Pioneer SX-1980 Transistor Modification

Ew.....ok...thanks. You must have used 2 pads for each transistor....correct? Because of the hole in the pad...........
I also understand that you greased them too...........

Great info.........just preparing myself for my own 'fix'.
 
You would not use two insulators per transistor. The replacements used have a single mounting hole as does the insulator. This mounting hole (unless you plan on drilling & tapping holes to mount) is not utilized. The transistors and insulators are carefully (you don't have a scew acting as an alignment guide) aligned and positioned into place and then clamped down using the exsisting two mounting holes with a fab'd clamp. Always ensure that the collectors are fully insulated afterwards.

I do not recommend using both the sil-pads AND heatsink compound. The berquist insulators are designed to be used without heatsink compound. Once the transistors are mounted into place that's it, they are a one time deal.

On the couple of 1980 output transistor mods I have done, I opted to fab my own insulators out of sheet mica. I don't have to deal with the alignment of the transistor and insulator holes.
 
Looks like I can get the original NEC's maybe 50 of each
NPN
2SD746A 220V 10A 200W Bmin=80 ft=15MHz

PNP
2SB706A 220V 10A 200W Bmin=80 ft=14MHz

They are 1980/1981 date codes. If anyone wants to stock up drop me a PM.
 
Looks like I can get the original NEC's maybe 50 of each
NPN
2SD746A 220V 10A 200W Bmin=80 ft=15MHz

PNP
2SB706A 220V 10A 200W Bmin=80 ft=14MHz

They are 1980/1981 date codes. If anyone wants to stock up drop me a PM.
I am exceedingly dubious about getting true NOS drivers. If you can get them, you are blessed. Beware of seriously inferior counterfeits out of China. They run for about as long as it takes to swallow your spit. They look good, unless you know what you are looking at.

Get pics and submit them to EchoWars for visual verification. I certainly would not buy a pot full without trying a few first. Your money. You decide.

Good luck,
Rich P
 
Looks like I can get the original NEC's maybe 50 of each
NPN
2SD746A 220V 10A 200W Bmin=80 ft=15MHz

PNP
2SB706A 220V 10A 200W Bmin=80 ft=14MHz

They are 1980/1981 date codes. If anyone wants to stock up drop me a PM.

Could you get'em?
 
Looks like I can get the original NEC's maybe 50 of each
NPN
2SD746A 220V 10A 200W Bmin=80 ft=15MHz

PNP
2SB706A 220V 10A 200W Bmin=80 ft=14MHz

They are 1980/1981 date codes. If anyone wants to stock up drop me a PM.
Looks like this is not happening...I would be curious about these..I'm in need of outputs...I'll probably just go with the echo mod
 
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The 1280 has base stopper resistors and emitter resistors on a daughter board that mounts the output transistors, so it gets a lot more complicated. I think Mark has a thread or two on it.

I don't know enough about the 1080 to comment on it.
 
In the case that only 1 or a pair of transistors is defective, Would the alternative transistors work if mixed with the original one ? Say top 2 would be replacement and the 4 bottom ones would be originals ?
 
In the case that only 1 or a pair of transistors is defective, Would the alternative transistors work if mixed with the original one ? Say top 2 would be replacement and the 4 bottom ones would be originals ?
What transistors are you talking about?
 
The whole idea of multiple transistors is to have similar enough characteristics that they share the current being supplied to the load. Mixing original devices with new On-Semi devices would throw that arrangement out the window.
 
The whole idea of multiple transistors is to have similar enough characteristics that they share the current being supplied to the load. Mixing original devices with new On-Semi devices would throw that arrangement out the window.


Thanks
 
FWIW, I have a number of 2SB706 (and a few of the 'A' variants), but finding any of the NPN's will be a challenge. If you do, I'll help out.
 
Done couple of these 1980 rebuilds now, as EW states the new outputs work just fine. One thing never resolved is the higher than spec bias with the adjusters turned to the minimum. I have seen values ranging from 50-70mv and would like to move that 100ohm trimmer more into the center of its travel. Any thoughts?
-Lee
 
You can play with the value of R29 (R30 for opposite chan). Drop to, say, 180 ohms and see if that helps. Or increase R37 (R38 opposite). 120~130 ohms maybe.

I do recall replacing the stock drivers with MJE15032/33, but don't remember anything about the pre-drivers (was 10 years ago bro!). Obviously we're dealing with lower Vf on the newer devices.

Edit: Changing R29/R30 won't do much, as the voltage drop through the resistor is controlled more by the value of R27/R28. Think I'd concentrate on the value of R37/R38.
 
Thank you sir :)
The over-riding concern is the reliability (or accuracy if you prefer) of the bias trimmers when dialed down to their stops. I have run into a new trimmer that was going full open intermittently when set to the low end which then kicks the bias sky high. I also recognize that running those new outputs at a higher quiescent value say 60-80mw does not hurt anything other than increase the ma draw at idle which warms up the heat sink marginally. Will report back with the result of changing R37/R38 when I get time to pull one of the amp cards out of my own 1980 to verify.
-Lee
 
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