I have a transistor in a guitar amp with the label ER3055 that needs to be replaced. I asked about another transistor that I needed to replace in a post a few days ago here and I tried using NTE to find a replacement. What I found was that, while nobody seems to have a replacement for "ER3055", there are replacements for "3055" or "2N3055". Is the "ER" prefix something like a manufacturer code (for an extinct brand) or is this something that is crucial to the transistor specs? The specs I found for 2N3055 here seem to match up with with the other transistors in the amp so I think that the "ER" is not necessary but I wanted to check with other people first.