Replacement for 70's Vintage Japanese TO-3

[Karl vd Berg]

Originally Posted by Ian Finch

Japanese designs historically focused on high Ft transistor developments. Some substitutions with On-semi types on other Sansui models such as AU517 have been claimed on various forums to sound no different. Some other designs do benefit from high speed, wide bandwidth topology but not all amplifiers are designed to make best use of such components, if I can put it that way. In fact, often the decision to fit them seemed unwarranted but that is how marketing and model variation costs are controlled too.

Then, there are guys that hear audio by the price and parts list too

The point is, that there is only a rule-of-thumb notion that high Ft is always necessary in every audio amplifier, yet this is plainly untrue. There is a small risk involved with fitting parts twice as fast as the originals and it is still your choice with unfortunately, few easy options.

Great!

It's a pity that we, having good old amps, are somehow forced to lean on different package sets. As original TO-3 replacements get limited and hard to find, most audio enthusiasts have to modify their gears. What happens if one have his AU-317/517 with the power TRs burnt?

Originally Posted by ilimzn

Actual TO3 devices to be used in older amps have unfortunately dwindled to perhaps 3 pairs

That's a fact. DIYers always will find some solution, but under a compromise...

Thank you, guys! You are an immense source of information!

[hitachi_nut]

LAPTs have been around before 1980. Sansui used them on the AU-717, G-8000, 8080DB, etc. that were manufactured before 1980. Majority of Sansui's 1978-88 BJT amplifier designs exclusively use Sanken LAPTs including the AU-X1 and their other feed-forward and X-balanced amplifiers which are typically wide bandwidth amplifiers with low THD specs. NEC also have their own version using ring-emitter technology that was used on the SX-1280.

Toshiba have their own low beta droop BJTs but they don't mention anything about it being a multi-emitter die design. I forgot the original part number that have was replaced by the ones I mentioned on my last post. ON Semi and Fairchild Semi have been selling their own SLOWER version of Toshiba's parts for years now and some are available in TO-3 package. .

Originally Posted by Ian Finch

I'm not sure about low beta droop or LAPT technology in 1980. I think it is a little later.

[tiefbassuebertr]

Originally Posted by hitachi_nut

LAPTs have been around before 1980. Sansui used them on the AU-717, G-8000, 8080DB, etc. that were manufactured before 1980. Majority of Sansui's 1978-88 BJT amplifier designs exclusively use Sanken LAPTs including the AU-X1 and their other feed-forward and X-balanced amplifiers which are typically wide bandwidth amplifiers with low THD specs. NEC also have their own version using ring-emitter technology that was used on the SX-1280.

Toshiba have their own low beta droop BJTs but they don't mention anything about it being a multi-emitter die design. I forgot the original part number that have was replaced by the ones I mentioned on my last post. ON Semi and Fairchild Semi have been selling their own SLOWER version of Toshiba's parts for years now and some are available in TO-3 package. .

most of them I have listed by post #1 about
bipolar (bjt) transistor families for audio power output stages

Not listed there are this Versions:
Complementary Bipolar Power Transistors for High Power Audio
there are also this interesting application note:
http://products.semelab-tt.com/pdf/A...teBipolars.pdf
maybe also of interest for repair service on vintage power amp stages from Japan and U.S.

[ilimzn]

Originally Posted by hitachi_nut

LAPTs have been around before 1980. Sansui used them on the AU-717, G-8000, 8080DB, etc. that were manufactured before 1980... NEC also have their own version using ring-emitter technology that was used on the SX-1280.

Sansui AU-717 and 8080/9090DB do not use LAPTs, the first time they were used was in the BA-F1 power amp and AU-919 integrated, then trickled down to all the versions and descendants of Sansui's DD-DC topology including X-balanced designs. NEC had their own LAPTs but pulled out of the market relatively quickly as Sanken's were better. Sony and Yamaha amongst others used NEC LAPTs.

Toshiba have their own low beta droop BJTs but they don't mention anything about it being a multi-emitter die design. I forgot the original part number that have was replaced by the ones I mentioned on my last post. ON Semi and Fairchild Semi have been selling their own SLOWER version of Toshiba's parts for years now and some are available in TO-3 package. .

These are so called 'tripple diffused' - they usually top out at around Ft=30Mhz, generally between 15 and 20MHz and are descendants of older TO3 parts mentioned in this thread. In general BJTs tend to have a trade-off between Ft and SOA, with LAPT technology offering quite a bit of extra ground to chose from. This is the reason why ONseni and Fairchild's parts are somewhat slower, they also ffer some improvement in SOA. As I said, Ft alone can be misleading. Other manufactirers made 3-diffused parts, notably Sanyo (it's semiconductor division has recently beeen sold and sadly most parts, some really good - mostly small signal and driver BJTs - discontinued ).
True LAPTs seem to be almost exclusively supplied by Sanken these days. A similar spec LAPT will usually top out at 2x the Ft of a 3-diffused part, sometimes even higher, and another telltale sign it's a LAPT is the 'peculiar' hump in the SOA graph when drawn with log scales (usually it's a straight line once SOA drops from the bare I x V = Pmax spec), LAPT's offer extra SOA.

[hitachi_nut]

ilimzn,

Do you have a good source for this info? According to the AU-517 brochure that can be downloaded here (Sansui AU-517 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine), they used "highly linear heavy-duty power transistor" term for the output transistors which is loosely a description for the LAPT. This generation is also when Sansui quoted frequency response in the >100kHz range.

Thanks.

Originally Posted by ilimzn

Sansui AU-717 and 8080/9090DB do not use LAPTs, the first time they were used was in the BA-F1 power amp and AU-919 integrated, then trickled down to all the versions and descendants of Sansui's DD-DC topology including X-balanced designs. NEC had their own LAPTs but pulled out of the market relatively quickly a.

[Ian Finch]

"highly linear heavy-duty power transistor"

Honestly, reading that description in advertising copy is about as definitive of LAPT technology as it would be in describing any other good quality audio transistor over 30 years ago. It may have inferred a difference, but so did most of the competitors brochures and press releases at the time, true or not.