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Quick question 564B
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Chuck Harris
It is a cute little scope, but very low bandwidth,
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something like 10MHz. Its HV transformer suffers from the epoxy disease that affects 547 scopes. They are quiet, not having a fan, and the plugins contain all the deflection circuitry (as I recall). I used to like them quite a lot back in the day, for audio work. The storage functions are finicky. -Chuck Harris Stephen wrote: Hi all, and Happy New Year 2021, |
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Chuck,
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Please tell me more about the 564B HV transformer epoxy disease! Thanks! Pete On Sunday, January 3, 2021, 8:07:20 a.m. EST, Chuck Harris <cfharris@...> wrote: It is a cute little scope, but very low bandwidth, something like 10MHz.? Its HV transformer suffers from the epoxy disease that affects 547 scopes. They are quiet, not having a fan, and the plugins contain all the deflection circuitry (as I recall). I used to like them quite a lot back in the day, for audio work. The storage functions are finicky. -Chuck Harris Stephen wrote: Hi all, and Happy New Year 2021, |
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Chuck Harris
It is a pretty well known phenomenon... well discussed
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on this group over the years... often by me. Around about the time the 547/545B scopes got designed, tektronix decided to make a universal HV compartment that was plastic, contained the EHT, the 5642 rectifiers, and the capacitors and resistors. The compartment was sealed to help keep dirt, critters, and carbon dust out. The sealing also prevented good cooling due to air motion. This required the transformer to run at a higher temperature than was allowed in the earlier 500 series scopes. The earlier scopes used beeswax to impregnate the transformer windings and tektronix was afraid that the wax would melt in the new sealed compartments (newsflash: it doesn't to any great degree... but I digress.) Instead of using beeswax to improve the HV breakdown characteristics of the EHT, they used an epoxy varnish to coat the windings. Because epoxy is rigid, and the tiny wires used in the EHT were easily broken, they added something to the epoxy to soften it, and probably also something to act as a fire retardant. The epoxy degraded over time, and greatly increased the losses inside of the EHT, making it thermally runaway. This has been dubbed the transformer epoxy disease. Some improvement has been witnessed from long baking at high temperatures, but it is only temporary, as the epoxy truly has changed. The only real answer is to replace the winding with new. Beeswax works better than the epoxy as when it gets laden with moisture, it gets hot, melts the beeswax, and releases the water vapor. Once the water vapor is gone, the EHT goes back to its usual warm self. The 560 series transformers were epoxy varnished, and then potted in an aluminum can using a clear silicon RTV. They still fail at about the same rate as the open core transformers in the 545B/547. Some have opined that the failure mechanism is due to the fire retardant that was added to the epoxy... if there was a fire retardant added to the epoxy. This opinion comes from a long history of problems that have come from fire retardant additives. -Chuck Harris petertech99h via groups.io wrote:
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Brenda
Hello Chuck,
My RM565 does have the aluminum can, but so far, it has been working like a champ so far. I am assuming that this will eventually fail. I do hope that it will hold out. But both of my 561A's and my 564 have the HV transformer out in the open. Not sealed in a plastic compartment. So, my question is, are these prone to the HV transformer disease as well? Both of my 561A's work very well so far but my 564 is in the project pile for now. Brenda |
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Chuck Harris
I don't like to assume anything. When they fail, worry about them.
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Some go on forever, it seems. Any of the transformers that use the brown epoxy are likely to fail at some point. It doesn't seem to matter if they are just dipped in a thin coat of epoxy, or molded in a block of epoxy. Somewhere during the 5000 and 7000 series tek seemed to get the EHT transformers right. They still did some strange things that caused failures, but at least the brown epoxy debacle was over. -Chuck Harris Brenda via groups.io wrote: Hello Chuck, |
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I have seen tektronix ferrite transformers broken for epoxy stress
-----Mensaje original----- De: [email protected] [mailto:[email protected]] En nombre de Chuck Harris Enviado el: martes, 5 de enero de 2021 4:52 Para: [email protected] Asunto: Re: [TekScopes] Quick question 564B It is a pretty well known phenomenon... well discussed on this group over the years... often by me. Around about the time the 547/545B scopes got designed, tektronix decided to make a universal HV compartment that was plastic, contained the EHT, the 5642 rectifiers, and the capacitors and resistors. The compartment was sealed to help keep dirt, critters, and carbon dust out. The sealing also prevented good cooling due to air motion. This required the transformer to run at a higher temperature than was allowed in the earlier 500 series scopes. The earlier scopes used beeswax to impregnate the transformer windings and tektronix was afraid that the wax would melt in the new sealed compartments (newsflash: it doesn't to any great degree... but I digress.) Instead of using beeswax to improve the HV breakdown characteristics of the EHT, they used an epoxy varnish to coat the windings. Because epoxy is rigid, and the tiny wires used in the EHT were easily broken, they added something to the epoxy to soften it, and probably also something to act as a fire retardant. The epoxy degraded over time, and greatly increased the losses inside of the EHT, making it thermally runaway. This has been dubbed the transformer epoxy disease. Some improvement has been witnessed from long baking at high temperatures, but it is only temporary, as the epoxy truly has changed. The only real answer is to replace the winding with new. Beeswax works better than the epoxy as when it gets laden with moisture, it gets hot, melts the beeswax, and releases the water vapor. Once the water vapor is gone, the EHT goes back to its usual warm self. The 560 series transformers were epoxy varnished, and then potted in an aluminum can using a clear silicon RTV. They still fail at about the same rate as the open core transformers in the 545B/547. Some have opined that the failure mechanism is due to the fire retardant that was added to the epoxy... if there was a fire retardant added to the epoxy. This opinion comes from a long history of problems that have come from fire retardant additives. -Chuck Harris petertech99h via groups.io wrote:
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I own a 561A and two 564Bs. They were mainstream in the mid 1960s. 10MHz bandwidth and a far sharper trace than you will ever see on a DSO. They all take the same series of two plugins, Vertical and Horizontal; (interchangeable if you like vertical traces or you could use two Vertical units for Lissajous figures and LF phase comparisons). The A version in both cases had a vacuum tube-based LV power supply, the B was all solid-state. Not such a big differentiation since the plug-ins were all hybrid tube/transistor units. There were lots of plug-ins, including sampling to about 500 MHz IIRC, SAs, single and dual differential amps, a wireable dual op amp unit, and up to 4 input channels. I have around 20 different plug-in types. The biggest deal about this family was the 564. It's a split-screen STORAGE scope storing waveforms electrostatically on the phosphor screen using secondary emission, with the upper and lower halves of the screen separately eraseable and settable to storage or non-storage mode. I believe this was the first widely adopted storage scope from any manufacturer. More than any other Tek units, this was the family that popularized plug-in scopes, so much so that HP started by disparaging them and ended by imitating them. One of my 564Bs is a Mod 121, which adds variable time delay auto-erase. The remark that the storage function is "finicky" is mostly only true if you try to calibrate it without following the manual. Once properly adjusted, mine have remained stable. Storage display contrast is a bit low, but very useable within the 10MHz bandwidth. They are also cheap to buy today. They're mostly reliable, with two well known problems: the CRT filament is supplied by a dedicated winding on the main power transformer but is elevated to -3300V by the HVPS. This has led to failures of the paper insulation on that winding. I fixed my 561A by adding a separate transformer with the secondary rewound (on a side-by-side nylon bobbin) with suitable insulation and leads long enough to reach directly into the HVPS box without splices or terminals. The leads were individually insulated with small tubing (there's only 6.3VAC between them, and double insulated with shrink tubing over that to withstand the 3300V. The other problem is the potting failure on the HVPS transformer. I think it may only affect the B series, but I have never had the problem. The 561/564 family could be thought of as the precursor to the 7000 series, and my main scope today is a 7854.
Cliff |
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widgethunter
Have 561A/Bs and 565 in service and consider them a favorite for general bench work.Had one bad 565 (bad filament winding - my 1st Tek scope) but now own two that work.GREAT scopes, very reliable.
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The 500 series was replaced by the 5000 series - it was not the precursor to the 7000s. Bernd Schroder -----Original Message-----
From: Cliff Carrie <cliffcarrie@...> To: [email protected] Sent: Tue, Jan 5, 2021 7:49 pm Subject: Re: [TekScopes] Quick question 564B I own a 561A and two 564Bs. They were mainstream in the mid 1960s. 10MHz bandwidth and a far sharper trace than you will ever see on a DSO. They all take the same series of two plugins, Vertical and Horizontal; (interchangeable if you like vertical traces or you could use two Vertical units for Lissajous figures and LF phase comparisons). The A version in both cases had a vacuum tube-based LV power supply, the B was all solid-state. Not such a big differentiation since the plug-ins were all hybrid tube/transistor units. There were lots of plug-ins, including sampling to about 500 MHz IIRC, SAs, single and dual differential amps, a wireable dual op amp unit, and up to 4 input channels. I have around 20 different plug-in types. The biggest deal about this family was the 564. It's a split-screen STORAGE scope storing waveforms electrostatically on the phosphor screen using secondary emission, with the upper and lower halves of the screen separately eraseable and settable to storage or non-storage mode. I believe this was the first widely adopted storage scope from any manufacturer. More than any other Tek units, this was the family that popularized plug-in scopes, so much so that HP started by disparaging them and ended by imitating them. One of my 564Bs is a Mod 121, which adds variable time delay auto-erase. The remark that the storage function is "finicky" is mostly only true if you try to calibrate it without following the manual. Once properly adjusted, mine have remained stable. Storage display contrast is a bit low, but very useable within the 10MHz bandwidth. They are also cheap to buy today. They're mostly reliable, with two well known problems: the CRT filament is supplied by a? dedicated winding on the main power transformer but is elevated to -3300V by the HVPS. This has led to failures of the paper insulation on that winding. I fixed my 561A by adding a separate transformer with the secondary rewound (on a side-by-side nylon bobbin) with suitable insulation and leads long enough to reach directly into the HVPS box without splices or terminals. The leads were individually insulated with small tubing (there's only 6.3VAC between them, and double insulated with shrink tubing over that to withstand the 3300V. The other problem is the potting failure on the HVPS transformer. I think it may only affect the B series, but I have never had the problem. The 561/564 family could be thought of as the precursor to the 7000 series, and my main scope today is a 7854. Cliff |
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