1971 Philco color Tube Hybrid

[Lain94]

A bit of a minor update but it is good news in regards to the CRT. I recently acquired my first CRT tester. It is a Sencore CR 161. From what I have heard online, Sencore is a trustworthy brand. After reading the instructions and manual, I quickly learned how to use the tester.

I tested the Ford Philco tv's picture tube at the normal 6.3 volts and all three color gun's emissions were GOOD! Also no shorts in the CRT were detected by the tester which rules out the CRT being the cause of the arcing I had been seeing in the HV cup area.

So it appears that I have a picture tube that is in great shape and with plenty of life left.

[Electronic M]

That's good. I would check other tubes of known working and non-working status to make sure the tester is telling you the truth. I've bought sets at the ETF where someone tested the tube good and it was very bad and tubes where they tested the tube bad and it was good.
It probably is good, but testers can lie to you so get a feel of it on multiple tubes of known performance to be completely sure, and get a better feel for your new tester.

[Lain94]

I finally got around to taking the whole chassis and tuner out of the tv. Cleaned up the wooden cabinet. Checked all the diodes on the tv, all diodes tested good. I am now recapping all the capacitors that are known to be bad. Mostly the bad ones were small low value electrolytic ones on the pcb board. A bit annoying to get into the tight spaces on the board. I much prefer working with point to point wiring.

Flyback seems to test ok based on measured ohm values via a multimeter and comparing to the schematic. Will be cleaning up the high voltage cup more thoroughly this time to make sure no carbon tracing happens, if necessary a Dremel will be used.

Replacing a burnt out 6.3Volt incandescent bulb that illuminates the tuner.





In summary:
Flyback good, capacitors that tested bad are being recapped to rule those out, diodes all tested good, CRT is in great shape, and cleaning the HV cup again in hopes of stopping the arcing that keeps happening within seconds of powering on the tv.

Replacing a burnt out 6.3Volt incandescent bulb that illuminates the tuner.

Also, I now have a NOS vintage RCA high voltage probe, so I can now test what actual voltage is coming to the CRT. A bit nervous using this as I have never done so before.

Question:
Is it possible that the sole/original cause of the arcing was a bad doubler or tripler? There is a white box on the back of the high voltage cage that is believe is a doubler or tripler. Also perhaps the voltage is set too high on the potentiometer that sets it?

A theory I had was that as the emissions performance from the old Horizontal tube had declined, the knob that upped the voltage output was turned up to compensate...until the horizontal tube finally had failed and went to air. Now with the new horizontal tube in it the voltage is too high at current setting.

https://imgur.com/a/Wqq1s8l

[zeno]

Most likely the box is a focus divider. They can arc. Its a like 300 meg resistor
that drops the HV to abt 6 HV for focus.
Never trust testers 100%. Most common mistake they make is it can
read bad but still be a good pix.
With HV probe just be sure you have a solid ground & touch the probe
right to the button. Sometimes when you lift the rubber you will get
an arc & hissing. Not to worry.

Zeno

[Electronic M]

If it uses a 6BK4 shunt regulator tube then turning the HV up actually reduces load/strain on the H output tube...A 6BK4 acts like a CRT but essentially conducts harder when the CRT goes dark to try and keep the load relatively constant.

Pulse regulator tubes 6HV5 work the opposite way... Instead of loading down the flyback output they modulate the bias of the output tube so the input sent to the flyback matches the power level it needs to maintain stable output.

Both circuits monitor the B+ Boost line as boost voltage is a good indicator of the load demands on the flyback/the sweep width and HV level...So if you hold boost constant you should get constant HV and deflection levels.

[Lain94]

Any idea what type of diode this is? I am having trouble identifying it. I have to replace it because the leads are too short to solder it back in safely.

https://imgur.com/a/nCO9EfE

[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.

[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