MLU FORUM  

Go Back   MLU FORUM > GENERAL WW2 TOPICS > The Wireless Forum

Notices

Reply
 
Thread Tools Display Modes
  #1  
Old 20-04-12, 10:07
Mike Kelly's Avatar
Mike Kelly Mike Kelly is offline
Fan of Lord Nuffield
 
Join Date: Feb 2003
Location: Victoria Australia
Posts: 5,607
Default AT5/AR8 in USA

The wireless forum is rather slow needs some input

This is an interesting thing .

An Australian WW2 era radio on the air in the USA .

The radio set was made by AWA in Sydney , primarily intended for aircraft like the Wirraway , Hudson and others . It was also issued to the army , the army nomenclature, WS 112 . AWM pics depict these sets in use in the SWPA mounted in Jeeps . And the Chevy Aust. signals van . And small vessels .... air sea rescue maybe



Mike


Thought you'd find this of interest....




-----Original Message-----
From: milsurplus-bounces@mailman.qth.net [mailto:milsurplus-bounces@mailman.qth.net] On Behalf Of David Stinson
Sent: Tuesday, April 17, 2012 1:39 PM
To: milsurplus@mailman.qth.net; ARC-5 List
Subject: [Milsurplus] Progress on Auzzie AT5-AR8 Set

The WWII Australian AT5 / AR8 set is on-the-air,
transceiving and making contacts.
I have had a great deal of help from our Australian members,
for which I am very grateful.

http://home.netcom.com/~arc5/AR8AT5/AR8AT5.jpg

Above the transmitter is a temporary junction box I built
to provide microphone bias, antenna and RX/TX switching.

I've connected them for 12 VDC operation.
The AR8 receiver is powered at 90 VDC using a homebrewed,
regulated 12V-to-90V DC/DC power pack.
The radio has excellent, loud audio and good operation.
I see no reason to pound the old veteran with 250 V
so I intend to keep it running at 90V,
even if I am fortunate enough to acquire an original power supply.
I'll just regulate it down.

The AT5 transmitter is running at full 550V B++ and 300V B+
using a rebuilt Hallicrafters 12V mobile supply.

While I have the normally-included external antenna tuner unit
which, in the original installation, handled antenna and T/R
switching, space is unavailable in the upcoming display
to include it. Adding the third box would give a footprint
half-again bigger than an ART-13. I need them operational
for HamCom, so I built a small external junction box to
handle these functions. When I build the permanant rack for
my station, I plan to install the ATU on a shelf above the TX/RX,
similar to this installation in an RAAF rescue launch:

http://home.netcom.com/~arc5/AR8AT5/..._AR8Launch.jpg

Here is a diagram of the homebrew switching box:

http://home.netcom.com/~arc5/AR8AT5/AR8AT5JB.jpg

Notes on the AR8:
I went through this set several years ago and
it's been in the "Round Tuit" que until now.
IIRC, every cap in it was good. If I changed any,
it was one or two. It needed the usual lubrications and
De-Oxits. The MF dial is cracked so I reenforced that.
The BFO needed to be re-centered, which was easy.
The dial calibration on HF is a little off.
Since it needed no other alignment, I decided to leave
the glyptol-locked adjustments alone and live with a
little "mental correction" on the dial reading.
Replaced a couple of short "rotten insulation" wires.
One curious thing: The filaments are strung to either
be wired for 24V or 12V, DC or AC. When
running them 12V, the manual calls for power pin
1 to be A+ and to tie pins 3 and 4 together for A-.
These A- leads get "earthed" in the external power
supply. However- in my set, if you connect it this way,
the chassis becomes +12 volts to "Earth," and if you
ground pins 3-4, you have a short. I don't know why yet.
I simply reversed the wires, using 3-4 as A+ and 1 as A-.
This worked fine and there's no electrical reason not to
connect it thus. It's actually OK with me, because I had
to do exactly the same thing with the AT5 transmitter,
but for other reasons.

Notes on the AT5:
Unlike the receiver, the AT5 required a nearly complete re-capping.
The original antenna connector is broken, so I've installed a
temporary "N" connector (no metal changes, of course).
I put a small screw between two turns in the tank coil,
effectively removing a turn and making the tank
suitable for loading a 50-ohm antenna:

http://home.netcom.com/~arc5/AR8AT5/AT5TANK.jpg

This delivers 25-30 watts of grid-modulated AM and
50-60 watts of CW out to my 50-ohm dummy load.
Rig is chirpy on CW, even when running original crystals.
I haven't looked into that yet.

In the original design, the microphone element is not
run against ground; it is series-connected between the
microphone supply in the external power unit, the microphone
element and the microphone transformer primary, which then
goes to "earth" via the A- and thus "earthed" filament string
connection to power connector pin 3. U.S. designs place the
microphone power running through the mic transformer, a
dropping or divider resistor, then the microphone element
and thence to ground. Since I'm using one of the microphones
I have on hand, I connected power pins 3 and 4 to A+ and
pin 1 to A- (the manual calls out the opposite)
and that provided A+ through the mic transformer primary,
out to a voltage divider/audio bypass and then through the
mic element to "earth." This worked well with good modulation
and plenty of audio and the filaments operate either way.
The transmitter VFO is surprisingly stable after warm-up.

For Safety's sake, I will be adding one actual modification:
if the plate blocking cap, C24 leaks, B++ will show up at
the antenna connector. I'm going to add a 2.5 mHy choke
from the antenna connector to ground so any such leakage
will be safely shunted.

One problem I have run-into: a low-frequency parasitic
oscillation which is creating low-level "spurs" either side
of the carrier. You can see it on the monitor scope and
hear them on a monitor receiver. While I haven't
worked on this yet, I'd bet coffee and donuts the problem
is the missing transmitter case and covers. All these long
cables running around and next to the PA are causing
low-frequency feedback. Covers for these sets are
made of "unobtainium" so I'm going to fabricate covers
for the transmitter and watch the parasitic go away... I hope ;-).

Speaking of parasitics, I need some advice:
The PA plate leads lack VHF parasitic suppressors
and are made in such a way that it would be destructive
to attempt to insert them at the plate caps of the 807s.
Should I decide they're needed, I'm thinking small ones
in the cathode and/or screen leads would work as well.
What do you think?

Now to build the display stand and work on those covers...

73 OM DE Dave AB5S

P.S. More AT5 / AR8 operational photos,
courtesy of our Australian members, at:
http://home.netcom.com/~arc5/AR8AT5/oppics/



__________________________________________________ ____________
Milsurplus mailing list
Home: http://mailman.qth.net/mailman/listinfo/milsurplus
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Milsurplus@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
_____________________________
__________________
1940 cab 11 C8
1940 Morris-Commercial PU
1941 Morris-Commercial CS8
1940 Chev. 15cwt GS Van ( Aust.)
1942-45 Jeep salad
Reply With Quote
  #2  
Old 20-04-12, 18:09
Mike Cecil Mike Cecil is offline
Registered User
 
Join Date: Jun 2006
Location: Cody, Wyoming, USA
Posts: 2,365
Default

....also supplied to US Forces under Reciprocal Lend Lease (RLL) arrangements.

Mike C
Reply With Quote
  #3  
Old 21-04-12, 03:02
Mike Kelly's Avatar
Mike Kelly Mike Kelly is offline
Fan of Lord Nuffield
 
Join Date: Feb 2003
Location: Victoria Australia
Posts: 5,607
Default Yes

Quote:
Originally Posted by Mike Cecil View Post
....also supplied to US Forces under Reciprocal Lend Lease (RLL) arrangements.

Mike C

Ah yes , true

The Australian radio industry manufactured various equipments for the US forces in the SWPA. A few Aust. sets have turned up in the USA . And, one of the GMH ambulance Jeeps has turned up over there as well . Seems like the yanks took a few things home when they left.

I have seen US army markings on these Aust. radio types

AWA AT21

AWA 3BZ

AWA AMR 101

Radio Corps. ATR4

I believe they also used the locally made mobile radar sets , because they were better than the US made sets. There was a few articles published in EA magazine years ago on this topic, the Aust. designed and built mobile radar sets were considered the best . Until the rest of the world caught up and overtook .

Mike
__________________
1940 cab 11 C8
1940 Morris-Commercial PU
1941 Morris-Commercial CS8
1940 Chev. 15cwt GS Van ( Aust.)
1942-45 Jeep salad
Reply With Quote
  #4  
Old 21-04-12, 03:15
Mike Cecil Mike Cecil is offline
Registered User
 
Join Date: Jun 2006
Location: Cody, Wyoming, USA
Posts: 2,365
Default

Ah, yes, the LW/AW radar sets (Light Weight/Air Warning), super-secret at the time, and mostly destroyed rather than sold off at Govt auction when no longer required. Thankfully one set survived, and is now on display at the AWM in Bradbury Aircraft Hall. They were 'super secret' because of the cavity magnetron that was the 'heart' of the system. Old hat, now, of course: every microwave oven has one, but not so at the time.

The RLL scheme was interesting and the range of things Aust supplied to US forces is astounding, including all those radios and radar equipments you listed above. I seem to remember that Australia supplied 3/4 of the US$ value of Lend Lease items received, back to US Forces as RLL items: everything from clothing and food to small ships. The books were still in the USAs favour, of course, but not bad for such a small population with a relatively narrow - and small - manufacturing capacity.

Interesting thread, Mike.

Mike C
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 15:52.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright © Maple Leaf Up, 2003-2016