Ampex electronics for the best possible sound

So the restoration of 2 MR-70 tape recorders has begun. The new capstan servo motor is pretty much designed and parts are starting to come in.
I took inventory of the Electronics units I have here and discovered that they are missing some key parts, which perhaps I may be able to source here since there seems to be more folks with MR-70s on this forum than anywhere else. To restore the 3 electronics units that I have, I need 1 record/output line amplifier module and three Sel-Sync plug-in modules. We are also interested in purchasing at least 1 additional complete electronics unit. If anyone on this board has a parts unit or a complete unit that they are interested in selling, please let me know.

On recapping the MR-70. Each electronics unit uses three 4-section capacitors that are 20uF/20uF/20uF/110uF at 450V which are used in the B+ supplies. Since Twist lock caps of that value are pretty impossible to get, I laid out a PCB that is the same size as the football-shaped phenolic mounting plates used to mount the original caps. It turns out that I can easily fit 1 ea 150uF and 3 ea 33uF 450V caps on the PCB, greatly simplifying upgrading the caps. I am considering the Rubycon BXW series which are rated for 10,000 hrs. at 105C. Since modern caps are +/- 20% tolerance, one should always increase the values used as replacements to ensure that the replacement caps are at least the same value as the originals. I will probably have extra PCBs left over, so if anyone need some to upgrade their MR-70 electronics, contact me. Let me know if you're interested so I will know how many to order.

Thanks!
Steve Hogan

I have located the sel-sync modules, but still need the line-amp module and another complete set of MR-70 electronics.

Steve

I know this thread is old but I wanted to thank everyone here for the inspiration and information.

I am a jazz saxophonist and I am working with Dave Dintenfass on converting an Ampex 300 or 351 transport with 351 electronics to 1/2 inch CCIR, and possibly 30 ips as well. Dave should be able to provide a suitable transport with appropriate modifications. I'm working with a friend who's successfully implemented 15 ips CCIR EQ on his 1/4 inch 351, so we are planning to do the same mods on the new set of 351 electronics I'm getting.

If anyone here has information on how to modify the 351 electronics to implement the AES 30 ips curve, that would be very helpful, as that's one thing we haven't sorted out yet.

Also, I realize members here have a lot of experience with this type of endeavor. I would welcome any help and advice of any kind about things to do or things to avoid while doing this.

The idea is to have a 1/2 inch tube deck to mix to, not just playback, as my friend and I are both professional musicians. Thank you!

Jerome Sabbagh

Tom B. said:

A Bigger Project

This project has been ongoing for over two years, but we're making progress and it's coming together. This is my 300 playback rig, which has both solid state (AG-350) and tube (350) electronics. The transport started out as a 300-3 and was modified with a four-speed DC servo capstan, Tentrol constant-tension on supply and fluid idler, similar to what is on the MR70. Rack is ex-Sonicraft.

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John French is building a custom head assembly with a Flux Std 350 head and Flux ME head, and adding a scrape-flutter idler. The headblock will have identical long cables so I can swap the different heads between the two electronics depending on playback preferences.

John Fletcher rebuilt the tube electronics and I did the AG units. Adding the DC capstan was an enormous effort; it took a month of planning and something like 60 hours to do the machining and transport mods to accept the motor/controller. It did however, turn the 300 into an exceptionally smooth-running machine.

Although it was intended to be a 1/4" machine, the transport retains the 1/2" rollers (in addition to the required 1/4" ones) in the event I decide to move more towards 1/2" tape.

Tom

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Very interesting project. May have some pictures to look how was installed DC capstan?