I am restarting a restoration project on a Spec-4 acquired a while back. One channel is out, and I replaced the output transistors, along with several transistors and several burned resistors on the power amp board. After bringing up power, there was no sound and I was just starting to take voltage measurements when poof - a couple of resistors and blown outputs again. I was discouraged and put this aside for a while to do some other restoration projects.

Now I am back on this, and have taken a more careful look at the outputs I purchased, I think some of these may be fakes, even though I purchased them from a local source I thought was reliable. This uses the Toshiba 2SD424R and 2SB554R, which I now understand are among the most faked transistors. I opened up one of the orignal 424's and one of the new ones, and the new one looks like a fake. So I don't know if that contributed to the problem, or it something else is wrong. At this point I would like to find either a reliable source for these, or use an appropriate substitution. The OnSemi cross reference lists the MJ15022 and MJ15023 as similar. Is this a good substitution for the Spec-4, or should I use something else?

I think the resident gurus mostly use ON SEMI MJ 21193/21194's as subs for the Toshibas. The 15022 ans 15023 probably work as well but are a little older designs.

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| What he said...use MJ21193/MJ21194, purchased from a reliable distributor, such as Digikey.

Thanks. I will give those a try.

And No More Fakes!

EW...

I have finally gotten around to ordering all the parts to "repair" my blown-up SPEC4. I have so many restoration commissions in my queue that I can't seem to get to my own gear. I bought enough parts to do it at least twice (just in case I miss something and let the smoke out of some new parts), except for the main supply caps (they are monsters, and cost accordingly). Hence, I may have some extras in my parts bins should I be able to help you at some point.

I'm a tape deck guy, but I think with the consultation you have graciously provided, I think I'll muddle through successfully.

I just wanted to thank you publicly for the help.

Thanks,
Rich P

Best of luck, boys...