What to replace KTD718 and KTB688's with? - diyAudio
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Old 11th November 2007, 09:46 PM   #1
spooney is offline spooney  United States
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Default What to replace KTD718 and KTB688's with?

I've been searching like crazy and have been unable to find an answer to this question.I have a 4 channel alpine with one bad channel.The complementary KTD718 and KTB688's are both done for.I have yet to find a clear answer as to what components might replace these parts?Do I simply need to find bi -polar audio output transistors with the same or higher maximum ratings?
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Old 11th November 2007, 10:13 PM   #2
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Join Date: Oct 2007
Default Do you got a data sheet?

Hi there, Data sheets will help you match. Here they are. PDF's in a Archive.

Cheers iUSERTLO72p
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File Type: zip ktb688.zip (73.2 KB, 38 views)
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Old 11th November 2007, 10:14 PM   #3
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Default and


Hope they help
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File Type: zip ktd718.zip (74.3 KB, 24 views)
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Old 11th November 2007, 11:45 PM   #4
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Location: Louisiana
Most of the distributors in the US are using the 2S prefix instead of the KT prefix. When you need a KTD718, search for 2SD718. The datasheet for the 2SD718 says it's an 8 amp transistor. The KEC datasheet says it's a 10 amp transistor. Otherwise, the specs are essentially the same. Generally, when I order the 2S parts, I get the KEC transistors.

Whenever you use the 2S prefix for a KEC part, you need to compare datasheets. Often, they are identical but sometimes, they are not. Sometimes, they're a completely different component.

If you want to get the original parts, order them from pacparts.com. They have one in stock but they'd have to order the other one. They are ~$11 each.

There are a couple of sellers on aBay that have the 2S versions for sale.

If the amp uses a screw to clamp the transistor (through an insulated hole in the tab), there aren't many options.
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Old 12th November 2007, 04:37 AM   #5
grjr is offline grjr  United States
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You could also trying replacing the outputs with cross reference parts from fairchild http://www.fairchildsemi.com/crossref/crossrefSearch.do

I have an amplifier that uses the same output transistors and will be trying to replace them with parts from fairchild soon.
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Old 12th November 2007, 11:42 PM   #6
spooney is offline spooney  United States
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Thank you guys for the help.The fairchild parts are readily available and appear to be better than the originals.
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Old 28th October 2011, 02:43 PM   #7
durwood is offline durwood  United States
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Join Date: Oct 2006
Thread revival.

Have an amp here with a blown output using the KTD718 O/KTB688 O. Since these parts are hard to find and it's not worth paying a premium for them I have 3 options. I am leaning towards the 2STW4468 O/2STW1695 due to price @digikey and the value of this amp, however the FJA4313 O/FJA4313 O has a bit closer specs and more current capability.

Anyone else have any opinions before I order the 2STW4468/2STW1695?

						KTD718 O	2STW4468	FJA4310 O	FJA4313 O
Price						N/A		0.79		1.59		1.55
Source								Digikey		Mouser		Mouser
 Collector-Base Voltage  	Vcb	 V  	 120  		200		200		250
 Collector-Emitter Voltage  	Vce	 V  	 120  		140		140		250
 Emitter-Base Voltage  		Veb	 V  	 5  		6		6		5
 Collector Current  		Ic	 A  	 10  		10		10		17
 Base Current  			IB	 A  	 1.0  				1.5		1.5
 Collector Power Dissipation 	Pc  	 W  	 80  		100		100		130
 Junction Temperature  	 	Tj  	 C  	 150  		150		150		150
 Collector Cut-off Current  	 leno  	uA	10		0.1		10		5
 Emitter Cut-off Current  	 lEBO  	uA	10		0.1		10		5
 C-E Breakdown Voltage  	 Vbrceo V	120		140		140		250
 DC Current Gain  	 	hfe  		80-160		70-140		70-140		80-160
 C-E Sat Voltage  	 	VCE(sat)V	2		0.5-0.7		0.5		0.4-3
 Base-Emitter Voltage  		Vbe	V	1.5		1.3				1.5
 Transition Frequency  	 	h  	MHZ	12		20		30		30
 Collector Output Capacitance  	 Cob  	pF	170		150		250		200
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Old 28th October 2011, 03:06 PM   #8
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Location: Louisiana
I use the FJA4213 and FJA4313 as replacements for all of the transistors like this. There has never been a problem with them.
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Old 29th July 2013, 08:18 PM   #9
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Pulling thread up one more time
Quick run down:
I own a Kicker zx700.5 marine case.
Yesterday I was driving and the power to the speakers seemed to be low.
Today I decided to check my gains with my oscilloscope, as I was adjusting levels the amp started to click (relay?) and the red light would flash. Output is gone obviously.
Now, I have had that happen before when I was testing my speakers for an extended time with the car off. I simply charged the battery and everything was fine.

Today, I can't get the amp out of the flashing protect mode with the clicking of the relay I would assume :/
Done so far:
1. Tested power and ground for resistance and solid connections.
2. Measured voltage at alternator, battery, amp. Close to 14V
3. Disconnected everything and ran the amp straight to the battery with short cables. Same thing happening.
4. I noticed while the amp was clicking it was getting hot in the corner by the fuses.

Please do not tell me I have improper wiring as I have demonstrated it is not that.

Now, I have taken the top off the amp and did some testing with my dmm on some transistors.

The RL speaker pins or Q410 are reading close to 0. Q4510 is reading around 600 on my dmm. Some of the pins for other speakers are reading abnormal numbers as well.

So my question is, could these have a short circuit or blown and now causing the amp to stay in a flashing protect mode? I have already ordered 4 of each to replace the four speaker channels. Should I believe this would be the main cause, because I can't see any signs of burning or malfunctioning electronics

Thanks in advance!

Last edited by NJaNeer; 29th July 2013 at 08:24 PM.
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Old 29th July 2013, 09:30 PM   #10
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Join Date: Dec 2005
Location: Northern California
You should start your own thread since your amp needs repair. This thread was for general replacement devices for out dated and over priced output devices on another amp.
By the way I would say your amp is blown, most likely outputs in one or more channels, and your testing method's will finish damaging the amp if you keep powering it up with failed components inside of it. try the links below for some tech training by Perry Babin...

Try Perry Babin's Tutorial links first:
Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links
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