KA-3500 Transistor Subs

gort69

AK Subscriber
Subscriber
Long story short - a KA-3500 that made a horrible hum, pop, scratchy sound at power up, then random pops when playing.

Did the switch cleaning routine, replaced vol pot, full recap, all to no avail. Set it on a shelf for a couple years.

Decided it must be the differential pairs - nope.

I decided to replace all of the transistors except for the 4 outputs and the 4 FETs with what I had on hand. Here's what I used - would appreciate knowing if I made any absolutely horrible choices that should be redone.

PS - The nasty noises are all gone! (The drivers seemed to be the culprits) DC offset is -28mv and -35mv. It sounds really good to me.

qe1-4 2sa620wn > ksa992fbu
qe5,6 2sc1885 > ksc2383yta
qe7,8 2sa620wb > ksa992fbu
qe9,10 2sa733 > ksa733cyta
qe11-14 2sc945 > ksc945cyta
qe15,16 2sa733 > ksa733cyta
qe17,18 2sc1735 > ksc2690ays
qe19,20 2sa850 > ksa1220ays
qe25, 27 2sa673 > ksa1220ays
qe26 2sc1222 > ksc1845

Preamp

q5-8 2sa640 > ksa992fbu
q9,10 2sa872 > ksa992fbu

Seems like a lot, but really only $4-5 in parts.

Thanks
 
Last edited:
Sometimes throwing parts at the problem is the way to go. For $5, it's hard to go wrong, if you know what you're doing.
 
I decided to replace all of the transistors except for the 4 outputs and the 4 FETs with what I had on hand.

The nasty noises are all gone! (The drivers seemed to be the culprits) DC offset is -28mv and -35mv. It sounds really good to me.

Outstanding! Restoring with modern semiconductors and great-sounding results.

Here's what I used - would appreciate knowing if I made any absolutely horrible choices that should be redone.

qe1-4 2sa620wn > ksa992fbu
qe5,6 2sc1885 > ksc2383yta
qe7,8 2sa620wb > ksa992fbu
qe9,10 2sa733 > ksa733cyta
qe11-14 2sc945 > ksc945cyta
qe15,16 2sa733 > ksa733cyta
qe17,18 2sc1735 > ksc2690ays
qe19,20 2sa850 > ksa1220ays
qe25, 27 2sa673 > ksa1220ays
qe26 2sc1222 > ksc1845

Preamp

q5-8 2sa640 > ksa992fbu
q9,10 2sa872 > ksa992fbu

Thanks for sharing your list!
 
I've had this running now all day for 4 days w/ a matching (sorta) KT-5500 tuner - powering up and down occasionally - not even the slightest issue with funny noises. Have to say that for an inexpensive little amp that I'm impressed.
 
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