30" Dumont/Crosley on eBay!!

[andy]

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[jshorva65]

I believe that set is based on the RA-119 design, but I noticed a significant difference between the Crosley version and the original Dumont. The Crosley chassis was possibly made by Dumont, but definitely a stripped-down version. Crosley's set lacks the Sola self-regulating power transformer(s) that was a feature exclusive to Dumont sets at the time. Incidentally, a Sola "ferroresonant" transformer was later used by Zenith on solid-state color chassis to provide regulated B+ in many models from the 1970's. Notice that the Crosley's power transformer is a conventional EI shell design mounted horizontally into a cutout on the chassis like many RCA sets (630TS, 721TS, etc.). The Dumont RA-119 photo shows the TWO vertically-mounted Sola transformers. Apparently, the one on the upper chassis powers the radio circuitry plus the RF/IF/Video/Audio of the tv while the one on the lower chassis powers the tv set's Sweep/HV circuits. Behind them, you'll likely see the large 1.75uF/850VAC oil-filled capacitors that were connected across the HV secondary. Those Sola transformers are HUGE (about twice the size of the transformer RCA used to power the 30-tube 630TS chassis). Notice that the Sola unit's height is about twice the overall width of the conventional transformer on the Crosley chassis (even though there's only ONE power transformer in the Crosley, located on the lower chassis). The Sola units aren't very efficient, but they produce fantastic voltage regulation over a wide range of line voltage and load current variation. They're designed to operate with a saturated core (and therefore produce LOTS of heat) to produce an output waveform that's essentially a squarewave. During my college years, I did some testing on one that I bought from a retired tv repair tech and it produced 800VAC+/-5%@100-800mA. Unfortunately, the transformer and cap weren't still attached to a vintage tv when I bought them, but the system made for some great experiments. I still have the V vs. I data that I wrote down from the tests (somewhere) and the transformer and cap are now powering the 50W/CH EL34 stereo amp that I built in 1992. The B+ (450VDC) is regulated to +/- 1% from 120mA-480mA by the electronic regulator (two 6AS7G tubes and a 6AU6) located behind the transformer. Starting up, the transformer makes a noise that resembles that of the compressor in a refrigerator. My Sola transformer has a 117V primary, 400-175-0-175-400 HV secondary, plus one 5V and two 6.3V windings. After about an hour of full-load operation, it's NORMAL for the case to be too hot to touch.

Originally posted by jshorva65
The Dumont RA-119 photo shows the TWO vertically-mounted Sola transformers. Apparently, the one on the upper chassis powers the radio circuitry plus the RF/IF/Video/Audio of the tv while the one on the lower chassis powers the tv set's Sweep/HV circuits.

The main (vertically mounted) chassis in the RA-119 includes the H & V sweep circuits in addition to the RF/IF/Video/Audio of the TV. There is no radio circuitry; FM radio is received via the continuous tuner and TV sound IF/audio stages.

The bottom chassis, which has its own B+ supply, is strictly a regulated 25 KV supply for the CRT, . There are (4) 6BG6 tubes: two on the main chassis operate in parallel to provide horizontal sweep. The other two, on the HV chassis, operate in parallel to drive the HV transformer (the HV supply has its own oscillator).

Since the HV supply would continue to operate in the event of a H or V sweep failure, possibly damaging the CRT, protection circuitry monitors the sweep and will not turn on the HV supply until sweep is present. This is accomplished by tubes driving relays!

[jshorva65]

The bottom chassis, which has its own B+ supply, is strictly a regulated 25 KV supply for the CRT, . There are (4) 6BG6 tubes: two on the main chassis operate in parallel to provide horizontal sweep. The other two, on the HV chassis, operate in parallel to drive the HV transformer (the HV supply has its own oscillator).

I'm not sure how I missed the earlier description of the RA-119's regulated HV supply, but it looks like the Crosley chassis is of a similar design. I see that there's a power transformer on the upper chassis on closer inspection, but only the end bell protrudes through the chassis cutout (like some RCA models, including 721TS, where the transformer was mounted under the chassis with only the end bell above the chassis).

Drifting somewhat off the topic of the 30" Crosley, but sticking with the topic of big-screen Dumont sets, wasn't there a Dumont (RA-100 or RA-101) with a 20" CRT in which the tv/radio section consisted of FOUR chassis? As I recall, an old-timer in the tv service business told me that set used several 6AS7G tubes in parallel on one of its chassis. He said they were the vertical sweep output tubes,

Originally posted by jshorva65


I see that there's a power transformer on the upper chassis on closer inspection, but only the end bell protrudes through the chassis cutout . . . .

wasn't there a Dumont (RA-100 or RA-101) with a 20" CRT in which the tv/radio section consisted of FOUR chassis?

John,

I missed seeing that 2nd power transformer on the Crosley . . .
re: your question about the 20" DuMont . . . YES! It is the RA-101 "Custom" made in 1946, and can be seen on Steve McVoy's web site at the following link: http://www.earlytelevision.org/dumontra-101.html

Du Mont made an earlier 20" set in 1940 (see below). It is the model 195 and uses a 20AP4 picture tube, which is unusual in that it is electrostatically deflected and has an intensifier ring next to the screen. This at the time when RCA's and GE's top-of-the-line sets had 12" CRT's!

Here is the model 195. I couldn't attach this image to the previous post.

[Eric H]

Well that explains something, my 49 Crosley with the 12" DuMont chassis has a huge power transformer.

Eric

[ChuckA]

Bill,

You can see the 20" RA-101A in the Westminster cabinet at my site http://www.myvintagetv.com/dumont_101a.htm. Actually there are 5 chassis, if you want to count the outboard horizontal PLL.

Chuck

[jshorva65]

I don't see any Sola self-regulating power transformers on any of the RA-101A's chassis assemblies. Was this transformer perhaps a postwar invention? Chuck mentioned in his description that the RA-101A was designed during the war, uses the same potentially lethal 60-Hz HV supply technology of pre-war designs, and that the RA-101B was equipped with a much safer RF supply for its HV. Very interesting. I don't see a thread specifically about the evolution of key manufactureres' designs with advances in technology...or of how some advances in technology were direct results of a demand for bigger tv screens, safer hv supplies, more reliable circuitry, better picture definition, lower cost, smaller size, etc. Perhaps separate threads covering the circuitry of early sets from an engineering perspective would be of historical interest...maybe an RCA thread and a Dumont thread since these two names were virtually synonymous with television between about 1939 and 1954. Speaking of Dumont, I'm curious to know why they would sell the design for what later became the Trinitron tube to Sony. Wasn't it Dumont that invented this single-gun tri-color tube?

Originally posted by jshorva65
Chuck mentioned in his description that the RA-101A was designed during the war, uses the same potentially lethal 60-Hz HV supply technology of pre-war designs, and that the RA-101B was equipped with a much safer RF supply for its HV. . . . Speaking of Dumont, I'm curious to know why they would sell the design for what later became the Trinitron tube to Sony. Wasn't it Dumont that invented this single-gun tri-color tube?

The beginning of post-war manufacturing appears to be the transition point from lethal 60 Hz supplies to flyback & RF supplies. Philo Farnsworth invented the flyback HV supply in the early 1930's and held a patent on it. This may explain why other manufacturers did not initially use it. (Farnsworth patent #2,059,219 "Generation of the High Voltage from the Horizontal Scan Frequency" issued Nov. 3 1936).

Re: DuMont
The tube that led to the Trinitron was the "Lawrence" tube, invented by Dr. E. O. Lawrence, who also invented the Cyclotron. This was a concept on paper only, Dr. Lawrence never built the tube. DuMont obtained the rights to it and attempted to build it, discovering that the design was flawed. They had named it the "Chromatron" and were working to correct the design flaws when Paramount Pictures, who owned the controlling interest in DuMont, forced them to sell it to Sony for the cash. Sony then completed the development work, and introduced it as the Trinitron. Paramount's interest in DuMont was financial only, they were not interested in the development of television. They ultimately caused the collapse of DuMont.

[Marlin Mackley]

Awright Eric, now I got a BONE to pick with you! I am close to Ohio, single, and nuts, and you pointed out this thing to me! Eric.
Ummm... I am broke but am interested in it. Normally I would ambush this kind of sale but I don't want to tread on any toes. I hope nobody is gonna get p....d if I go for it. I don't want to get into a bidding war with friends.

Well.. here goes, wish me luck!
Marlin

[ChuckA]

Marlin,

Looks like you're hell bent on getting that Crosley set!


Good Luck


Chuck

[Marlin Mackley]

Chuck;
Yup, I am a fanatic without a cause and I believe in it!

I just realized that this thing won't fit in my van so if successful will hafta borrow a pickup and use GOOD tarps. Counting my chickens before they cross the road of course....
Marlin

[Rob]

Marlin,

Assuming you are successful, and we all are rooting for ya bud! , put blankets between the set and the tarp, especially if it is one of those newfangled cheap tarps, as the wind fluttering will destroy the outside of the set otherwise. I know.

Rob

[Marlin Mackley]

Rob;
Thanks for the advice. The tarp I have is a good one and I got lotsa blankets. I hauled a 6 foot book case 550 miles from Dallas two weeks ago on top of the van and it was unscathed. I do miss my old big van though. A Dodge streach Ram 250 with 1 ton springs. Now THAT could haul some tv's!
Marlin