[MrFixr55]

Hi MZip,

2V tubes for the early battery sets are directly heaters just like the 1.4V tubes in your set, not center tapped and were designed to be run off a 2V lead acid cell, 2.5V Eveready Air cell or 2 #6 dry cells in series with the required dropping resistor.

If you are designing a battery powered system to provide 90V for the B+, don't worry about powering an LM317 from a 6V battery for the tubes.  Running the tube filaments from a 1.5V alkaline D cell is not harmful in any way

[Arran]

Rich;
Some battery radios were really quite elaborate, at least the models that were available on the Canadian market, and I think that the market for them was around a bit longer, as there was no concerted rural electrification program, and transistor radios were not cost effective until 1958 or so. Having an extra RF or IF amplifier tube was pretty typical, even in sets of the 1940s.
Regards
Arran

[RodB]

Arran,

I remember restoring an AC/DC portable that had an elaborate AC to DC switch that put the tube filaments in series when using AC and rearranging for two sets of 2 to get 3 volts in DC mode. At first I didn't know what was happening until I noticed that the filament voltage was two D cells.

[Arran]

Rob;
What you had there was what those in the business used to call a "three way" portable, so it could be AC mains operated, DC mains operated, or battery operated. I think I had an RCA portable from the mid 1950s like that, and many Motorola's worked that way, many did not, like the tube Brand Z T.O. sets, those had the tube filaments in series. If you want really elaborate for a portable, G.E manufactured a series of 2 volt "wet cell" radios with a built in AC battery charger, they are VERY heavy though.
Anyhow what I meant by elaborate in battery radios was that there were some high end battery sets that had a TRF amplifier stage, shortwave bands, and a push-pull power output stage, I remember running into one of the Rogers models in one of the books, a console model, that had eight tubes, with four "B" batteries. Most of the time manufacturers would opt for using a vibrator power supply for the more elaborate battery models, even including a magic eye tube, I think there was a Brand Z shutterdial model like that but this Rogers (or Deforest Crosley) ran directly off of batteries, A, B, and C, no magic eye though.
I think I mentioned that Stewart Warner that is in the restoration lineup, it uses four 2 volt battery tubes, but with a 6.3 volt vibrator supply, with a synchronous vibrator. I want to get that working as it's the first battery radio I have had that I could practically use on batteries, specifically a 6 volt sealed lead acid battery, 2 volt battery tubes should be very economical on battery life.
Regards
Arran

[radiorich]

Hello Arran,
Yes, it makes sense about battery sets being more common, and I’ve also come across older ones in the rural areas where I live, with plenty of farms and ranches scattered among the valleys and mountains.
Rob I have portable set up like that troo.

Sincerely Richard

[MZip]

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!

[MrFixr55]

You may have to ask someone more expert than I am but I am not sure that low voltage will kill these tubes. Almost all of the battery sets and most of the battery / utility sets I own have the original tubes.

[David]

Low voltage will not kill the tubes. If using 1.5 volts battery for the heaters good to go if you measure the battery a fresh one no load the reading will be 1.65-1.75 under a load you will read 1.5 volts. I tried using recharigble no load 1.4-1.5 volts under load 1.2-1.25 volts performance was lacking.    More info    https://philcoradio.com/phorum/showthread.php?tid=17660

[Arran]

It's preferable to operate battery tube filaments at slightly less voltage if anything, the book says 1.4 volts so I would guess that they were intended to run on a fresh 1.5 volt carbon zinc "A" battery under load. Some battery tubes don't like running at lower filament voltage, the 1R5 is notoriously fussy for the oscillator stopping, or not starting if it falls below 1.4 volts, a 1A7 doesn't seem to care as much. What kind of rechargeable are we speaking of, a Lithium, NiCad, Nickel Metal Hydride?
Regards
Arran

[David]

I was using NMH batteries. Over the years have rebuilt a number of power packs for tools using NMH as a sub for NC. The  NMH do not have the memory problem. Have some Porter Cable tools from the 80s have rebuilt the packs more than once. GE made some portable radios in the 70s using NC batteries easy to change over. Rebuilt a power pack for a Radio Shack HTX 202 using NMH. David

[Arran]

This is useful to know as NiCads are not as easy to find these days, they seem to sell NiMH cells even in the dollar stores for cordless phones and the like. I have a number of Lithium cells from those E-cigarette/vape things, there is a store here that sells disposable ones and one the liquid goes they chuck them away. The issue is finding charger that works with them, so probably the USB slot in the computer, I think they are 3.3 to 3.6 volts, but the charger has to be current limiting I think.
Regards
Arran

[MrFixr55]

The standard LI metal hydride cell is the 18650, usually 3.7V 3Amp-hour. Chargers for these cells, as well as the cells themselves abound on Amazon

[David]

Looking for cells try ebay.  https://www.ebay.com/sch/i.html?_nkw=&_a...kastarusa1        another https://www.ebay.com/str/batteriesinaflash

[MrFixr55]

Try this search. Lists 18650 batteries and chargers.
https://www.ebay.com/sch/i.html?_nkw=186...m570.l1311

[DaleHCook]

The battery box isn’t to scale from a real battery so another deviation.

A project of mine which has been on a back burner for a while is battery eliminator for my Motorola 45B12 farm radio. It was sold with a high capacity A-B battery, with 1.5 volt A battery, and 90 volt B battery. That is an Eveready 759 battery or equivalent. The goal is to build a battery eliminator which, when on display with its power cord removed, looks like an Eveready 759. Some of you know Robert Lozier, whose expertise in antique radio restoration and conservation includes crafting beautiful replica batteries. He has made available on his site graphics which he has scanned from vintage batteries. See his battery art page.

I asked Robert if he had scanned a 759 or equivalent. He had scanned a 759, but had not yet prepared the artwork before putting it online. He was kind enough to send it to me, and I can Photoshop it to make it ready to use. I already had a JFD replacement plug for the battery cable (the original looks a bit ratty), which is a 4-pin. I found a seller of the battery socket on the auction site, and bought two. I already had an old-style 2-conductor TV power cord socket and a matching cheater cord.

The battery eliminator will look like an Eveready 759. The power cord socket will be on the back side of the battery, facing the chassis. With the cord removed for display it should look very convincing.