[Andre Jute]

HEATSINKING

No 57 in Andre's Handy Shortcuts
also
No 113 in Andre's Rules of Thumb for the Mathematically Ten-Thumbed

Let's say you have a component (resistor, tube, whatever) which needs
to be kept from overheating. You can make a heatsink by bolting
aliminium angles to a backplate to make fins.

The permissible temperature rise is the permissible temperature less
the room temperature which we assume is 30 degrees.

The heatsink rating is usually given in degrees Celsius of rise per
Watt of power dissipated by the device, assuming a perfect junction.
Thus, divide the permissible temperature rise by the power of the
device.

The minimum area of heatsinking you want to achieve this rating is
appromimately 50 divided by the square root of the area in square
centimetres.

You count all area exposed to free-flowing air: both sides of the
outside fins plus the outside of the backplate but not its inside if
enclosed.

So we have

50/(sqrtA in cm) = (permissable rise in degrees C)/(power in watts)

which is good for checking if an existing heatsink will do the job, or
we can calculate how big a heatsink must be to do the job with this
more convenient formulation

A = (C/(W*50))*(C/(W*50))

and the answer is in square centimetres.

HTH.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[jack]

From a defunct U.S. electronics DIY magazine -- you don't even need thumbs.

http://www.tech-diy.com/heatsink_nomograph.gif

[Andre Jute]

On Feb 5, 4:20*pm, "jack" wrote:
From a defunct U.S. electronics DIY magazine -- you don't even need thumbs..

http://www.tech-diy.com/heatsink_nomograph.gif

Thanks, Jack. That nomograph will do fine for small stuff. But for
real he-man stuff, amps with transmitting tubes and suchlike pastimes
of fellows with toupees on their chests, permitted temperature rise of
less than one degree per watt is the norm, and those heatsinks should
be calculated by the formula.

HTH.

How will you ever get to be a tubie if you do things the easy way?

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[Jonathan Wilson]

Andre Jute wrote:

HEATSINKING

No 57 in Andre's Handy Shortcuts
also
No 113 in Andre's Rules of Thumb for the Mathematically Ten-Thumbed



I'm new to the group.
Where can I get the rest of these shortcuts and rules (assuming there really
are more?)?

I tried google but all the results that pulled up are No. 57.

Thanks,

JW

[Andre Jute]

On Feb 13, 6:36*am, Jonathan Wilson wrote:
Andre Jute wrote:
HEATSINKING

No 57 in Andre's Handy Shortcuts
also
No 113 in Andre's Rules of Thumb for the Mathematically Ten-Thumbed

I'm new to the group.
Where can I get the rest of these shortcuts and rules (assuming there really
are more?)?

Heh-heh! I was gently ribbing the fellows here, all wrapped up in
their hifaluting flame wars, that once upon a time we on RAT had
something to offer diligent newbies. The nearest to hints and tips I
come is my netsite Jute on Amps:
http://members.lycos.co.uk/fiultra/JUTE%20ON%20AMPS.htm
You'll want to pay particular attention to The KISS Amp, which is a
book which shows how to design an amp from scratch, including all the
considerations you might take into account:
http://members.lycos.co.uk/fiultra/T...mp%20INDEX.htm

I tried google but all the results that pulled up are No. 57.

Thanks,

* * * * JW

In general, you should have copies of the tubie bible. the Radio
Designer's Handbook, 4th edition, and an ARRL (American Radio Relay
League) annual from around the end of the tube era (say early to later
1950s) for reference and bedside reading. Books by Crowhurst are also
good; articles by Crowhurst are on the net and can be downloaded as
well.

HTH. Good luck.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[Iain Churches[_2_]]

"Jonathan Wilson" wrote in message
...
Andre Jute wrote:

HEATSINKING

No 57 in Andre's Handy Shortcuts
also
No 113 in Andre's Rules of Thumb for the Mathematically Ten-Thumbed



I'm new to the group.
Where can I get the rest of these shortcuts and rules (assuming there
really
are more?)?

I tried google but all the results that pulled up are No. 57.


Morning Jonathan. The advice Andre gave you is sound,
but there are no real shortcuts:-)

RDH4 is excellent, though a bit heavy going.
Other useful additions to your library include:

Bruce Rozenblit: Beginner's Guide to Tube Audio Design
Morgan Jones: Valve Amplifiers.

Welcome to RAT.
Iain