On Tue, Aug 21, 2012 at 10:02 AM, Bob Blick wrote: > On Tue, Aug 21, 2012, at 09:47 AM, Justin Richards wrote: >> As a novice, finding replacement transistors for the amp section that >> are pin compatible, cheap and readily available has proved to be time >> consuming. >> >> Currently a 2SD314 NPN (T220) is in the output stage. TIP31C(T220) >> appears similar , as is 2N3055 (T03) and the circuit board has been >> designed to take either T220 or T03. >> >> min/max hfe for 2SD314 and 2N3055 are 40/320 and 20/70 respectively. >> >> As amp designers must consider a range of hfe's anyway and as I have a >> handful of these (both TIP31C and 2N3055) it seem like the right >> decision. (I intend to change the other side PNP to it its complement >> MJ2955 and similarly in the other channel) > > Either choice is likely to be OK. But the 2N3055 is a lot tougher. If > you are running 4 ohm loads it would be a better choice, especially if > your amplifier has higher than 50 volts total supply voltage (+-25 > volts). Or if you expect it to handle the occasional short circuit. > > On the other hand, finding non-counterfeit transistors in TO3 packages > is getting harder, so you might have a TIP31A or worse inside the 2N3055 > package. In which case using a TIP31C would be a better choice :( > > Best regards, > > Bob > > -- > http://www.fastmail.fm - One of many happy users: > http://www.fastmail.fm/docs/quotes.html > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist You should keep an eye on the HF roll off of the modified amp. The fT of the old transistor is much higher than the 2N3055, and the gain at 20kHz for the 3055 isn't specified. Also, depending on the feedback configuration of the amp, it may expect faster output transistors, causing further changes in the forward transfer function. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .