First TV without PwrTransformer?

[NewVista]

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

[Eric H]

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

[dieseljeep]

Originally Posted by Eric H

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

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

[NewVista]

Originally Posted by Eric H

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

What year was VT-71?

[bandersen]

[QUOTE=NewVista;3113697]

Originally Posted by Eric H

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

What year was VT-71?

Came out in 1947.

[Tom Albrecht]

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.

[jr_tech]

Originally Posted by Tom Albrecht

Early Emerson 10" sets included transformerless designs.

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

[dieseljeep]

Originally Posted by jr_tech

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

Our first family TV was the 12" version of that chassis, a later run.
It had two larger selenium rectifiers and two smaller ones. It had two B+ supplies, stacked to provide 390 volts for the vertical sweep. It had a mess of electrolytics, where the five 25Z6's were originally and a ballast tube.
The transformer was rather large and only furnished the 6 volts, for the heaters and a separate 5 volt winding, for the 5V4 damper.
It always amazed me, that they went through all that trouble, instead of just using a regular transformer and vacuum tube rectifier.

[NewVista]

Originally Posted by Tom Albrecht

Indeed. Most 7" electrostatic sets did not have a power transformer...

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!

[dieseljeep]

Originally Posted by Tom Albrecht

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.

I was surprised to see the 7" Emerson Electrostatic set, using only a 140 volt B+ supply.
It was interesting to see how they could do it and everyone else had to use a doubler.
I'm sure, they considered DC operation, as well.

[Tom Albrecht]

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.).

[Zenith26kc20]

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

[Phil Nelson]

I believe they both date from 1947.

Phil Nelson

[NewVista]

Originally Posted by Phil Nelson

I believe they both date from 1947.

Phil Nelson

The transformerless Emersons?

[wa2ise]

Originally Posted by Tom Albrecht

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.

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.