When did high-voltage transistors become common?

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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.

Re: When did high-voltage transistors become common?
Pimpom wrote:
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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.  

https://www.radiomuseum.org/tubes/tube_bu208.html



.....  Phil  



Re: When did high-voltage transistors become common?
On Friday, 14 August 2020 at 10:12:23 UTC+1, snipped-for-privacy@gmail.com wrote:
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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

Re: When did high-voltage transistors become common?
On 8/14/2020 2:42 PM, Phil Allison wrote:
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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.

Re: When did high-voltage transistors become common?
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

Re: When did high-voltage transistors become common?
On 8/15/2020 12:43 AM, piglet wrote:
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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.

Re: When did high-voltage transistors become common?
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  

When did high-voltage transistors become common?
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)

Re: When did high-voltage transistors become common?
On Friday, August 14, 2020 at 5:23:26 AM UTC-4, piglet wrote:
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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.

Re: When did high-voltage transistors become common?
On 2020-08-14 06:38, Michael Terrell wrote:
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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
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Re: When did high-voltage transistors become common?
On Friday, August 14, 2020 at 8:26:59 AM UTC-4, Phil Hobbs wrote:
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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.

Re: When did high-voltage transistors become common?
On 8/14/2020 4:08 PM, Michael Terrell wrote:
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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.

Re: When did high-voltage transistors become common?
On Friday, August 14, 2020 at 2:38:54 PM UTC-4, Pimpom wrote:
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   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.

Re: When did high-voltage transistors become common?
On Friday, 14 August 2020 at 19:38:54 UTC+1, Pimpom wrote:
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ll solid state except for the horizontal drive!  
Quoted text here. Click to load it
y only used a vacuum tube for the HV rectifier and the CRT. The audio outpu
t transistor was around 125VDC. It used an Allen Bradley carbon comp resist
or for a fuse, Anything else wouldn't open in time to protect the output tr
ansformer.  
Quoted text here. Click to load it
t.  
Quoted text here. Click to load it

Yes. Car radios were initially all HT valve, then ponly the output valve ne
eded HT, then 12v valves but an output transistor. My hybrid one proudly sa
ys 'transistor' on it, well it does have one.


NT

Re: When did high-voltage transistors become common?
On Friday, August 14, 2020 at 5:23:26 AM UTC-4, piglet wrote:
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Wow, look out there may be heffalumps!  
George H.  

Re: When did high-voltage transistors become common?
Haha! Thanks George, my daughter is marrying a Zambian in Zambia. Have spied zebras and antelope but heffalump are elusive. Travelling during a pandemic is weird.

piglet

Re: When did high-voltage transistors become common?
On Saturday, August 15, 2020 at 2:25:05 AM UTC-4, piglet wrote:
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Awesome!  Some hope for grand kids to spoil then.  
(Or perhaps you have 'em already?)  My son has had a  
girl friend for several years... which looks promising.  
My daughter is more interested in other women, which doesn't  
make kids impossible, but does need some external input.  

George H.    

Re: When did high-voltage transistors become common?
On 2020-08-14 02:39, Pimpom wrote:
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Dunno.  I used an 811A in an experimental setup in 1991 though. ;)

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: When did high-voltage transistors become common?
On 8/14/2020 2:39 AM, Pimpom wrote:
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Here's a pretty good article:

<http://www.righto.com/2012/02/apple-didnt-revolutionize-power.html#ref65

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.

Re: When did high-voltage transistors become common?
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 88nC

Not 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 40pF

Little 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
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