This leads me to another question. I couldn't get a 200pf cap used in K6 the H. AFC couplet. So I'm guessing that a 220pf would work?

Also the 5000pf caps used in K1 Blanking, K6 Vertical Integrator, and K8 the CRT Isolation couplets will be replaced with 4700pf caps.

Also the 8000pf caps used in K2 Audio, and K3 Sync Coupling couplets will be replaced with a 8200pf cap.

Anybody see any problems with those subs?

Thanks.

If you mean 220pf as a substitute for the 200 in the first sentence, then yes, all of the substitutions should be fine (all within 10% of the desired value).... I suspect the original parts are 20% anyway.
Are you going to be using the set with a VCR? Most older sets do not do well with a signal from a VCR because the horizontal AFC is too slow (causes flagging of the top of the picture) reducing the 200pf to 150 or so, possibly could help if this is a problem.

jr

Yes, I corrected my post. Typically I don't use a VCR. Maybe I should use a 180pf instead of a 220pf just in case?

I just looked at some old notes and now think that c 39 is the likely candidate to change to decrease the horiz AFC time constant. :scratch2:

jr

OK. I'll go with the 220pf cap.

Another question. Do you think that for the 1500pf 1KV NPO cap used in K5 the Vertical Feedback couplet I can use a SMD? The package is 1812 and I can solder leads on it or just solder it to my pcb boards that I'm designing?

Don't know... never played with SMD parts.

jr

I don't see any reason why not other than the difficulty in soldering. So long at it has the proper dielectric characteristic and voltage rating, the packaging doesn't matter.

An acquaintance from college learned a valuable lesson doing a SMD based senior design project: Order at least 3 boards and at least 3X any SMD parts needed, since it probably won't come together right the first time and you'll end up destroying parts in the process of getting it right.

To get some experience with SMDs, get a hold of a junk board out of a computer, router or BPC TV set. You can unsolder SMDs by using a pair of soldering irons, one at each end of a cap or resistor. Be aware that newer stuff used unleaded solder, which melts at a higher temperature. Sometimes adding some leaded solder helps to get the solder holding the SMD to melt. I've had success with larger SMD resistors (ones about 1/10 inch long)

I find the concern about SMD parts a little surprising. I've worked professionally with SMD parts for over a decade. Its really not much of a problem unless you are dealing with large IC or very small parts. I regularly worked with resistor and capacitors as small as 0402 size. For something like that you do need a stereo microscope, sharp tweezers and small iron tips. Just melt some solder on one pad, position part with tweezers and remelt the solder blob. The first connection will hold the part while you do the other connections. The small two terminal parts you can actually remove by melting the solder on both pads at the same time by laying the iron against both pads and then pushing the part off the pads. Clean up one pad and put down the replacement. Larger parts will require solder-wicking each connection before removing part.

I'll have no problem working with the SMD's.

The boards are almost fully designed. Some are just a little taller which won't be a problem. I designed them using 1W resistors, hence the reason they are a little taller.

Parts are on order for them.

I still don't know if 200V will be enough for the 82pf cap in K6. It is connected to the plate (pin 3) of V4, the Sync Separator tube. The schematic shows 70V on pin 3. But then there's a resistor R39 at 150K connected to the 265V supply. The 82pf cap is on the resistor side and plate of V4 of that 265V. I'm not smart enough to be able to figure out what the voltage should be except that it should be at least 70V.

Another question. The fusistor is 5.6 ohms. I'm going to replace it with a resistor and a separate fuse. The parts list doesn't show what the wattage rating is. I did an Ohm's Law calculation based on 120W and came up with a 5.6 ohm 5.6W resistor. I'm going with a 10W wirewound enamel resistor. Do my calcs seem reasonable and a 10W seem right? I'll go with probably a 2 1/2 amp fuse.

Keep in mind the fusistor is only on the B+, not the tube filament string. I'd guestimate something around 200-300 mA of current.

Also the reason for the resistor is that the old rectifiers can't take the surge current. Modern are more robust especially if you go with 1N5408s. The resistor value isn't critical.

I also suggest adding another fuse to protect the whole set.

Bob,
Thanks for the quick reply. The TV is rated at 150W or 1.3A. Less the 600ma filament string gives me .7A through the Fusistor. If I'm reading your reply correct, I really don't need a Fusistor, just a fuse upstream of the filament tap off....right? I could easily relocate the filament tap off to the downstream side of a fuse.

I used an 8ohm 5 Watt resistor, to give a bit of extra surge protection with today's higher line voltages. I also added a fuse IIRC, 2 amp slow blow.

200 volt rating for the 82 uuf cap should be fine, as the 150 k resistor and the 2 33 k resistors in series form a voltage divider network. The total resistance of the divider is 216 k (150+33+33).... 66k out of 216 k is about 30% .... 30% of 265 volts is about 80 volts. When the tube warms up and starts drawing current, the voltage at that point drops about 10 volts more to 70 volts.

jr

Hmm, 0.7A seems high, but I can't fault your math. I'd still use either a resistor or a thermistor. It'll give the set a soft start and help preserve those old parts.

Motorola (CDTS-581) and RCA (CTC11) used inrush current limiters in some early-1960's TVs to lessen inrush on tube heaters in particular - I use the CL-90 made by GE. It is 120 ohms cold and rated for 2 amps. Works for most all monochrome TVs and tube radios. I like to think a transformer can be made to live longer.

The CL-90 works for almost everything but color TV, then a CL-70 has lower cold resistance (47 ohm) but rated at 4 amps, which most older sets draw up to.

Jr is right about the voltage across the 82 pf increasing every time the set starts up from cold because the tube isn't drawing current. This does point out however that when something is designed that it is difficult to cover all the bases. If the 33K resistors in K4 increase a lot in value or open up then the voltage will be higher. This could also happen if in troubleshooting someone disconnects K4. Its hard to foresee every possibility.

I have a 200v cap coming. On the other hand, I can always order a 82pf 1KV SMD that will fit the through hole pads well enough. Maybe I should hust go with one of those?

I'm done with the design of the Couplets. If you get a chance would you mind going over them to see if I have them correct?

Thanks.

I think SMDs would lead to a smaller package, and then you could epoxy dip it for an authentic look. And better reliability.

My only question is, can they take any voltage spikes on them? This might be an issue. (Don't forget startup, before the tubes are conducting...)

What are you using for the PCB design, btw?

If there was enough demand, you could get them made by a PCB place and stuffed and all. With the plethora of places overseas, this is surprisingly cheap now...

On K7 the junction of the 560 pf and 3300 pf needs to connect to pin 2.
I wish the schematics were drawn easier to follow, more nearly like your layout.:)

Good catch! I missed that one on my first look. Like the way the distributec R/c was done in k4.

jr

Wow, I missed that there was a connection there! Thanks.

I made the PCB's today. Basically I use the Press-N-Peel method. Or another name is Toner Transfer. I run the sheet through my laser printer set on 1200dpi and the iron on the pattern on a clean, really clean copper side of the board. Peel off the sheet, then etch, drill, and trim to size.

Here are the boards with the toner transferred to the copper.

Here they are. Ready to encapsulate. Can you find the 82pf 200V cap?

Nice work!

Thanks Tim.

Very neat. Would you bother to encapsulate them? They look very nice as is. Other than authenticity I can't see a reason to. In the (admittedly highly unlikely) event of a component failure you can replace a component if left unencapsulated.

Very nice!
Out of curiosity, where is K8 located in the set? I don't remember seeing it when I did mine a few weeks ago. :scratch2:

jr

Yeah, I thought of leaving them as they are. But then encapsulated them.

Thanks. K8 is located on the top of the main chassis. It goes between the main and CRT chassis. Looks a lot like a ceramic disc capacitor.

http://i1060.photobucket.com/albums/...psklgvsxqs.jpg

Slaps forehead!
I remember unsoldering a "ceramic cap" when I pulled the chassis... since I generally leave ceramic caps alone, I paid no attention to it.:o

jr

I thought that might have been the case.

Ready to solder in!

http://i1060.photobucket.com/albums/...pshwmrhee9.jpg

The paint I used.

http://i1060.photobucket.com/albums/...psfgjrcciq.jpg

All installed.

http://i1060.photobucket.com/albums/...psrjiijz9w.jpg

One last question. The audio transformer mounted on the main board. Do I need to be worried about Silver Mica Disease? Do the caps need replaced?

Anybody know how to get the cover off of the audio transformer?

I removed the can by flattening the dimples with a smooth jawed pliers. I then pinched the can so I could withdraw the coil assembly. I wanted to inspect for any silver mica disease. None here.

http://i1060.photobucket.com/albums/...psobfriykp.jpg

http://i1060.photobucket.com/albums/...psx9kzevgc.jpg

http://i1060.photobucket.com/albums/...psylzwr6vs.jpg

The idea of couplets always intrigues me. When I used to repair colour TV's in customers homes back in the 70's there was a Thorn model 4KA set which used a similar component called a Thick Film Unit which was essentially a couplet. It used maybe half a dozen of them and they were notoriously unreliable. You'd replace one only to have it fail a week later. Made techs look like fools unfairly. Yours will last forever I'm sure.