[ARC5] On the air

Sun May 21 21:57:58 EDT 2017

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/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

______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

|  | Virus-free. www.avg.com  |

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20170522/7adddd9a/attachment.html>