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RE: Dynaco 400 amplifier problems,

All appear to be good suggestions, and thanks again.

One problem with working on Dynaco equipment is the transistors that are marked only with Dynaco part numbers. They can make it tricky for a technician in some cases. An early example: in the Dynaco Stereo 120, the output devices were originally identified in the early-production construction manuals as 2N3055, a very widely available TO-3 power transistor. But what Dynaco really put in there, and sent out if you bought replacements from them by the Dynaco part number, were transistors in the same case but of higher rating (perhaps they were "selected" 2N3055). Many Stereo 120 were "fixed" with locally-purchased or mail-ordered 2N3055s, because they were very inexpensive; even back then, about a dollar apiece. However, a transistor could meet the minimum specifications for a 2N3055 and yet be inadequately rated for operation in the Stereo 120. I don't know how many of those Stereo 120s are still functioning and still capable of being operated today, but I still have two that were used for years as loaners for customers, because they cost me next to nothing and I wouldn't cry if one blew up. Probably many of the ones "fixed" with cheap or surplus-store 2N3055s blew up again after being repaired, and their owners gave up on them, selling them for next to nothing. Later, Dynaco finally updated the construction manual with 2N transistor numbers for devices that did meet the requirements for safe, stable operation in the Stereo 120.




GP49


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