About 50 years ago, I was asked to make a high voltage constant current supply for a medical research lab. The requirement was
600V at up to 30mA. I stacked two EL84 tubes in cascode (a 6L6GC cost more and was less easily available). Television arrived here in this remote place a decade later and I used TV FB transistors in an apparatus for a local college.Looking back on those times, I'm wondering when high-voltage power transistors first became common in the more advanced countries.
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** I have a home brew prototype tube amp module in my workshop using p-p pair of EL84s in low bias class AB. B+ is 650V and screens at 325VDC.
Power out is 60W sine wave, with no sign of red plating.
The TO3 pak BU208 is an early TV flyback type - appeared in or about 1971.
..... Phil
Early 1970s , there was a short period around 1970 when TV sets were all solid state except for the horizontal drive!
piglet (Using google groups on a phone while travelling in Africa)
solid state except for the horizontal drive!
Motorola's 'Quasar' solid state color TVS came out in the late '60. they only used a vacuum tube for the HV rectifier and the CRT. The audio output transistor was around 125VDC. It used an Allen Bradley carbon comp resisto r for a fuse, Anything else wouldn't open in time to protect the output tra nsformer.
My dad bought one of these TVs when they first came out. I still have it.
Dunno. I used an 811A in an experimental setup in 1991 though. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
That whole "with its works in a drawer" thing was apparently an early example of turning a bug into a feature--those things were notoriously unreliable.
Cheers
Phil "grew up watching Admirals" Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Here's a pretty good article:
The Apple III computer (1980) PSU used a MJ8503 transistor in TO-3 package as the flyback switch, it was rated for 800 volts CE, 150 watts dissipation, 10 amp pulse current, and 2000 nanosecond rise and fall times, so switching frequencies into the 10s of khz.
As I understand it that was a state-of-the-art high-voltage power transistor of the late 1970s.
BU208 & its relatives became common in TVs in the 70s. Before the 208 TVs normally used 2 transistors stacked or a horizontal output valve. There were other oddballs like SCRs used occasionally but I don't remember when.
NT
Television first came to my region when some army people discovered in 1980 that they could catch a station in neighbouring Bangladesh. For the first year or so after that, only B&W Indian sets were available and they all used a BU205 (not BU208). Then smugglers started bringing in Japanese colour TVs via Burma - National (Panasonic), Sony, Toshiba, JVC, Sansui........
Repairing TVs took up much of my time during the '80s and early
90s. It was well nigh impossible to stock all of the variety of high voltage transistors used by those Japanese models. Luckily, a BU508 and a few Japanese types from the 2SD and 2SC series could replace most of them. My own 27-inch Sony from the early '80s used an IGBT.
I heard that there was a period when car radios used tubes with
12V anode supply in the RF sections and transistors for AF output. The purpose was to obviate the need for a vibrator to generate a high voltage plate supply.I doubt IGBT existed early 1980s pretty sure what you?re thinking o f was GTO gate turn off thyristor which enjoyed a brief summer as horizonta l output driver device, I think mainly one or two mainly European set maker s used them.
piglet
Within just the last decade, single transistors finally overtook tubes even in niche circuits -- to be honest, this is probably not so much a technological leap, as it simply being economical for manufacturers to target that space.
Example: IXYS IXTX1R4N450HV
4.5kV 1.4A 960W 40 ohm 88nCNot that 960W is a realistic figure, as usual, but it's probably good for
100W or more with adequate heatsinking (splurging for a nice thick AlN insulator would be a nice touch, at these voltages).Compare:
6LW6 7kV 1.4Apk? 40W 40pFLittle data on this particular tube, but we can assume it saturates somewhere around 50-100V at that 1.4A peak, and maybe is capable of 2A or more (at somewhat higher voltage drop). So, comparable on-resistance. Likewise, safe to assume around 150V grid drive is needed to switch it, giving a grid charge somewhere around 10nC (which, at the 15 times higher voltage swing, is 1.7 times more grid power).
The MOSFET may not perform very well, as MOSFETs go; the long channel has a long transit time. Though it seems to be limited by internal R_G more than that (t_r = 60ns is the published figure).
The tube can go about as fast as you can push it, which is pretty challenging for so much swing (especially if you only have more tubes to generate that swing), but also suffers from stray inductance through its poorly connected octal socket, and tall body. (Contemporary Compactrons usually made two connections to each grid.)
Anyway, the transistor handily outperforms the tube in most absolute measures... not to mention size and not needing 18W of heater power.
Supposedly there are single MOSFETs and IGBTs out there, rated for upwards of 10kV, using SiC. Haven't seen anything near that from the usual suppliers; they may be special order, or restricted (a few would make a lovely near-field EMP generator). Have seen papers discussing their use on distribution lines (so, ~4.8kV AC, direct connection -- no transformer required), for grid and maritime purposes.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/ "Pimpom" wrote in message news:KkqZG.70924$rc6.15448@fx06.ams1... > About 50 years ago, I was asked to make a high voltage constant current > supply for a medical research lab. The requirement was 600V at up to 30mA. > I stacked two EL84 tubes in cascode (a 6L6GC > cost more and was less easily available). Television arrived here in this > remote place a decade later and I used TV FB transistors in an apparatus > for a local college. > > Looking back on those times, I'm wondering when high-voltage power > transistors first became common in the more advanced countries.
Ah, old age. I checked the schematic and the H-out device is a common 2SD725 BJT. The IGBT (or whatever it is) is the pincushion output device. The type number is SG264 but the symbol is obscured by one of several huge characters from an unknown language. A search for the datasheet turns up only unrelated devices.
The TV was apparently a high-end, state-of-the-art model with all kinds of inputs and outputs and connector types. It used a huge number of ICs and discrete parts.
That could be a fet. I have seen pincushion correction done with a medium power MOSFETs and they were just beginning to appear in consumer gear early 1980s.
piglet
Westinghouse were doing 300V in TO82 in 1962 2N1015/6(F) 350V in TO49 in 1962 2N1829/36 350V in TO83 in 1963 2N2129/30 Delco (GM) were doing 300V in TO36 in 1963 2N3079/80 400V in TO3 in 1965. DTS-4xx 500V/600V in TO36 in 1966 2N2582/3/4/5 700Vcex in TO3 in 1968 2N3902
TI(UK)/Sescosem 750V in TO3 in 1968 BU105 550V in TO3 in 1969 BU112
I don't expect any were common before 1970. Darlingtons in 1972.
Lots of articles about safe operating area, and a few about using series devices in regulators up to 1500V input, after
1972.RL
I salvaged BU105s from the scrap pile behind a TV repair shop in the UK around 1970 or 1971, so they must have been in production for a while then.
John
It was still working, 40 years later. I last fired it up in 1999 and it sti ll had a good picture, but it was starting to get 'Fish Eye' where the bond ing was separating from the safety glass.
I converted a metal cased 21" version into my first color monitor in the mi d '80s.
Most problems were caused by idiot techs o handled the connectors and let b ody oils and sweat on them. This set was hit by lightning twice. It blew ou t the RF preamp in the VHF tuner, both times. It had one electrolytic fail, during all those years. It had a 23EGP22 CRT. No doubt the worst rectangul ar color CRT ever built. I replaced it when it was seven years old. It was so gassy that it took over a half hour to get a decent image, if the power had been out. The 'Instant On' feature wasted some power, but it tripled th e useful life of that tube.
I replaced it with a 25" Black Matrix CRT. Everyone who saw it, insisted th at it wasn't the same TV.
The biggest idiots soldered the modules to the chassis connectors, making t hem unrepeatable.
Bendix/ford did that, while GM/Delco had already switched to all transis tor designs. One early GM model had a removable radio, that connected to a power amplifier when you slid it into the rest of the dash mounted radio. I think that was a 1959 model? I should still have the manual, somewhere.
I found a really cool use for the c-b junction of a horizontal-output transistor that accidentally had the ideal doping profile. It's not made any more, of course.
My great little 3KV Bertan 215 bench power supply has one tube inside. I bought a couple of spares.
I'm just going by dates on app notes and spec drwgs. By that date, they will have been in distribution, though unlikely at commodity pricing, while single-sourced.
RL
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