F5 power amplifier

[CBRworm]

I used 2 of his 10.080 x 7 heatsinks for a stereo set. The fins were already vertical.

I found them to be more than sufficient for my F5 which has a pretty good amount of open air around it in an air conditioned room.

I think BarredBoss might be a vendor here with a subforum.

[compressit]

Could you or anyone else on this board comment on the audible differences (improvement) between an amp using chokes versus .1 ohm resistors in the amp PS?

Yes I can,it is MUCH better. It measures better and sounds alot better than it measures. Don't take a drooling looser like compressit's word for this though.
See post 4935

[jacco vermeulen]

Originally Posted by tinitus

what it is I see on those graphs

Temperature Coefficient = Tempco= TC
TC for a resistor is in ppm/C, unit of the Temperature Coefficient for a MOSFET is mV/degree, as in : mV change per degree.

The F5 is biased at 1.3A, you can find the Tempco at that current level from the set of curves in the graph.
TC of a single device is not interesting, the F5 output stage is not a single device but a "complementary" pair.
To compare the thermal runaway of different pairs requires determining TC for the entire output stage.

(it's when you look at the curves of the Bad Bad IRFP9240 when things become interesting)

[tinitus]

Originally Posted by jacco vermeulen

(it's when you look at the curves of the Bad Bad IRFP9240 when things become interesting)

I sense you are being ironical

Ok, lets try it then
Please point out the FIGURE ?. we should be looking at ?
http://www.oup.com/us/pdf/microcircu...s/IRFP9240.pdf

To me it seems some curves are going opposite way of what I would expect, which confuses me

[jacco vermeulen]

Figure 7 is the Vgs-Id graph.

The famous hump IRF P-channel has Zero TC at Id=2A, TC is less than 2mV/degree at a drain current of 1.3 Amp

(Zero TC doesn't happen for the FQA12P20 untill Id reaches 12 Amps, 2SJ201 even has to go beyond the graph axis limit to make ends meet)

[Russellc]

Originally Posted by alazira

Hi,
Set the bias pots to zero. On CVillers' board he has legs 2&3 together which means you turn completely counter clockwise to zero it. On Peter Daniel's board he has pins 1&2 together which means you start with the pot turned completely clockwise and bias it by turning it counter-clockwise.

Thank you for this piece of information, should help many first fire-up
BBQs....

Russellc

[Russellc]

Originally Posted by alazira

Hi Russellc,

It's tough to find a case for the F5, much less one that looks like Peter Daniels'. I too liked his build and have finally put together an ugly sister (only one channel so far).

I searched eBay until I found appropriate sinks and aluminum bars from Home Depot along with a hacksaw/miter box (labor intensive). I also had to learn to drill & tap holes (not very difficult actually)

Is it running yet? Thanks for the post.

russellc

[tinitus]

Originally Posted by jacco vermeulen

TC is less than 2mV/degree at a drain current of 1.3 Amp

(Zero TC doesn't happen for the FQA12P20 untill Id reaches 12 Amps, 2SJ201 even has to go beyond the graph axis limit to make ends meet)

I have to admit I still dont really see it clearly, but I take your word fore it
But he 150 degree and 25 ditto crosses around the point you mention
Is that what you point at, thermal instability
Nelson says its more reluctant to thermal runaway

But you seem to conclude that the Toshiba might be worth the exstra cost
That it should be considere
Thats really all I wanted to know
Thanks Jacco

[generg]

Originally Posted by Nelson Pass

By the way, I don't recall mentioning that different Mosfets
have different temperature coefficients, for example the
temperature coefficient for Vgs of the Fairchild devices is
about twice that of the IR parts.

This means that temperature compensation is less necessary
for the IR parts.

Needless to say, other manufacturer's parts are likely to
vary also.

Thanks Papa Nelson, now I know better why I had to be so patient to bias my F5 with Fairchild devices without termistors. In the next days I´ll have a check on the behavior of the IR devices. It is a great pleasure to look at the differences small changes can make.

[Beftus]

Originally Posted by Russellc

Thank you for this piece of information, should help many first fire-up
BBQs....

Russellc

Couldn't agree more, though I would say it would help to prevent BBQs... This bit is also crucial information!