Is this drawing correct?

[swingarm63]

It seems that the tip147 should be a pnp ? Is this the wrong component ?
Is it a tip142 instead?

Thanks

 

[rayma]

That NPN schematic is correct, just upside down. Correct part number is TIP-142. Don't forget the heat sink.
Which book is this from?

 

[swingarm63]

I could not find this in the 3 books i have on hifi-guitar preamps and power supplies. I must have found this on the net at some point.
I'm not sure. Also I have not worked a lot with these devices, but isn't a tip147 a pnp? Just want to make sure, before I do this.

 

[rayma]

The TIP-142 is NPN. The TIP-147 is PNP. See page 1/10 here.
https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00000914.pdf

 

[swingarm63]

But on the sheet it says PNP the 142 is a NPN, No?

 

[rayma]

Yes, the schematic has a typo. But not the data sheet.
The circuit as drawn requires an NPN transistor.
Watch out for the needed power dissipation in the TIP, plus derating.

 

[swingarm63]

Ok yeah its a 142 got it.

Thanks rayma.

 

[swingarm63]

LOL It took a while to "sink in"!

 

[rayma]

That transistor could dissipate around 10W for 2 pairs of output tubes.
I suspect the book said to mount it directly to the chassis for a heat sink.
Which would work, since the tab is at ground potential (the secondary's center tap is at -50VDC.)

 

[audiohead]

http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm

Check out this link. The section titled "A Mosfet B+ reducer"

The circuit as shown in post #1 is jacked up.

Art

 

[rayma]

Pretty much the same thing.

 

[gorgon53]

Strange logic... npn 142, pnp 147

 

[audiohead]

As my hero Rod Coleman said this circuit (post #1) does not inspire confidence.

I have played with mosfet circuit years ago. It works.

Art

 

[audiohead]

I forgot to mention that if the darlington is npn then the zener diode is drawn upside down. and the 100 Ohm resistor?

The mosfet circuit, the drain source voltage is VZ+VGS.

Art

 

[gorgon53]

This fet circuit, as drawn, wont work. It needs an enhancement type fet.
Zener is not upside down, it is as it should be, so is the 100ohm resistor

 

[swingarm63]

Oh did Rod poo poo this circuit?

 

[swingarm63]

Well maybe this circuit came from the prior power supply book by Merlin, that he decided not to continue selling?
Anyway, thanks for the advice. I need to drop about 40 volts.

 

[swingarm63]

What would you guys recommend to get the job done?

 

[gorgon53]

What type of load? Min and max current?

 

[swingarm63]

Its a preamp so not very much, maybe 35ma total