Recently Acquired 1969 Motorola Color Tube Tv

[old_tv_nut]

Originally Posted by Lain94

Also, should I be wary of whether or not the oscilloscope can handle the high voltages in the horizontal sweep circuit? ...

Definitely should be wary. Don't try to measure the horizontal output plate, the damper, HV rectifier, focus rectifier, or anything on the flyback transformer.

[old_tv_nut]

The exceptions that are OK to measure are lower voltage pulses like those for AGC or burst gate - but measure those in the circuits where they are used, not at the flyback itself, to prevent accidentally contacting a higher-voltage terminal.

[Lain94]

All diodes have now been tested in circuit using both my multimeter and my capacitor wizard (the manual claimed it could find shorted or leaky diodes in circuit).

All diodes seem to be ok, no shorts, none are open, and all are behaving as they should on the multimeter including the two that the sams photofact said to check if horizontal frequency is off. So that now leaves tube V8 as the last thing the photofact suggests checking. This is a horizontal oscillator tube the voltage levels going through this tube are far lower than from other tubes such as the horizontal output. Would it be safe to measure at one of the pin on this tube? Max voltage going through this tube per the schematic is about 275 volts, other pins on tube have lower voltages.

Should I suspect this tube as possibly being weak? Obviously heater is ok as this is a series string set and I doubt any shorts since that would cause other electrical issues and symptoms. The tube is 6GH8A. I do not have this tube but supposedly I may have some tubes that can substitute for it and have the same pinout and heater voltage and current such as 6EA8. Is it OK to substitute 6GH8A with a known good 6EA8 for this circuit and application to rule out a bad tube?

[Lain94]

Update:

Doh! I did not realize that the diodes X11 and X12 were germanium and not silicon ones. Most of the diodes in the tv are indeed silicon but these two are germanium. They are painted black on the glass which confused me. I pulled them both off the tv and noticed the voltage drop as being .50V to .60V for both of them during the multimeter diode function test which is way too high for germanium 1N34A diodes. Voltage drop should be about .3V

So I got two replacement germanium diodes which were the correct voltage drop and soldered them in place.

Also the 6GH8A tube has been tested by my recently acquired and working EICO 667 tube tester. The 6GH8A in this tv appears to be an original one. There is SOME leakage but not an unacceptable amount among the elements. The emissions are just barely in the red weak zone. I compared the emissions to a known good NOS RCA 6GH8A and sure enough the NOS tube had very good emissions and no short or leaks.

I replaced all three can caps as well at this point finally with quality nichicon ones, Hopefully this will all make a difference.

[Lain94]

Another Update: Well I think I made a mistake. Apparantly those diodes were in fact silicon ones. Apparantly a long long time ago a company made "Transitron" branded glass package silicon diodes....

The motorola tv has a total of three of these, two of which were x11 and x12...which I replaced with 1N34a diodes...

What is strange is the photofact part list says they are 1n34a which confuses me. Everything else on the part list matches up. The only things that did not were the lack of a remote control unit or FM/AM radio built in.

It is almost as if they later started putting in these silicon diodes instead of the germanium ones.

Any idea what this is all about?

They are glass painted black with a green arrow on one end and two yellow stripes on the other end.

I could find almost no information at all about these diodes on line and not a single image or photo of them aside from a very old black and white photo of one on a product catalog from the 1960s.

Here are some pictures of what one of them looks like.

https://imgur.com/a/20mRzIC

[ARC Tech-109]

I've seen those in the Japanese electronics from the same era, they're germaniums. Had a nearby lightning strike take out the chroma and phase detect diodes in my T940 Magnavox, got creative with some wafer sockets and 6AL5's to replace them.

[BeamT]

Can you identify the resistor that is burned in half just adjacent to the diode in your last picture? Looks like it might be a 33K (orange, orange, possibly a 3rd orange) You can see scorching in the area? Did I miss a reference to this in an earlier post?

Nice TV!

[Lain94]

Oh yeah that resistor was one of two that actually did get burnt and failed open. I had it replaced way back quite some time ago. I should clarify that these pictures are older ones I took of this tv the first time I actually looked at the chassis.

I think those two resistors either were already burnt or got that way back when I had that ceramic shelled wax paper safety cap fail way back. (This issue was fixed and was not too hard to fix once I realized what had happened)

[Alex KL-1]

Last year I acquired a delta gun TV, and at testing, I'm desperate due to lack of any image. And a faint image appeared with bias pots maxed out. I think the CRT was dead. But then I noted that the G2 bias caps are paper-in-oil, and I decided then to change it for polypropilene caps. Voilà! Image back, with great brightness, at middle of adjusment!
The bias normally have relatively high DC resistance, so bad caps can upset correct adjustment.
If you not checked yet, is good to check if cathode, G1 or G2 have messed DC voltages due to leaky caps or drifted resistors. Also serves for various other faults you have found or will encounter. Unfortunately, older sets are not so reliable like 80's+ sets...

[Lain94]

Originally Posted by Alex KL-1

Last year I acquired a delta gun TV, and at testing, I'm desperate due to lack of any image. And a faint image appeared with bias pots maxed out. I think the CRT was dead. But then I noted that the G2 bias caps are paper-in-oil, and I decided then to change it for polypropilene caps. Voilà! Image back, with great brightness, at middle of adjusment!
The bias normally have relatively high DC resistance, so bad caps can upset correct adjustment.
If you not checked yet, is good to check if cathode, G1 or G2 have messed DC voltages due to leaky caps or drifted resistors. Also serves for various other faults you have found or will encounter. Unfortunately, older sets are not so reliable like 80's+ sets...

I noticed that there were a relatively large number of paper oil caps in this tv as they are many of these older sets from the early 1970s and earlies. I definitely am going to end up eventually recapping all the electrolytics, any remaining wax papers I may have overlooked and the paper oil ones too.

Even if the ESR has not went bad yet, they can still be leaky as I have learned is often the case when at operating voltages.

[Lain94]

Originally Posted by ARC Tech-109

I've seen those in the Japanese electronics from the same era, they're germaniums. Had a nearby lightning strike take out the chroma and phase detect diodes in my T940 Magnavox, got creative with some wafer sockets and 6AL5's to replace them.

Yeah I was hoping they were germaniums like the part list said. It is just so confusing to me because of how obscure these particular brand are. Did they made both silicon and germanium ones to look like that with the green arrow and yellow lines? And ouch sorry to hear about the lightning strike...I know a great number of electronics falling victim to lightning strikes including a now very rare Monorail computer I had back in the 1990s.

And you replaced diodes with 6AL5s? That sounds pretty interesting, I actually had the same thought in my mind about replacing unreliable germanium or even early silicon diodes with some vacuum tube diode equivalent. Care to send me info about how you did the mod to the tv?

I always wondered what a vacuum tube tv would look like if even all the diodes were tube as well as opposed to selenium, silicon, or germanium.

[ARC Tech-109]

The mod was easy enough, just a couple of those wafer sockets and some thin wire. Follow the basic diode cathode & anode connections and find 6.3v to run the heaters. The thing about the 6AL5 is there is no junction "breakdown" voltage, they will forward conduct at once there is heat on the cathode with only a few pf of capacitance. The only downside if you will is the heater to cathode capacitance and the need to decouple the heater itself beyond a few MHz.

The real b**ch of the lightning strike is it was roughly a mile down the road but it followed the telephone trunk and found its ground at my QTH killing several pieces with the EMP as the Magnavox was not even connected to anything at the time, it took out all of the germaniums for the chroma, phase det and the diodes in the AM/FM stereo tuner (combo set)

There were a number of variations of those japanese germanium diodes, some had a low forward while others were twice as high being they were stacked internally. A silicon diode has a forward bias of 0.72v while germanium is 0.3v at its knee point, I don't recall the number for those glass diodes you have but they were like lice in the early 70's stuff from the likes of Panasonic... they were everywhere.

"Pure germanium is known to spontaneously extrude very long screw dislocations, referred to as germanium whiskers. The growth of these whiskers is one of the primary reasons for the failure of older diodes and transistors made from germanium, as, depending on what they eventually touch, they may lead to an electrical short." (Givargizov, E. I. (1972). "Morphology of Germanium Whiskers". Kristall und Technik. 7 (1–3): 37–41.)

[n8nagel]

Originally Posted by Lain94

I noticed that there were a relatively large number of paper oil caps in this tv as they are many of these older sets from the early 1970s and earlies. I definitely am going to end up eventually recapping all the electrolytics, any remaining wax papers I may have overlooked and the paper oil ones too.

Even if the ESR has not went bad yet, they can still be leaky as I have learned is often the case when at operating voltages.

Understand I'm coming at this from being an audio guy... common wisdom in audio land is that electrolytics are always suspect after a couple decades, film types are usually good, ceramics can go either way, and PIO types are also usually good. Is there something about higher operating voltages in a TV set that makes PIOs suspect? I'm not saying you shouldn't check them, or even that that is wrong, I'm trying to learn here.

[ARC Tech-109]

The paper/oil caps will pop without warning or provocation, electrolytics dry out and are known to go leaky both physically and electrically. Disk ceramics are quite stable and I've had numerous film caps go bad from being exposed to the high temps and voltages in vintage tube gear. Another to consider are the carbon comp resistors that get baked from radiated heat, nothing like a 6L6 or pair of KT88's to cook them. 50+ years of absorbing moisture cold only to be baked dry again when the heat is on, I'm also an audio guy and have over 40-plus years of experience with tubes so I know what you're dealing with. Case in point is my Magnavox T-940 AstroSonic. The IF gain would drift down as the set warmed up due to the resistors drifting up thus dropping the plate voltage. As an experiment I dynamically tested each resistor in circuit, Simpson 260 on the leads while heating the suspected resistor with a soldering iron at 45 volts (220F tip) and watched it drift up beyond the 10% tolerance rating. The set spent its first 14 years entertaining us kids, been in the family since new and it's going to get all new resistors in the near future.

[n8nagel]

Originally Posted by ARC Tech-109

The paper/oil caps will pop without warning or provocation, electrolytics dry out and are known to go leaky both physically and electrically. Disk ceramics are quite stable and I've had numerous film caps go bad from being exposed to the high temps and voltages in vintage tube gear. Another to consider are the carbon comp resistors that get baked from radiated heat, nothing like a 6L6 or pair of KT88's to cook them. 50+ years of absorbing moisture cold only to be baked dry again when the heat is on, I'm also an audio guy and have over 40-plus years of experience with tubes so I know what you're dealing with. Case in point is my Magnavox T-940 AstroSonic. The IF gain would drift down as the set warmed up due to the resistors drifting up thus dropping the plate voltage. As an experiment I dynamically tested each resistor in circuit, Simpson 260 on the leads while heating the suspected resistor with a soldering iron at 45 volts (220F tip) and watched it drift up beyond the 10% tolerance rating. The set spent its first 14 years entertaining us kids, been in the family since new and it's going to get all new resistors in the near future.

Interesting. My only experience with "really" old stuff is two receivers from the early 60s, which mostly used the axial "ceracaps" not the disc types like you're thinking of and a few electrolytics. I have been told by different people that the ceracaps are usually good and also that they're garbage, answer depends on who you talk to LOL. All I actually know is on my H.H. Scott receiver one of the ceracaps just got replaced because that and a couple weak tubes were what was keeping the MPX from working correctly. Most PIOs in audio land are actually for speaker crossovers and there they tend to have indefinite life. I don't think I've seen many films in tube gear, only more modern solid state stuff and again in speaker crossovers, so they don't get exposed to really high temps unless they're in a power amp and even then they're usually away from the output transistors.