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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
I'm afraid I did't record values on mine for those. I also don't have my workbench BM8000 completely assembled for testing right now. Otherwise I could do a quick measurement.-sonavor
I hope to replace the connectors this weekend. If everything works well, I will report back on the temperatures.
Hmm I might have been wrong on TR210.
I did another round of tests and it appears that my IR temperature gun is not very accurate. What I think I was measuring was the heatsink of TR211 (BF857) which is too hot to touch for more than half a second. In fact, all the BF857s get quite hot both in the left and right output amplifiers (75℃ for TR211 vs 65-70℃ for TR207/TR107/TR111).
I'm assuming that high temperatures are expected for these transistors... Is there a benefit in replacing these with BF858s as I have read some people do? Or wouldn't that really affect heat generation?
Sorry..I have been slowed down due to parts. I started on the updates to the display and ran out of LEDs (lost/damaged couple of them). Half-way through and waiting on LEDs now.
krais: Is there a benefit in replacing these with BF858s as I have read some people do? Or wouldn't that really affect heat generation?
Is there a benefit in replacing these with BF858s as I have read some people do? Or wouldn't that really affect heat generation?
No.The heat dissipated will be the same regardless of the max operating voltage rating of the transistor.
They run warm. That's normal.
Martin
I put my workbench BM8000 back together and the BF858s run around 68 degrees C on that one.
-sonavor
Thanks for measuring Sonavor and apologies fo the late response (I have been preoccupied with work lately).
Today I did another round of temperature measurements, this time with a small thermocouple pressed against the BF857 heatsinks. TR211 measures at 88 degrees C and the other BF857s on both channels settle at around 82 degrees C (after a warming up period of around 20 minutes, no audio input and volume set to zero).
Quite a significant delta with your measurements. However still within the working range of the transistors and given they run hot at both the right and left channel not necessarily indicative of a problem perhaps?
Finally it's time to wrap this one up. I did some additional tests but concluded that heat dissipation is probably fine. Frequency response, power output and listening tests did not show any additional problems (in fact it sounds amazing). Here is the the Beomaster in its full glory after reassembly.
Many thanks to Sonavor, Martin, Manfy and others for all the incredibly helpful advice and tips. When I started this project I knew I was in for a challenge given my limited domain knowledge and experience. I faced quite a few problems and setbacks (some due to my own fault) but with your help I managed to get the BM8000 restored and learned a great deal along the way. Thank you!
Nice work. Your Beomaster 8000 is an excellent example of one. I think you will find, as I have, that the more you listen to it the more you like it.
-Sonavor