Need Transistor Help - Page 1
Forum section: electronics / beginners

author: gomez
author_rank: Newbie
timestamp: February 27, 2014, 05:02:43 pm
content: Greetings!I'm in the midst of trying to restore an old Rock-ola 454 juke from the early 1970's. When I got to the power amp section, two of the output transistors were missing. The transistors are 2N3055c, which , apparently, have been discontinued for quite some time.I don't understand enough about transistors to determine if there is a suitable substitute. As I mentioned, the original is a 2N3055c. There are other variations that are still available, including the 2N3055 and 2N3055G. They seem similar. However, there are slight differences in their specs. Given the application, the differences may or may not be relevant. If there are any transistor gurus out there who can help, I truly would appreciate it.Thanks!

author: granz
author_rank: Regular Contributor
timestamp: February 27, 2014, 05:30:17 pm
content: Any of the 2N3055 versions should work fine for that. Often the letter on the end just indicates the pinout, so just confirm that your replacement has the same pinout at the 2N3055C. I looks like the 2N3055G is the same pinout, but double check. The idea of the standard numbers is that they are interchangeable between manufacturers.

author: gomez
author_rank: Newbie
timestamp: February 27, 2014, 07:08:48 pm
content: Thanks for the information. I'm a bit of a newbie and still trying to absorb some of the basic principles about how transistors work. One thing I do know from looking at the schematic; both channels are powered by a set of matching NPN 2n3055 transistors (no letter designation on the schematic). The actual unit, itself, has a matching pair of 2N3055c transistors for one channel and the other channel circuit board has only an empty space where, I assume, another matched pair once resided.I cross referenced the 2 (C & G) and only spotted 2 differences:Collector Base Voltage: C is 80V, G is 100VCollector Emitter Voltage: C is 60V, G is 70VWould these differences, given the application, be anything to be concerned about?I also checked and it appears that pin out is same for both.Thanks, Again!

author: uwezi
author_rank: Unknown
timestamp: February 27, 2014, 09:23:20 pm
content: Quote from: gomez on February 27, 2014, 07:08:48 pmMost transistor amplifiers are constructed in a way which makes the transistors easily replaceable and not rely too strictly on transistor parameters. This also, because transistor parameters usually spread quite wildly (in the past even more so than today) even within a batch of transistors made at the same time in the same factory.The differences you spotted tell you mainly that the G-type can also be used for higher supply voltages.At some point in time I have been fixing audio amplifiers with rows and rows of 2N3055 in a single channel - never cared about the exact subtype.

author: kg4arn
author_rank: Unknown
timestamp: February 27, 2014, 10:46:54 pm
content: Those are breakdown voltages so the G version has a better spec than the C version and thus it would be okay to substitute. Assuming of course that all else is approximately the same, which it will be because the main part number is the same.I agree with the other post that usually circuits are designed so that there is a fair amount of margin.

author: gomez
author_rank: Newbie
timestamp: February 28, 2014, 04:50:14 am
content: I certainly appreciate all of the help (from all contributors)....and learning more than I knew before I posted the question.Looks like the G version should work just fine.Just in case anyone was curious....I scanned the output section schematic (due to size I had to do it in 3 separate scans) and uploaded pdfs to a file drop site. Links below.Again, thank you for your help and good advice.Page 1 of 3:http://www.filedropper.com/rock-olaampsectschpg1of3_1Page 2 of 3:http://www.filedropper.com/rock-olaampsectschpg2of3_1Page 3 of 3:http://www.filedropper.com/rock-olaampsectschpg3of3_1