I just measured an amp I built two years ago and have used almost 24/7 since. The power transformer cover gets up to about 65°C but I have a Hammond in a KT88 amp that will hit 95°C and Hammond said it's within spec but then undid an "engineering change" that will result in 10°C cooler temperatures.
Thats a lot of current, what is the ripple current rating of the first DC filter cap in the filament supply?.. over worked caps get 'hot' too.
well funnily enough I have been looking at the approach to smooth a quotes 10.5V AC on the mains transformer to provide a smoothed DC. I tried to model in PSDUD2 but having learning curve challenges! anyway it's a CRC from full bridge to 47000 uF - 0.82R - 47000uF where the 0.82R is placed on the plate to cool it down. See images, its difficult to see without understanding the 3D layout but there is a space for air to be pushed to the back of the amp and up via holes in a copper top plate.
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are the parts all rated to handle 1000 volts? You may be getting some internal arcing due to insulation breakdown. 55 is on the warm side but not melt down levels of heat. If you can arrange natural convection where cooler air is drawn in as the hot air rises away you might drop the temp. If the air just sits there you end up with heat soak. Try using the fan to pull away the air instead of blowing on the amp, it might work better.
The DC heaters are just 10V but 3.25A so across 0.82R there is two ~9W heaters that warm the plate up.
Thanks for all the guidance - to start with I am going to try a simple solution that may have some effect. Since the heat problem comes from the top of the plate interfacing with the choke and transformers nearby the underside location of the power resistor, I am going to try a heat sink on the top of the plate in this location, not ideal but super simple to try 🙂
Ok - so this might be useful to others, but is perhaps just my particular case, but I thought I would share it. I have reduced the temperature by about 6 Deg C or so. Ambient last night 28 Deg C (hot day in the UK!) and I was able to keep the choke and transformers to a maximum of 50 Deg C. I tried it with thermal paste as you can messily see...... before I clean it up and use thermal tape for a more permanent installation.
