[ARC5] On the air

[AKLDGUY .]

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/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
>
> 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
>
> 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
>
> Hope someone picks up an idea or two.
> 73 de Neil ZL1ANM
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20170522/fc1f9c9f/attachment.html>