[ARC5] On the air

Sun May 21 23:38:02 EDT 2017

Thank you.
Very simple. The plan from the start was to build a 4 level rack similar to
the one shown (which is for my BC-230 transmitter) with room for a command
set receiver rack on shelf 2 and a command set transmitter rack on shelf 3.
The MFJ tuner would be on the top shelf, 4, with antenna relay up there too.

Based on the dimensions of a 3-bay ARC-5 rack, about 600 mm width and 550
mm depth was required. I figured I would need all of that, and was right. A
single chassis that size would be awkward to unbolt and lift out for
repairs or mods. How would I get it out from between the angled pillars?
Can't be done except by tilting, and it would be a heavy and awkward task.

Construction would also have been awkward with all my drilling and cutting
carried out on the back steps and the assembly needing to be taken out and
brought back in frequently.

The present construction means I can detach any two-unit chassis assembly
and simply pull it forward.

73 de Neil ZL1ANM

On 22/05/2017 2:02 PM, "J Mcvey" <ac2eu at yahoo.com> wrote:

Hello Niel,

Nice neat, heavy duty work!
I was wondering why you decided to use modules instead of building one
chassis?

On Sunday, May 21, 2017 6:41 PM, AKLDGUY . <neilb0627 at gmail.com> wrote:

I'm assuming everyone can now see the photos I posted?

73 de Neil ZL1ANM

On Sun, May 21, 2017 at 5:51 PM, AKLDGUY . <neilb0627 at gmail.com> wrote:

Here is a description with photos of my AN/ARC-5 setup which I completed a
few days ago and operated for the first time on the New Zealand AM net on
Friday night, 19 May 2017. Operation was not very successful, but I was
heard. My antenna is very poor and I struggled to get into the local SDR
receiver, my primary aim.

I've owned the T-19 ARC-5 for a decade and a half, but never had the
enthusiasm for procuring HV transformers for a power supply. A few months
ago, I obtained a Thordarson mod transformer, and then a dynamotor. The
latter made the power supply so simple.

This view shows the setup exactly as used on the Friday night net. Power
supply at right is 0-16 VDC, 25 A, set to 13 V and connected to the 12 V
gel cell which provides ooomph for starting the 12 V, 14 A dynamotor. The
transmitter and MFJ tuner are sitting on a rack that normally mounts my
BC-AO-230 transmitter, and the lower shelf consists of the BC-230's power
supply and is not relevant here.

https://photos.google.com/ photo/ AF1QipOouvSiAsF0etl5eZE1tLY9by
wxdc1AZgmwjUhf
<https://photos.google.com/photo/AF1QipOouvSiAsF0etl5eZE1tLY9bywxdc1AZgmwjUhf>

https://photos.google.com/ photo/AF1QipO9tKJVQgK28nV-
7VkwbLE-3Y8MaO1oAxdZmQd2
<https://photos.google.com/photo/AF1QipO9tKJVQgK28nV-7VkwbLE-3Y8MaO1oAxdZmQd2>

The following view shows, at right, the heater/selector-relay supply (25.6
VDC regulated).

In the middle chassis at rear is the relay that switches the 13 VDC to the
dynamotor, and the heater transformer for the 2E26's (heaters wired for
12.6 V with junction grounded). At front is the transformer that supplies
the relays and the speech amp. On this front chassis is room for a 200 V
supply for my ARA receiver, which may be the next project.

 At left is the speech amp chassis (front) and the 2E26 modulator tube pair
and Thordarson transformer (rear). The 2E26 screens are regulated at 150
VDC by the 0A2 on the rear of the front chassis. The 3 dry cell batteries
provide 25 V bias to the 2E26's, adjustable by a pot in the left black box.
The right black box consists of meter sockets for PA and 2E26 plate current.

https://photos.google.com/ photo/ AF1QipPJ2aMdDeyN77Ew9xSVxWGv6C
dkMxzHi_XHXgLN
<https://photos.google.com/photo/AF1QipPJ2aMdDeyN77Ew9xSVxWGv6CdkMxzHi_XHXgLN>

The following photo shows the rear of the T-19. The black boxes contain
dropping resistors for the VFO (right, orange wire) and 1625 screens (left,
yellow wire). The resistors are made up of 4K7, 5W units in series (the
largest value of 5W readily available).

https://photos.google.com/ photo/ AF1QipPvtVCIDNtPPzz9EJ4yukETGy
nJlJzhKZrSbUd1
<https://photos.google.com/photo/AF1QipPvtVCIDNtPPzz9EJ4yukETGynJlJzhKZrSbUd1>

The last view is of the underside of the speech amp & modulator, by far the
most complex of the 3 twin-chassis units. Speech amp is 3 X MPF-102,
driving an LM-380N on the small perf board. This drives the 8 ohm tap of a
standard multitapped line transformer, whose "secondary" is 5,000 ohms.
Because there is no centre tap on the 5,000 ohm winding, an artificial one
was created by splitting the load resistance into two 2K7 resistors with
their junction decoupled with a 47uF, 35 V ESR electrolytic capacitor. The
2E26 grids are not to be driven into grid current in Class AB1, so they
must not be driven greater than 25 V (50 V grid-to-grid). This setup is
easily capable of developing 80 or 90 volts peak, measured from grid to
grid.

No attempt was made to make the speech amp compact; I had plenty of space
and my eyesight is not so good for fiddly stuff any more, hence the half
watt resistors.

https://photos.google.com/ photo/ AF1QipOlKXE3sldmC0Idq5egpoFXpq
vVtU3icxGGJkDR
<https://photos.google.com/photo/AF1QipOlKXE3sldmC0Idq5egpoFXpqvVtU3icxGGJkDR>

Hope someone picks up an idea or two.
73 de Neil ZL1ANM

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