Pioneer SA-508 power transistors

[EifX]

Hi there,

I have SA-508 on my bench and one of the power transistors is shorted. I have searched on the interweb, but they are hard to find:
- (2S)D883A (PNP)
- (2S)D773A (NPN)

Does anyone know which equivalents I can use to replace them?

 

[EifX]

I have been searching, and I have found a 'equivalent'.... I think, but it isn't in the same package. The original transistor is in a TO-220 and the equivalent NTE36 is in a TO3P package.
In that package I can't swap them over but need to drill holes in the heat sink.
Anyone has better ideas?

 

[larryderouin]

2sb773A not 2SD. NTE is absoolutely last resort. Not worth the time or effort to convert it to TO-3's.

These are XM20 PKG (commonly referred to as BATWING type). No direct replacement for type, although Mark the Fixer has used other type (TO-220 or TO-126 IIRC) with more heatsinking, to make operational. ONSEMI/FAIRCHILD should have TO-220 with specs that meet or exceed the originals.

 

[EifX]

Guys,

I have found a little goldmine in relation to these transistors.
Yesterday evening I was roaming on the interweb in search of these transistors and I came across a store in Germany that sells the second best of these transistors.
I am going to order 2 of each. I got an email that the store has 10 - 2SB617 and 5 - 2SD588.
Also look at the rest of the transistors they have....all of them are the ones from old audio equipment.
Hopes this helps.

https://www.radiokoelsch.de/2SB617-Transistor-NEC
https://www.radiokoelsch.de/2SD588-Transistor-NEC

 

[petehall347]

you could check out mje------ transistors .you will need hold down bars making or use the metal from the old transistors . or drill and tap the heat sink .
about 1/5 of the price you have been quoted .

 

[EifX]

I have installed the transistors I bought from the German store. They are the same housing and work like a charm.
I would advice anyone to have a look at the url's I posted earlier. They have a lot of different old stock supplies for vintage audio.

 

[EifX]

OK, the amp works, but something bugs me about it.

When I open up the volume (on the test bench with signal generator connected) the amp makes a high-pitched noise.
I think it is the transformer (I hope not) but how can I determine what is wrong?
Is it normal that the amp generates a high-pitched noise at high-power? I have searched the internet and found that it has something to do with oscillation.
But how can I determine where this problem's origin is?

The voltages seem OK. I replaced the main caps with lager ones. The originals where 8000uF and I replaced them with 10.000uF

I hope someone can point me in the right direction.
Thanks in advance.

 

[llwhtt]

Change your test frequency, does the noise you hear change too? If so that's normal and only reason you hear it is because there are no speakers to drown it out. If it was oscillating it would be at such a high frequency you can't hear it.

Crat

 

[EifX]

Change your test frequency, does the noise you hear change too? If so that's normal and only reason you hear it is because there are no speakers to drown it out. If it was oscillating it would be at such a high frequency you can't hear it.
Crat

Ok, I understand what you say, but I have 8 Ω loads resistors connected. Should the resistors function as the speakers and remove the noise?

 

[llwhtt]

The noise you hear is the circuit, the power xfmr, possibly the heatsinks, it's all normal without speakers to drown it out. Tube amps are even more noisy as you can hear the output xfmr singing. The frequency of your noise changes with your input signal?

 

[EifX]

The noise you hear is the circuit, the power xfmr, possibly the heatsinks, it's all normal without speakers to drown it out. Tube amps are even more noisy as you can hear the output xfmr singing. The frequency of your noise changes with your input signal?

Ok, I'll try it when I'm at the bench. Thanks for the reply

 

[petehall347]

its the outputs singing .try playing some music to confirm .

 

[EifX]

it's the outputs singing .try playing some music to confirm .

I tried playing music and it sounds fine. I thought that the music was louder than the noise, so that is why I didn't hear it.
Only thing now is that the left channel is weaker than the right channel....that is bugging me to

 

[EifX]

Ok, I tested it according to the advice I got and ...yes the noise changes when varying the test signal.
So there is no problem. Is played the amps yesterday for hours and sounds perfect.
Thanks for all the support