Screwy Admiral 19A11 recap job

[Kamakiri]

Admiral 19A11 I picked up recently had some vertical linearity issues, so even though the HV deflection caps in the set appeared to be relatively new, I figured I'd start there. This set had been (mostly) recapped and was working when I got it. In fact, it works pretty well, aside from a low volume issue.

But here's the weird thing.....

Two of the caps for the horizontal deflection were disc caps, but the other three .005 6kV caps were replaced with .01 uF @ 10KV caps!

Now, never knowing WHY the last tech did what they did, here's a shot of this section in the underside of the chassis. Can anyone think offhand of a good reason to substitute these cap values? As in, some part change that required these capacitance values?

[M3-SRT8]

Probably a case of "close enough." The Service Tech probably had nothing closer on hand.

When I usually come across capacitor "mods" like that, I'll check to see if it was prompted by a Service Bulletin. If not, I replace them with the same value (and type) that came from the factory, with a higher voltage rating, if possible.

I say "usually" because sometimes there are good reasons to go to a different type of cap. 60 years of progress cannot be ignored.

[Kamakiri]

I'm thinking you're right, because even though the set works, the underside is a mish mosh of original wax caps, orange drops, and other assorted flavors. I pulled and replaced the Spragues and wax caps post haste.

I happen to have the correct values and the chassis is on the bench, so might as well just replace them and give it a try. Thanks

[Kamakiri]

Got the new caps in, and much to my surprise, the picture's about the same as it was. Vertical is compressed at the bottom, and some mild intermittent pie crusting.....which I assume is unrelated to the linearity issue.

I was always under the impression that in electrostatic sets, that the vertical linearity was more or less controlled by the deflection caps.

[bandersen]

The deflection caps do have some effect on linearity if the wrong type or size is used, but mostly they just couple the oscillator AC signals to the HV DC on the plates. I suspect your issue lies with the 6SN7 vertical oscillator or 6SL7 vertical output circuits.

[robert1]

I would suggest that you check all the resistors in the vertical oscillator / output circuit to see if they did't drift out of spec. there are several 1 meg & higher resistors used in that circuit & they ARE prone to drift.
i restored a 19A11 in the late nineties & found the same problem.

[Kamakiri]

Here's a pic to show what I've got with an indian head test pattern. There's so many different types of capacitors in this set that I think I'm gonna start by just redoing the ones in the vertical circuits and see where that leaves me, then work my way to the resistors from there. Normally I don't suspect orange drops for being faulty, but I'm half wondering if the values used were correct, since the deflection caps obviously weren't.....

[kramden66]

if all else checks out and doesn't change anything alter the vertical 6kv caps or in this case the 10kv caps , when i had linearity issues on a set like that changing the values effected the linearity and made things more uniform, ask me to remember the values - i can't at the moment , maybe it was it had to be closer to .005 or something odd.
mike

[dtvmcdonald]

The first thing to try is just piling on the caps (in parallel) for the
vertical output-deflection plate coupling caps. Find what you can
at the required voltage and get up to .02 or .025 uF.
Film, ceramic, just pile them on.

Next, if that does not work, get out your 15 or 25 kV HV probe, hook to a scope, and
check each side of the caps. Remember to use DC coupling!
That's important!

[robert1]

Resistor values in the vertical output / driver stages are very critical. there are two resistors (r64 & r65) which are supposed to be 4.7 meg. from what i can see on the picture, they appear to be different values. they also appear to be not the originals. check those first as they will be the ones that will have a drastic effect on the linearity. they both have got to be the exact same values.

[Kamakiri]

After replacing 3 old Sangamos in the set, it's starting to straighten out nicely. I left the orange drops for the time being. Only cap that's original to the set I didn't have, which is a 4 uF @ 150V. It's labeled as a stabilizing cap.

[Kamakiri]

Originally Posted by robert1

Resistor values in the vertical output / driver stages are very critical. there are two resistors (r64 & r65) which are supposed to be 4.7 meg. from what i can see on the picture, they appear to be different values. they also appear to be not the originals. check those first as they will be the ones that will have a drastic effect on the linearity. they both have got to be the exact same values.

You're good! I also noticed that. I didn't have that value, so those will be on my next order

[Bill Cahill]

You can use four point seven, or, five mf. That is an important cap.
Bill Cahill
Oh. Sangamo caps were cheap replacements, and, I have never found one to be good.

[Kamakiri]

Got the resistors changed last night, along with the 4 uF stabilizing cap (used a 4.7 @ 250). Added the blanking circuit from Phil Nelson's website while I was in there. It's not looking too bad

[Kamakiri]

One thing that it DID do, which seems to have disappeared, I've never seen before.

One thick line of loss of horizontal hold scrolling up the screen....snapped a quick pic of it with my phone.