KA 8300/701 transistor not original or replaced?

7 hertz

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i just got a kenwood trio ka 8300 or also known as ka 701 in the US.
i played it and hooked it up on my infinity sm 120. i was surprised that it was not that good sound as i expected. it turned out that i pushed the volume at 12 o'clock. the sound was that not loud enough and the infinity woofers don't bounce a bit. as if it was in a muting set. i did tried my technics amp a S-VU60 on the infinity. they sounded full and loud. i opened the cover. discovering the power transistors are some what different.( i saw some photos of the ka701 in the bare. and i saw the 3pin transistor which was mounted sideways on the heatsink. connected to a small chip plate and wires to the main amp board.). mines is different the transistors is mounted vertically. and reads (TOSHIBA 2SA 1943). is this the original transistors for this kenwood amp?does this affect the sound value and power output of the amp? i have doubts its been replaced?.. can you please help?

cheers.

one thing more.. the last and 4th transistor on the heatsink has different polarity connected while the other 3 has the same. ill post some photos later thanks.
 
the KA-8300's that I have do not have output transistors.. there are large 10 pin IC chips # TA-100W
sure you have the right model number??

John M
 
i just got a kenwood trio ka 8300 or also known as ka 701 in the US.
i played it and hooked it up on my infinity sm 120. i was surprised that it was not that good sound as i expected. it turned out that i pushed the volume at 12 o'clock. the sound was that not loud enough and the infinity woofers don't bounce a bit. as if it was in a muting set. i did tried my technics amp a S-VU60 on the infinity. they sounded full and loud. i opened the cover. discovering the power transistors are some what different.( i saw some photos of the ka701 in the bare. and i saw the 3pin transistor which was mounted sideways on the heatsink. connected to a small chip plate and wires to the main amp board.). mines is different the transistors is mounted vertically. and reads (TOSHIBA 2SA 1943). is this the original transistors for this kenwood amp?does this affect the sound value and power output of the amp? i have doubts its been replaced?.. can you please help?

cheers.

one thing more.. the last and 4th transistor on the heatsink has different polarity connected while the other 3 has the same. ill post some photos later thanks.



Trio KA-8300 japanese model of Kenwood KA-701 uses the output transistor 2SA1105/2SC2508F from Sanken.
 
the KA-8300's that I have do not have output transistors.. there are large 10 pin IC chips # TA-100W
sure you have the right model number??

John M

thanks for your reply John. yes you are correct. the ka 8300 in the US are the ones with VU meter amps i think this is your amp model. it is different on these japs version of the KA 8300 it is a solid face amp with one big power supply and 4 big caps inside. i think its a ka 701 if it was released in the US market, or in somewhere else countries.

here are some photos.
 

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Trio KA-8300 japanese model of Kenwood KA-701 uses the output transistor 2SA1105/2SC2508F from Sanken.
thanks, so you think the toshiba transistor 2sa1943 is not compatible replcement? ill post some more photos later so you can see the actual transistor itself..
 
now i can see 2 different output transistor 2 on both ends are toshiba 2SA1943 and 2 on both centers are 2SC5200. just like diepbtt said i think the original transistors are from Sanken 2SA1105/2SC2508F.
 
here are some photos of toshiba 2SA1943/2SC5200 transistors. NOT ORIGINAL I SUPPOSE I SEE SOLDERED POINTS! all 3 transistors have the same polarity monted on the chipboard. the last one is different PNP conection. is this what causes the weak output drive? besides the transistor of not being original contributes factor too? any owners of this amp have the same issue? thanks
 

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here are some photos of toshiba 2SA1943/2SC5200 transistors. NOT ORIGINAL I SUPPOSE I SEE SOLDERED POINTS! all 3 transistors have the same polarity monted on the chipboard. the last one is different PNP conection. is this what causes the weak output drive? besides the transistor of not being original contributes factor too? any owners of this amp have the same issue? thanks


Trio KA-8300 original output transitor:
I have read that should be better replacement with sanken 2sa1215/2sc2921
 

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Last edited:
Those Toshiba might be replacements, but they are excellent devices and are NOT the cause of whateveritis you might be or might not be hearing.
 
Cleaned the rca sockets and the volume pots. Now sounds a bit louder on 10 o clock position. Ill hook it up on a lower wattage speakers bookshelves. Lets see what happens.
 
I picked up and repaired a KA-701 a few months ago and it's worth noting that this amp needs to be turned up more than most other amps I've come across. This may be related to the "stepped attenuator" style pot it uses. It seems to be calibrated differently to most "log" pots. It gets pretty loud high once you do turn it up further though.
 
I picked up and repaired a KA-701 a few months ago and it's worth noting that this amp needs to be turned up more than most other amps I've come across. This may be related to the "stepped attenuator" style pot it uses. It seems to be calibrated differently to most "log" pots. It gets pretty loud high once you do turn it up further though.
Another timely reminder that the position of the volume control is not generally any indication of a problem.
 
I also note that the RF shield around the input PCB and the fuse holders on the main PCB seem to be missing in your shots. Unless you removed those yourself it looks like the unit has been seriously hacked up.
 
I also note that the RF shield around the input PCB and the fuse holders on the main PCB seem to be missing in your shots. Unless you removed those yourself it looks like the unit has been seriously hacked up.
hmm, yes i did noticed that . 3 fuses are missing and their mounting . it appears to be just 3 straight thin wire across, or its just the japanese version's original layout? i did not do anything to it. one thing i've noticed is the last and fourth output xisitor as you can see the polarity on the pins are different. the other three outputs are the same. the last one is kinda twisted. i know this output transistor should be PNP config..... im really confused:scratch2: i did check the collector end emiter pins and reads just fine.. wow this is a big puzzle. that attenuator pot is really.. arrrghh.. i just dont know how it will be restore to its original sound. many reviews i read says its a very good amp.
do you agree?
 
The strange thing is that there are a few other pictures of the KA-8300 without the fuses and RF shield if you do a google image search so it may have been how some versions were released.

I know some of these had Sanken outputs but my KA-701 has Fujitsu branded output transistors. They appear to be original though as they are the same on both channels and don't look like they were re-soldered at any point.

I don't have the cover off mine at the moment to check the wiring but I did find a pic on this Japanese site that appears to show the swapped wires on the rightmost output transistor of another KA-8300.

http://blog.livedoor.jp/jt8085jp/archives/51613895.html

I assume the wires running from the main PCB to the tiny PCB being crossed over on the rightmost transistor is the issue you are concerned about?

Even more strangely is the some pictures seem to show the output transistors mounted on the heat-sink vertically while others show them horizontal. I suspect that the design may have evolved over the time it was produced so I wouldn't presume yours has an error.

I'm certain that the transistors in your unit aren't original. The heat-sink still has the holes for the originals and appears to have been drilled to take the replacements. The main difference between those Toshiba parts and the originals is probably going to be the Gain Product Bandwidth. I believe the originals had a pretty high bandwidth.

That said I doubt it will make much difference to how it sounds in reality. The original specs for this amp rated the frequency response up to 400KHz. I know my (apparently fairly good) hearing tops out somewhere between 15 and 17KHz and very few tweeters get above 50KHz so there's a lot of bandwidth to spare in the design.

After replacing the caps in mine it's a great sounding amp in my opinion. It's my main amp at the moment and I have no reason to change it. Very clean sounding. It's not thin in the bass department. Perhaps pure is a better way to describe it overall. I certainly wouldn't call it warm but it's not harsh either. It's more that you don't know it's there.
 
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