I've just been done on ebay. Both output transistors on a Kenwood A-97 amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at a reasonable price?

I've just been done on ebay. Both output transistors on a Kenwood A-97
amplifier had blown. Ordered the pair from ebay, installed them,
working, great. Turned it off to put it back together and noticed the
heatsink was really hot on the repaired side. I found that the base
voltage on both transistors was low. Swapped both transistors from the
good side to the repaired side and its now fine. Put the new ones in the
good side the and now the good side has got hot and all the voltages
have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at
a reasonable price?

What was the base-to-emitter voltage on the questionable transistors,
when the amp is idling? How does it compare to the working parts?

These parts (when genuine) seem to be Darlingstons, not just single
transistors. You may have been sold a pair of mislabeled standard
transistors instead - this would probably result in over-biasing and a
high idle current.

Or, possibly they're genuine parts, but have a higher beta than the
ones for which the amp was spec'ed? The beta bin would be a
one-character A, B, or C, possibly stamped on the lower left corner of
the plastic. If that's the case, they might work OK with some
adjustment to the idle/bias settings.

TIP142/TIP147 *might* be acceptable substitutes although their gain
seems lower.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Dave Platt"


These parts (when genuine) seem to be Darlingstons, not just single
transistors.

You may have been sold a pair of mislabeled standard
transistors instead - this would probably result in over-biasing and a
high idle current.

** For sure.


Or, possibly they're genuine parts, but have a higher beta than the
ones for which the amp was spec'ed?

** Nonsense.

Output transistors are typically biased with a voltage that varies with the
temperature of the heatsink.


TIP142/TIP147 *might* be acceptable substitutes although their gain
seems lower.


** The fact they have a Vce of 100V as compared to the originals with 140V
is far more of a worry.

The BDV65C and BDV64C darlington pair is closer at 120V Vce.

The OP can measure the +/- DC rails see if the total is more than 120V.


..... Phil

The design uses an STK350-030 ic to drive the output transistors. According to the service manual, at idle, the output from the driver ic to each transistor base should be around 1.2 volts. These new ones are causing that voltage to drop to around 0.6 - 0.8v, and this is with the bias adjustment full up.
I tried using one of the new ones with an old complimentary one from the good side and this caused a massive imbalance in the idle bias 1.4v for the good one and 0.6 for the suspect one. Can i assume from these voltages that the replacement's are not darlingtons? 0.6v is right for a single transistor and 1.2v (approximately double) for a darlington?

Regards

fruittool wrote in message
...

I've just been done on ebay. Both output transistors on a Kenwood A-97
amplifier had blown. Ordered the pair from ebay, installed them,
working, great. Turned it off to put it back together and noticed the
heatsink was really hot on the repaired side. I found that the base
voltage on both transistors was low. Swapped both transistors from the
good side to the repaired side and its now fine. Put the new ones in the
good side the and now the good side has got hot and all the voltages
have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at
a reasonable price?




--
fruittool


Any external giveaways as yo piracy?

ground surface ?
smudged printing or looks as though logo was stamped with a potatoe die?

On Thu, 25 Oct 2012 20:06:24 +0000, fruittool
wrote:


I've just been done on ebay. Both output transistors on a Kenwood A-97
amplifier had blown. Ordered the pair from ebay, installed them,
working, great. Turned it off to put it back together and noticed the
heatsink was really hot on the repaired side. I found that the base
voltage on both transistors was low. Swapped both transistors from the
good side to the repaired side and its now fine. Put the new ones in the
good side the and now the good side has got hot and all the voltages
have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at
a reasonable price?


http://www.bdent.com/ only carries genuine semiconductor
manufacturer's lines. Chuck

I tried using one of the new ones with an old complimentary [sic]
one from the good side and this caused a massive imbalance
in the idle bias 1.4v for the good one and 0.6 for the suspect one.
Can I assume from these voltages that the replacements are not
Darlingtons? 0.6v is right for a single transistor and 1.2v
(approximately double) for a Darlington?

It sounds as if these aren't Darlingtons.

Do you have a way to measure the current gain? It should be at least 1000 --
probably higher.

William Sommerwerck wrote:

I tried using one of the new ones with an old complimentary [sic]
one from the good side and this caused a massive imbalance
in the idle bias 1.4v for the good one and 0.6 for the suspect one.
Can I assume from these voltages that the replacements are not
Darlingtons? 0.6v is right for a single transistor and 1.2v
(approximately double) for a Darlington?

It sounds as if these aren't Darlingtons.

Do you have a way to measure the current gain? It should be at least 1000 --
probably higher.


Pull one of the new transistors and check it with an ohm meter. If it
tests like a single transistor, it is.

I had this same concern, each rail is 52V. Your suggested parts seem closer but, would i have to change both pairs to keep the response of both channels identical?

On first examination there's nothing particularly suspect but, after checking what the proper markings would be, it turns out the gain classification (A, B or C) is missing on one and is the letter 'O' on the other. Another giveaway is the LOT number, it should be one number for the last digit of the year and one letter 'A' for January to 'L' for December. Both have three numbers and no letters.

Regards

Do you have a way to measure the current gain?
It should be at least 1000 -- probably higher.

Pull one of the new transistors and check it with an
ohmeter. If it tests like a single transistor, it is.

I assume you're referring to the base-emitter junction.

"fruittool" schreef in bericht
...

Dave Platt;2949536 Wrote:
I've just been done on ebay. Both output transistors on a Kenwood A-97-
amplifier had blown. Ordered the pair from ebay, installed them,
working, great. Turned it off to put it back together and noticed the
heatsink was really hot on the repaired side. I found that the base
voltage on both transistors was low. Swapped both transistors from the
good side to the repaired side and its now fine. Put the new ones in
the
good side the and now the good side has got hot and all the voltages
have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at
a reasonable price?-

What was the base-to-emitter voltage on the questionable transistors,
when the amp is idling? How does it compare to the working parts?

These parts (when genuine) seem to be Darlingstons, not just single
transistors. You may have been sold a pair of mislabeled standard
transistors instead - this would probably result in over-biasing and a
high idle current.

Or, possibly they're genuine parts, but have a higher beta than the
ones for which the amp was spec'ed? The beta bin would be a
one-character A, B, or C, possibly stamped on the lower left corner of
the plastic. If that's the case, they might work OK with some
adjustment to the idle/bias settings.

TIP142/TIP147 *might* be acceptable substitutes although their gain
seems lower.


The design uses an STK350-030 ic to drive the output transistors.
According to the service manual, at idle, the output from the driver ic
to each transistor base should be around 1.2 volts. These new ones are
causing that voltage to drop to around 0.6 - 0.8v, and this is with the
bias adjustment full up.
I tried using one of the new ones with an old complimentary one from the
good side and this caused a massive imbalance in the idle bias 1.4v for
the good one and 0.6 for the suspect one. Can i assume from these
voltages that the replacement's are not darlingtons? 0.6v is right for a
single transistor and 1.2v (approximately double) for a darlington?

Regards




--
fruittool

No doubt you were sent single transistors instead of Darlingtons. The latter
have two diode drops Vbe so 1.2V-1.4V instead of 0.6V-0.7V. If you did not
find out already you could check using the diode tester of a common
unimeter.

petrus bitbyter

"fruittool"

'Phil Allison

** The fact they have a Vce of 100V as compared to the originals with
140V is far more of a worry.

The BDV65C and BDV64C darlington pair is closer at 120V Vce.

The OP can measure the +/- DC rails see if the total is more than 120V.


I had this same concern, each rail is 52V. Your suggested parts seem
closer but, would i have to change both pairs to keep the response of
both channels identical?


** LOL - err, no.

You really are a babe in the woods.....


..... Phil

"fruittool"

TIP142/TIP147 *might* be acceptable substitutes although their gain
seems lower.


The design uses an STK350-030 ic to drive the output transistors.
According to the service manual, at idle, the output from the driver ic
to each transistor base should be around 1.2 volts. These new ones are
causing that voltage to drop to around 0.6 - 0.8v, and this is with the
bias adjustment full up.

** That will only make the transistors you have get very hot.


I tried using one of the new ones with an old complimentary one from the
good side and this caused a massive imbalance in the idle bias 1.4v for
the good one and 0.6 for the suspect one. Can i assume from these
voltages that the replacement's are not darlingtons? 0.6v is right for a
single transistor and 1.2v (approximately double) for a darlington?

** Yep.

Non darlington devices in that amp will not only run hot but deliver much
less that full output power into a load.

The fact is you simply have NO driver transistors unless darlingtons are
fitted.


..... Phil

"William Sommer******"

Pull one of the new transistors and check it with an
ohmeter. If it tests like a single transistor, it is.

I assume you're referring to the base-emitter junction.



** Darlington power transistors all have inbuilt diodes from collector to
emitter - a very rare thing among regular transistors.

The base emitter junction will also read higher than usual on an ohmmeter,
the difference being more obvious with an analogue type on the ohms x1 range
than with a DMM on "diode test".



..... Phil

"William Sommer******"


It sounds as if these aren't Darlingtons.

Do you have a way to measure the current gain? It should be at least
1000 --
probably higher.


** Most transistor checkers will not read correctly with power darlingtons.



.... Phil

N_Cook wrote:
fruittool wrote in message
...

I've just been done on ebay. Both output transistors on a Kenwood A-97
amplifier had blown. Ordered the pair from ebay, installed them,
working, great. Turned it off to put it back together and noticed the
heatsink was really hot on the repaired side. I found that the base
voltage on both transistors was low. Swapped both transistors from the
good side to the repaired side and its now fine. Put the new ones in the
good side the and now the good side has got hot and all the voltages
have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at
a reasonable price?




--
fruittool


Any external giveaways as yo piracy?

ground surface ?
smudged printing or looks as though logo was stamped with a potatoe die?

off ebay is a good clue they're not legit.

"Cydrome Leader" wrote in message
...
N_Cook wrote:
fruittool wrote in message
...

I've just been done on ebay. Both output transistors on a Kenwood A-97
amplifier had blown. Ordered the pair from ebay, installed them,
working, great. Turned it off to put it back together and noticed the
heatsink was really hot on the repaired side. I found that the base
voltage on both transistors was low. Swapped both transistors from the
good side to the repaired side and its now fine. Put the new ones in the
good side the and now the good side has got hot and all the voltages
have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at
a reasonable price?




--
fruittool


Any external giveaways as yo piracy?

ground surface ?
smudged printing or looks as though logo was stamped with a potatoe die?

off ebay is a good clue they're not legit.






Particularly if they ship from China, Hong Kong etc.



Gareth.

"Gareth Magennis"
"Cydrome Leader"

off ebay is a good clue they're not legit.


Particularly if they ship from China, Hong Kong etc.


** The only offer I see on Ebay for the 2SD2385/2SB1556 pair is from a UK
dealer called "elmassari" in Surrey.

He has a big range of spares for sale at low prices and some of it must be
fakes.


..... Phil

That's the one but the package is labeled ELECTRONIC COMPONENTS, SEMICONDUCTORS, PARTS, TRANSISTORS, INVERTERS, TRANSFORMERS | DALBANI and electronic component suppliers and distributors, Nikko Electronics for semiconductors, transistors, capacitors all major brands of spare and replacement parts.

I found CHS - replacement remote controls, instruction manuals, audio & video accessories, electronic components & spare parts to have what i need. Anybody know anything about them?

2Sd2385
and
2Sb1556

To me, the pictures look genuine, the site looks a reasonable quality and has a uk landline number unlike the other site with it's 020 number.

What do you guys think?

Thanks,
Ant

I found 'CHS - replacement remote controls, instruction manuals, audio &
video accessories, electronic components & spare parts'
(http://www.chsinteractive.co.uk/) to have what i need. Anybody know
anything about them?




Yes, Charles Hyde, I seem to recall, used to sell Tascam and other spares -
I bought some from them.
They were always ridiculously expensive, but they would definitely not
knowingly be dealing with pirated parts.


Gareth.

Will wonders never cease ? This place actually has a datasheet ! (they failed me so much I no longer bother, but at the end it said "PDF" so I got it)

http://www.datasheetcatalog.org/data...shiba/3250.pdf

If you really cannot get them you can make Darlingtons, but I don't recommend it. However when you look at the internal diagram you see the the EB junction on a meter is not going to read like a Darlington because of the 100 ihm resistor across the EB junction of the output. You would only see the drop of the driver EB junction. Depending on your meter it might read 0.100 higher, but will not read 1.2 volts as you might expect.

You are not ordering a million of these things, if the right part is a bit more expensive it is worth it. Like someone said B & D, but then I don't know where you are. If not in the US, dealing internationally can be a PITA.

J

"fruittool"


To me, the pictures look genuine,


** But you are an utter idiot.




..... Phil

http://www.datasheetcatalog.org/data...shiba/3250.pdf


** Shame the schem in the above omits the reverse diode across the C and E
terminals.

Easiest way to pick a power darlington with an ohm meter.


..... Phil

Actually it might not have one, there is no law.

With two resistors, a DVM and a 12 volt supply you can measure the hfe quite easily.

That 100 ohm resistor is much more important, otherwise the Icex of the first transistor at the very least will always be applied to the base of the second transistor. The Ice leakage numbers for the whole device would look like germanium.

J

Actually it might not have one, there is no law.


** Every darlington power transistor made has a reverse diode from C to E -
it is part if the structure of the chip.

All power mosfets have a similar diode.


With two resistors, a DVM and a 12 volt supply you can measure the hfe
quite easily.

** But you gotta be real quick or the device will cook.


That 100 ohm resistor is much more important, otherwise the Icex of the
first transistor at the very least will always be applied to the base of
the second transistor. The Ice leakage numbers for the whole device would
look like germanium.


** Hogwash.

The 100ohm resistor is there to improve the switch off speed of the power
transistor plus increase the breakdown voltage a little.

Leakage current in the driver transistor is only a few microamps, at most, a
current level the output device can barely amplify at all.


..... Phil

On 10/26/2012 7:21 AM, chuck wrote:
On Thu, 25 Oct 2012 20:06:24 +0000, fruittool
wrote:


I've just been done on ebay. Both output transistors on a Kenwood A-97
amplifier had blown. Ordered the pair from ebay, installed them,
working, great. Turned it off to put it back together and noticed the
heatsink was really hot on the repaired side. I found that the base
voltage on both transistors was low. Swapped both transistors from the
good side to the repaired side and its now fine. Put the new ones in the
good side the and now the good side has got hot and all the voltages
have dropped the same as they did when they were on the repaired side.

Does anyone know where i can get a genuine pair of these transistors at
a reasonable price?


http://www.bdent.com/ only carries genuine semiconductor
manufacturer's lines. Chuck


http://www.pacparts.com/part.cfm