Recently Acquired 1969 Motorola Color Tube Tv

[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.)

[Lain94]

Originally Posted by 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.)

Germanium whiskers? Never heard of them, I learned something new today! I have heard of tin whiskers though and how they are a problem in particular with many old pots in electronics and can cause at best an annoying intermittent popping sound from shorts, or at worst cause a chain reaction of issues. I always knew germanium transistors were more prone to fail than the newer silicon ones. I also knew germanium transistors would blow up but I did not realize that germanium could grow whiskers!

I will look over the old tvs I am working on to see just how many germanium are in these tvs and test them all.

[Alex KL-1]

Originally Posted by Lain94

Germanium whiskers? Never heard of them, I learned something new today! I have heard of tin whiskers though and how they are a problem in particular with many old pots in electronics and can cause at best an annoying intermittent popping sound from shorts, or at worst cause a chain reaction of issues. I always knew germanium transistors were more prone to fail than the newer silicon ones. I also knew germanium transistors would blow up but I did not realize that germanium could grow whiskers!

I will look over the old tvs I am working on to see just how many germanium are in these tvs and test them all.

I've heard about this: https://nepp.nasa.gov/whisker/anecdo...tor/index.html about these transistors. According with this investigation, the can is responsible for wiskers in classic old transistors, but I don't know if germanium is also responsible in some form/model also.

[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.

[Electronic M]

Originally Posted by n8nagel

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.

PIO caps in tube gear are usually Japanese made and usually found in Japanese made TVs (Motorola used some Japanese made parts as it was trying to get friendly with Matsushita), and they tend to be bad (electrically leaky).

The tubular ceramics were made by a variety of companies across 3 decades. I've seen some sets where they were fine and I've seen some sets where they were open or shorted. In GE Portacolors they tend to explode and spray bits of conductive foil all over the circuit board. In the newest application I'm familiar with Zenith 22-5001 safety caps used in CCII TVs of the 70s they're used in the flyback circuit and when they open they cause the HV to skyrocket, and if they short they trip the breaker on the TV...

[Lain94]

Originally Posted by Electronic M

PIO caps in tube gear are usually Japanese made and usually found in Japanese made TVs (Motorola used some Japanese made parts as it was trying to get friendly with Matsushita), and they tend to be bad (electrically leaky).

The tubular ceramics were made by a variety of companies across 3 decades. I've seen some sets where they were fine and I've seen some sets where they were open or shorted. In GE Portacolors they tend to explode and spray bits of conductive foil all over the circuit board. In the newest application I'm familiar with Zenith 22-5001 safety caps used in CCII TVs of the 70s they're used in the flyback circuit and when they open they cause the HV to skyrocket, and if they short they trip the breaker on the TV...

Yeah sometimes they do actually work and are ok, it is kind of a gamble. I don't believe that wax paper ceramic caps can be reformed at all like electrolytics can they? Regardless after seeing what happened to one in my motorola, and how it just suddenly blew up and flung ceramic shrapnel out the tv....yeah I will never trust those caps ever again. Ceramic safety cap fool me once, shame on you old wax paper safety cap. Fool me twice? Not gonna be a second time for that lol.

[Electronic M]

Originally Posted by Lain94

Yeah sometimes they do actually work and are ok, it is kind of a gamble. I don't believe that wax paper ceramic caps can be reformed at all like electrolytics can they? Regardless after seeing what happened to one in my motorola, and how it just suddenly blew up and flung ceramic shrapnel out the tv....yeah I will never trust those caps ever again. Ceramic safety cap fool me once, shame on you old wax paper safety cap. Fool me twice? Not gonna be a second time for that lol.

Paper dielectric caps typically don't reform, and even if they do is it really worth the risk?

[ARC Tech-109]

Tin whiskers were job security for the GE MASTR guys as they would grow in the front end castings and short out the helicals causing the receiver to go deaf. They also used germaniums in the EP38A10 regulator section and they would often go on strike without warning taking the +10v supply down.

[Yamamaya42]

A non polarized electrolytic capacitor is used when the circuit is primarily AC, biased with little or no DC voltage, so using a polarized one would be quite detrimental.

[Alex KL-1]

From some old makers datasheet, for "normal" electros I see that is possible to use with <10% rated voltage in reverse; ie. a 63V cap will survive to a "-6.3V" according with this. And this applies to a superimposed AC also.
If AC+DC is less than this rule of thumb, I think that is possible to use. Or at least for testing.
In fact, I accidentally prove it sometimes
Note: the maximum AC current is also to be in account, but is unlikely to be too high on a normal TV subcircuits.

[Alex KL-1]

Originally Posted by Alex KL-1

From some old makers datasheet, for "normal" electros I see that is possible to use with <10% rated voltage in reverse; ie. a 63V cap will survive to a "-6.3V" according with this. And this applies to a superimposed AC also.
If AC+DC is less than this rule of thumb, I think that is possible to use. Or at least for testing.
In fact, I accidentally prove it sometimes
Note: the maximum AC current is also to be in account, but is unlikely to be too high on a normal TV subcircuits.

Of course, will be a waste of big size capacitor, but at least, guaranteed for testing.

[old_tv_nut]

Another thing to try for replacing a non-polar electrolytic cap is to get two polar caps, then wire them in series with opposite polarity. However, this may be a problem in high-current applications like the convergence circuit. Better to be safe and get an actual non-polar replacement.

What value and rating is this cap?