[Boatanchors] Power source schematic for Atwater Kent TRFs. etc. (long)

Thu, 23 May 2002 13:59:23 -0400

Hi Todd:

Usually I document my work using OrCad, and as you may know, I typically
offer my machine-readable files to interested list subscribers. However,
this power-source project was so straightforward that I barely kept notes,
and I did not capture the schematic electronically.

However, I have all my hand-drawn sketches and Ohm's law calculations on
scratch paper, and would be happy to photocopy them and send them off to you
either by FAX or via US Snail (if you send me an SASE).

Essentially it consists of an appropriately sized power transformer and
rectifier (your choice), feeding a string of Zener diodes for the B-plus
source.

I used what diodes I had in my junkbox, namely three 22-V 5-W Zeners in
series at the bottom of a string, followed by a 24-V Zener, a 33-V Zener,
and a 30-V Zener, all fed via a 2-kohm, 5-W resistor off the 250-V
unregulated output of my rectifier's pi-filter.

This string gives me simultaneous outputs at about 22-V, 44-V, 66-V,, 90-V,
125-V, and 150-V, as well as the unregulated but filtered B-plus. It's
perfect for battery substitution on old TRF sets.

For C-minus, where little current will flow, I used a separate winding and
rectifier/filter (mine required a voltage doubler), feeding an LM350
3-terminal regulator. The circuit is out of the handbook, and includes an
adjustment pot. This supplies 1.2-V to 20-V at up to 500 mA (overkill).

I also used another rectifier/filter and LM350 on a huge heatsink for 1.2-V
to 7-V at 3-A, for the filament lines (the A supply).

All of the voltages are brought out to 5-way terminals on the unit's
front-panel. In that way, I can jumper terminals just as you would if you
used a number of batteries in the old days.

As I'm inclined to do with my homebrew gear, I added metering to the supply,
using what meter movements I had around here, and applying Ohm's Law. I have
the meters set to read voltage and current on each variable source, using
DPDT toggle switches so one meter can read both values (there are two
dedicated meters; one per source). For the fixed B-plus, I use only a
voltmeter.

My meter calibration pots are on the rear panel. I used a 5.6-ohm wirewound
resistor to derive an IR drop to feed the current metering circuit in the
bias source, and a 0.05-ohm resistor in the filament source. These don't
impose too much burden, and the output voltages are adequate.

Vy 73, AI2Q, Alex in Kennebunk, Maine  .-.-.

-----Original Message-----
From: Todd Bigelow - PS [mailto:[email protected]]
Sent: Thursday, May 23, 2002 10:26 AM
To: [email protected]
Cc: [email protected]
Subject: Re: [Boatanchors] Atwater Kent

Alex -

If you have a component list and/or schematic, I'd sure like to build one as
well. I have an old AK-10 which was stored in a closet for years. It was in
the
first-ever load of radio gear I got back in the early 80s. I removed all the
components and refinished the board which had been left by an open window,
and
removed one turn of wire that couldn't be returned to the end coil. It looks
great and I'd love to make it play again. I've yet to come across a good
eliminator with adjustable voltages and refuse to trust just anything.

Your experience is one I've always dreamed of. To be able to pick up signals
from an old battery set while fiddling with all three dials and the
associated
rheostats must be great!

73 de Todd/'Boomer'  KA1KAQ

AI2Q Alex wrote:
<snip>

> I recently restored a Model 10 breadboard that was given to me 30 years
ago.
> After rewinding one of the TRF coils, I built a B+, C-, and A battery
> "eliminator" for it, and fired it up.
>
> It works! You can imagine the grin on my face to copy BC stations loud and
> clear on a radio built back in the 1920s!
>