TW Bespoke Units
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TW Electronics 1958 - 2000

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TW Bespoke Units

TW 140MHz Amplifier

The 140MHz 500watt amplifier shown in the photograph above was built by TW specifically for the British Iron and Steel Research Organisation.

TW 2m 1kW Amplifier

These units were made by TW as custom items for the Enfield College club station, G3VZN where John G3LAS (who kindly sent in the above photograph) was a lecturer in Electronic Engineering at the time.

John also provided the following information.

The top item is obviously a Phase II transverter sitting on a 2m AM/CW transmitter. The rack on the right is a rather super 2m linear with, I think, a pair of 4CX250B tubes. I had a special licence for 1kW at the time for experimental purposes. All this kit worked well for a few years until the engineering faculty was moved to Bounds Green. Sadly I don't know what became of it after that.

Tom Withers G3HGE also provided some information about these units.

The gear in the picture was housed in Imhoff enclosures and used their excellent chrome handles. I used this style of cabinet for all major projects. I can claim no credit for the actual circuit design of the 2m amplifier (which came from a QST VHF manual). I remember buying brand new 4CX250B's and airflow bases for this project. Neutralising the amplifier was an exacting process and involved removing really small sections of 'neuting' wires. The 4CX250B's required air cooling and I used AirFlow Developments of High Wycombe for the axial fan, while the valve bases came from Thomas and Betts.

The EHT was around 2kV and in order to avoid accidental contact with this lethal voltage, I used Shinohara plastic meters mounted on a wooden backplate. In hindsight, I made one error in that I made no provision for by-passing the amp to allow the driver to be used barefoot. I did rectify this ommision later but cannot recall the exact details. All drilling and piercing was done by me, and I still have the QMax cutters !!, but happily not the blisters !! The shack at Enfield was reached by a steep ladder and to get our gear in situ was quite an effort.

I also remember that having built the 1kW amp, we had no dummy load capable of handling such power levels. The solution was simple. I used a dipole at around 10ft just outside the works. At full power it was possible to get a field strength reading in excess of half a mile away!! The coax to the dipole was hot to the touch !!