Kenwood Eleven III Transistor Sub

[Beavs]

Have a Model Eleven III that needed a good cleaning and re-lamp and seemed to be working great on the bench. After getting it all put together letting it play for a few hours, loud distortion would start to develop intermittently regardless of source. I'm making the assumption that transistors or IC's in the control amp section may be the cause and want to have parts on hand before pulling this out of the sleeve again (though open to other opinions, bad solders joints seemed to be a probable cause as well).

Anyway, I have subs on hand for Qi3 and Qi4 on the control amp board. The other two transistors Qi1, Qi2, on that board were stock 2SC1222(U) or 2SC1345(E) which appears to be a known noisy transistor. Looks like standard AK recommendation replacement for these would be KSC1845, but stocks are out on these and I don't currently have any on hand. On a tranny cross reference site I saw 2SC1815's listed as a sub for the stock ones. I have 2SC1815's on hand measuring hFE of 430 and Vf of 670mA, stock link here:
https://www.mouser.com/ProductDetail/512-KSC1815YTA

Would these be suitable replacements? Schematic screenshot below:



Next question about the IC's which are original TA7129P and all that I could find on AK or the rest of the internet was an NTE1462 but generally doesn't seem to recommended as a replacement based on quality. Are there other options for replacing these IC's if necessary?

 

[Oilmaster]

2SC1815 (KSC1815) will work very fine for Qi1/2. Rank Y will have a lower Hfe than rank U of the 2SC1222, but the circuit is not depending on the transistor's Hfe (as rarely any audio circuit ever does). It will result in a slightly higher base current drawn by Qi1/2, but that will be lavishly supplied by R155/157.

Notorious source/cause of bad sound in small signal stages are oxidizing contact surfaces of switches such as S13 at the output. Dismantle and clean it as well (no spray treatment). S20 at the input is probably even a bigger cause of problems.

 

[Beavs]

2SC1815 (KSC1815) will work very fine for Qi1/2. Rank Y will have a lower Hfe than rank U of the 2SC1222, but the circuit is not depending on the transistor's Hfe (as rarely any audio circuit ever does). It will result in a slightly higher base current drawn by Qi1/2, but that will be lavishly supplied by R155/157.

Notorious source/cause of bad sound in small signal stages are oxidizing contact surfaces of switches such as S13 at the output. Dismantle and clean it as well (no spray treatment). S20 at the input is probably even a bigger cause of problems.

Thanks for the reply on this, good to know that the 2SC1815 can be used in a pinch since I have no 1845's on hand, and stocks are still out on those. I actually ended up resolving this without replacing any transistors or IC's that I had suspected could have been the problem source. I reflowed a bunch of the solder joints while waiting for a response on the transistor subs and it seemed to resolve the problem. None of the solder joints stuck out visually as having issues but with the track record of others reporting bad solder joints on these I figured it was worth a shot.