short vertical height, only to fold over and crowd past a certain level, and not enough horizontal width, again with crowding past a certain level? Currently working on a Halicrafters and a Tele-Tone. And they both exhibit the same symptoms. The only 7 inch set that seemed to have enough to fill the screen was a Motorola VT71 that I worked on.

Anyway, I have gone through both sets, caps replaced, verified and replaced some tubes, verified filament voltage is correct in the stings etc. Checked all and replaced most resistors in the vertical and horizontal circuits with some improvement, but still not able to stretch the picture fully across the screen. If I lower the HV, this will enable me to accomplish that but now I’m only down to about 3kv and picture quality suffers.

On a variac, the picture doesn’t actually start to shrink until I lower the voltage below 90, and I don’t get any extra picture expansion if I temporarily crank it to 130 V. I do gain some brightness though.

Bandersen has many videos on u-tube about e-sets, I have little exp in the subject, having yet to finish the T-TONE 149 I got this year, working mostly on tape decks.

The vertical section will always be more fussy when it comes to parts out of tolerance, so it's always good to check it end to end with a very discerning eye, and if any doubt, put in new known good parts, and especially if 2 resistors of same value are linked, like are on the control plates, sample a few, like 10 and pick the closest match, it will help with linearity.
And do watch his videos, they are very helpful.
bandersentv - YouTube

What did you replace the hi voltage caps with? Disc caps will cause this problem.

Hi, I used Wima 6kV film caps on both sets

I never tried those. I tried Russen disk caps and they didn't work correctly. These worked but are not cheap: https://www.justradios.com/ASCcapacitors.html

Wima caps should be fine. I've used them in several sets.
Did you replace all the resistors in the HV bleeder network down to the vertical deflection plates?

that's what I got for mine, the co$t'y ones from Just Radios, I just need to finish the bloody thing, instead I have just focused on 4 tube based tape decks this year. :tears: I now have 9 Reel too reel decks, most of which are tube driven, Is that too many? :O

Check ohms on the verticle pots and related resistors. Wouldn’t hurt to confirm b+ voltage.

I didn’t replace them but they do measure within their tolerance. There has been a ton of out of tolerance resistors on this set but everything I have found has been replaced. Every resistor on the vertical and horizontal amps have been replaced, and most others on the oscillators.

I did replace just about all those resistors on that deflection circuits. On the tele-tone tv, B+, B++ and B- all measured within 5% of their Rider manual specs. I was kind of surprised by this, but a good surprise. I still have to verify on the Hallicrafters.

On both sets, the deflection amplifiers just seem to be running out of steam. They will amplify to a certain point until the image bunches and folds over a bit. At this point on both sets, I could get the image just to barely fill the masks, but it would be nice to figure out how to get some headroom

All new or known good 12SN7s I assume? :O

Indeed, subbed NOS in the questionable areas.

The only thing I can suggest at this point is, start with the voltage and resistance checklist on the SAMS, like I have for my T-Tone TV 149, and look for things that are way abnormal, especially in the sweep amp area, it might give you some clue as to what is going wrong.

Maybe look into any mica caps had a similar problem until I changed them.

Definitely check all Mica, they seem to have gotten to an age where their lifespan is beginning to fail. I replaced several in the past year or so. But be advised when you change Micas You may need to do a total alignment again as the original values are so critical in any tuned circuit.

Specifically in the verticle and horizontal sections

I’m still struggling with this problem. I agree that mica caps are no longer deemed as reliable. I have seen my share of failures on recent restorations so they have all been replaced in this set and any set going forward.

Is the high voltage up to where it should be?

Yes, I’m able to measure about 4.9 KV Max, but at this point, the picture is the smallest and will not fill the mask. I can lower the HV down to about 4.3 KV and the picture is large enough, but I am losing brightness and sharpness, so unfortunately, that is not an option.

So updates on some things done on the Tele tone set. I replaced most of the resistors in the HV divider network for the horizontal and vertical plates. The HV focus network resistors checked OK, plus I don’t have enough to replace those at this point.

I checked the measurements per the Sam’s measurements on the horizontal and vertical amplifier tubes and most were spot on, with some differences on the plate voltages as follows:

V15 12SN7 vertical deflection, pin two should be 290 V, and I’m measuring 270, pin five should be 190 V, I’m measuring 204. The cathode voltage was 11.5 versus 12 V as indicate in Sams.

It sounds like it's almost struggling to make the full 5k HV, and loading down the LV PS.

This may help.
https://www.ebay.com/itm/283515730784
I have one working fine in my Magnavox Brittany tv, It will boost HV a tad bit because it does not have the voltage drop of a normal glass high voltage rectifier, you also don't have the strain of having to light the heater, so more power goes to making HV.

Something to think about.
It's almost as if something is loading down B+ B++ B- as you turn up HV. :O

Those SS rectifiers are nice, I have one in my CTC5. I don’t believe I have a HV issue in this set, although a bit low, it could be a product of my divider I use to measure it slightly pulling it down. But as the HV increases, the beam gets harder to deflect, hence the picture shrinkage

Are the b+ diodes up to the challenge or are you using the selenium rectifiers.

As far as I can see, looking at the schematic for my T-tone 149, the energy derived to deflect the beam is taken from the same 5k that is also applied to the anode via pin 9, so as the HV goes up, there should be more energy to defect the beam, via through the .005 caps and the 12SN7 amps and eventually to the -b rail.
Seems you should be able to coax more than 4.9 k out of it.

When I do get to mine, I will go with the SS option.

Okay, so I have replaced all the resistors for every piece of the horizontal circuit and the vertical circuit as well as the deflection dividers and focus divider. Picture quality, and size increased ever so slightly, but I still can’t fill the entire mask on the Tele tone. The width and height pots are not maxed out, but it gets to a certain point when the picture folds in on itself.

As HV increases, the beam requires more energy to deflect, I suppose these dividers are adding more of that energy to the deflection plates, but the allowable picture size does get smaller with more HV on this TV.

Right. You many need to decrease the HV a bit to fill the screen.