This month's attic treasure is a 1968 ITT Mackay Marine 3010-C.
If you've served shipboard or been around maritime HF receivers, you know that this type of equipment is in a class by itself. Design specs demand reliable service in harsh environments, the ultimate in sensitivity, and reception of MW, CW, MCW, SSB and FSK signals within its frequency range.Weight, bulk and expense are not a problem.
Many hams and DXers consider this to be one of the finest receivers ever made. This triple-conversion receiver covers a frequency range of 70Khz to 30 Mhz, but it will operate down to 10 Khz with reduced sensitivity. Coverage is spread over 15 two-megacycle bands. It has 17 tubes and weighs in at a little under 50 lbs. Part of the reason for the enormous weight is the cast aluminum chassis which keeps each stage isolated in its own cubicle. To ensure ultimate RF shielding, the bottom plate is secured with 40 screws. The 3010 also has an unusual RF amplifier tube, an Amperex 7788. This is a high transconductance pentode highly sought after by audiophiles, making it rather expensive.
The 3010 relies on precision construction for accurate mechanical tuning. The design engineers at Mackay came up with an elegant and unique solution: the main tuning knob drives the tuning capacitor directly -- no chance of backlash from dial cord, belts or intermediate linkages. Frequency display is via a film dial which is 90 inches long and calibrated in 2 Khz increments; about the size of 16 mm film, but made of woven fiberglass. It is driven by the tuning capacitor through a toothed belt drive. There's also a built-in 100 Khz crystal calibrator to provide checkpoints throughout the entire frequency range. The sheer coolness of tuning this receiver makes it well worth the price of admission.
The 3010 uses the same mechanical filters as the Collins 75A-4. It has a 3.1 Khz filter installed for medium selectivity, and an empty socket where an optional 500 Khz CW filter could be added for narrow CW reception. There's also a built-in 6 Khz crystal filter for broad selectivity. Never mind double-conversion, this is a triple-conversion superheterodyne receiver! Image rejection is around 80 dB throughout the entire tuning range. No tracked circuits are used, eliminating complicated mechanical ganging arrangements and the hassle of tracking adjustments during alignment procedures. Finally, band switching is greatly simplified: the 3010 has a robust two-section rotary switch, rather than the complicated multi-deck band switch used by Hallicrafters and other ham receivers. The result of this triple-conversion circuitry is a specification for all images down 80 dB or more.
Mackay began as a telegraph company in 1884, and evolved into a manufacturer of marine communications gear during the 1920s. It eventually grew into a large multinational, was acquired by ITT in 1940, and divested in 1987. Mackay no longer manufactures its own marine equipment, but is a sales and service organization with centers in 15 U.S. Ports and seven international locations.
This particular receiver was recovered in the early 80s during a dumpster diving expedition at MIT. It worked, but had a nasty hum in the audio (which we've yet to resolve despite investigating all the usual suspects). Beyond that, the sensitivity and overall operation of the 3010 has exceeded all expectations. Its reputation as a dream receiver is well deserved. DX results are spectacular. The limiting factor is the rising atmospheric noise level common in all developed regions of the globe.