Advice on Battery Eliminator Connections?

[Winky Dink]

I have an Atwater Kent Model 30 which is powered by my ARBE III. Resetting the ARBE III for different radios is cumbersome for me. Even with 9-pin connectors, I have to change jumpers and reset the A+ voltage.

So, I wanted a dedicated power supply for my favorite radio, the AK 30. As luck has it, a couple of summers ago I bought a Bosch Nobattry for ten bucks.



To get to the point--I gutted the Nobattry and built a K-101A Battery Eliminator Kit (from AES via Amazon) to put inside it.



I thought I’d just duplicate the ABC connections that I used with the ARBE III or follow the Atwater Kent battery diagrams. They differ slightly in the C- connection--maybe it’s not really a difference. Then, the K-101A instructions makes one mention of connections for negative bias, and it seems to be different as well. On top of that, I have a 171 “power tube” in the last stage which requires higher B+ and more-negative bias than the standard tube used in all of the battery wiring directions.

Here is an Atwater Kent Model 30 schematic, and a summary of the diagrams or notes from Atwater Kent, ARBE III, and K-101A.





I have no problem with A and B voltages. I’m unsure of the C connections.
- The K-101A C- is adjustable from zero to -22 volts.
- The diagrams above assume -4.5 V grid bias at 90 volts B+.
- The UX171 data sheet specifies -16.5 V grid bias at 90 volts B+.

I will be most grateful for advice on the C connections.

Link to a highly illuminating 11-pic series on what I’ve done with the Nobattry:

https://flic.kr/s/aHskyeMTdS

[init4fun]

Hi Henry ,

Im not sure I understand your question . You say the unit will give up to -22 volts and the tube only needs -16.5 of grid bias , I'd adjust it for the -16.5 and call it good . You mention the instruction specifying -4.5 volts but it says that is for one particular tube type , the 201A or 301A , and that other tubes will use the value of grid bias as listed "In the instructions packed in each tube carton" .

A quick peek at the 71A's specs reveals that at +90V plate the bias will be -16.5V with 10MA of plate current flowing . You could connect a meter measuring in MA into the plate circuit and adjust for 10MA or less .

Interesting to note , the 71A can operate as high as +180V plate , -40.5V grid bias , at 20MA plate current . You'll have to stick to your +90V plate however , since the specs at even +135V plate call for -27V of grid bias , and your C supply maxes out at -22V .

PS , in the Atwater Kent drawing , they have the A- and B- strapped together with the green wire between terminals 2 & 3 , this is proper and is what I'm used to seeing . So why does the ARBE unit's drawings show the B- connected to the A+ ? I think I would connect it the way Atwater Kent has it wired .....

[dieseljeep]

I agree with the last poster, regarding the AK battery connections.
I built my Coronado farm radio supply, from scratch, using the thin plywood breadboard format. It looks alright.

[Winky Dink]

Thanks, Guys.

I thought that I had posted this reply earlier today, but probably I didn't notice that I had been logged off before clicking "post quick reply."

My primary question was about the discrepancies in the C+ jumpers (straps?):

Atwater Kent says: C+ to A- to B-
ARBE III says: C+ to A-
K-101A says: C+ to B-

Although I'm not sure why, my guess is that all three configurations are functionally the same. Am I right?

I may try experimenting with these configurations to see what the output voltages are.

Regarding the B- to A plus/minus discrepancy between Atwater Kent and ARBE III--I've been using the ARBE III setup, and it works OK.

Thanks again. Sorry for the delayed response.
- Henry

[jr_tech]

Originally Posted by Winky Dink

My primary question was about the discrepancies in the C+ jumpers (straps?):

Atwater Kent says: C+ to A- to B-
ARBE III says: C+ to A-
K-101A says: C+ to B-

Although I'm not sure why, my guess is that all three configurations are functionally the same. Am I right?

I may try experimenting with these configurations to see what the output voltages are.

Regarding the B- to A plus/minus discrepancy between Atwater Kent and ARBE III--I've been using the ARBE III setup, and it works ok.

They are not quite the same, since there is a 5 volt or so difference between the two points. Either way may work ok, but the bias and overall plate voltage relative to the "cathode" will be different.

jr