07-30-2026, 12:31 PM
Hey guys, thanks for all the tips! A couple of things - battery eliminators are out. I mentioned that to my friend and he doesn’t want it to be plugged in or to add a hole to the box for the power cord.
About the 317 vs DC-DC converter, I got rid of a lot of the switching noise by hanging a cap across the output but there is still some noise affecting sensitivity. That’s why I looked at the low pass pi filters. I set up my own test rig to experiment with (since I don’t have the radio right now) and it looks like the pi filters on input and output rails have killed a lot of the noise. The higher switching frequency harmonics are way down now but I haven’t tried them in the radio circuit yet. It could be that it was the higher harmonics causing the issues. If I can get decent reception (it’s already pretty good with that cap), the advantage of the DC-DC converter is it drops out pretty clean when the battery voltage gets too low without staying sagged down. But it’s up in the air for now if this is going to work. Maybe?
The LM317 is first fallback. Its output sags but I’ve got an LED I’m putting across the battery supply where it will go out when the battery voltage gets too low. That way, he can see if the batteries are getting low before doing any damage to the tubes.
A single 1.5V battery is the last resort. I’ll need to see if I can get a good range on an LED to still get a voltage indication that helps. I really want to keep the filaments happy since I know who will get to fix it again if it has any issues. ?
But it would have been easier with a battery eliminator / linear regulator setup that has no voltage sag. As is, I’m kind of pushing what he’s willing to accept since he just wants the radio as stock as it can be. It’s important to me to accommodate because when we were both working, he went the extra mile on anything I asked him to do for me. He was/is a machinist and would hand me jewels of machine work every time. Extremely impressive. So anyway, that’s why the questions and discussion. Hands are a little tied. Not really but you get the idea. He’s reasonable so if it turns out an eliminator is the best way I’m sure he’d be good. But I want to get it fully portable if possible.
I do appreciate the replies, though, and thank all of you for the input. I’m not a tube guy. I came from digital/analog/IC land. Cheers!
About the 317 vs DC-DC converter, I got rid of a lot of the switching noise by hanging a cap across the output but there is still some noise affecting sensitivity. That’s why I looked at the low pass pi filters. I set up my own test rig to experiment with (since I don’t have the radio right now) and it looks like the pi filters on input and output rails have killed a lot of the noise. The higher switching frequency harmonics are way down now but I haven’t tried them in the radio circuit yet. It could be that it was the higher harmonics causing the issues. If I can get decent reception (it’s already pretty good with that cap), the advantage of the DC-DC converter is it drops out pretty clean when the battery voltage gets too low without staying sagged down. But it’s up in the air for now if this is going to work. Maybe?
The LM317 is first fallback. Its output sags but I’ve got an LED I’m putting across the battery supply where it will go out when the battery voltage gets too low. That way, he can see if the batteries are getting low before doing any damage to the tubes.
A single 1.5V battery is the last resort. I’ll need to see if I can get a good range on an LED to still get a voltage indication that helps. I really want to keep the filaments happy since I know who will get to fix it again if it has any issues. ?
But it would have been easier with a battery eliminator / linear regulator setup that has no voltage sag. As is, I’m kind of pushing what he’s willing to accept since he just wants the radio as stock as it can be. It’s important to me to accommodate because when we were both working, he went the extra mile on anything I asked him to do for me. He was/is a machinist and would hand me jewels of machine work every time. Extremely impressive. So anyway, that’s why the questions and discussion. Hands are a little tied. Not really but you get the idea. He’s reasonable so if it turns out an eliminator is the best way I’m sure he’d be good. But I want to get it fully portable if possible.
I do appreciate the replies, though, and thank all of you for the input. I’m not a tube guy. I came from digital/analog/IC land. Cheers!
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