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  #1  
Old 10-29-2014, 11:18 PM
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rca2000 rca2000 is offline
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Did ANY tube (chassis) sets use flyback power for the CRT fil or some other low B+ so

I am just curious..I was VERY surprised to find out that some early solid state BW sets have some B+ source derived from the flyback. I originally did not think this started till the early 1970's. Then...I saw the diagram for the 1968 model SS zenith 19" set--and SOME versions derive most of the low B+ sources from the fly. The fil comes from the Power tranny I believe though.

I was ALSO surprised to see that the 73 model Philco SS chassis --the one that had SCR deflection--used the fly to power the CRT fils. This IS a cold chassis--and DOES have an I-O tranny--so I expected it powered the fil. But No--it ONLY does so when the set is off. When ON--the fly takes that load. Same thing for the Motorola sets with the JA SMPS supply--in standby--a fil tranny powere the fils--BUT--when on--the SMPS does so.

BUT--does anyone out there know--did ANY tube chassis sets--have any fly derived sources(OTHER than the boost or video bias line, or "pulse" signals) for lower B+sources...like nearly ALL SS sets made after about 1978 or so? and did any of the power the CRT fils with the fly ?

Just curious...

Last edited by rca2000; 10-29-2014 at 11:19 PM. Reason: Error
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Old 10-30-2014, 09:04 AM
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zeno zeno is offline
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I know of none, color or B&W. I had worked on a few
of the first 2 19" Zenith SS 19" B&W sets ( one modular & one plug in
transistors) & never noticed it. BTW those & the first 12" are RARE sets!

When you get to transformerless SS sets there are a ton of advantages.
Weight, size, lower value ($) filter caps, well regulated, dont need
power wasting dividers etc. The very fact that tube jobs dont
need regulation & use less filtering makes the added cost &
complexity not worth it.

73 Zeno
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  #3  
Old 10-30-2014, 10:37 AM
old_coot88 old_coot88 is offline
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I know of none either, having been in the trade for some 30+ years. I do remember being quite surprized at the 'radical' new concept of scan-derived power supplies when they started appearing in SS sets.
The concept made total sense. A 'hard switch' (a power transistor or SCRs) driving the flyback enables a much 'stiffer' supply than could be driven by a lossy, heat-dissipating tube.
The biggest problem though, was the rate at which the transistors and SCRs would blow out (which kep us busy).

Last edited by old_coot88; 10-30-2014 at 01:29 PM.
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Old 10-31-2014, 08:56 AM
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Giulio Maiocco Giulio Maiocco is offline
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There were flybacks advertised on some Philips handbooks meant to be utilized with tubes (PL81 and PY81) and the CRT filament power derived from one winding. These sets were mainly portable ones with a special CRT with low filament power (11V 0,068A IIRC) and about 11" diagonal

I personally have never seen one of these sets, but if time premits, I'll scan and post the relevant pages on my Philips handbook

Cheers

Giulio
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Old 11-17-2014, 09:18 PM
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Findm-Keepm Findm-Keepm is offline
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Some Motorola tube color sets had a pulse winding on the bottom of the fly for AGC and color keying/syncing, but no filament or B+ windings. We had one 23EGP22 set that worked, just had cruddy color shadowing caused by a shorted pulse winding on the fly. We held out for a junker set from another shop, and robbed just the bottom winding to fix our set.
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Old 11-18-2014, 06:58 PM
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Well, there was the couple of turns of high voltage wire to run the 1B3 or such very high voltage rectifier tube, but that was done since day one of TV...
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Old 11-19-2014, 09:48 PM
Geoff Bourquin Geoff Bourquin is offline
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I wouldn't think pulling power for low voltage loads would be good for the horizontal output/damper tubes.
Also, in the tube days were there any solid state rectifiers that worked well at 15.75 kc? A tube rectifier for low voltages would have been terribly inefficient.

Last edited by Geoff Bourquin; 11-19-2014 at 09:53 PM.
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Old 11-20-2014, 06:21 PM
old_coot88 old_coot88 is offline
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Quote:
Originally Posted by Geoff Bourquin View Post
I wouldn't think pulling power for low voltage loads would be good for the horizontal output/damper tubes.
Very true. The H.output tube in particular, just to drive the yoke and sustain HV, is already running near its maximum plate dissipation rating. Further loading would push it into red plating.
Tubes are inherently lossy compared to 'hard' SS devices (e.g., power transistors and SCRs) which can drive and sustain a much 'stiffer' supply than tubes can.
Quote:
A tube rectifier for low voltages would have been terribly inefficient.
True, and for the same reason. Too lossy compared to SS diode.
Quote:
Also, in the tube days were there any solid state rectifiers that worked well at 15.75 kc.?
Well, there were selenium stacks used in convergence panels in color sets. Also the boost diodes and 'stick' focus rectifiers in color sets were selenium, as well as stick HV rectifiers in BW sets.
Gotta remember HV is generated not by the 15.75 kc fundamental, but by the sharp "fly-back" interval of that sawtooth wave. That's up in the RF region, equivalent to around 80 kc or so. That's what the HV rect, focus rect etc. were dealing with.

In those days, silicon diodes were not fast enough in those regimes, whereas seleniums were.

Last edited by old_coot88; 11-20-2014 at 06:31 PM.
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  #9  
Old 12-04-2014, 01:41 PM
Alastair E Alastair E is offline
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Many years ago, I had a customer with a Very old Philips G6 hybrid colour set with an equally tired CRT.

As he didn't want to spend anything much on it, and I told him I could temporarily improve things.

I added a separate 4 or 5 turn winding to the Flyback and attached this to the heaters instead of the original supply....
The winding I altered turn by turn over a year or two period to keep the picture sorta OK, the owner knew the writing was on the wall for the set, but it gave them time to save for a replacement....

Eventually--There was more light from the Back of the set--Than the front--Its incredible how much overvoltage a heater can take, providing its ramped up nice and slow--like the line-stage did!!

I was surprised that the line-stage could supply ALL that extra power without seriously reducing the EHT or scan width....

In the end for a larf as I had supplied a replacement set and taken the G6 in Part-Ex, I matched the brightness of the heaters by using a standard variable PSU.
To get approx the same light/whiteness of heaters, I had to put 30 odd volts into the 6.3V 0.9A heater, and it was taking summit like 4A!
--They made 'em to Last in them thar days....
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Old 12-04-2014, 02:15 PM
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Was the horizontal output SS? 30V*4A=120W! the average HO Tube is rated for <20W IIRC, so if it was tube I can't imagine how the horizontal stage could supply that...For more than a few seconds.
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Old 12-04-2014, 06:40 PM
Alastair E Alastair E is offline
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Quote:
Originally Posted by Electronic M View Post
Was the horizontal output SS? 30V*4A=120W! the average HO Tube is rated for <20W IIRC, so if it was tube I can't imagine how the horizontal stage could supply that...For more than a few seconds.
I know--Mad innit! I don't know Why it worked--but it did! The PL519 (bit like a 6KD6, so 45W Plate diss) was obviously working very hard, perhaps a dim glow from its anode--but it kept running for about 3 months like that before the CRT was just dead at the end--Not surprising really--It had got pretty hot too, the blue-lat magnet had melted somewhat and the glass inside the neck had gone silvered!.....

Also--a Line O/P valve is used as a switch--not in a linear mode, therefore dissipation in the valve is lower than one would expect,--bit like when they are used for RF work--you can push a 6KD6 to produce 200W or more of RF energy, same principle applies--the valve is still within its ratings as its used as a switch, the tuned circuit does the rest.....

--Even so though, its a bit mad when you think of it!
--The daft things we do in our youth--I would Never do anything like that now--That thing really was a fire-hazard thinking back.....

Last edited by Alastair E; 12-04-2014 at 06:53 PM.
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Old 12-04-2014, 07:04 PM
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Quote:
Originally Posted by Alastair E View Post
I know--Mad innit! I don't know Why it worked--but it did! The PL519 (bit like a 6KD6, so 45W Plate diss) was obviously working very hard, perhaps a dim glow from its anode--but it kept running for about 3 months like that before the CRT was just dead at the end--Not surprising really--It had got pretty hot too, the blue-lat magnet had melted somewhat and the glass inside the neck had gone silvered!.....

Also--a Line O/P valve is used as a switch--not in a linear mode, therefore dissipation in the valve is lower than one would expect,--bit like when they are used for RF work--you can push a 6KD6 to produce 200W or more of RF energy, same principle applies--the valve is still within its ratings as its used as a switch, the tuned circuit does the rest.....

--Even so though, its a bit mad when you think of it!
--The daft things we do in our youth--I would Never do anything like that now--That thing really was a fire-hazard thinking back.....
Okay NOW I can believe that story. You can get a lot out of switch mode supplies, and tubes can handle several times their rated current/power dissipation if it is in the form of brief impulses. Still pretty amazing the horizontal stage and CRT did not fail catastrophically.
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