♫♪ My little cheap Circlophone© ♫♪

[terranigma]

Originally Posted by heinz

The only problem i am experiencing: The driver Transistors and 2n3019 are getting too hot to touch. Did anybody else a build usind the tight packed powerflux pcb? Is there a clever way to use a heatsink on the to-39 package?
Thank you.

I built a pair of same pcb, yes 2n3019's are hot but it is not a indicator of any fault. Heatsinks are hot too.. you have to attach a small piece of heatsink at least, rather using them naked.

I will post pics of my current setup soon.

@Powerflux

Can you prepare an alternative version respecting my suggestion related with power rails route and pads?

[powerflux]

Originally Posted by terranigma

I built a pair of same pcb, yes 2n3019's are hot but it is not a indicator of any fault. Heatsinks are hot too.. you have to attach a small piece of heatsink at least, rather using them naked.

I will post pics of my current setup soon.

@Powerflux

Can you prepare an alternative version respecting my suggestion related with power rails route and pads?

i could, but since it it such a minor modification, some graphical editing with MSpaint like in your example should be sufficient and faster than me and eagle printing PDF's...

[Elvee]

Originally Posted by heinz

Hi,

i made a circlophone based on powerfluxes pcb (see the attached picture). I did use the transistors originaly proposed in the schematic. Voltage ist +-25V.
Power draw (no signal) from Transformator is approx. 10W.

That's normal: this is "warm" class AB (sort of)

The only problem i am experiencing: The driver Transistors and 2n3019 are getting too hot to touch. Did anybody else a build usind the tight packed powerflux pcb?

If there are no resistor inversions or mistakes, the power in each transistor should be ~25V x 13mA = 325mW.
Since the Rth(j-a) is 219°C/W, this means the junction is 71.18°C above ambient.
For 50°C ambient, this translates into 121.18°C junction temp, or, taking into account the Rth(j-c) of 35°C/W, a case temp a little under 110°C.
Probably too hot to touch for many people, but not a concern: this is not a plastic case, and whilst it would be unwise to operate near the 200°C abs max rating, temperatures below the eutectic (~170°C) are perfectly safe in the long term.
If you feel uncomfortable with such temperatures (it is completely output-power independent), there are small tube or chimney-like TO39 heatsinks compatible with Powerflux's design.
You can also use alternative transistors having a Cob <15pF and Ft>75MHz (do not exagerate in that direction though) like the BF819: the TO202 acts as an integral cooling clip.
BF458 and many other are also suitable, but they are more or less obsolete.
Anyway, you can leave your 2N3019's as they are: there is no risk or problem, even in the long term.
Just make sure the resistors are OK, and the zeners have the right voltage and are not shorted.

PS:
the proximity effect of the transistors increases the apparent temperature, but at supply voltages of 25V, this is not a concern.
None of my prototypes has heatsinks fitted, the transistors are almost as close as in Powerflux's PCB, and one of them operates at 40V

[terranigma]

Originally Posted by terranigma

Heatsinks are hot too.. you have to ...

What? I meant "Drivers", not "Heatsinks" of course.

[Elvee]

Here are two examples of cooling clips for TO5/TO39.

One is a very small, tube-like shape. It could be used in any situation, even where there is very little space.
It is marked "THM 1115" (probably Thermalloy).

The other is a corrugated, chimney-like, and is more obtrusive.


Between these two extreme, one can also find medium-sized grooved cylinders.
I have no example to display unfortunately.

[danielwritesbac]

Can NXP BCP53 be used instead of the discontinued Philips BD140, or will the modern version not handle the heat? I can't find a TO220 with specs like that.

[kenpeter]

BD140 are still made in TO126 by: Fairchild, ST, and OnSemi. Probably others too.

[mickeymoose]

This is the heatsink I used:

Edit: I replaced the MJE15031 (see Elvee' next post) with the 2N3019 in this setup. I am still looking for a suitable transistor in a TO220 or similar package. E

[Elvee]

Originally Posted by danielwritesbac

Can NXP BCP53 be used instead of the discontinued Philips BD140, or will the modern version not handle the heat?

I am afraid not: even with 25V rails, the quiescent dissipation is already ~=1W, and the dissipation is heavily output-power-dependent.
That's too much for BCP53.

But even if you exclude "newer" BD140's, there are numbers of TO126 alternatives: some 2SAxxx, and 2SBxxx, I think OdysseyBmx opted for one of those, I'll be able to give you some more details next year....

Mickeymoose has based his version on MJE15031 (TO220). That's heavy artillery, but it works provided the VAS is not too oversized: when you combine slow and/or high capacitance VAS + drivers, stability issues begin to appear.

There will be a fix in Mickey's final version, but the simplest option is to use adequately-sized devices for the job.

[powerflux]

wait. BD140 discontinued?? seriously?

those transistors are beauties..