Silvertone 8106

[Doug66]

My L15 sound take off coil arrived today, and I have a couple of questions before I install it. The Miller replacement coil 1471-a has a resistor soldered across two lugs and also has two 4.7 caps.

The guy at Moyers, where I bought the coil, emailed me and said that his book said to delete them if my old coil doesn't use them. Therefore I will take out that resistor. However, the old coil uses two 33pf caps which I replaced. Should I keep the 4.7pf caps in the new coil or change them to the 33pf caps?

[DavGoodlin]

What does your new coil measure compared to the existing one?
Sams schemo shows 4 ohms, and if the new one measured the same as the old one, inductance is likely the same, so it may be better to use only the 33pF caps.

The only way the 4.7 pF would work is if the resonant frequency can be found within the tuning range of L15. The resonant frequency is likely 4.5 MC, so the sound is both amplified by the video amp tube AND taken off via L15 without loading down the video signal going to CRT cathode

Of course, you need to tune the primary and secondary slugs per the sams schematic, which may not have a method simpler than using a signal generator and oscilloscope.

I often did the sound take-off (secondary) by ear but always use a plastic hex tool.

[Doug66]

I tried the coil with both the 4.7pf and the 33pf, and it worked better with the 33s, so I went with them. Sound is pretty good now, so I'm back to the horizontal.

As the set warms up, the horizontal loses sync several times. The horiz hold control is very touchy. The slightest movement of the slug causes a huge shift in the pic, and the lock range is very small.

Could this be caused by too much pic width? Here is why I am asking this. My set uses a width sleeve inside the yoke. When I started on this set, I found a piece of metallic tape inside the yoke for a width sleeve. Don't think it was original, and it was crumpled after I separated the yoke from the CRT. My CRT is one that stays in the cabinet, so I am using a test CRT. See pic for what was in my set vs the sleeve I am trying. New sleeve is wider.


I couldn't get that piece of tape back in the yoke properly, so I've been restoring the set with no sleeve meaning maxed width. Yesterday, I checked in my junk box and found a yoke with a width sleeve, so I tried that.
I could see a reduction in the width, but after a minute I heard some arching in the yoke, and I lost HV. Pulled out the new sleeve, and HV was restored. I thought maybe there is a bare spot on one of the yoke windings, so I have coated the windings with Corona dope and am waiting for it to cure.

I also replaced the horiz output tube, and no change.

[DavGoodlin]

You may be onto something.
Try putting an AM radio in proximity to areas of suspected arcing.
Arcing of anything will usually cause a loss of horizontal sync.

The next thing to look at for your sync issue requires an oscilloscope so you can see if sync pulses are making it from the video amp through the sync sep 6EB8 and amp tube 5U8 to the 6CG7. The K-dots all over the place show the resistors and capacitors in the Kluster-packs (AKA integrators) and any one of those could cause your issue. Check those tube voltages....

[Doug66]

Not too much luck today with it. After the corona dope cured, I reinserted the width sleeve and it immediately started arching. I had used the lighter amber corona dope to coat the yoke windings, but I have not used the thicker orange stuff, and it's curing now.

I also discovered something else. I was watching bandersen's series on Zenith bug eye sets last night. In that series, he encounters width sleeves for the 1st time. He describes them and mentions the spring clip that holds them in place with a ground wire. I hadn't don't that, so I went back out to the parts chasses where I got that width sleeve out of a yoke, and sure enough, there was that grounding clip. However installing it made no difference. Still arching.

Continuing to watch his series on the Zenith sets, I noticed his yoke had a cardboard sleeve insulating the yoke windings. So is the correct set up: yoke, cardboard sleeve, then width sleeve inside the cardboard b ut still against the tube neck, or should the width sleeve be directly in contact with the woke windings?

[old_coot88]

Originally Posted by Doug66

... should the width sleeve be directly in contact with the woke windings?

Nein! Nyet! By all means insulate it with something more substantial than spray-on dope if there's enough clearance.

[ScottTV1962]

Just a thought, have we checked the horizontal hold pot for tin whiskers? Even if it ohms out correctly, I'd sneak a peek inside and clean it good. I had a tough dog once with the same indication you have, and turned out to be that simple.

[DaveWM]

did you check R36?

[Doug66]

Ok, here is where I am at. I decided to take the full size CRT out of the cabinet and try it. With the width sleeve in, I'm getting too much width on the right side and not enough on the left. Centering rings won't compensate for this. See pic.

Horizontal is still messed up. First off, it's not a pot. It's a coil with a top slug for find adjustment and a bottom slug for course adjustment. I'm going to check with Moyers tomorrow to see if they have a replacement. All my Sams has is the original Silvertone # 10-121-1.

Dave, I had replaced R36 earlier, but the other night decided to experiment and tried a 6800 ohm, 10K, and 15K. All that happened was I had to turn the hold to a different frequency, and it was still unstable.

I checked all the voltages on the 6CG7, and they are normal. I then moved back to the sync. V5 Sync Sep 6BH8 SB 7.5V on pin 3, and I have around 25.
Also on the Sync Amp 5U8, Pin 8 SB 9.5, and I have around 25V also.

I have rebuilt K1, K3, & K5. K2 seems to be tied into these problem areas. Perhaps I should rebuild K2 next.

[Giulio Maiocco]

Doug, sorry to not being able to help you out about your width issue, but one thing in your message popped out to my eyes: the 2 adjustments on the horizontal coil are NOT for fine/coarse adjustment!

This is the typical synchroguide horizontal oscillator and, for proper operation, it should be set in the following way: first, you set the horizontal hold pot at half of it's travel, then you short out C48 (the .01uF capacitor in parallel with the horizontal waveform coil) and, with the upper slug, you should sync the image on the screen. Then you remove the short on C48 and, with an oscilloscope connected at the junction of the 2 coils, you should obtain a combined waveform composed of a sawtooth and a sinewave, just like this one: http://www.rfcafe.com/references/ele...cs-world-3.jpg. You should pay attention that the "tip" and the "shoulder" of the sine part of this waveform are at the same height.
If this particular oscillator is not properly aligned, it could cause every kind of strange behaviour in a TV set.

If you already knew that, then I apologize having stated the obvious

Cheers

Giulio

Edit1: I rechecked the schematic, your TV doesn't have a horizontal hold pot, so disregard this 1st step
Edit2: The place to put the 'scope probe is called "G" on the schematic you provided. If, after tweaking the slugs, you still have instability, you should check the waveforms coming from the sync separator, if these have the correct shape and amplitude, then keep in mind that all the mica capacitors in the hor AFC/oscillator circuit are suspect, as these are under lot of electrical stress and can definitely fail. These capacitors MUST be perfect and NO leakage!
Note3: Your R36 (or R38?), the 8,2K is the screen grid dropper for the Hor. output tube. Changing it's value affects the frequency because the B+ voltage for the hor oscillator is derived from the B+ boosted. Changing the resistor does in fact have an effect on the B+ boosted source because it lowers or raises the power the 12AV5 gives out.

[Doug66]

I'm back on this again and really need some help. I've been looking for a yoke, and Moyers found a Thordarson Y97 which is supposed to be an exact replacement for mine, Silvertone 80-2-4.

When it arrived today, the instructions said to take out the two 220 ohm resistors in parallel with the 560 ohm resistors to duplicate the original. When I took the cover off the yoke, which is stamped Y97, I only found two 150 ohm resistors.

trying to compare the instructions with my original Sams even got me more confused. My original yoke only has 3 wires going to the socket, while this one has 5.

I've enclosed a scan of the instructions, the yoke section of my Sams, and a pic I took of the replacement yoke.

Thanks for any help.
Doug

[Giulio Maiocco]

Hello Doug, please no panic, the solution to your issue is simpler than you think!

About the resistors value and the instruction to desolder the two 220 Ohm, then the more logical conclusion I came to is that the original parallel of 220ohm and 560 ohm gives a final value of 157ohm, pretty close to the 150 ohm you found. The best way to fix this problem is to simply discard the 150 ohm in your yoke and solder a couple of 560 ohm ones in their place.

To fix your other problem, first thing to do is to disconnect the orange wire coming from your new yoke, this is not required in your TV. I would simply snip it from the tab inside your new unit and pull the now "dead" wire away. So, now we are at 4 wires instead of the original 5, yikes!! This, again, is very simple to take care of, simply unite the Yellow and black wires and consider it a single wire. Again, me being me, I would make a jumper inside the yoke body and exit from it with our 3 wires.

Please, pay attention to the replacement yoke plug pinout, as drawn, it is wrong! (as an example, the red wire, called pin#7 does in fact go to pin 8 of the plug, so, unless i'm barking up the wrong tree, something is amiss!)

Also, if your new yoke does not have the series RC cell (68pF 3000V + 1000ohms) across half of the horizontal deflection coils, you'll have to transplant it from your old unit.

I hope I was of any help to you, not a pain, unfortunately my english is not too good

Cheers

Giulio

[Electronic M]

A favorite practice of mine when subbing yokes is to do the initial connections with clip leads so if I have it wrong I can power it off reconfigure the connections and try again before the tube heaters go completely dark...

[Doug66]

After I panicked last night, I sat down an reread the instructions and figured it out, but thanks for the help.

Now I have a new issue. I've got the new yoke installed and did a power up. I have no Hi voltage. Checking voltages on the 6CG7 gives good readings on both plates, pin 6 and 1. I don't have any negative voltages on pins 2, 7, 8.
High voltages probe shows nothing on CRT anode, plate of 12AV5, or pin e of Damper.

[Giulio Maiocco]

Good afternoon Doug,

You are missing your negative voltages because the horizontal oscillator is not working, also, your High voltage is missing because of this!
As a quick check, please control the continuity of the 50 Ohm part of coil L22 and that you obtain about 490Kohm between 6CG7's pin 2 and ground. If these 2 tests do not point to a "smoking gun", I'll suggest you some other tests to perform to help straight out your problem.

I really doubt it is the 6CG7 itself, as it is a reliable tube, but did you try a spare tube?

Cheers

Giulio