Sailor Transmitter and Receiver Refurbishment

 The refurbishment exercise described here should be useful to restorers in that it covers a number of techniques that will be applicable to many similar equipments.

The equipment is a marine transmitter/receiver manufactured about 30 or 40 years ago in Denmark by the Sailor Company.

 The transmitter is an AM (amplitude modulated) rig that puts out signals, much like the BBC stations on medium and long waves. There's also an alarm feature that will send automatically on the MF distress frequency. The receiver has a much wider frequency coverage than the transmitter, but has a number of preset channels matching those on the transmitter. Single sideband and CW can also be received. The two units together with matching loudspeaker are fitted into a rack which can be installed in a small ship and powered from a low voltage DC supply. The technology employed is a mixture of transistors and valves. The latter being employed in the high power RF transmitter stages. Transmitter HT supplies are developed by a substantial transistor inverter and the modulation by a high power transistor amplifier.

The overall condition of the numerous pieces of equipment, making up the installation, is generally pretty poor as they've been exposed to sea air and, even though the manufacturers have plenty of experience in providing suitably proofed radios, as they are in the business of selling marine transmitters and receivers, anything left for a long time in an unheated salt-laden environment will eventually deteriorate.

As you can see from the pictures there are patches of rusty metal where the finish has been compromised. I think the original finish is green paint with a nylon coating. The latter presumably to give some resilience to knocks and the subsequent penetration of the paint finish to bare metal. The panels are predominantly just screwed onto backing plates and clearance holes are provided around meter fronts etc. Underneath the painted panels, the backing plates are plated steel and water or damp air has caused these to oxidise and rust.

Not only were rust patches widespread but, in the case of the receiver, damp penetration was evident between the nylon coating and the green paint. This had caused unsightly discolouration for which there was no simple remedy.

The panels removed ready for refinishing

 Fortuitously, the receiver and the two transmitter panels are fitted over sheet metal front panels on their respective chassis so that when the painted fronts are detached the equipments are still fully assembled.

Because of the discolouration of paint and the rusting of the panels the original finish had to be removed completely and replaced with a new enamel finish. This in itself was straightforward but of course all the signwriting was lost.

There are a number of ways of replacing the lettering. A silk screen process could have been used but this would have cost many hundreds of pounds as the number of panels involved is quite high. The method chosen was to apply press-on lettering. This is an awkward process as, whilst the lettering is being done, the applied letters are very prone to damage. Getting the lettering horizontal is not easy and getting the spacing right almost impossible to do by eye. Even applying light pencil lines for guidance is tricky as they cannot readily be removed without accidentally damaging the fragile lettering.

The colour of the lettering used in the Sailor equipment is white and this severly restricted the choice of font etc as most products are in black. Unfortunately, the Sailor font size appears to be 15 and, this not being a common size, sheets of font sizes 14 and 16 had to be purchased.

Lettering the receiver front panel was not straightforward either as the designers had used a lot of linear markings. Strangely the manufacturer of the lettering sheets hasn't thought to provide sheets of straight lines, so a combination of two solutions was adopted. First, the lettering sheets have various lines on them used in conjunction with the headings and general sheet markings and, secondly, a sheet of arrows was purchased so the shafts of the arrows could be used to make linear shapes.

Where letters had been damaged or where the transfer from the sheets was imperfect I had to apply a white paint. Even the finest touch-up pencil was too broad so I had to make a tiny knib-like tool from a cut-down plastic tube used for cotton buds. By applying paint from the touch-up pen to the knib I was able to fill in any gaps in the letters but if damage was too great, or if letter spacing was too bad, the letters had to be rubbed off and reapplied.

Once the lettering was complete the panels were carefully cleaned then sprayed with a clear matt lacquer. This was fairly quick to dry and was not as difficult to use as a spray-on paint, which too often acquires spatters and runs if too much is applied. The lacquer provides a hard wearing finish and hopefully restores a reasonable barrier to salt laden air. I found that extra lettering can be added after the first coat of lacquer has been applied.

The Sailor 56D transmitter

 This picture shows the transmitter, as it was received. It employs a 12 volt version of the 6146 as a crystal oscillator driving 3 similar valves wired in parallel.The transmitter and the receiver are mounted in a rack in which is also mounted a matching speaker in similar shades of green and rust. The power supply for the whole system is 24 volts at lots of amps and the cabling and terminations for this are at the rear of the rack.

That's not just reflections from the meter faces; the scale markings disappeared long ago from a surfeit of sunlight, leaving blank, or almost blank, aluminium faces. The plan was to remove the meter scales and redo these in black press-on numbers, however I couldn't get numbers in a small enough font so, after scanning the Internet for a suitable product, I downloaded an excellent program for designing meter faces. Although this gave only ten free passes I managed to design and print duplicates of the originals in three sessions. At least I hope they're duplicates as I could only see one of them very faintly and the other two only showed up vaguely after scanning them and using lots of enhancing. I even got a reasonable copy of the trademark, which I was able to add to the new designs.

Below are the newly restored transmitter panels roughly assembled for a trial fit, and the three new meter faces on white paper stuck to the original metal plates

 

 

For ease of maintenance the top section of the transmitter hinges upwards. This reveals the underside of the valve sockets and the top of the DC-DC invertor.

 

 

The 56D Receiver

 Discolouration of the paint finish is clearly evident. It's also clear that the overall paint finish has altered over time and is now completely different to the matching transmitter above.

In fact when the project is finished the two sets will look better than the originals because the paint finish will be exactly the same. The receiver had been painted in a light hammered finish that looked odd when compared with the transmitter and the rack.

The loudspeaker case contains a 4-ohm driver whose cone securing material has rotted away. A modern unit will be fitted.

   

 The repainted front panel with new lettering and the loudspeaker partly assembled.

The knobs for the equipment are of very high quality and, although they looked to be in poor shape, the tarnish and corrosion disappeared after treatment with hot soapy water and the use of a brass bristled brush. One of the most difficult tasks was to remove the knobs in the first place as they had rusted onto the shafts and their steel screws had corroded into the brass bushes. Some screws had to be drilled out and afterwards the holes had to be re-tapped the next size up.

There were lots of annoying little jobs involved in the refurbishment, apart from reconditioning the knobs, as replacement parts are no longer availble from the manufacturers. In order to make the overall finish look respectable I had to respray the black receiver dial and carefully remove corrosion from many of the screws as countersunk types in chrome are not easy to come by since industry generally shifted to pan-head types to cut costs about twenty years ago. The chrome speaker grille and the receiver dial bezel needed treatment as these were pitted from corrosion. All the black bakelite fittings were badly marked by salt and needed a variety of treatments to restore a reasonable finish.
   As the reassembly phase was some time after the equipment had been dismantled some difficulty was found in working out the sequence. The transmitter/receiver pair has been designed to be installed together in a rack but the actual order the parts must be bolted together is not entirely logical. The rack itself is not the traditional type of nineteen inch type but more a concoction relying on the cabinets of the equipments being bolted together using additional metal panels and a small frame.
 The original cable harnesses, although looking at first in poor shape, responded well to hot soapy water anfd soon looked as good as new. Earthing the various items is made throuigh a nickel plated metal plate that fixes under the wiring label on the rear of the transmitter case. What can't be readily seen in the pictures is a wide copper strip that is anchored to the RHS of the earthing plate. This is used to complete the aerial circuit. Two multi-plugs on flexible cables connect to the transmitter chassis whilst the heavy current connection is made via a socket bolted to the rear of the case, into which a mating connector locates as the transmitter is pushed into the case. Connections to the receiver are carried by cables tereminating at a choc block above the earthing plate. The cables pass through the rear of the loudspeaker case to the connection panel at the side of the receiver.

 

 

 The equipment assembled before final adjustments have been made. The receiver needed aligning to take care of component ageing etc.

The small box at the bottom left is a matching transformer used for DF working. It conmnects between a special DF aerial socket on the receiver and a loop aerial.

The main aerial connects to the porcelain insulator at the top left of the transmitter upper chassis. As ashipborne aerial cannot generally be a standard 50 ohm dipole the output of the transmitter has to be able to match into virtually any impedance of aerial, hence the usual type of aerial socket found on an amateur band transmitter will not do. The RF voltage at the aerial connection may be extremely high, hence the need for a substantial insulated connection post.

The power connections to the rig are made in various colouredc cables and these easily confuse as it was found at the outset that a capacitor in the receiver had been reverse connected and had exploded.

In keeping with cable colours used in the USA, some of the live 24-volt wiring around the receiver was black and ground or 24-volt negative was in white. To add to confusion, some of the receiver 24-volt positive cables were coloured brown and at the main termination panel red was used for positive and black for negative. Without a circuit diagram it was quite tricky establishing the proper connections as within the receiver there is a large stabilising zener to reduce the 24-volt supply rail to a more manageable 9-volts. Connection to the receiver battery supply line was via the zener, a large ballast resistor, a voltage selection switch allowing various supply options, including built-in batteries and an on/off switch at the rear of the volume control.

Testing this rig posed a problem. Most high current power supplies are designed for 12-volts. Higher voltage versions are hard to come by unless one's prepared to pay lots of money. Whilst walking around Wimborne Market I spotted exactly what I needed. A chap was selling 12-volt lighting transformers. These were rated at 225VA, which works out at about 18Amps or so. I bought three for £3, the outputs of two connected in series will provide 24-volts at 18Amps. Another few pounds got me a few near-360 degree moving coil meters from the same chap. One read to 40-volts and another to 20Amps. I used three 2N3055 power transistors in parallel, with their bases set by a 3-terminal regulator. The best I could do from my junk-box was rated at 15-volts so I placed a 10-volt zener diode in its ground connection and this resulted in a stabilised output of 25-volts off load and 24.5-volts at full load.

When I tried the Sailor the valves lit nicely but the HT supply remained at zero volts. The rig uses a DC-DC converter and I found its transistors had deteriorated to the extent that they got very hot and little else. As DTG2400 germanium power transistors are scarce and expensive I looked around the workshop and found a pair of silicon types with better ratings than the old ones. With only a little persuasion they started up and provided the required 600-volts of HT.

I found the key connections and fired up the transmitter. After changing an open-circuit screen resistor it turned out about 20-watts or so into 50-ohms. Plate currents for the three 12-volt versions of the 6146s were about the same and stood at 50mAmps. This represents a total DC input of about 82-watts so 20-watts output doesn't look too good. Something is keeping the plate current low and also reducing the efficiency to about 25%. I varied the grid bias but the plate current didn't change. This isn't what I'd have expected.

Testing is proceeding....

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