HK430 with static in left channel after recap

Hi,

I have almost fully recaped this HK430 except for the four big fat 4700/35. I tested them, they are right in value and have a leak current under 150µA under 25V. Around 200µA/250µA at 30V so I guess they are ok. I also left the two 2200/35 under the chassis as I need to order them.

When I turned the amp on, I kept my finger on the power switch. Under a first test, I had the radio working ok but when passing in AUX I noticed some light static in the left channel. This static ended up in a low 100Hz in the speaker so I immediately switched the amp off to avoid further damage. The output transistors are all ok. While the left channel still works, it has lower gain in FM mode so I need to send a sine wave at both inputs of power board to see where the problem comes from.

After checking this thread I read that some transistors should be replaced in the differencial and current source. I did it several times on other amps (especially with these 2-in-1 transistors).

My question is what is best to replace:
- the three 2CS1345 for the differencial (they have oxided legs): would KSC-1845A be enough ? I read in the linked thread that I need a matched pair with a gain of at least 1000 in the diff and at least 500 in the current source. The recommended replacement is a ZTX694B but since the post is 7 years old this sub could be discontinued already.
- the 2SC458 as well with oxided legs. What best sub for this one ?

Thanks !

David

2SC1815 will be an upgrade to both 2SC1345 and 2SC458. Definitely change out the diff inputs and their current sources.

Thanks ! So I should put the KSC1815. Having see the KSC1845 also suggested in other posts, I wonder which is best. As a matter of fact, the 1815 has a gain of 70min whereas the 1845 is 400min.
Should the diff use a matched pair with 1000min gain and the current source 500min as I have read somewhere ? Else, what's the minimum gain to use ?

Actually, now that I'm a little more awake and a little less likkered up. I would go with KSC1845 for the diffs and use 2SC1815 to replace the 2SC458. 1815 has better current carrying and gain linearity than 1845. 1845 has more gain and a higher VCE. Better for diff pairs.

I used KSC1845 at all places. The amp seems to work great but misses a bit in the higher treble, although I only did the test using cheap technics speakers in the lab... I'll use KSC1815 for the 2SC458 if I have some in stock. I saw other posts where 1845 replaced the 458 so I guess both types should work fine.

The static which I had came from a stupid solder residue which more or less shortened two tracks on the preamp board. Problem solved...