Krell KSA 100mkII Clone

[AndrewT]

Hi,
there are two pots to adjust.
For output offset voltage and output bias current.

[Upupa Epops]

Really big space for own creativity....

[jacco vermeulen]

Originally posted by Mark A. Gulbrandsen
Thats a KSA-80 (USA model # ) guys

Told you SO and SO

[Patrik Floding]

Any news on those diodes?
BTW, isn't this thread unusually quiet? I assume everyone is building away on their amps!

(I'm not, I'm thinking about casework, heatsinks, etc, etc.)

[Flodstroem]

Originally posted by Patrik Floding
Any news on those diodes?
BTW, isn't this thread unusually quiet? I assume everyone is building away on their amps!

(I'm not, I'm thinking about casework, heatsinks, etc, etc.)

Yeh, I presume they have their heads very close to the PCBs´ soldering components like a turbo and thinking who will be the first to post pics of the finished crown-jewel

You mention casework/chassis and I plan to buy a custom design chassis from the Italian company Hi-Fi2000. They have all equipments that is needed for to do custom works, and they also have stated it officially.

I have done some drawings for a complete chassis for to fit together with my Australian Conrads heat sink type MF-350-151.5 (2 heat sinks for a mono block, no fan in my cases). I shall order 6 or 7 chassis from them. Anybody interested to join in?

Regards

[grimberg]

Originally posted by Flodstroem

...Australian Conrads heat sink type MF-350-151.5 (2 heat sinks for a mono block, no fan in my cases).
Regards

I am using two of those per monoblock for my KSA-50. I am not sure they are large enough for the KSA-100.

[Patrik Floding]

Originally posted by Flodstroem


Yeh, I presume they have their heads very close to the PCBs´ soldering components like a turbo and thinking who will be the first to post pics of the finished crown-jewel

You mention casework/chassis and I plan to buy a custom design chassis from the Italian company Hi-Fi2000. They have all equipments that is needed for to do custom works, and they also have stated it officially.

I have done some drawings for a complete chassis for to fit together with my Australian Conrads heat sink type MF-350-151.5 (2 heat sinks for a mono block, no fan in my cases). I shall order 6 or 7 chassis from them. Anybody interested to join in?

Regards

I too plan on building monoblocks with no fans.
However, I was planning to try to have the transformers in separate chassis. Not sure if it makes sense, but I was hoping doing so might give some audible benefits.

Knowing what you are prepared to spend on transformers, I'm not sure I could afford these caseworks anyway!

[AndrewT]

Hi,
270W dissipation through a pair of MF35 151.5 will raise Tc quite high. Is MF350 different?
Are you intending to use To3 or To264 packages?
Conrad specify their sinks @ 80Cdegrees above ambient. One must correct the Rth s-a for the lower temperature difference that most designs demand.

Using To264, I would expect Tc to be about 47Cdegrees above ambient. In hot weather this could lead to Tc approaching 80degC and 250W devices must be de-rated to 140W.
A few devices could run slightly hotter due to Ib differences and tolerance spread in the thermal coupling to the sink.

To3 will survive much better but I would still recommend a better pair of sinks. Corrected Rth s-a<0.1C/W

[Flodstroem]

Originally posted by AndrewT
Hi,
270W dissipation through a pair of MF35 151.5 will raise Tc quite high. Is MF350 different?
Are you intending to use To3 or To264 packages?
Conrad specify their sinks @ 80Cdegrees above ambient. One must correct the Rth s-a for the lower temperature difference that most designs demand.

Using To264, I would expect Tc to be about 47Cdegrees above ambient. In hot weather this could lead to Tc approaching 80degC and 250W devices must be de-rated to 140W.
A few devices could run slightly hotter due to Ib differences and tolerance spread in the thermal coupling to the sink.

To3 will survive much better but I would still recommend a better pair of sinks. Corrected Rth s-a<0.1C/W

Andrew, Yes you are right about the dissipation, it will be 270 Watts if running the amp as the originals at idling currents.

My calculation says: correction factor for 37° over ambient will be ca 1.28 and the C/W for the MF35-151.5 is 0.21 (sorry I confused you, but my mistake)
Then each sink could handle 37/(1.28 x 0.21) which means ca 138 Watts and this is one side (one rail side) there is two of those sinks on my mono block so maximum sink temp will be calculated like this: 28° (at hottest summer) + 37° rise, a maximum of 65°C. But consider this: I havnt calculated dissipation help from the well ventilated chassis and there is some small heat sinks on the back of the main sinks that also help to rise the dissipation factor.

Normally our house temp is between 22° to 24° the most of the time here in our location in the Western Norway and I have estimated the fin- temperature to be between 55 and 60°C. Its not that hot, is it?

I Im going to use 6 pair of the metal, 250W transistors so each transistor must handle 270W/12 =22.5 Watts of dissipation, and without looking in the data sheet, it could look like a security factor of 11 not included the running temp correction factor.

Knowing what you are prepared to spend on transformers, I'm not sure I could afford these caseworks anyway!

Patrik, you have a point here, but in my case, I will spend most of my money on the transformer, PCBs´, Computer graded Electrolytics. If chassis should be an expensive affair then I had to reconsider it seriously.

[loek]

Kind off...
Sorting out resistors for this beast ....

Loek