A question about amperage

[Electronic M]

Originally Posted by decojoe67

I spoke with someone I work with that's trained in electronics and he said you have to go above what you need in amps due to loss with the terminal connections and wiring. I need 3.0 minimum, so I am going to just use the ARBE III for the B and the 6V-20AH battery I have on order for the "A". This "Power-Sonic" battery (http://www.atbatt.com/power-sonic-6v...Fc1KDQodpJEK5Q) appears to be designed for several types of applications, so I am fairly sure it will do the job with the limited use the radio will have. I can easily return back to the "A" tubes and just use the ARBE III exclusively, but I really want to stick to my goal of operating the set with the early tubes.

He did a very good job summing up what I was saying, except I disagree on terminal losses....You loose voltage with terminal resistance, not current.

IIRC about 2-4 years ago I saw a presentation on the design of the ARBEIII from it's maker at the MARC Extravaganza meet. It seemed like a fairly conservative design to me. If your radio needs 3 amps and the supply can handle 3 amps (on the output terminals you intend to use), then it should probably work....I'd try it, and see if the supply runs reasonably cool, and that it is not adding hum...If you see excessive hum or heat then you are overtaxing the supply and should try another.

[decojoe67]

Originally Posted by Electronic M

He did a very good job summing up what I was saying, except I disagree on terminal losses....You loose voltage with terminal resistance, not current.

IIRC about 2-4 years ago I saw a presentation on the design of the ARBEIII from it's maker at the MARC Extravaganza meet. It seemed like a fairly conservative design to me. If your radio needs 3 amps and the supply can handle 3 amps (on the output terminals you intend to use), then it should probably work....I'd try it, and see if the supply runs reasonably cool, and that it is not adding hum...If you see excessive hum or heat then you are overtaxing the supply and should try another.

Thank you Tom. I think in the end I'm going to be using the set with the A UV's being I like to play my sets. It's been a very surprising to me to see just how much better the A tube UV's are. It's really like night and day. No wonder I don't see anyone else using the early tubes in the set!

[Kevin Kuehn]

Those puppies are really bright! And I'm sure folks took advantage of that light source back in the day.

One very important point missing from the previous discussions is that all batteries have an equivalent internal series resistance. It's roughly based on the chemistry and the physical size of the plates. But in general a lower AH capacity battery would have more internal resistance than a larger one of the same construction. It's this internal resistance that is the real reason your voltage was pulling down more so when you tried the smaller AH capacity batteries. Based on ohms law(V/I=R) if your battery voltage was being pulled down 1.5 volts under load, you'd divide 1.5 volts by 3 amps, which gives an equivalent internal series resistance of .5 ohms. If you pull even more amps through that same .5 ohms then you'll have a proportionally larger internal voltage drop. Hope that all makes sense.

[decojoe67]

Originally Posted by Kevin Kuehn

Those puppies are really bright! And I'm sure folks took advantage of that light source back in the day.

One very important point missing from the previous discussions is that all batteries have an equivalent internal series resistance. It's roughly based on the chemistry and the physical size of the plates. But in general a lower AH capacity battery would have more internal resistance than a larger one of the same construction. It's this internal resistance that is the real reason your voltage was pulling down more so when you tried the smaller AH capacity batteries. Based on ohms law(V/I=R) if your battery voltage was being pulled down 1.5 volts under load, you'd divide 1.5 volts by 3 amps, which gives an equivalent internal series resistance of .5 ohms. If you pull even more amps through that same .5 ohms then you'll have a proportionally larger internal voltage drop. Hope that all makes sense.

I get the gist of what you're saying Kevin. If you look back years ago at the battery set-up for these very early sets, they were hefty looking batteries. The set just jumped to life with the large 6V/20amp battery.

[jr_tech]

Those filaments look very bright... I hope that you are not exceeding the 5 volt specification by turning the rehostats up too far with the new battery, which will severely shorten tube life. Can you measure the filament voltage?

jr

[old_coot88]

Originally Posted by jr_tech

Those filaments look very bright... I hope that you are not exceeding the 5 volt specification by turning the rehostats up too far with the new battery, which will severely shorten tube life. Can you measure the filament voltage?

jr

The non-A tubes' filaments were non-thoriated and ran that bright by design. The 'A' tubes' thoriated filaments could run much cooler at 1/4 the amperage