Nakamichi PA7II- are 2SA1837 and 2SC4793 suitable replacements for 2sc3298 and 2sa1306 in this amp?

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#101
Yes its tech
HighTec said:
Why would you change 2SA1306/2SC3298 if they're working OK ? :scratch2:

Edit: btw, the only substitutes I came across are 2SA1837/2SC4793 still manufactured by UTC. There is also 2SA1668/2SC4382 manufactured by SanKen.

https://www.profusionplc.com/type/transistor
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Yes its technically working now but is definately hotter than the same transistors on other side. They are not super hot like they were-they are touchable now but the other side is only warm. Thinking running super hot for awhile might have degraded them and although as BSST suggested it may not be the issue I would just like to take them out of the equation because if they did fail it might be catastrophic. I had looked at 2sa1837/2sc4793 before but didnt choose due to lower collector current. The 2sa1668/2sc4382 seem to meet the specs better I think so may give them a try. Thanks for the suggestions and pdfs.
 
#103
If you want to try 2SA1668/2SC4382 be sure to buy them from a reliable source. I see a lot of fake c*ap on the internetz. Some of them are hilarious, with Toshiba logo for example ! :yikes:

This is the place where I buy them. Unfortunately there are some stock shortages recently.

https://www.tme.eu/en/details/2sa1668/pnp-tht-transistors/sanken/

Edit: 2SC3298/2SA1306 were among the best drivers. I don't see a direct replacement. Maybe someone could give a better suggestion btw.
 
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#104
+/- 80V rails is about 160V rail-to-rail, so you've still got 20V margin against the 180V red line of those substitute transistors. 😉

I think it's wise to have the new transistors in reserve for repair, but if heat is the issue, I recommend taking voltage measurements across all those emitter resistors, both in the problem channel and the "good" channel for reference. I recommend tabulating in a spreadsheet and believe the side-by-side data might be insightful.
 
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#106
*bump

Do what BSST suggested first. Btw, when you pulled out the original 2SA1306/2SC3298, did you do a quick diode test between the leads ? Heck, don't say you didn't ! gto127 you're not helping us. This will end up in a disaster mate. You were already close to it. Probably the Almighty gave you a second chance ! 😉 🙂

/me... from now on, I'll just sit in the corner and watch this thread... 😉
 
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#107
HighTec said:
*bump

Do what BSST suggested first. Btw, when you pulled out the original 2SA1306/2SC3298, did you do a quick diode test between the leads ? Heck, don't say you didn't ! gto127 you're not helping us. This will end up in a disaster mate. You were already close to it. Probably the Almighty gave you a second chance ! 😉 🙂

/me... from now on, I'll just sit in the corner and watch this thread... 😉
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I did do a diode test- must have been breaking down under higher voltage.
 
#109
BSST said:
+/- 80V rails is about 160V rail-to-rail, so you've still got 20V margin against the 180V red line of those substitute transistors. 😉

I think it's wise to have the new transistors in reserve for repair, but if heat is the issue, I recommend taking voltage measurements across all those emitter resistors, both in the problem channel and the "good" channel for reference. I recommend tabulating in a spreadsheet and believe the side-by-side data might be insightful.
Click to expand...
Do you happen to know if these transistors need to be matched? I can see due to scarcity finding matched ones would be hard to do.
 
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