I have a 3U amplifier case from Modushop. Each side has 2 heatsinks (i.e. 4 in total) that are connected only by the box frame (2 small 'beams' on the top and bottom of the enclosure). Even though the heatsinks touch at their junction, I assume that the thermal conduction between the 2 heatsinks might be problematic - the 2 heatsinks might run at different temperatures?
When mounting the output pair transistors of a power amplifier is it best to:
1) Mount one transistor on each heatsink?
2) Try to mount the transistors such that they 'straddle' the gap between the heatsinks?
Or am I just worrying more that I should? 🙁
The amp is a stereo 30W Hiraga Class A.
Thanks for viewing.
When mounting the output pair transistors of a power amplifier is it best to:
1) Mount one transistor on each heatsink?
2) Try to mount the transistors such that they 'straddle' the gap between the heatsinks?
Or am I just worrying more that I should? 🙁
The amp is a stereo 30W Hiraga Class A.
Thanks for viewing.
Hello,
I did have the 30 watt with the original parts sold in France long long time ago. The heatsinks are getting hot so i would try not to make them heat up one another.
The original publications about this amp always did talk a lot about having enough airflow across the heatsinks.
In your country it might be even more important because of the climate.
I do remember that if you touch one of the drivers( so making its temperature rise) the dc at the output of the amp wil change. SO it is a good idea to connect them with a piece of aluminum ( of course electrically isolated!! ) to make them have the same temperature)
greetings, eduard
I did have the 30 watt with the original parts sold in France long long time ago. The heatsinks are getting hot so i would try not to make them heat up one another.
The original publications about this amp always did talk a lot about having enough airflow across the heatsinks.
In your country it might be even more important because of the climate.
I do remember that if you touch one of the drivers( so making its temperature rise) the dc at the output of the amp wil change. SO it is a good idea to connect them with a piece of aluminum ( of course electrically isolated!! ) to make them have the same temperature)
greetings, eduard
Keeping the transistors at the same temperature is very important.
If one were to run a bit hotter, it will reduce it's Vbe and increase it's hFE.
These will combine to draw a bit more Ic current. Now you are onto the thermal instability slope and it goes downhill all the way to possible blowup.
You can detect this on a test set up.
Put two paralleled devices close together on a single heatsink. use accurately matched source resistors and accurately matched collector resistors and accurately matched base stoppers.
Apply a fixed supply voltage and apply a driving voltage to the two base stoppers. See how closely matched the two devices are when they are relatively cool and if that changes as they warm up.
Now dismount and insert an extra thermal washer on one of the devices and repeat the test. The one with the thicker (more thermal resistance) washer will have a higher Rth c-s and will run the device with a slightly higher Tc, even when Pq is the same.
You will be able to measure the deterioration in the intended equal currents. It will get worse as the devices warm up. It will get much worse when the devices become hot. Try for a Tc~80°C
If one were to run a bit hotter, it will reduce it's Vbe and increase it's hFE.
These will combine to draw a bit more Ic current. Now you are onto the thermal instability slope and it goes downhill all the way to possible blowup.
You can detect this on a test set up.
Put two paralleled devices close together on a single heatsink. use accurately matched source resistors and accurately matched collector resistors and accurately matched base stoppers.
Apply a fixed supply voltage and apply a driving voltage to the two base stoppers. See how closely matched the two devices are when they are relatively cool and if that changes as they warm up.
Now dismount and insert an extra thermal washer on one of the devices and repeat the test. The one with the thicker (more thermal resistance) washer will have a higher Rth c-s and will run the device with a slightly higher Tc, even when Pq is the same.
You will be able to measure the deterioration in the intended equal currents. It will get worse as the devices warm up. It will get much worse when the devices become hot. Try for a Tc~80°C
Last edited:
Thanks Eduard,
Guess I'll have to find a way to bridge the gap or place both transistors on one heatsink.
Thanks Andrew,
Had an idea things would go haywire if the temperature differential got out of hand - but seems worse than I had anticipated!
I've attached a quick photo of the PCB and the twin heatsink gap 'problem'. (would have been better if I'd done this to start - just lazy I guess)
Cheers,
Tony
Guess I'll have to find a way to bridge the gap or place both transistors on one heatsink.
Thanks Andrew,
Had an idea things would go haywire if the temperature differential got out of hand - but seems worse than I had anticipated!
I've attached a quick photo of the PCB and the twin heatsink gap 'problem'. (would have been better if I'd done this to start - just lazy I guess)
Cheers,
Tony
Attachments
Hello Tony,
I would just use some short wires sop you could attach the transistors a bit more in the central part of the heatsink. Just like it was done in the original Hiraga. Especially if your current and supply voltage is similasr to the original one.
Normally the drivers did not have a heatsink so i guess just a piece of alu or copper will do. Dont forget the washers.
Greetings, Eduard
I would just use some short wires sop you could attach the transistors a bit more in the central part of the heatsink. Just like it was done in the original Hiraga. Especially if your current and supply voltage is similasr to the original one.
Normally the drivers did not have a heatsink so i guess just a piece of alu or copper will do. Dont forget the washers.
Greetings, Eduard
- Status
- Not open for further replies.