I took out the main drive power transistors and need to know does the dot on the board denote base or emitter,I actually found this baby only plugs in one way and the dot was meaningless,the symptom was a loud buzz in all four outputs,once the power transistors were removed I noticed the unit had been apart before and one of the mica insulators was missing,I found it in the shell an now we are in business thanks all,B
Quote from: brett on August 14, 2013, 05:23:30 PM
I took out the main drive power transistors and need to know does the dot on the board denote base or emitter
Use the datasheet, Luke!
How did they design the board? They had a part in mind, and made a footprint by following its datasheet.
If the board designers had any brains, the dot would go to whatever is "pin 1" in the part's datasheet. But it's best not to rely on such markings.
Is this what you have? http://www.futurlec.com/Transistors/2N3055.shtml
Pin 1 is base; Pin 2 emitter; metal case is collector.
agree and add: that colour dot probably means a measured current gain range, or a measured (selected) voltage capability.
As in: 2n3055 is "officially" rated for 70VCE, yet I measured them as routinely surpassing 80V, and a few as high as 115V .
It was common practice to measure them, mark with a colour dot (hint, hint ;) ) , use the best for 100/200W amps and the "regular" ones for 50/60W amps.
So your dot probably means: "use a yellow dot transistor in this position".
What does yellow dot mean?: that would be an in-house SUNN convention.
22-3055 is the Sunn part number for the 2N3055. In the Concert Series power amp, the four transistors should be matched for lowest DC offset at the output. One of the transistors has a grounded collector so it doesn't need an insulator. A frequent failure on these amps is that a short develops in the driver transformer. The easiest way to find it is to remove the four output transisitors, power the amp up and measure the output voltage with no load. This will also confirm that the bias resistors have not drifted in value. Before you install the transistors, verify the base to emitter voltage at each transistor socket and that the emitter resistors are ok.