Transistor replacements

circuit

Sorry again.

This is the first time I attach a circuit here, and I got a message that the image was too big.

Let's hope this time it goes through.



Carlos
 

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Carlos

The 2SC1775A is a Hitachi device and the datasheet should be available on their website. So far as I know, it is still current and should be readily available.

According to my databook, the 2SA896 and 2SC805 were made by Sony. I'll email you the specs that I have. A Google search indicates that there are a number of (surplus?) suppliers listing these devices.

Geoff
 
Coil

My apologies again.

Yes, Nelson. There's an output coil in parallel with the 10R/5W resistor at the output. There's no coil value specified on the Luxman circuit.

On that drawing I didn't put it, as I had done it just for my personal use. My mistake.

The input is also a small pcb, where a cascode differential is used. Nothing fancy. The hybrids were sold as such by Luxman, some having FETs and later types only bipolars, if I am not wrong. It doesn't use any DC servo or feedback cap, and it's quite stable. You set DC offset and you're done. There's a DC protection although.

Model was 5M21 and construction just great. A bit old (around 18 years) but still hold its teeth.

This amp belongs to a friend of mine, and we are thinking of cloning it with better pcbs and parts. The original boards were phenolic, and I think fiber boards would already be an improvement.

Quality passive part replacements already bettered things. But I think dual mated transistors might improve things a bit more on the first stages. May that be so?

Some comments I got was that the circuit is probably Kaneda's.


Carlos
 
Updating circuit

Hi!

I'm back again with more inforamtion on the Luxman amp. Here's the complete 1st stage for you to see.

We could find out what the hybrid piggy-back consists of. In fact there seems to be a problem with one of the input dual FETs on one channel.

Could find the FET part at Audio Lab, reasonably priced.

The trimming pot at the input was unusual for me. I wonder if a trimmed FET wouldn't work better as CCS at the input instead of a plain resistor.

Comments?


Carlos
 
Updating circuit

Hi!

I'm back again with more information on the Luxman amp. Have a look at the complete 1st stage.

We could find out what the hybrid piggy-back consists of. In fact there seems to be a problem with one of the input dual FETs.

Bought the part at Audio Lab, reasonably priced.

The trimming pot at the input was unusual for me. I wonder if a trimmed FET wouldn't work better as CCS at the input instead of a plain resistor.

Comments?


Carlos
 

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carlmart said:
Hi!


The following transistors belong in a Luxman power amp:

· 2SC 1775 A
· 2SA 896
· 2SC 805

Can anyone suggest where to find them or likely replacements?

Where can I get their specs? Would it be wise to use replacements?

The Luxman manual says it's alright to use replacements, as long as specs are the same.

HERE IS MY SUGGESTION

Transistors of many types are available at:

http://www.ceitron.com/

Web site prices are

2SC1775 at $ .27 each
2SA896 at $1.45 each
2SC805 at $3.65 each

I hope this helps. Use the original part numbers when ever possible to avoid problems or call backs. I have used this company lots of times and they provide excellent service.

John Fassotte
Alaskan Audio
 
Data For NEC <font face="symbol">m</font>PC63H
<table width="75%" border="1" cellspacing="0" cellpadding="4">
<tr><td > Spec </td> <td > Typ. </td> <td > Min. </td> <td > Max. </td> <td > Note </td></tr>
<tr><td > V<sub>GS</sub> (V) </td> <td > -60V </td> <td > - </td> <td > - </td> <td > - </td> </tr>
<tr><td > I<sub>A</sub> </td> <td > 10m </td> <td > - </td> <td > - </td> <td > - </td> </tr>
<tr><td > P<sub>D</sub> (W) </td> <td > 0.25/ch </td> <td > - </td> <td > - </td> <td > - </td> </tr>
<tr><td > I<sub>GSS</sub> (A) </td> <td > - </td> <td > - </td> <td > -1n </td> <td > -20V<sub>GS</sub> </td></tr>
<tr><td > I<sub>DSS</sub> </td> <td > - </td> <td > 1mA </td> <td > 18mA </td> <td > 10V<sub>DS </sub></td> </tr>
<tr><td > V<sub>GS(off)</sub> </td> <td > - </td> <td > -0.3V </td> <td > -4.2V </td> <td > 10V<sub>DS/</sub>10<font face="symbol">m</font>A I<sub>D</sub> </td> </tr>
<tr><td > gm </td> <td > 4mS </td> <td > 2mS </td> <td > - </td> <td > 10V<sub>DS</sub>/1mA I<sub>D</sub></td> </tr>
<tr><td > Cis </td> <td > 6pF </td> <td > - </td> <td > - </td> <td > 10V<sub>DS</sub> </td> </tr>
<tr><td > Crs</td> <td > 1p6F </td> <td > - </td> <td > - </td> <td >10V<sub>DS</sub> </td> </tr>
<tr><td > <font face="symbol">D</font>V<sub>GS</sub> </td> <td > - </td> - <td>-</td><td>60mV</td><td > 10V<sub>DS</sub>1mA I<sub>D </sub></td> </tr>
</table>


Regards
James
 
<a href="http://www.datadart.com/">Audio Lab of Georgia</a> had 5 left for US$ 1.93 each, but I believe they are all gone now, might be worth an email to see if they can/will be restocking.

uPA63H is an Nch depletion mode device and the voltages in the data book I used appear to have an erroneous -sign (thanks Carlmart).

60V JFETs are few and far between, stocking up might be advisable.

If originals cannot be found you might want to visit <a href="http://www.linearsystems.com/">Linear Systems</a>, they has one of the best range of JFETs I know of.

Regards
James
 
Re: Re: Transistor replacements

alaskanaudio said:
carlmart said:
Hi!


The following transistors belong in a Luxman power amp:

· 2SC 1775 A
· 2SA 896
· 2SC 805

Can anyone suggest where to find them or likely replacements?

Where can I get their specs? Would it be wise to use replacements?

The Luxman manual says it's alright to use replacements, as long as specs are the same.

HERE IS MY SUGGESTION

Transistors of many types are available at:

http://www.ceitron.com/

Web site prices are

2SC1775 at $ .27 each
2SA896 at $1.45 each
2SC805 at $3.65 each

I hope this helps. Use the original part numbers when ever possible to avoid problems or call backs. I have used this company lots of times and they provide excellent service.

John Fassotte
Alaskan Audio


The uPA63H is also available from the source I mentioned for $1.75 each. These are common items and actually quite easy to get. If you need to match buy more than needed and then sort them out.

John Fassotte
Alaskan Audio
 

Bigred

Member
2007-07-03 9:49 pm
Looks Like its a Beautiful Boat Anchor

Well it looks like I've got a nice Luxman boat anchor here. This amp uses a specialty Luxman developed IC in the pre-driver stage. Luxman calls it a FET hybrid dual monolithic linear IC. Packed into this IC block is the differential input stage, the constant current and cascode circuits. I'm sure there is someone that could come up with a work around using discrete components but this is certainly beyond my level. What a damn shame. I would certainly appreciate and be indebted if anyone knows where I might obtain one of these IC's or knows of a possible work around. I guess if there is any bright side I always have 2 heavy duty toroidal transformers and some nice decibel meters and circuit. :bawling: :bawling:
 
Well it looks like I've got a nice Luxman boat anchor here. This amp uses a specialty Luxman developed IC in the pre-driver stage. Luxman calls it a FET hybrid dual monolithic linear IC. Packed into this IC block is the differential input stage, the constant current and cascode circuits.

I think not. If I remember well, only the cascode is in that IC, and if I am not wrong not even the resistors for the cascode. The other parts are on the main board.

I'm sure there is someone that could come up with a work around using discrete components but this is certainly beyond my level. What a damn shame.

You could use modern replacements for the FET and transistors, like those used by Borbely in his The Audio Amateur first power amps, not the all-FET latest ones.

You could use a pre-drilled small pcb and adapt it.

The first thing is to back-engineer the small monolithic ICs. If you have one you can do that.


I would certainly appreciate and be indebted if anyone knows where I might obtain one of these IC's or knows of a possible work around.

I am pretty sure that's impossible to get.