Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 2nd 19, 08:48 PM posted to sci.electronics.design,sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

Since my dual 2N3055 driven flyback power supply was accidentally thrown
away, I was pondering building another until coming across subject
mentioned assemblies. They're on eBay and elsewhere. Looks like various
drivers with flybacks. Example: https://tinyurl.com/y4lzxt85 Questions
would be:

1) Do these have built in diodes? I DO want to be able to drive a HV
multiplier.

2) Performance/ versatility/ durability comments? Any specific
recommendations of one over the other, etc? Most seem to fall within the
$15-$20 US range. The 3055's with flyback and tripler could output 30-40
KVDC with mA's available. Could one of the prebuilt Chinese units do the
same?

Might be cheaper to buy than to build another from scratch so your
thoughts/ experiences appreciated.

Thank you,
Jon

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Old November 3rd 19, 01:27 AM posted to sci.electronics.design,sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

Jon I wrote...

Since my dual 2N3055 driven flyback power supply was
accidentally thrown away, I was pondering building
another until coming across subject mentioned assemblies.


Haha, 2n3055, you're talking 45 years ago!!
For the last 35 years, we use MOSFETs.

They're on eBay and elsewhere. Looks like various drivers with
flybacks. Example: https://tinyurl.com/y4lzxt85 Questions ...


Might be cheaper to buy than to build another from scratch
so your thoughts/ experiences appreciated.


It's a shame they never provide schematics or similar
information. You do get a nice set of parts, and can
reverse engineer to get the schematic, and then start
making changes.


--
Thanks,
- Win
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Old November 3rd 19, 06:01 PM posted to sci.electronics.design,sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

On 11/2/19 8:27 PM, Winfield Hill wrote:
Jon I wrote...

Since my dual 2N3055 driven flyback power supply was
accidentally thrown away, I was pondering building
another until coming across subject mentioned assemblies.


Haha, 2n3055, you're talking 45 years ago!!
For the last 35 years, we use MOSFETs.

They're on eBay and elsewhere. Looks like various drivers with
flybacks. Example: https://tinyurl.com/y4lzxt85 Questions ...


Might be cheaper to buy than to build another from scratch
so your thoughts/ experiences appreciated.


It's a shame they never provide schematics or similar
information. You do get a nice set of parts, and can
reverse engineer to get the schematic, and then start
making changes.


Interesting that there weren't more responses. I would have thought
some folks would have tried them out for the "tinkering" value alone.
And the cost would have covered just the cost of a single flyback, at
least of the kind I used to use. There are also the Chinese Marx
generators that appear to be driven by these circuits. They call them
"levels" when referring to number of stages with what appears to be 20
stage the highest level (20 level) offered. They specify "10-15 cm"
spark lengths with their "6 level" generator which makes sense with a 20
KV flyback driver circuit. There are videos around of the Marx
generators though, but hard to confirm spark lengths claimed.

Well, I had some trouble with the 3055's. Too much arcing at tripler
output would burn them out quickly and they way I had everything set up,
they were a pain to change out. I finally switched out to a more robust
transistor and had no more problems, but I couldn't tell you which
transistor that was now. It has been some time.

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Old November 3rd 19, 07:47 PM posted to sci.electronics.design,sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

In article t,
says...

Many are using the 2n3771, 32,33 series or there about numbers to
replace the 3055's for more power and reliability.




make those last numbers 72 and 73.



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Old November 3rd 19, 07:53 PM posted to sci.electronics.design,sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

Jim Horton wrote...

Interesting that there weren't more responses.


I'm a big user of eBay and AliExpress, and purchase lots of
high-current and high-voltage stuff, to supplement my pile
of unusual parts, but I'd not come across the items you found.

Well, I had some trouble with the 3055's. Too much arcing
at tripler output would burn them out quickly ...


MOSFETs are more robust than BJTs, in that they can handle
excess drain voltages, and simply go into a safe avalanche,
the same as a zener diode (however the breakdown comes with
ns response times, so the wiring must be low inductance).
MOSFET gates are vulnerable, but if they're driven with a
serious gate-driver IC, with low-inductance wiring, they're
quite robust. The issue is high RF-frequency during arcing.


--
Thanks,
- Win
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Old November 3rd 19, 11:06 PM posted to sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

Ralph Mowery wrote:

--------------------

I have seen some pictures of the internals of the 2n3055 transistors
from China and some had a very small silicon area compaired to the
'good' ones. They would test good but probably only good for about 1/2
to 1 amp.


** 2N305s have been around since the mid 1960s and undergone number of chip redesigns in that time.

The JADEC specification does not determine the chip itself - only its overall performance. Long as the watts, volts amps, gain and Ft etc are OK you can label it as a 2N3055.

After discovering fake Motorola power BJTs in 1982, I began cutting the tops of dead and suspect TO3 examples to see what was inside.

Verrry interesting ....

In the case of 3055s, older examples use a large chip with solid metal bonding attachments. Later ones, particular from Motorola use a much smaller chip with aluminium wires. Nothing wrong with either.

Some of the fakes I came across were 2N3055s relabelled as the vasty better MJ15003 types. Others turned out to be high voltage switching devices with tiny chips and even power Darlingtons - visible by the presence of a smaller transistor on the same chip.

One particularly egregious fake from India had two chips inside, wired in parallel in a desperate attempt to meet the Motorola spec. But that idea does not work.

Another fact that I uncovered is that Motorola like to change the chips inside their power BJT devices without warning. Devices sold since the 1990s as the classic 2N3773 or MJ802 types are in fact MJ15003s relabelled.

Fine for new designs, which is all Motorola ever consider, but can cause all sorts of strange behaviours in older ones. Repairers beware.

Plus the price is double or triple that of the more recent part.

Anecdote:

A famous audio engineer from the UK called Doug Self got trapped by this.

He published a design in Wireless World magazine for a "Blameless Amplifier" using MJ802 and MJ4502s from a stock of old ones he had. It had vanishingly low THD.

When folk built his design using the parts and PCB as specified they could not achieve nearly the same result.

Lots of weeping and gnashing of teeth went on in the letters pages.

Nobody ( but me it seems) figured out the cause was Motorola being deceptive.


...... Phil


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Old November 3rd 19, 11:33 PM posted to sci.electronics.design,sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

On 4/11/19 5:53 am, Winfield Hill wrote:
Jim Horton wrote...

Interesting that there weren't more responses.


I'm a big user of eBay and AliExpress, and purchase lots of
high-current and high-voltage stuff, to supplement my pile
of unusual parts, but I'd not come across the items you found.


An AliExpress search for "Flyback Driver Circuit" comes up with the same
item in the top few hits: https://www.aliexpress.com/item/32769816552.html
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Old November 4th 19, 02:01 AM posted to sci.electronics.design,sci.electronics.repair
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Default online Chinese flyback with driver assemblies questions

On 11/3/19 2:46 PM, Ralph Mowery wrote:
In article , says...
I'm a big user of eBay and AliExpress, and purchase lots of
high-current and high-voltage stuff, to supplement my pile
of unusual parts, but I'd not come across the items you found.




You have to be careful of the ebay China parts. Seems that many of the
high power and some other parts are not up to what they are suppose to
be.

I have bought some things from China via ebay. Most have been good.

I did buy some RF transistors and they would hardly make any power after
about 7 MHz and replaced them with some RF Parts company and those had
the full power at 30 MHz where I wanted to use them.
Friend bought some rated for about 5 or 10 watts and all 6 of them were
bad from the start. The first 2 he put in fried his circuit. He
measured the other 4 before instlling them and they were all shorted.

I have seen some pictures of the internals of the 2n3055 transistors
from China and some had a very small silicon area compaired to the
'good' ones. They would test good but probably only good for about 1/2
to 1 amp.


It's a shame China parts can be so varying in quality, but I too am not
immune although in a different capacity: faucet vacuum aspirators. I
had a really nice glass one, US made, that would pull up to at least 28"
Hg with standard faucet pressure, then one day my carelessness broke it.
It was a Kimax? and they were no longer available, so I decided to
try a stainless steel aspirator from China. It could hardly pull 15"
Hg, a far cry from the advertised 28-30" Hg! I contacted the seller and
got an immediate refund with no argument, so I'll bet, at least in this
instance, that there were a lot of insufficient aspirators. That wasn't
the only one I tried as I tried out several other metal ones, but none
would pull vacuum like the glass one did. That's when I finally decided
on a single stage pump but, after 2 years, that Chinese made pump has
leaked.





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