Help with 70's Yamaha guitar amp

[Jazz P Bass]

WooHoo!

[zintere]

Thanks very much everyone.my board is numbered with all the ID numbers , but they are still quite different from any of these schematics. What I can tell you buy comparing them diagram wise , compared to the one Enzo sent is: I've replaced tr20,tr21,and tr22. I replaced them with new old stock and they all still test good. . The mains in mine are different. Mine uses 2 - 2SD425's. I pulled the mains and checked them and one of them is bad. So i guess I got a long wait , cause to put identical NOS replacements in , I have to order them from China. I will try to keep you all posted. Thanks again.

[52 Bill]

Thanks very much everyone.my board is numbered with all the ID numbers , but they are still quite different from any of these schematics. What I can tell you buy comparing them diagram wise , compared to the one Enzo sent is: I've replaced tr20,tr21,and tr22. I replaced them with new old stock and they all still test good. . The mains in mine are different. Mine uses 2 - 2SD425's. I pulled the mains and checked them and one of them is bad. So i guess I got a long wait , cause to put identical NOS replacements in , I have to order them from China. I will try to keep you all posted. Thanks again.

Why do you feel the need for NOS replacements? Anything that you order from China will likely not be true NOS transistors.

The 2SD425 transistors may not be original to the amp and could be replaced with any number of other transistors with no problems.

[oc disorder]

As long as they handle 100v @ 12A Bill !
Silicon NPN Power Transistor
2SD425 VCBO 140v IC 12A
2SA1090 VCBO 100V IC 12A (shown in schematic)

Just got lost and found this .. well might be useful one day


EchoWars has done some magnificient research re Replacing The STV-3H and STV-4H Diodes over at AudioKarma
(The Yamaha has one)
Replacing The STV-3H and -4H Diodes | Audiokarma Home Audio Stereo Discussion Forums

Conclusion..." So, thus far, the only devices that I have found that mimic the originals reasonably well is the UF1004 (three UF1004's for an STV-3H and four UF1004's for a STV-4H), which is a bit of a bummer, as the device size and the lead thickness make it an unwieldy replacement. What I did do, to minimize the lead diameter issue, is to clip the original leads and use small leads cut from 1/4W resistors to join adjacent diodes. That at least bypassed the lead size issue...if only the body of the UF1004 was a bit smaller."