Very early TV sets (1930's) used electrostatic deflection and a CRT that ran on about 5 KV I have seen examples that generated the required voltage from a line powered transformer.
Most B&W TV sets did use a flyback step up circuit to generate the 10+ KV needed for the larger electromagnetic CRT's, however it was not a true SMPS since all of them ran open loop. The earliest "sweep tube" was the 6BG6 which is derived from the 6L6 family. The 6DQ6 came later (50's maybe).
The advent of color TV required a regulated HV supply since there were now 3 distinct electron beams inside the CRT, each operating at a different current. These sets used a shunt regulator operating at 27,000 volts. Again, open loop. Late 1950's. Shunt regulator tube was a 6BK4.
When it was discovered that a triode with 27KV on it's plate makes an excellent X-ray generator, the shunt regulator was moved to the primary side of the flyback where it only sees a few KV. Quasi open loop, since the output voltage is not sampled and used as feedback. Late 1960's early 70's.
Some solid state TV sets did actually begin regulating the HV via a tapped resistor on the 27KV supply that also supplied the focus voltage (about 4 KV). I remember an RCA XL100 that did this in the early 70's. Flyback switching was done using a pair of SCR's since suitable transistors for a 25 inch TV were not yet available. I left the TV repair world about then.
The earliest example of a tube SMPS that I have seen was used in the Tektronix 504 scope. It used a 6DQ6 to generate all the high voltages needed for the scopes operation. There are multiple outputs similar to a modern computer SPMS, and regulation is achieved by a feedback loop from one of the output voltages which controls the screen grid of the switching tube. Vintage, early 1960's.
I worked in a calibration lab in the early 70's where we maintained about 50 of these that ran 24/7. Most often needed repair, dim display caused by a weak 6DQ6.
The schematic is at the end of the service manual, which is here.
http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Tek/504.v6.pdf
True, hence the word "flyback" whose origin is that the HV was produced during the short period in which the electron beam returned to the beginning of a new scan line (flew back).
Not to forget the heater current for the HV rectifier tube was taken from a single loop of wire wound around one leg of the flyback xfrm's core.
And the plate voltage of the HOTube was stepped up from 250 to 350+ diverting the energy from the leakage inductance of the xfrm into a cap by means of yet another high tech tube, the booster diode; this is called a "regenerative snubber" nowadays ...
b.t.w. most everything in this part of the forum is "talking 50/60 years old Technology" ...
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