Survival stories from Himatangi Radio

Get a couple of radio technicians talking and it’s amazing the stories you’ll hear. The conversation below with Jon Asmus and Rex Johson began with a simple question from me about one of the Himatangi Radio transmitters, then moved into memories of some of the dangers that technicians faced at Himatangi.

My initial question related to some photos Jon supplied of the Marconi HS51 transmitter which had been installed at Himatangi Radio in 1958 – about ten years before he started working there.

The completed Marconi HS51 transmitter with covers in place

The completed Marconi HS51 transmitter with covers in place. Courtesy Jon Asmus

Marconi HS51 transmitter in service

Marconi HS51 transmitter in service. Courtesy Jon Asmus. Click to enlarge.

I was curious about the second photo, and wondered where the front doors to the transmitter had gone. I couldn’t see any way for them to slide into the cabinets so concluded that they may have been removed, and decided to ask Jon.


Jon Asmus

Jon Asmus

A very interesting question. It looks like this is a publicity pic (there appears to have been a number of them around that period) and that the striking visual impact of all the meters and controls required the removal of the doors. Pretty boring with them all on, even if open. I do not remember removing them all during maintenance.

Another thought that has recently surfaced (it takes longer these days) is that there was a ‘transformer room’ outside the transmitting hall behind HS51. When in there doing maintenance – and I cannot remember what exactly what that entailed – we had to insert metal pins into mechanical systems to negate having the whole room flooded with gas that was there as a fire containment system.

In the background of that HS51 pic, behind the technician, is a lattice-like structure. This was a diabolical device designed to allow the replacement of failed fluoro tubes in the lighting runs set in the ceiling longitudinally along the center of the transmitting hall. It was wheeled into place (sequentially along the hall) and a pull rope used to raise the collapsed second level upwards to the top of the outer. It was then locked into place (rather dubiously) and the rope then used to to tie the two levels together in the middle to try (in futility) to stop the top moving too much when you climbed up there. A nervous experience up there at the best of times. I recall several occasions when a tube was dropped from the top (accidentally?) and created a gunshot noise that achieved two things: a lot of attention and a lot of cleaning up of molecular-sized fragments.


Rex Johnson

Rex Johnson

Re the HS51 doors, I think they were just removed for the photo shoot. Takes under 1 minute, as the doors just lift off pins and get stacked against a wall somewhere. You can see the pins on the left-hand side of the picture on the first and third vertical supports. Like Jon, I never removed any for maintenance purposes.

Re the HS51 Transformer Room, I agree with Jon that whatever we had to do in that room it was trivial – possibly just cleaning dust off insulators or similar.

Gaining access to the power room, however, was not trivial and was potentially life threatening, so we are lucky to be here to say we survived our maintenance duties.

Outside the room was a bank of Halon gas bottles which were connected by a series of ropes and pulleys to a heat sensitive link inside the room. Raising the temperature in the room (i.e a fire) would start a chain reaction of the ropes releasing their tension, heavy weights at the gas bottles dropping towards the floor forcing gas cocks to be slammed open and Halon gas to jet out of about six cup-shaped nozzles at ceiling level around the power room perimeter. This gas-swamping system extinguished any fire – and the life of slack technicians.

Just to be clear about Halon, Wikipedia says: “Bromotrifluoromethane, commonly known as Halon 1301, R13B1,[3] Halon 13B1 or BTM, is an organic halide with the chemical formula CBrF3. It is used for fire suppression and refrigeration. Human exposure to Halon 1301 can be toxic, affecting the central nervous system and other bodily functions. Additionally, it is known to contribute to the depletion of Earth’s atmospheric ozone layer when released. As such Halon’s use as a refrigerant has been virtually eliminated and alternatives are being used increasingly for fire suppression.”

To avoid the possibility of becoming a ‘slack technician’, the procedure was to place a wedge against a wire rope section near the gas bottle bank. The wedge forced a metal ball clamped onto a wire section of the activating rope to be forced against some metal fingers that stopped the ball from moving anywhere. Inadvertent failure of the heat-sensitive link in the power room during maintenance would release tension on the first ropes, but wedging of the metal ball prevented the final exciting events.

A Halon-gas-powered air-raid siren mounted on the wall was to gain attention around the building that the fire alarm system had activated.

Death by fire and toxic gas having been averted, the next challenge was to avoid death by frying from high voltage sources. Having wedged the ball and opened the power room door, the technician was confronted by an earthing pole mounted diagonally across the entrance, effectively barring access. The wooden pole was lifted from its socket and, while still standing safely at the doorway, was touched to various high-voltage terminals to bleed any charge from giant capacitors. That being achieved, one stepped inside and performed one’s maintenance programme, whistling cheerfully.

Re the “lattice-like structure”, I confess to having once caused that gunshot-like noise from the top of the gantry. In my own defence, I had just removed a dud fluorescent tube from its holder when someone keyed a nearby high-powered transmitter, the fluorescent blazed into life in my hands and I rapidly released it.

Sigh, death by fire, gas, lightning, being shredded by glass fragments, or leaping backwards off a gantry in surprise. And that was on good days!