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.

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. :scratch2:

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

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

I believe they both date from 1947.

Phil Nelson

The transformerless Emersons?

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

What year was VT-71?

[QUOTE=Eric H;3113659]The Motorola VT-71 would probably be one of the first.[/QUOTE

What year was VT-71?

Came out in 1947.

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.

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!

Usually if you see selenium rectifiers, it's a hot chassis set. . .

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.

Another question arises of when the series-string TV arrived in UK/Continental Europe? Doubt if it would have preceded US experience.

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

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. :scratch2:

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. :scratch2:

British ...AC/DC doesn't really arrive until about 1949.

Peter
Thanks for that info, was curious about this. The British really embraced this idea early on, not sure if it was because of aggressive price competition or the challenge of an elegant engineering solution?

I think it would be simply the cost reduction of not supplying a beefy mains transformer.

Peter

IIRC the Britts have 240VAC service so I have to imagine that (at least for radios) it had to be a challenge getting the tube heaters to sum up to that voltage.

Yes, transformerless valve (tube) radios in the UK were pretty horrible things with large resistive droppers throwing away heat. Capacitive droppers are a possibility but were probably not favoured again on cost grounds.

Peter

Yes, transformerless valve (tube) radios in the UK were pretty horrible things with large resistive droppers throwing away heat. Capacitive droppers are a possibility but were probably not favoured again on cost grounds.

Peter
The AC-DC sets built in the US, weren't only built for cost reasons, but there was a lot of DC districts in the larger cities.
Philco built a few, strictly 110 volt DC sets, in the early 30's. They used paper power supply caps, in case it was connected reverse polarity.
BTW, didn't Britain have DC districts in some of the larger cities, as well.

Yes, leaving aside industrial supplies it seems that there were still a few areas with DC supplies right into the 1960s.

http://www.vintage-radio.net/forum/showthread.php?t=41380

Peter

Yes, leaving aside industrial supplies it seems that there were still a few areas with DC supplies right into the 1960s.

http://www.vintage-radio.net/forum/showthread.php?t=41380

Peter

I was reading some information on early British television, at the website, "405 alive".
I never realized that, there was such a thing as a TRF television set. :scratch2: I know the US, had some entry-level sets, but never a TRF design. :boring:

Quite a few early British TVs were TRF. There was only 1 TV channel and no immediate prospect of more so a fixed tuned TRF was a simple and economical approach. TRF designs continued to appear until around 1952, with different models being sold in different regions which used different channels for the BBC service.

AFAIK the first British set without a mains transformer was the Pye B18T from July 1948: http://www.thevalvepage.com/tvmanu/pye/body_pye.htm this was also the first Briitish set to employ flyback EHT. It was also a TRF.

Both Jeffrey and I are owners of early British TRF sets. The TRF section is very obvious when you remove the back of these sets.

Peter

http://www.scottpeter.pwp.blueyonder.co.uk/hmvback2.jpg

...Pye B18T from July 1948: http://www.thevalvepage.com/tvmanu/pye/body_pye.htm...

Good informative link, their W.W. Ad (below pictures) claims it was the first with direct-to-AC power.
There would be no turning back now, other manufacturers would have to follow!

The British had now found a way to reduce the price of television sets!
They had found two ways, the other was to quote the price in Guineas!

Vacuum tube design minimalism reaches its apotheosis with the GE Porta-Color. Even the Japanese couldn't beat it on price - and they had a similar vertically-integrated large corporation model to GE.

Kuba says "we can make money in Europe with this TV". Their version has a single diode to obtain required B+ from 220vAC, add a few more diodes for Simple-PAL, bringing affordability to the marketplace.

Just 8 years after GE ceased production of the profitable Porta-Color, they sold all GE & RCA TV business to the French who believed they make money building TVs in the US - second guessing Jack Welch of GE? How'd it go? The French Co's stock 'TCH' went from €600 down to €1. A bigger crash than even the high flying Northern Telecom of Canada.