Solid State amp not working-Help!

[flyingtele]

I have a solid state guitar amp thats now going. it has no makers name on it. The output transistors have gone, and it just emits DC. I have tried looking for replacement transistors, but I cant find any. The code number on them is K D998 and K D778. If anyone knows of a suitable replacement or an equivalent that would be greatly appreciated.

[Steve Conner]

I guess they would be 2SD998 and 2SD778. A quick google search shows that those part numbers are NPN and PNP audio power transistors, so I was probably right.

If you can't get those, the MJL3281 and MJL1302 are more modern audio transistors in the same package. They are powerful devices with lots of gain that should work in just about anything. You also get them as 2SA3281 and 2SA1302. I'll leave you to figure out which is NPN and which is PNP

PS watch out for fakes: http://www.diyaudio.com/forums/showthread/t-5064.html

[Mars Amp Repair]

HMM,
something sounds wrong. The 'D' variety of Japanese transistors are ALWAYS

[Mars Amp Repair]

hmm,
something sounds wrong. In the world of Japanese transistors, the 'D' variety are ALWAYS the NPN transistors (so are the 'C' variety). The 'A' & 'B' are ALWAYS the PNP variety.
I show the 2SD998 as being a 10watt 1.5a transistor & the 2SD778 as only being a 100ma 400mwatt. I'm guessing the 2SD778 is a driver or a bias transistor while the D998 is the actual power transistor.
I show the 2SD998 subbing to a 2sc2324 (K) or 2sd1645 or 2sd2011, and the 2SD778 subbing to a 2SC2396 or 2sd637 or 2sc4038. Of course in the audio low wattage world, there are a myriad fo transistors that would function well here.

2sc2396 is fairly common & available from MCM. 2sd998 is also available from MCM.

So, there are either 2 or 4ea 2sd998 power transistors with one positive rail, or 2sd998 & some 2sa or 2sb compliment power transistors with + & - rails. Hope that helps...g

[Enzo]

I don't even like 2SD998 as an output. a 10 watt xstr means the amp would only be about a 2 watt amp. Seems unlikely.

Further, unless this is a tiny single ended amp, I would expect both outputs to be either the same in quasicomplementary or one of each polarity in true complimentary.

Can you post a photo?

Can you tell us what the power supply voltages are? Or what is the DC voltage coming out towards the speaker?

What package are these outputs?

[Steve Conner]

Sorry for the bad information guys, I think my Google-fu was weak that day

[MarkusBass]

Could it be KTD998 from Korea Electronics: http://www.datasheet4u.com/html/K/T/...nics).pdf.html (click on the DataSheet View link) complimentary to KTB778?

Marek

[Enzo]

NOW we're talking!

[Mars Amp Repair]

Cool,
Nevah hoid of 'em. Yah hopes yaz loins sometin new evah day! g