An appreciation of an Ampex 351 tape deck

tapepath

Well-Known Member
Feb 20, 2014
21
2
53
#1
For several years I've been working on restoring an Ampex 351 tape deck. I began this project before the fairly recent resurgence of interest in all things connected with magnetic tape machines. 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 was very fortunate that I was able to buy a complete transport in excellent shape from a retired Ampex engineer. 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 also joined an online Ampex group and began saving relevant posts and taking note of people who were authorities on the subject.
Ampex 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). Either way this has been both good news and not so good news. 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. The less welcome news is that as a result they are expensive to buy even in the most battered condition. I managed to acquire three of them, two in really bad condition and one less so. 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 purchased the set of replacement circuit boards (power supply, recording and playback) as a fall back if I couldn't revive the original boards.
If this thread is of interest I'd be happy to continue detailing this journey.
 

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Mike Lavigne

Member Sponsor & WBF Founding Member
Apr 25, 2010
8,309
1,781
400
#4
I owned an Ampex 351-2 for a few years. It was one of those in portable cases and was in very good condition and lightly used. The cases were deteriorating but the gear was nice. I also had a second set of electronics in pretty good condition. I had a local Ampex guru Dave Dintenfass (Full Track Productions) ready to rebuild it and had delivered it to him to begin.

https://fulltrackproductions.com/service bulletins/Quick_notes_on_Ampex_reel_motor_overhauling_REV_1.1.pdf

Then I bought new speakers and amps and needed to fund that so sold the whole lot to my friend Ki Choi.

Not sure I would have ever really played with it as I love my Studers, but as an icon it would have been nice to have it sitting here.

Very cool stuff!
 
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tapepath

Well-Known Member
Feb 20, 2014
21
2
53
#5
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. 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. 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. I wanted to convert the transport from a constant torque design to a constant tension system at least on the supply motor. Fortunately I was able to source an Inovonics Tentrol 400 that I was able to get operating and installed. 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. The result is a constant and adjustable level of tape tension throughout the complete playback.
 
Jan 23, 2011
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Amsterdam holland
#7
Nice project to save such a machine .
I did it once( had it done actually ) with a studer A 80 .
It was sitting not running / useless in a small studio , because the guy didn't have the money to have it repaired properly
I paid 1 K (it was a guess really , it could have been a major issue ) I had it repaired/ recapped for 800 and sold it for 3750 .
Its the only time I ever made a profit from any of my audio adventures:)
Its now in a recording studio doing its thing
 
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tapepath

Well-Known Member
Feb 20, 2014
21
2
53
#9
Yes, that photo was taken after I'd replaced all of the push buttons for tape control, both take up and supply motors, had the capstan motor rebuilt and installed the tape tension control assembly. This photo shows the front of the machine with the NOS faceplate I was fortunate to find. DSC_0079.JPG
 

tapepath

Well-Known Member
Feb 20, 2014
21
2
53
#10
Now that the transport was finished and the high impedance playback head assembly was installed I could begin work on the electronics sections. My goal was to first rebuild the power supply on the least damaged unit and get it working properly and learn a bit about how everything was put together. Then I could focus on the remaining two units that were needing the most amount of refurbishing. After doing this I was able to disassemble the two chassis and have the pieces of the enclosures sand blasted and powder coated with a finish as close as possible to the original. The same company was able to photo engrave the lettering on the back panel. I then removed all of the components on the six circuit boards, ultrasonically clean and rebuild them with new parts. DSC_0063.JPG
 

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