F5 power amplifier

[Russellc]

Originally Posted by cviller

If your board is already mounted, you can measure across R3 and R4 instead - their legs are tied to P1 and P2 respectively.

Stuffed, but not mounted......

Russellc

[Tea-Bag]

Originally Posted by tinitus

THAT is really very good news


dammit, I had promissed myself I would lay off this kind of hysteria

Hysteria, that's part of the thing here too.
Seriously, Cviller's F5 at BAF09 was on one big chunk of aluminum. Just bias it to normal bias, or till it reaches 55C at room temp, whichever comes first.

Cutting sinks with a Non ferrous blade is kind fun, but a mistake can make a set look really ugly.

[tinitus]

Originally Posted by jacco vermeulen

take a wild guess =>

Ofcourse
That heatsink might actually very well be the exact one I have
Fore that one 200mm is the optimal limit where cooling gain curve flattens, and cooling gain becomes less beyond this length
Which indicates that 2x 200mm is more effective than 1x 400
Now thats settled, I can spend some money on other more important parts instead

[jacco vermeulen]

Close to 100% more effective.
SK56 is the most common 300mm heatsink in these parts.
The curve of the Seifert KL-146 shows even better that it levels out at 200mm height, the KL-146 is close to identical to the Fisher SK56 that i posted earlier.

My Al-J's do +100W of heat on 2 SK93 heatsinks of 55mm length, with boards from the GB at Holger's analog-forum.de
(are topped by hardened glass panels : Anordna shelfs for IKEA's Lillangen series, come with pre-drilled corner holes for peanuts. I bought 100 of the old series for ~$0.29 each )

[AndrewT]

a 100mm high sink can dissipate X watts.
A 200mm high sink can dissipate ~1.4*X watts.
A 400mm high heatsink can dissipate ~2X watts.
A 800mm high heatsink can dissipate <<~2.8*X watts.
A group of four 100mm high heatsinks in a row or forming four sides of a square chassis can dissipate 4X watts.
An 800mm heatsink cut into 8off 98mm high lengths to form two monoblock chassis can dissipate ~8X watts.

Assuming the back plate is thick enough and that deltaT(s-a) is the same for each.

[Beftus]

Originally Posted by AndrewT

a 100mm high sink can dissipate X watts.
A 200mm high sink can dissipate ~1.4*X watts.
A 400mm high heatsink can dissipate ~2X watts.
A 800mm high heatsink can dissipate <<~2.8*X watts.
A group of four 100mm high heatsinks in a row or forming four sides of a square chassis can dissipate 4X watts.
An 800mm heatsink cut into 8off 98mm high lengths to form two monoblock chassis can dissipate ~8X watts.

Assuming the back plate is thick enough and that deltaT(s-a) is the same for each.

Interesting. Proof that sheer size doesn't matter.

[tinitus]

Originally Posted by Beftus

Interesting. Proof that sheer size doesn't matter.

That very nice info on relation between various lengths, and good to know, really good explanations
But bare in mind that its simplified to understand the relations
Note that almost all different heatsink designs behave different with various lengths
Ofcourse the number of outputs used, relative to sink size, and how they are spread/mounted have to matter as well
Fisher site is comprehensive and good to study to get some understanding of the effectivenes of various heatsink designs
Roughly, the longest finning seems better, and expencive
Also very wide heatsinks appears to be good, but of little use with only 1 pair output
Unless you do it like the master do it
I have no doubt that when 2 smaller heatsinks fore each channel is suggested in F5 manual, its well knowing that they are easier to get, and maybe cheaper as well
And makes nice small monoamps

[Brian Kingsbury]

After 3 days of cutting, stripping, soldering, mounting and quadruple checking I just finished wiring up my F5 and fired it up for the first time. Rail voltages checked out okay. Once things warm up all the way I'll finish setting the bias. It's a good thing it's starting to get chilly here because this amp gets niiiice and toasty. I can't wait to give it a listen. This is my first DIY amp from scratch so I'm really excited.

[Variac]

Congratulations!!
Mark

[jackies]

After reading countless pages of this thread, I think somebody did this - but let me ask just to be shure - can I power this amp from a single 33v secondary if I create a "virtual ground" with two 1k resistors?