30-01-2023, 01:13 PM
Quote:Do the valves last a reasonable time?
Yes and no. The oscillators and dividers don't stress the valves much, nor do they demand high performance; valves with relatively low emission work more or less as well as new ones. I have six organs with valve tone generators; all are running mainly on their original valves in this section. In the divider organs all stages run continuously, so the working conditions are quite standard. In the Miller with individual oscillators, they are keyed by switching the HT, therefore the valves are run for much of the time with heaters at full but no cathode current. Indeed, some of the rarely-used oscillators surving unpopular notes at the ends of the compass might only see a few seconds of emission per year, despite having their heaters running many hours per week. Many of its valves are original, so one day I would like to study the effect of the extended standby conditions on the cathodes. They are, for whatever reason, somehwhat low in cathode/heater insulation. The amplifiers are another matter and often have very tired valves as they do run at their maximum ratings.
Quote:have you had to replace the wiring looms on any?
Not replaced any yet, although it is sometimes necessary to join up looms that have been severed to separate parts of an instrument. Where the tone generators are external to the console, they are often placed in some convenient place such as a vestry or dedicated cupboard where they are accessible for servicing but out of the body of the church. The interconnecting cable, usually 250-350 cores and encased in flexible conduit, is often equipped with connectors, or at least a convenient tagboard; however, having been installed in a building for 70 years, it is not uncommon to find the cable trapped within the building fabric or inaccessible to unfasten, requiring a cut either side and a re-join. Recovering the model 365 from Anderston Kelvingrove church in Glasgow, one of the church volunteers put in some heroic efforts accessing hidden parts of the loom in ceiling voids etc, to unscrew its cleats, only to have it jam tight during the final extraction through a structural penetration, never to move again. Pic 1 in post #22 shows a typical loom re-join job about to begin.
Organ wiring is usually jig-made, particularly where blocks of 32, 61 or similar numbers of cores are needed. Pins are mounted in boards with the correct spacing for the fan-outs, and spools of wire are run back and forth looping around the pins. The resulting loom is laced at the ends and bound with cotton tape in sections with no break-outs, then removed from the jig. As mentioned upthread, this obviates the need for colour-coding or labelling in many instances, as the function of each core is pre-determined by its position. There is a hole, tag or slot for every core and so long as you start out correctly, all will fall into place. In large or long looms, two precautions are often taken to overcome damage and attrition through maintenance. A few inches of extra length on each conductor is left formed into a neat coil at the terminations, enabling damaged / burnt / fatigued ends to be cut off multiple times through the life of the installation without disturbing the loom, and in case any cores are broken outright, spares are included. Coiled-up spares can be seen at the top left of pic 3 in post #22, in front of the threaded rod, and one per row down the middle of pic 2. In both cases these are DCC (cotton) insulated.
Coming up soon is a project to restore two Compton Theatrones, including serial No.1 from 1938. (about six Theatrones survive, only one in nearly original condition.) These historically-important instruments have been in a single private ownership since the mid 1960s where they were part of a very elaborate dual-console setup in a large purpose-built organ room. So elaborate, that the six sets of tone generators, 14 channels of amplification, power supplies etc had an outbuilding to themselves, with a vast array of cables connecting them to the music room. The owner was technically skilled and carried out the installation himself over many years, but he was also an unstoppable modder, who altered every single nut, bolt, connection and component just because he could, adding a switch here, a relay there. The result for these Theatrones is that they have been modified almost out of recognision, with an extra manual, three times as many stops as they originally had, etc.
Making a curatorial decision on how to conserve or restore them was complex. The installation was so unique that there was clearly some value in conserving it outright. A careful assessment was made, with input from multiple experts, of the different experiences that the finished project could offer according to the approach. The conclusion was that examples of original instruments are sufficiently scarce, their original role sufficiently important, and the possibility of high quality result sufficiently high, that return to the original configuration was the preferred option. The consoles will need to be stripped bare, the woodwork comprehensively overhauled, many new pieces made and fitted, then refinished. All the working components will need overhaul, refitting and finally rewiring. The same is true to a lesser extent of the generator racks, which have been retrofitted with different generators.
The reason that I mention this project here, is that a complete replacement wiring loom will be needed. If possible, I will be making it using original 1930s DCC wire, salvaged from discarded looms that I have saved from the scrap-man. Hopefully, sections of original console looms can be incorporated, with their original lacing etc. An interesting jigsaw puzzle.
The two pics below are the 'same' instrument, one as it left the factory and one as I acquired it. I cannot explain the choice of colours.
