Charger Specs for Rockwell 74k Calculator

[rprosperi]

I recently acquired a nice Rockwell 74k calculator, which appears to be from May '76. The original batteries are still in-place, and incredibly have not leaked and will still take a charge for a short while. The seller posted pics of it running, though when received it would not turn on.

Does anyone have one with the original charger to confirm the proper Voltage and polarity (I presume tip-positive and probably either 3 or 6V, as these were the most common at the time.) The machine uses 3 x AAA, NiCd 1.2V, 180mAh cells, which will be replaced once the unit is properly tested/verified. The jack is the smaller RCA type (I think this is a 2.5mm jack).

All info appreciated.

p.s. Thanks to Gene for pointing it out.

[Zaphod]

I wonder if the 24k II used the same battery setup ?

If it did , the mains adaptor would appear to be a very loosely regulated adaptor



If you can access the battery terminals , you should be able to positively (pardon the pun) confirm the polarity with regard to the socket.

[rprosperi]

Update to the update: Likely the key difference is yours is for UK (240V/50Hz) and the one I found is for US (120V/60Hz).

Thanks for the info Zaphod. I'm not certain if the 74k originally came with that one, but another member that has a 74k came with a different one:

Model: DC-410P
Output: 4.5 VDC 100mA
Tip: Positive

This is more of a traditional small black 'wall wart' design. I was able to easily locate one and will post a family photo once I receive the adapter.

Thx again.

[Didier Lachieze]

(05-29-2018 09:26 PM)Zaphod Wrote:  I wonder if the 24k II used the same battery setup ?

If it did , the mains adaptor would appear to be a very loosely regulated adaptor

Wonderful dual purpose device: as a CHARGER it provides 4.5V - 100mA to charge your calculator, but you can also use it as an ELIMINATOR (!!) to provide 7.5V - 50mA to the calculator you want to eliminate

[rprosperi]

(05-29-2018 10:35 PM)Didier Lachieze Wrote:  Wonderful dual purpose device: as a CHARGER it provides 4.5V - 100mA to charge your calculator, but you can also use it as an ELIMINATOR (!!) to provide 7.5V - 50mA to the calculator you want to eliminate

I wondered about that too... and concluded that may not be the best word to use.

Anyone know what the purpose of ELIMINATOR power mode is for? Initially I guessed it may be used to run the machine without batteries (thus eliminating the need for batteries) but at least on the 74k model, the batteries seem to be soldered-in, so that doesn't make sense; perhaps this model is different.

Was/is this term commonly used on similar adapters?

[Dieter]

(05-30-2018 01:05 PM)rprosperi Wrote:  I wondered about that too... and concluded that may not be the best word to use.
...
Was/is this term commonly used on similar adapters?

I never heard of this term before, but Google exists. ;-)
Take a look at this Wikipedia page: https://en.wikipedia.org/wiki/Battery_eliminator. The section on the historic background may explain this special term.

So this Rockwell charger is a device that can (1) charge the battery with its 4,5 V /100 mA output, and it can also (2) power the calculator directly with 7,5 V / 50 mA.

I think in German this would simply be called "Netz-/Ladegerät", i.e. a device that can be used as a charger ("Ladegerät") as well as an AC-adapter ("Netzgerät").

Dieter

[Zaphod]

(05-30-2018 01:05 PM)rprosperi Wrote:  Anyone know what the purpose of ELIMINATOR power mode is for? Initially I guessed it may be used to run the machine without batteries (thus eliminating the need for batteries)
Was/is this term commonly used on similar adapters?

Yes , it was ... (and yes it was to describe a battery eliminator - I.e. to use a product without batteries) I thought you guys already knew that...


The current output is not a lot on this particular unit and I would guess it’s probably slightly more than 7.5volts completely unloaded , when loaded with just the calc (no batteries fitted - 50mA load) it would drop to approx 7.5volts, with the extra load of a rechargeable battery installed (100mA load) it would drop down to 4.5volts (~the terminal voltage of the cells).

It’s possible it just has some series current limiting resistor internal to the adaptor.

[rprosperi]

Thanks Dieter and Zaphod. As noted, I did initially presume it was meant to run the machine without batteries, however the 74k machine (or at least the sample I have) has a 3xAAA battery pack soldered into the case, so it didn't seem to make sense, unless of course this term was widely used to simply mean running the device directly from the adapter (e.g. if batteries were dead).

Anyhow, while the term itself is not new to me, this form of usage is. If this was common in UK (presumably in the 70's at least), is it still widely used? For example would a current mobile phone's power adapter have the name Eliminator on it, or would a random millennial walking the streets of London know this name?

Also, does the 24k model have a removable battery?

[ijabbott]

(05-31-2018 12:48 AM)rprosperi Wrote:  Anyhow, while the term itself is not new to me, this form of usage is. If this was common in UK (presumably in the 70's at least), is it still widely used? For example would a current mobile phone's power adapter have the name Eliminator on it, or would a random millennial walking the streets of London know this name?

I don't think so. Depending on its purpose, the terms "mains adapter" and "charger" are common.

[Didier Lachieze]

It's the first time I see ELIMINATOR written on an adapter/charger.

[Chasfield]

Maybe the same psu could have been used with other UK built models in the range that were powered by regular dry AA cells. A switching jack plug would take them out of circuit. Hence, battery "eliminator".

It is interesting that the psu is dual badged as "Sumlock Anita". The calculator shown (built in Japan?) was from the transition period as Rockwell International waded into the UK based company, just before asset-stripping the place and closing down calculator production. Like Commodore, they looked into their crystal ball and saw that calculator makers were about to get badly burned.

[Zaphod]

(05-31-2018 12:48 AM)rprosperi Wrote:  Thanks Dieter and Zaphod. As noted, I did initially presume it was meant to run the machine without batteries, however the 74k machine (or at least the sample I have) has a 3xAAA battery pack soldered into the case, so it didn't seem to make sense, unless of course this term was widely used to simply mean running the device directly from the adapter (e.g. if batteries were dead).


Also, does the 24k model have a removable battery?

There's no proof that the mains adaptor/charger/PSU/Walwart shown in my photo is actually the one that was supplied with that 24k calc in the photo... I just picked the pic up off ebay. It could well be from some other Rockwell or Sumlock product that happens to work with that calc. I dunno.