An appreciation of an Ampex 351 tape deck

tapepath

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Feb 20, 2014
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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

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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

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Feb 20, 2014
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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.
 
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andromedaaudio

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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

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Feb 20, 2014
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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
 
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tapepath

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Feb 20, 2014
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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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sigitask

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Jan 5, 2020
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I refurbishing also one 350. But it is not so nice like yours.
 

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tapepath

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Feb 20, 2014
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Hello,
Thank you for your comments, I appreciate connecting with other people who enjoy these classic machines. Many years ago I began assembling components for both the electronics and the transport. At the time there was a great deal more opportunities to find people who were selling NOS transport components. People who had spare motors and brake mechanisms were selling just to get rid of them and the prices were fairly reasonable. The electronics were different, they were much harder to find and always expensive. I managed to find a complete transport being sold by a retired Ampex engineer that was in very good condition and I used it as the basis of the final assembly. I substituted NOS components as I found them, most recently a new faceplate for example.
 
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sigitask

Member
Jan 5, 2020
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Hello,
Thank you for your comments, I appreciate connecting with other people who enjoy these classic machines. Many years ago I began assembling components for both the electronics and the transport. At the time there was a great deal more opportunities to find people who were selling NOS transport components. People who had spare motors and brake mechanisms were selling just to get rid of them and the prices were fairly reasonable. The electronics were different, they were much harder to find and always expensive. I managed to find a complete transport being sold by a retired Ampex engineer that was in very good condition and I used it as the basis of the final assembly. I substituted NOS components as I found them, most recently a new faceplate for example.
Thank you for answer! maybe you still have contacts this persons who had NOS Ampex parts? I was tired with reel motors, old even after changing bearings is noisy, shafts is bend etc. I bought accidentally NOS reel motor, and it was absolutely silent. So old bearings was much better as today. I need 2 Nos rell motors and some nos parts.
 

sigitask

Member
Jan 5, 2020
43
1
8
59
Hello,
Thanks for answer! Maybe you still have contacts this persons who had NOS spare parts? I need some items. Im tired with reel motors. Arrived with bended shafts, we tried to fix ir but now we have not centered rotor. Need new reel motors to.
 

sigitask

Member
Jan 5, 2020
43
1
8
59
Hello,
Thanks for answer! Maybe you still have contacts this persons who had NOS spare parts? I need some items. Im tired with reel motors. Arrived with bended shafts, we tried to fix ir but now we have not centered rotor. Need new reel motors to.
So you put new front plate to preamp? It is not easy to get NOS plate. I have to make renovation for plate. Polishing is not problem, but after necessary to make new scripts. It is not easy.
 

tapepath

Well-Known Member
Feb 20, 2014
41
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213
Hello,
I'm afraid I no longer have that person's contact information, sorry. I can very highly recommend Dave Dintenfass at Full Track Productions located in Seattle, WA. www.fulltrackproductions.com is his website. He is an authority on Ampex equipment and offers skilled rebuilding services on motors. He rebuilt the capstan motor I use and it is quiet and seems completely new.
The faceplates on the electronics can be resurfaced by a competent machine shop. As I understand it the printing is not applied to the surface. Rather it is stamped into the metal and then paint is applied over the top filling in the graphics. This means that minor surface scratches can be removed by a very light surface removal. I chose a different approach, I carefully polished the surface using Flitz metal polish using cotton balls several times. Then I used a good quality car wax to seal the surface and allow easy fingerprint removal. I also bought a third complete electronics chassis and chose the two best looking faceplates for the final assembly. 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.
 

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