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space_charged · 11th Jul 2019, 10:34 pm

Yes all very much as I thought, not saturating or rise/fall time too long.

I thought the 2SD625 WAS a darlington. The data I have on it suggests it has a MINIMUM hfe of 120 which is going it some for a power transistor.

The BU931 does work, but gets too hot. As its high gain, I'm assuming it will saturate. I guess you are really confirming my worries about it not being fast enough.

Thanks for the tip about C520. I had my eyes on it anyway.
Just to clarify, I started off trying to repair a KV9000 that had a blown (b/e open) 2SD625. As it was expensive and hard to get I tried some modern transistors. The only one that actually produced a picture was the BU931.

I then switched to my WORKING KV9000 in case there was some other fault confusing the transistor substitution experiments. The results on the the otherwise fully working set were exactly the same as the original non-worker.
To do these experiments to find a reliable substitute LOT, I removed the 2SD625.

If I put it back, then the set runs normally and 2SD625 runs only warm.

I have sourced a 2SD625 and it has now arrived so maybe this is a wild goose chase. Still it would be nice to know what is going on and also to have a suitable modern equivalent.

I will try your idea of lowering R514 and see if I can get it to work with lower gain transistors.

Thanks for the thought that 2SD625 is NOT a darlington. I assume the hfe is lower than the 120 (min) quoted by a well known web site on transistors.

Off to try an ordinary high voltage/current non darlington with reduced base drive resistor R514, and thanks for all the replies and help

C

11th Jul 2019, 10:34 pm	#12
space_charged Hexode Join Date: Dec 2014 Location: West Midlands, UK. Posts: 315	Re: Sony 2SD625 line output transistor Yes all very much as I thought, not saturating or rise/fall time too long. I thought the 2SD625 WAS a darlington. The data I have on it suggests it has a MINIMUM hfe of 120 which is going it some for a power transistor. The BU931 does work, but gets too hot. As its high gain, I'm assuming it will saturate. I guess you are really confirming my worries about it not being fast enough. Thanks for the tip about C520. I had my eyes on it anyway. Just to clarify, I started off trying to repair a KV9000 that had a blown (b/e open) 2SD625. As it was expensive and hard to get I tried some modern transistors. The only one that actually produced a picture was the BU931. I then switched to my WORKING KV9000 in case there was some other fault confusing the transistor substitution experiments. The results on the the otherwise fully working set were exactly the same as the original non-worker. To do these experiments to find a reliable substitute LOT, I removed the 2SD625. If I put it back, then the set runs normally and 2SD625 runs only warm. I have sourced a 2SD625 and it has now arrived so maybe this is a wild goose chase. Still it would be nice to know what is going on and also to have a suitable modern equivalent. I will try your idea of lowering R514 and see if I can get it to work with lower gain transistors. Thanks for the thought that 2SD625 is NOT a darlington. I assume the hfe is lower than the 120 (min) quoted by a well known web site on transistors. Off to try an ordinary high voltage/current non darlington with reduced base drive resistor R514, and thanks for all the replies and help C