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Argus25 · 21st Oct 2019, 5:11 am

If you look carefully at the battery eliminators which I posted links to in the two articles in post #3, you will notice how the filament supplies have over voltage protection incorporated. I think this is an essential part of a good battery eliminator.

In addition, it is important that if you have a battery eliminator with a range of HT output voltages derived from a regulated supply, that you have to allow for a scenario where a connection say to a 135V output might be disconnected and connected to a lower voltage output say 90V by the user. The charge storage in the actual radio (its own filter capacitors) then attempts to inject energy back into the eliminator regulators, say being transistors or IC's, which can destroy them. This is the purpose of the additional diodes you see in series with the HT outputs on the multi-voltage output eliminator. So there needs to be protection for the outputs being forced higher than their normal values. It is often these sorts of things that get completely neglected in many battery eliminator designs.

In addition it is better for these units to have some fusing after the main reservoir capacitors as the fuse values can be lower than when they have to support the initial turn on current surges charging the eliminator's capacitors. Again, these are some of the subtle details that get ignored in many eliminator designs.

21st Oct 2019, 5:11 am	#30
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: DIY battery eliminator for valve radio If you look carefully at the battery eliminators which I posted links to in the two articles in post #3, you will notice how the filament supplies have over voltage protection incorporated. I think this is an essential part of a good battery eliminator. In addition, it is important that if you have a battery eliminator with a range of HT output voltages derived from a regulated supply, that you have to allow for a scenario where a connection say to a 135V output might be disconnected and connected to a lower voltage output say 90V by the user. The charge storage in the actual radio (its own filter capacitors) then attempts to inject energy back into the eliminator regulators, say being transistors or IC's, which can destroy them. This is the purpose of the additional diodes you see in series with the HT outputs on the multi-voltage output eliminator. So there needs to be protection for the outputs being forced higher than their normal values. It is often these sorts of things that get completely neglected in many battery eliminator designs. In addition it is better for these units to have some fusing after the main reservoir capacitors as the fuse values can be lower than when they have to support the initial turn on current surges charging the eliminator's capacitors. Again, these are some of the subtle details that get ignored in many eliminator designs.