Most relevant specs to determine new transistors

[62vauxhall]

A Kenwood KA-7300 and matching tuner were given to me when I told the owner the amp needed money spent on it. That being so, he just wanted them gone so I obliged.

In an earlier thread, I mentioned that one channel had high DC offset which I hoped would be cured after all the electrolytics were replaced. That is now done with the exception of three bi-polars and the big filters. I can get the latter locally. (If needed) but the non-polarized will need to ordered online, most likely from Mouser.

It was a bit disappointing when checking offset again after hours of work to find it had not changed.

While it may be that one of those bipolar caps could be at fault, my suspicion is now directed to some transistors which I read have been known to be responsible for this problem in these amplifiers. Those plus a 1N5244B Zener diode that I have not tried finding yet.

Since I will just be ordering literally a couple of capacitors, I may as well get those new transistors at the same time.

But I am having a problem in that I don't know exactly what specs need the highest consideration when using Mouser's product finder which looks to have a near limitless number of boxes to tick.

I would not be above accepting suggestions from someone familiar with such things as to what specific transistors and diode I can get from Mouser.

I leave for work at 5AM and not home until 9 or 10PM so I do all my online stuff in a truck cab via a mobile phone with a 3" screen. I would be beholdin' to anyone for info or advice.

What I'm trying to replace are:

2SC2911 - NPN - TO126
&
2SC1209 - NPN - TO92

The differential transistor pairs were also cited as possible culprits. But luck is with me for once as I have on hand some suggested replacements for those - leftovers from my Toshiba amp refurbishing extravaganza.

 

[62vauxhall]

I answered my own question at least partially anyway.

Last night I pulled both pairs of 2SA750 transistors and replaced them with crudely matched pairs of 2SA970's. I left the amp on overnight and DC offset this morning was below 50mv, about half what it was.

I read that what's in there already are considered pretty good so I don't think I'll bother replacing the other two transistors that were suggested. Especially since I may have gotten the offset as low as it's going to go with this type of amplifier meaning one with power amp modules, If that is, what I read about those is correct.

I still intend to complete the re-cap once I get the called for three bipolar electrolytics. One local parts shop had none that were radial but the other did. Unfortunately only one 47uF was on hand and I need two.

I'll special order those and in the meantime, clean the switches and, God willing, listen to it for a few days. Some hype about Kenwood KA7300's on AK and about it having an exceptional phono stage - a poor man's Model 600/700. Having owned a Model 600 for nearly 30 years, I guess I'll see about that.