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05-03-2023, 10:19 AM
Hi Champ81
Absolutely leave the bleeder resistor in place.
Capacitors can retain charge for an extremely long time and with the voltages inside a tube amp you can have a nasty surprise. For example, a customer brought his Marshall to me for a repair. When I took the chassis out of the amp sleeve and was setting it up on my bench I got a good zap from the main filter which still had a voltage of over 400V on it after at least an hour of disuse.
It is a good practise to install bleeder resistors in every kind of amp and PSU. You only "see their absence" in cheaply designed products.
Your skin temperature is 24C and you can usually touch things that approach 40C - beyond that you definitely cannot hold your finger in contact with the hot device. You can gauge temperature by "proximity" without touching the device, which we naturally do anyway.
As suggested above, using a component with a larger body will allow the part to operate at a lower temperature for a given amount of heat. The large part has more surface area and its thermal resistance should be lower than for a smaller part. It is best to keep the surface temp of components to less than 50C and otherwise as low as you can within reason.
"Laser" thermometers are quite inexpensive now and are very handy when you want to probe a circuit and measure component body temperatures. Every device has a thermal resistance rating, or its data sheet shows a graph of temp / dissipation. The meter will read the surface temperature and you can use the thermal resistance to calculate the internal temperature, which will have a specified maximum.
Any resistor or component that dissipates heat - which is all of them except capacitors - must be mounted in a manner that allows that heat to escape and so its heating won't damage or effect adjacent components. This is why all of our kit notes specify to elevate power resistors off the PCB. In the case of your hot resistor, you do not want PVC-insulated wires in contact with it as the insulation will melt.
Just use the 'quick reply' instead of quoting the entire reply each time.
Absolutely leave the bleeder resistor in place.
Capacitors can retain charge for an extremely long time and with the voltages inside a tube amp you can have a nasty surprise. For example, a customer brought his Marshall to me for a repair. When I took the chassis out of the amp sleeve and was setting it up on my bench I got a good zap from the main filter which still had a voltage of over 400V on it after at least an hour of disuse.
It is a good practise to install bleeder resistors in every kind of amp and PSU. You only "see their absence" in cheaply designed products.
Your skin temperature is 24C and you can usually touch things that approach 40C - beyond that you definitely cannot hold your finger in contact with the hot device. You can gauge temperature by "proximity" without touching the device, which we naturally do anyway.
As suggested above, using a component with a larger body will allow the part to operate at a lower temperature for a given amount of heat. The large part has more surface area and its thermal resistance should be lower than for a smaller part. It is best to keep the surface temp of components to less than 50C and otherwise as low as you can within reason.
"Laser" thermometers are quite inexpensive now and are very handy when you want to probe a circuit and measure component body temperatures. Every device has a thermal resistance rating, or its data sheet shows a graph of temp / dissipation. The meter will read the surface temperature and you can use the thermal resistance to calculate the internal temperature, which will have a specified maximum.
Any resistor or component that dissipates heat - which is all of them except capacitors - must be mounted in a manner that allows that heat to escape and so its heating won't damage or effect adjacent components. This is why all of our kit notes specify to elevate power resistors off the PCB. In the case of your hot resistor, you do not want PVC-insulated wires in contact with it as the insulation will melt.
Just use the 'quick reply' instead of quoting the entire reply each time.
