Hover on the flag at the left side, top of my posts and read the text there.
The power transistors are mounted on a small, custom heatsink that is visible on the rear panel shown in your pics. With the low bias current, this should be OK even at an ambient of 30C or so. The amplifiers won't be specifically designed to work at a max of 20C but the designer probably just did not consider other markets or end users other than in the UK, Europe and North America.
The problem comes when you have inefficient speakers and need to turn up the volume. The heatsink then becomes much hotter and cannot dissipate the extra heat fast enough, particulary with modern, compressed music. You can easily check that after the amplifier has reached operating temp. If you cannot keep a finger on the sink for more than 3-5 seconds, it is at or above a safe power level. Logically, just avoid playing it loud at parties etc. as this is when most failures occur. You could place a fan at the rear but it may be annoying if you listen to fine jazz or classical style music, for example.
My heat problem was with the tuner section. Though its FM section is good, it uses regular Zener diodes instead of proper varactor or varicap tuning diodes. Zeners are much cheaper but usually have a greater temperature coefficient. So the tuner works fine until the ambient temp. rises during the day. Above 27C or so, there is a whoosh sound as the tuner loses AFC lock and the FM station. It then won't work properly until the room cools again in the evening. Air conditioning or a partial redesign is the answer but neither will be easy or cheap for everyone.
@Ian Finch
Oh, Australia! Sorry, using tapatalk so the flags dont appear.
Good to know that if and when I can get this running, the temp shouldnt be a problem.
Oh, Australia! Sorry, using tapatalk so the flags dont appear.
Good to know that if and when I can get this running, the temp shouldnt be a problem.
