FS: Ampex MR70 1/4" 2-track (stereo) 7.5 / 15ips tape machine - completely refurbished / ready for operation

srs148

Well-Known Member
Jan 3, 2016
83
34
250
Additional photos available via the eBay listing and more will be uploaded.
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mr70_11.jpg

Ampex MR-70 analog tape recorder, desirable and extremely rare with total production estimated at less than 80 total units built. Painstakingly restored by member Tom Bassi, his may be the cleanest, most complete, and most extensively serviced MR70 ever brought to market. Play back your master tapes using the same electronics as the Tape Project.

Very rare & sought after Ampex MR-70 analog tape recorder, ¼” 2-Track (Stereo) running at 7.5 and 15ips. This MR70 is turnkey and ready-to-run.

Original ¼”-format transport, exhaustive rebuild, replaced/rebuilt anything and everything that required attention. Full control box rebuild/recap with power supply updates, fresh capstan assembly.

Nuvistor electronics with four selectable eq curves. Rebuilt, recapped, all new hand-picked Nuvistors. Original neon ready/record indicators replaced with LED’s. Line, record and bias amp modules present and rebuilt. Rare EQ covers included.

Heads/guides recent rebuild / relap by JRF magnetics (head report included), in excellent condition. Adjustable azimuth PB, rolling entry/exit guides with new bearings.

In addition to the electronics, extensive time has been put into refurbishing the furniture. The original 2-Track roll around console with hard-to-find trim pieces present, including rare transport control box guards and transport locks.

This is a complete and ready to run machine, so all cables including power cable, transport/electronics interconnects, bias cables, and jumper plugs are included.

Calibrated for ATR Master Tape. Can be calibrated to your tape formula of choice at time of purchase. Machine will not fully erase modern tape without modifications, so we suggest bulk erasing before recording.

A bound copy of the Ampex service manual is included along with the JRF head report paperwork, etc.

The deck is available for inspection and demo in-person in Central New Jersey for serious buyers.

Payment
Payment via ACH transfer or other cash equivalent method of payment. No PPal or credit cards.

Shipping
We will help coordinate crating of the MR70. Buyer is responsible for safe transport of the machine as well as shipping insurance.

Local inspection and pickup is strongly preferred
 
Beautiful machine. Good luck on selling it. At $25K, it is on the upper end of what most people have been paying for 15ips 2 track machines. I think the purchaser would be wanting the top level performance, pristine condition, and the extreme rarity. Looks like the MR-70 was introduced in 1965, a decade or so before the ATR-100 series. I'm curious, is that the reason why it won't completely erase modern tapes? I don't have any issues with erasing on my Ampex ATR-102's.

Larry
 
The key word here is “modern”, so Larry’s statement is basically correct. The ATR-10X machines were designed during a time when tape formulations had evolved to fairly high fluxivity levels and the erasure current followed accordingly. In the 1960’s Ampex engineers designed the MR-70 erase circuit for what was “modern” at the time…..approximately -64 dBm for full erasure depth. To erase modern formulations we’d need an additional 6dB.

Unfortunately a stock MR-70 cannot do that. Even if we could get a bit more energy out of the electronic’s bias amplifiers the master oscillator’s (located in the transport chassis) stability would probably collapse at higher drive levels..

There are a few solutions to consider:

Keep the machine stock, since this was a restoration we chose this path. Most people who would record with this machine would either start with new tape or bulk-erase what they already had (good idea in general).

2) Use an outboard signal generator with low-impedance output (~ 50 ohms) during record to drive the bias amps a bit harder.

3) Build a ‘black box’, something that installed temporarily between the transport and the record electronics and provided the necessary erase energy, but keep the machine ‘stock’ if necessary. This is the path we’d take if someone said it absolutely HAD to erase available tape.

4) Try substituting a Woelke erase head which should have more erasure depth with the same bias current. But again, this is a departure from stock. And….John French did a wonderful job on the heads we chose for the project.

Summary: erase solutions are available but were not considered fully since they were out of the scope of the restoration.

Tom
 

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