1977 20w class A little help please.

[Yabanjin]

Hello I need some help with the 1977 nelson pass 20w amplifier.
I am confused about the transformer.
In schematic it's 14v +- and in bom its writed signal 56-12
Signal 56-12 is 2x6.3v......
And someone can say me if I can use 2n5878 in place of 2n5877 because I don't find enough 2n5877 from the same brand....
The 2n5878 are PMC brand anyone have experience with this brand ?
Thanks

 

[Zen Mod]

you have picture/schematic of PSU , why on earth you need BOM specification of xformer?

xformer secondaries are 28Vac center tapped , per picture on top of page 5

so , two independent secondaries of 28Vac (CT) , where one goes per channel

that will give you something around +/-17Vdc for rails

and say that you need 250VA xformer

2N5878 is same part as 2N5877 , with higher voltage breakdown



PMC - dunno , doesn't ring a bell ...... but I'm probably younger than these parts



edit: you can probably use decent 2N3055 instead

 

[Malotron]

PMC = Lambda Semiconductors > Lambda Advanced Analog > International Rectifier
IRC = International Resistive Corporation > TRW > TT Electronics
Milspec parts- one small step for aerospace... one giant leap for Class A amps

 

[Yabanjin]

Thanks for the reply.
Sorry im not enough experienced with transistors for know what to choose as equivalent transistors if the reference from schematic is not the same as what is still available.
I follow your advice and order 16 rca 2n3055.
Let's try the two ! Rca 2n3055 and Pmc 2n5878.

About BOM and transformer I just follow the instructions from the pdf I find in pass diy site.....
In schematic it's yes -+14v but in bom you find signal 56-12 transformer...... Signal 56-12 is -+6.3v transformer....
Im not expert sorry for asking something that look stupid.
It's my first class A transistors amp I build it before trying alept F4 or F5 turbo.

 

[Yabanjin]

PMC = Lambda Semiconductors > Lambda Advanced Analog > International Rectifier
IRC = International Resistive Corporation > TRW > TT Electronics
Milspec parts- one small step for aerospace... one giant leap for Class A amps

Sorry for asking.... You mean PCM transistors are good one for amplifier ?

 

[Zen Mod]

no need for excuses , we all started somewhere

however - you need to be more careful in few things :

- xformer itself is not having +/- voltages (think AC !)

-look here : 56-12 Signal Transformer | Transformers | DigiKey

 

[Zen Mod]

Sorry for asking.... You mean PCM transistors are good one for amplifier ?

paraphrase of - one small step for a man , one giant step for mankind

 

[Yabanjin]

About transformer yes I know they are two secondar or one center taped.
28v ac with middle point or two 14v ac.
Im sorry for my poor english it's not easy to explain well.
About transistors it's really not easy to find good brand from all this old transistors like 2n5877 from Motorola..... I need 16 pices...
Like the 6 RCA1A15.... Impossible to find them I have hardly find Motorola 2n5682....
I still need heatsink you have some advice for the size I need to use for one channel without using a cooling fan ?
Thanks

 

[drjbf1]

This was a good amp, but I think a smaller Aleph may be a simpler first build?

 

[Yabanjin]

This was a good amp, but I think a smaller Aleph may be a simpler first build?

I find this one really simple....
The only problem is to find old stock of good brand vintage transistors....
I like old and experience myself what my ears find the best between old and new technology...
Until now the reference in beautiful amp for me is Quad 2....sounds beautiful but not strong enough....

 

[Zen Mod]

then find more adequate speakers

Quad 2 , even if not newest thing is town , is recipe for many pleasant hours

then build new amps for fun , not because you must find better one

 

[Zen Mod]

You can substitute in lots of modern parts and it will likely work just fine.

Keep in mind that those output devices are Darlingtons.

damn

I'm blind

I saw beta around 20 and up in my ECA VRT

Pa - ya didn't mixed it with A40 ?

 

[Nelson Pass]

Older designs with modern transistors work just fine, usually better.

Being a pretty simple circuit, not too fussy about exact parts.

Pick some nice bipolars from On-Semi or other from distribution, matching
or exceeding voltage, current, and dissipation limits.

 

[Zen Mod]

......

Pa - ya didn't mixed it with A40 ?

 

[Yabanjin]

Older designs with modern transistors work just fine, usually better.

Being a pretty simple circuit, not too fussy about exact parts.

Pick some nice bipolars from On-Semi or other from distribution, matching
or exceeding voltage, current, and dissipation limits.

Thank you for your advice Mr Pass.
I heard in France your mono blocks with preamp on Dynaudio confidence c2 it was really wonderful for me.
With the huge Proac and musicalfidelity huge amplifier it was the two best system I never heard until today.
Thank you