9090 Driver Amp. Transistors pinout caveats

[tnsilver]

I had a crack in my 9090 F2546 PS board and the pre-amp section would not get it's 36VDC feed so I had a go at fixing it. It was tough to find and in the process I shorted something and the ground pin of the driver amp sparked and following the damage aftermath I had to rebuild my driver amp, which landed me on a bunch of transistor pinout pit falls. I thought I might share...

TR01...TR04 Heads-up

To begin with, this is my fixed F2436 for reference, but if you are just looking at the picture for transistor orientation, better read on:

This is a late version F2436, the last of the Sansui Parts shop stock which I purchased back in 2010. It had a rather unusual configuration for TR01...TR04. Usually, these are all 2SC1708 transistors, like with this older version driver amp:

But mine had this:

I did not pay attention to TR03/TR04 being 2SC1845 and that was a mistake. The result was I got close to rails voltage on the right channel blue wire going to the relay. Here is the pinout of the two types:

So naturally, they are now positioned in a rather asymmetrical configuration as displayed in the reference picture.

TR05/TR06 Replacements

The stock Toshiba 2SA818 transistors orientation is like this:

The pinout looks like this:

But the replacement KSA1381ES pinout deserves special attention:

The KSA1381ES ECB pinout does not match the original EBC of the 2SA818. Luckily, Sansui had punched an alternate pinout on the driver amp board and the KSA1381ES need to be elevated and installed starting from the upper 'E' pin hole:

I kind of missed that part at the first attempt and installed the KSA1381ES in the same configuration as the 2SA818. The result was rails voltage on both grey and blue wires that go to the protection relay. Bummer! If I only had a post like this on AK for reference...

TR09/TR10 Zetex Replacements

This is quite straight forward. The stock form of the driver amp with the Toshiba 2SC1628 looks like this:

The original transistor pinout is as follows:

The Zetex ZTX694B are a good replacement but their pinout is different:

So naturally, they need to be soldered upside down (or backwards, if you will) taking into account the reversed pinout:

No issues with replacements for the power transistors

So you all know its 2SD381 => MJE15030G or MJE15032G for the TR11/TR12 and 2SB536 => MJE15031G or MJE15033G for TR13/TR14, the replacements have the same pinout, so no issues there.

What in the world replaces the bias transistors 2SC984?

I have no idea. Lucky for me I did not need a replacement but in the back of my head I seem to remember these are unobtanium and some of the suggested replacements need their body isolated or something... Lemme know if you got an idea, I'd be more relaxed knowing it can be done.

 

[Hyperion]

This ^^^ is a really beautiful post Tom, useful anywhere when these substitution questions come up. (e.g. also AU-9900, AU-11000, BA-2000, BA-5000 et al)

Those 2SA818 and 2SC1628 really suffer badly with age, losing gain and making the amplifier sound lifeless, they should be replaced with your suggested subs at every opportunity.

A word about the 2SC984, its a TO1 case design with no connection to the can - this is important, as wherever it is used in Sansui gear, substitutes should have none of their internal connections (collector usually) internally connected to the can. Metal cased transistors like this are difficult to find, so as a sub, most now use a plastic case replacement (correct me if I am wrong here), although there are reports of a source for the original being found from time to time.

 

[Overundr1]

Excellent posting and write-up sir, thanks
-Lee

 

[Magnus Back]

For TR09 and TR10 (2SC1628), is ZTX694B or KSC3503 preferred?

 

[Hyperion]

Either ZTX694B or KSC3503 will work well, personally I prefer KSC3503 as, in this case it is complementary (or 'paired') with the the replacement transistor for 2SA818 which is KSA1381.

In other words 2SC1628 is a complementary pair with 2SA818, therefore their replacements should also be complementary as KSC3503 is to KSA1381.

 

[Magnus Back]

Either ZTX694B or KSC3503 will work well, personally I prefer KSC3503 as, in this case it is complementary (or 'paired') with the the replacement transistor for 2SA818 which is KSA1381.

In other words 2SC1628 is a complementary pair with 2SA818, therefore their replacements should also be complementary as KSC3503 is to KSA1381.

Thank you, that makes 100% sense.

 

[roger2]

Either ZTX694B or KSC3503 will work well, personally I prefer KSC3503 as, in this case it is complementary (or 'paired') with the the replacement transistor for 2SA818 which is KSA1381.

In other words 2SC1628 is a complementary pair with 2SA818, therefore their replacements should also be complementary as KSC3503 is to KSA1381.

@Hyperion I am putting together a Mouser order which will include parts for the F-2436-1 driver board of my 8080.

Currently the 1381 is available in E hfe rank, while availability for the 3503 only goes up to D rank. Isn't less than ideal that the hfe rank of those complementary pairs would not be matching? Is this a potential problem or just nit picking on my part?

 

[Hyperion]

Currently the 1381 is available in E hfe rank, while availability for the 3503 only goes up to D rank. Isn't less than ideal that the hfe rank of those complementary pairs would not be matching? Is this a potential problem or just nit picking on my part?

It would be nice if they were the same gain rank, but they work OK - I have recently changed several pairs that were 'E' & 'D' - and they were fine.