Re: 549 transformer question


Michael A. Terrell
 

Chuck Harris wrote:
Hi Dave,

I have thought about this over the last several days, and you
are probably right. I never tested my conjecture, it was just
an inkling that I had.

Tektronix wasn't a stupid company, they did things usually
for good reason. I am sure they used sine wave oscillators for
HV production because they were in the transient measurement
business, and knew a slew of 50KHz high voltage flyback harmonics
would be just too darn much fun to suppress, so they settled for
an easier to filter, more harmonic free sine wave approach.

And, yet, I have still pondered their choice for quite a few
years. Mostly, because it also appears to have been one born
of expedience.

I don't suppose I would have ever even pondered the HV section
of tektronix scopes, had they just worked. I certainly never
did until I was introduced to a pair of time worn 545B and 547
scopes that entered my collection.

And yet, as smart as Tektronix was, they had a host of HVT failures
when the TV set manufacturers didn't. And it took them 10 years
of seemingly fumbling around to come up with a solution.
Chuck, TVs had a lot of bad fybacks, often burnt to a crisp. The early, wax sealed were the worst. The heat they generated would cause the coating to deform, and if the home wasn't air conditioned you would find drops of wax on the floor, under he set on some models. They were a lot more reliable after the switched to the silicone rubber molded designs, but it wasn't unusual to have to modify a chassis because the OEM had to redesign a flyback. A couple GE color flybacks came in a new steel subchassis, because there were so many differences. Spring and fall in S.W. Ohio had the highest failure rate, in homes with people who smoked. Nicotine would cover the outside of the CRT, increasing the load on the Second Anode supply. We saw about 90% of the failures during these times as the humidity spiked, making the nicotine more conductive.

BTW, the first color TVs used the venerable 807 tube for the Horizontal output tube. I laugh when hams deride using 'sweep tubes' for RF, when they started out as improved versions of the 807. The first change was to re-base it from a five pin base to an octal base.

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