On 15/02/2016 12:32 AM, wrote:
On Sunday, February 14, 2016 at 6:36:26 AM UTC-5, alpibucky wrote:

YIKES!

It would depend on the vintage, design, general ruggedness and much
more. Ideally, you will find a schematic for the item you intend to
repair, and replace accordingly. There are more than a few options.

A very common power transistor is the 2N3055. Which in most devices
may be replaced with the more rugged 2N3772, possibly requiring some
attention to the bias settings. I have five devices from three
different manufacturers, Euro and US that use the 3055, most of which
have been replaced with the 3772, one of which needed bias adjustment
(could have been left alone with a small increase in measurable
distortion).

**The 2N3055 and 2N3772 are both EXTREMELY low performance power
transistors. They should really only be used for DC and very low
frequency applications and NEVER for (high quality) audio. In fact,
single diffused silicon devices don't have much place in any audio product.

Best to either use the original devices, or select replacements VERY
carefully. For my part, I am presently servicing a Sansui amp from the
1980s. It is proving extremely difficult locating suitable output
devices, without installing flat pack devices in place of the original
TO3s. The client wants the amp to perform as original and he wants it to
LOOK original. The devices are rated to 40MHz. Finding TO3 devices at
that speed is proving difficult.


That is ONE, and only ONE example. And all of these amps used NPN
outputs in PP. Many use NPN/PNP configurations.

My advice would be to look at the OEM transistor(s), and then look up
*that* part and find out what options may be available. If you are
going to make a habit of this, invest in a tester that will allow you
to match parts. It is often not entirely necessary, but I have found
it makes for better results as transistors do not drift as much as
tubes as they age.

**Correct. Original part numbers are always best.


--
Trevor Wilson
www.rageaudio.com.au

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