Solid State Guitar Amp Forum | DIY Guitar Amplifiers
Solid State Amplifiers => Amplifier Discussion => Topic started by: Stewen on March 24, 2011, 04:48:32 PM
Hallo ! Am working with this bassamp and it´s not easy for a "tubeampguy" like me...... haven´t been soldering transistors
much since the 60-ties ! Wonder if its important to select matched powertransistors and /or drivertransistors ? And , can for example the drivertransistors have been damaged even if they is OK when controlled with an ohmmeter ? Will a hfe
test tell more about their condition ? About ten or so transistors on this board is the type "surfacemonted" . I must say , I don´t like them !!!! Can I change at least some of them to TO92 types with the same data but higher voltagecapacity ? For example : BC 847B to BC 546B , and BC 857B to BC 556B ? I have ordered some books to
learn more about solid state amps but not sure they will answer my questions so I´m happy if you can give some advice.
Regards Stewen
I like Laneys very much, but I hate their using (for many years now) that mixed through_hole/SMT parts mix.
I would not touch original parts unless actually damaged, and if replacing them , would stick to ooriginal ones; SMT if they are so.
That said, on a Murphy's Law late Saturday "urgent" repair work, I have sometimes replaced an SMT one with a TO92 version, with closely cropped, pretinned legs , a bench mounted loupe, very good light and steady hand, but do not exactly *recommend* that.
I have a small stash of general purpose BC¿846/856? SOT23 case (SMT) transistors just in case.
Hook your dead amplifier to a series lamp bulb limiter, no speaker attached, and measure voltages looking for "impossible" ones: you should have your power rails, although somewhat lower because of the lamp limiter , your +/-15V , *no* DC on the output, more than 5V across transistors with close to .65V from base to emitter, etc.
Good luck.
Thanks Fahey for Your answer ! I really appreciate that ! Today I got Randy Slone´s book by the postman ! Have just done a quick look , and it seems to be a good book ..... talks about poweramplifiers .. Regards Stewen