First TV without PwrTransformer?
 

Cost-cutting Hot Chassis, inspired by '40s/'50s tube mantle radio design.
Anyone know who was first? Motorola in the early 1950s?

The Motorola VT-71 would probably be one of the first.

Indeed. Most 7" electrostatic sets did not have a power transformer. The exceptions were cases that did, like the Admiral 7" set. And the stream of transformerless sets never stopped. Early Emerson 10" sets included transformerless designs.

As an interesting side note, Admiral, RCA and Zenith, never built a transformerless set, until the mid-50's, late 1954. :scratch2:

I remember the model 606 with 5 25Z6 rectifiers for B+, but didn't they use a transformer for the 6.3 volt heaters?

jr

There are some strange sets out there with transformers for filaments and voltage doublers for the B+. Zenith had some sets like this, which appear to be "safe" when you see the (relatively large) power transformer, but turn out to be hot chassis designs. A particularly dangerous design for the unsuspecting technician. The Emerson 606 and related designs with all the 25Z6s are also of this type -- exactly as you remembered.

The Emerson 614D and 637A were early cases of 10" Emersons with no power transformer at all. Other examples of relatively early 10" completely transformerless sets include the GE Locomotive (models 800, 805, 10T1, etc.).

When were the 3 inch pilots made? Did they predate the Motorola's?

I believe they both date from 1947.

Phil Nelson

The transformerless Emersons?

What year was VT-71?

[QUOTE=NewVista;3113697]Came out in 1947.

Usually if you see selenium rectifiers, it's a hot chassis set. For some reason, they rarely used vacuum tube rectifiers in series string hot chassis sets. They did use vacuum tube diodes for damper diodes, likely because seleniums were too slow. But most series string sets had excessive heater voltage to burn in power resistors, so a vacuum tube rectifier could have made sense. Something like a 25V @450ma heater, for say 150ma plate current and a PIV around 400V. Yes, you'd have voltage drop to to B+, but seleniums do that too. At the cost of the tube and a socket, you'd save a power resistor and a selenium rectifier. Same amount of heat to ventilate. A "What if" kind of question...

For the filament transformer hot chassis sets, you could throw in a 5V secondary and use a 5U4 with both plates strapped together.

I forgot about the 7" Motorola, definitely late '40s I guess, and many ways to get shocked, like that 750v deflection sawtooth - Oh My how that hurts! - will never make that mistake again!

wa2ise:
Just discovered your excellent webpage on history of AC/DC radios as background for this technology - which led to the adoption of this engineering experience to television - around 1947 it appears.

Another question arises of when the series-string TV arrived in UK/Continental Europe? Doubt if it would have preceded US experience. Anyone know? Perhaps a UK collectors blog could answer this.

I think this is correct. Just post war British sets largely followed pre-war designs and the start or AC/DC doesn't really arrive until about 1949.

Peter