Head assemblies for either full (single) track, half track or two track stereophonic (351-2) operation are available.ĬCIR equalization can be obtained on request when ordering equipment.
AMPEX 351 INPUT TRANSFORMER SERIES
Along the way I bought a NOS electronics faceplate, but the graphics for the speed control setting were different from the version I was using so I didn't use it.A basic recorder/reproducer in the 351 series consists of a tape transport for operation at tape speed pairs of 3-3/4 inches per second (ips) and 7-1/2 ips or 7-1/2 and 15 ips, a headĪssembly for use with l/4-lnch magnetic tape, and an electronic assembly which contains the record amplifier, reproduce amplifier, bias and erase oscillator, and power supply - all featuring etched board construction. I also bought a third complete electronics chassis and chose the two best looking faceplates for the final assembly. Then I used a good quality car wax to seal the surface and allow easy fingerprint removal. I chose a different approach, I carefully polished the surface using Flitz metal polish using cotton balls several times. This means that minor surface scratches can be removed by a very light surface removal. Rather it is stamped into the metal and then paint is applied over the top filling in the graphics.
As I understand it the printing is not applied to the surface. The faceplates on the electronics can be resurfaced by a competent machine shop. He rebuilt the capstan motor I use and it is quiet and seems completely new. He is an authority on Ampex equipment and offers skilled rebuilding services on motors. I can very highly recommend Dave Dintenfass at Full Track Productions located in Seattle, WA. I'm afraid I no longer have that person's contact information, sorry. The result is a constant and adjustable level of tape tension throughout the complete playback. This system uses a tachometer attached to the supply motor assembly that varies the motor's operating voltage as a function of the amount of tape present on the reel. Fortunately I was able to source an Inovonics Tentrol 400 that I was able to get operating and installed. I wanted to convert the transport from a constant torque design to a constant tension system at least on the supply motor. I had managed to find NOS supply and take up motor assemblies and decided to send the capstan motor to Dave Dintenfass at Full Track Productions for an overhaul. The transport is fairly easy to dissemble, the three motors are removed from the central control box using Cinch-Jones type plugs and unbolted from the main mounting plate. My overall plan was to first get the transport section looking and working as perfectly as possible and to try and improve on the tape handling aspects of the 1958 era design.
If this thread is of interest I'd be happy to continue detailing this journey. I purchased the set of replacement circuit boards (power supply, recording and playback) as a fall back if I couldn't revive the original boards. Another result of this near cult status is there are small companies that support the restoration and modification of them and produce printed circuit boards and replacement output and input transformers. I managed to acquire three of them, two in really bad condition and one less so. The less welcome news is that as a result they are expensive to buy even in the most battered condition. The good news is these electronic units are not consigned to the trash pile but are gathered up in any condition and offered for sale. Either way this has been both good news and not so good news. I also joined an online Ampex group and began saving relevant posts and taking note of people who were authorities on the subject.Īmpex 351 record and playback electronics have obtained a valued status among some current recording engineers as a "golden era" microphone preamplifier (this view is poo-pooed by the veteran old hands as an example of the dreaded classic "phat-toobe" syndrome). Equally important I began to collect service manuals, schematic drawings and service bulletins detailing the history of this design and how changes occurred as the evolution of magnetic tape evolved. I was very fortunate that I was able to buy a complete transport in excellent shape from a retired Ampex engineer. This meant that I was able to buy at reasonable prices complete transports and electronics chassis, multiple head assemblies and duplicate motors and spare parts. I began this project before the fairly recent resurgence of interest in all things connected with magnetic tape machines. For several years I've been working on restoring an Ampex 351 tape deck.
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