NAD 3020 drivers

[wuffwaff]

Hi,

I´m trying to repair an old NAD3020. One channnel has lost it´s output transistors (2N3055 /MJ2955) and one driver 2N6551.

The output transistors are easy to get but I can´t find any suppliers for the 2N6551 or 2N6553.

Since it seems to be asimple 60V / 1A device there must be quite some parts that are suitable as a replacement.

Any suggestions what could be used as a driver pair instead of the 2N6551/6554?

William

[lineup]

2N6551/6554 are 75 MHz TO-202 transistors, max 10 Watt

This is very much like BD139/140.
They should be a perfect replacement.

2N6551 2N6554 Datasheet PDF

[Eva]

BD139 and BD140 should be fine. Dissipation may be an issue because TO-202 have a small built-in heatsink, so bolting some small metal sheets to the backs of BD139/140 is advised.

[Tube_Dude]

In the last incarnations of the 3020 with the suffix I (improved ?? ) , they already use the BD139 / 138 as drivers...

[Giaime]

Nah, mine is one of the oldest (champagne faceplate with "series 20" logo) and already has the BD139/BD140. My thoughts are that NAD put in what they had in the parts bin

It's a beautiful amp, now it's my main amp (yes, I'm serious).

[lineup]

Originally posted by Giaime
Nah, mine is one of the oldest (champagne faceplate with "series 20" logo) and already has the BD139/BD140. My thoughts are that NAD put in what they had in the parts bin

It's a beautiful amp, now it's my main amp (yes, I'm serious).

Yes, Giame.
I found you tell about your NAD3020 in your homepage.


Quote:
Here's my lovely amp, the "highly sought after" NAD3020, the very first series (with the "Series 20" logo).
This is one of the only photos I've been able to find on the Net for the "champagne" version.


In the The Class-A Amplifier Site
there is NAD 3020 schematic

[wuffwaff]

Hi,

thanks! I will try them and also change the pair from the other channel.

Do the newer ones with BD139/140 have little heatsinks or not?

William

[Tube_Dude]

Originally posted by wuffwaff


Do the newer ones with BD139/140 have little heatsinks or not?

No, they don't use heatsinks ,certainly because the rails are only
+- 28 volts.

But it's not a bad idea to use a small one... just in case...

[wuffwaff]

Hi,

I´ve replaced the transistors and would like to see if the amp is working.
Is there anything that needs to be set like bias or so? I can only see VR5 wich feeds power supply voltage to the input. Is this for offset adjusting?

William

[Tube_Dude]

Originally posted by wuffwaff
I can only see VR5 wich feeds power supply voltage to the input. Is this for offset adjusting?

Yes, VR5 is for offset adjusting...


The BD 139/140 see from the front and the pins in your direction :

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