1971 Philco color Tube Hybrid

[Lain94]

Originally Posted by Electronic M

Looks like a silicone diode. If it's one of the power supply rectifier diodes that are fed 60Hz from the transformer then you really only need to know 2 specifications of the original to replace it with a modern part. Those specifications are PIV (peak inverse voltage) and current rating, and make sure the new part has those numbers as high or higher.
For power supply rectifiers I stock 2 types that can handle everything....1N4007 (1A, 1KV PIV) and a 1N51?? that's rated for 3A 1KV PIV....The higher current part is pretty much never necessary, but anything over .75A I try to use it for so I'm not running the 1A part too close to it's rating.

In convergence and detector diode applications switching time, junction drop, and capacitance become more important.

Boost and focus/HV applications are pretty much the same as B+ rects but with faster switching time requirements.

Thanks! I will probably just replace it with a 1N4007 then if that will safely work as I have a whole bunch of those in my parts box.

[Lain94]

Well I feel pretty dumb lol, this whole time I was recapping the Ford Philco chassis and looking at it forever and hours and hours and kept wondering why there was a crusty looking "wire fuse" connected to the circuit breaker....I failed to look for what it was in the schematic. It turns out that it is a posistor which looks to have failed long before I ever got this tv. The thermistor that is connected to the degaussing coil looked melty and I believe had failed already before (The degaussing coil was removed from the chassis in the tv before I even opened it up for the first time after getting it last year). Luckily when I had ordered the replacement thermistor for the ford philco tv it also came in the same package with a replacement posistor for the ford philco. I was looking all over the chassis assuming the posistor would still have been physically intact but apparently all that is left are the lead wires that went to the disc of it.

Perhaps this may be the primary cause of my HV rectifier cup arcing....

I have a few more minor things to do and will be putting this chassis back in soon to test to see if the HV cup arcing issue is resolved. All tubes have been tested and ruled out as causing any issues, no leaks or shorts. I have an Eicco 667 tubes tester which I recently got and use for testing tubes and have gotten consistent believable results from it, when testing both known good NOS tubes as well as likely tired used ones.

[zeno]

Check your degaus. Most sets back then used a thermistor & glowbar.
The thermistor falls apart & the DGS keeps running. All the TV current flows through the coil & globar & you get melt down. On MOST sets you can jump out
the thermistor to test the rest of the set. Newer sets use a different scheme &
some old ones used a relay.

73 Zeno
LFOD !

[Lain94]

Update: Replaced the thermistor connected to the degausser coil plug which goes into the chassis, also replaced the posistor that is connected to one of the terminals of the circuit breaker. Double checked all connections and put it all back together to turn it on for a test for the first time in many many months. Fully recapped all electrolytics as well and checked polarity and connections.

This time the arcing is NOT happening in the HV cup socket like before but INSTEAD it is happening at the bottom of the HV cage inside towards the underside of the flyback...the arcing was much more intense and bright too....scared the beejezus outta me and I of course immediately turned the set off in an instant when this started. Like before sound circuit which is solid state works fine, the lightbulb i put in to replace burnt one on tuner lights up fine and looks great...so i guess that is an accomplishment?, and there was not apparant signs of trouble elsewhere which leads me to suspect the flyback is arcing due to an internal short (i tested the primary winding from cap for HV rect tube at one point to the other being the horizontal output tube's cap. and ohms were within range per schematic.) Will be testing other windings now for signs of trouble. Perhaps the flyback is exposed and having HV leaking through it in a blind spot in the HV cage that I could not see? I will admit I there was a spot on the flyback on the underside that I can not see when doing visual inspections. Flyback is not hardened indicating it was not heavily used. And it looks ok on most of what I could see in the past...but I am getting suspicious now...

On the positive side...I can either seal it up if that is the case or...I also have a NOS thordarson replacement flyback ready to go! lol

[Electronic M]

I'd try to stop the arcing first. Generally shorting does not cause arcing as it usually loads the flyback and luggs down the voltage. Case in point I have a Panasonic hybrid that had an oil filled cap on the flyback short and it didn't make any HV or arcing, and the H output tube was redplating like mad despite having plenty of drive from the osc.

Arcing is normally either the result of failing insulation, conductive dirt bypassing insulation, or excessive HV.

[Alex KL-1]

Just remembering, maybe this can be useful: when I restored my Telefunken B&W TV years ago, I'm unable to stop arcing from any point from HV cable. Even with original cable apparently clear, it arced. Subbing it from a dead donor modern flyback cured it.

[Lain94]

Update: I finally made the decision to replace both the old flyback and hv tube cup socket. I successfully installed the NOS thordarson flyback and verified ohm values and it definitely looks better made than the old one and better insulated. I am keeping the old flyback though and will be putting electrical grade silicon all over it to insulate it and will have it available in the future to try using again if needed. I am installing the nos socket for the HV rect. tube tonight and once all that is done will be testing this tv yet again and hoping that solves the issue.

It is clear to me where the arcing had happened this time and it basically punched a hole through the rubber insulation around where the three wire winding is at as the two wires leave the stick it is wrapped around. Insulation basically failed there. The new one appears to use what may be fiberglass or...asbestos maybe instead of rubbed to insulate those two wires coming up from the three coil winding under the tire.

Will upload photos tonight when I am able to.

[Lain94]

Old flyback removed vs new flyback before installation

https://imgur.com/a/NxeYmOE

[zeno]

Keep in m ind for arcing EVERYTHING is at 25 KV above ground.
Tube, socket, filament winding, HV lead & any small parts at the socket.
So they can arc anywheres.

[Lain94]

One more question: In regards to the three winding wire loop under the rubber tire of the flyback transformer; does it have polarity and if so how do I know which is which in regards where to where each one for each of the two posts of the HV rect. tube socket the old one was at? The schematic does not show any polarity for the two wire leaving the three wire winding so I am assuming it does not matter which of the two posts they go to as long as each goes to the ones that the old flyback went to.

[Lain94]

I circled the part of the schematic where that winding is at. I see no indicators differentiating either end of the winding.

https://imgur.com/a/CDJ7p21

[mrjukebox160]

No polarity on that.

[Lain94]

Thanks, I just wanted to be sure before I turned it on again. Now the arcing problem suddenly went away after putting in the new HV cup socket and flyback transformer. The new problem is the 6CG3 damper tube started rapidly redplating within just 10-20 seconds of me turning the tv on to test it and I then quickly turned the tv off as soon as I saw this.

No other tubes were showing red-plating or any other signs of trouble. No other symptoms present, I heard the high pitched frequency which sounded normal as all the tube filaments including the CRT glowed. I am pretty sure the horizontal drive is working and just am unsure what is causing there to be so much current suddenly going through the damper now.

I read online that sometimes the yoke can be shorted and cause it. I already replaced all the electrolytics and was careful to make sure they were put in correctly so I highly doubt that was the issue.

[zeno]

Test for dividers is inspection for cracks, bulges, heat etc.
Beyond that the focus voltage needs 6KV +- from it. Third wire is
ground or nearly so.

Zeno

[Electronic M]

If it started red plating as soon as you replaced the flyback, then the flyback replacement caused it...the more wires you swap at once the more likely a screw up is, also once in a while part subs aren't as functional in circuit as Sam's thinks.