Philips DP70

The DP70 consists of a monocoque, cast iron chassis containing the mechanism, which is completely oil-immersed on the non-operating side. Jan-Jacob Kotte believed that the use of heavier materials to absorb vibration reduced instability in the projected image, and this is certainly reflected in the design of the DP70: a complete outfit, including the bases and reel magazines, weighs 1,004 lbs – which is half a ton. The DP70 was also significantly more expensive than any single gauge theater projector on the market: a US customer was quoted $6,225 for one in 1966 ($44,942 in 2014, adjusted for CPI inflation), which was around the cost of a typical three-bedroom suburban home at the time.[7] The price asked for a double set without lenses asked in West-Germany in 1956 was 42,510.00 Marks, which at the rate of exchange at that time (4:1), related to 10,627.50 $ for the pair, or 5,313.75 $ per projector.[8] That price was higher than 35mm only projectors, but still reasonably low if compared to competitors like Bauer U2.[9] The low price and reasonable quality was an important part of the success. Because the DP70 was built to commission for a customer in the United States, it is a very unusual example of a European-designed piece of industrial machinery with fasteners that have SAE rather than metric dimensions.

Detachable reel magazines can be fitted (e.g. to enable the projection of nitrate film in accordance with safety regulations), or removed (e.g. to enable projection using an external film transport device such as a platter or tower, or to fit an external audio reader) as needed. Special fire trap rollers for nitrate were also available, to comply with fire regulations in some jurisdictions. Separate magnetic and analog optical audio heads are built into the mechanism itself, enabling all 5/70 magnetic and 4/35 optical formats to be projected without the need to adjust or replace any audio components. The change of gauge is done by swapping some gate components, pad roller assemblies, reel spindles and the lens, and in some cases making minor adjustments to the lamphouse. This procedure can be completed by a competent projectionist in 5–10 minutes, which is a major reason for the DP70's popularity with venues that show 4/35 and 5/70 prints interchangeably.

Because the DP70 was intended for use with 70mm film and in large theaters with a long throw to a big screen, several features were included to disperse the intense heat generated by the more powerful lamps with which it was often used. The gate assembly includes copper components which are silver-plated, and a liquid-cooled plate that is fitted with a water pipe surrounding the aperture opening. The use of liquid recirculating equipment and distilled water was encouraged. A single-blade shutter designed to rotate at very high speed (up to 3,600 RPM) doubles as a cooling fan. Unlike other projectors of its hi-power kind, the DP70 did not offer forced-air cooling of the film itself, which is known to be a key feature to prevent overheating of the film and the major nitrate-fire prevention measure. A water cooled pre-shield just assists in keeping the gate and metal parts cold, not the film.[10]

The DP70 as shipped from the factory was equipped for dual speed operation, at 24fps (the frame rate at which almost all 4/35 prints with a combined soundtrack are projected) and 30fps, the frame rate used in the original Todd-AO system. The original version of the DP70 used separate drive motors for 24fps and 30fps operation, whereas the AAII had a single motor and a dual locking pulley mechanism on the main drive shaft to change the speed of the mechanism. There were also several other more minor changes in the AAII.

Because many of the DP70s remaining in use today are in repertory venues that screen a wide range of formats, including prints of silent movies that require a lower frame rate than 24, very many have now received aftermarket modifications that will typically enable any speed between 16 and 30. Since US market DP70's came factory equipped with capacitor start capacitor run synchronous motors that lock their speed (1,800 RPM in the USA) to the AC line frequency (60 Hz in the USA), the most common way of doing this has been to add a variable frequency solid state AC inverter (Baldor Inverter) and suitable 3-phase motor. Most European units were sold employing asynchronous motors, which added slip to the synchronous speed (1500 RPM at 50 Hz) to achieve the required 24 frames (1440 RPM) and 30 frames (1800 rpm), without gearing requirements in the original construction.