David Macnaughton and his Fascinating World of Amateur Radio



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David VK2BA standing beside the BA320




If you have worked me on AM on either 29MHz or 7.125MHz in the last decade then the chances are good that I was using this transmitter

I like to give my home brew projects type names. This section describes the BA320 transmitter. It started life as the BA300, a 29MHz transmitter on 30th June 1999 in the peak of the last solar cycle and was used daily talking to US stations on 10M AM. With the demise of the of the daily US propagation with the reducing sunspots, it was decided to modify the unit so it could be used on 40M AM. It now operates on either of the two bands.

The result has been the BA320.







This is the home made cabinet of the BA320 cabinet with all the modules removed.

If I had any sense I would have taken a new set of photos of each module when I had them out but I didn't!

The modules are from bottom up:

1:  1400 volt power supply

2:  Modulator with class AB1 813's

3:  Control and meter panel

4: Exciter  unit

5: Dual band PA with single class C 813. 


The top two units - the RF PA with the single class C 813 and the two band exciter.

To change bands just turn the knobs to yellow for 40M or blue for 10M. Then just carefully tweak it up.

The PA unit with the 813

This is an early photo, before the modifications to make it a two bander.

 Exciter unit of the BA320

This is an early photo, before the modifications to make it a two bander.

Tube line-up: 12BY7 multiplier, 2E26 multiplier, 2E26 driver

This is the Control and Meter unit - the meters indicate Grid Drive, Screen Current and Plate Current. This unit was not painted because it has to be taken out of the transmitter. Too hard! If it ever fails and has to come out, then I will paint it. This unit also has the screen over voltage protection (4 x VR150's in series and a bias regulator (1 x VR150)

The 150 watt modulator with two 813's in class AB1. It has clipping and filtering built in but I vey rarely use this feature.

I think that clean audio is better than using clipping and filtering.

Tube line-up: EF86 speech amp, 6SL7, 6SN7, 6H6, 6SN7, 2 x 813

The modulator unit

The modulator of the BA320 - a pair of 813's glowing like the setting sun