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Ampex 351 master/slave electronics

Discussion in 'Vintage Analog Gear' started by DeVille, Apr 9, 2013.

  1. DeVille

    DeVille Active Member

    Hi, this is my first post. I've been lurking on here for years and soaking up a ton of great info, so a big thanks to all the contributors! Now to my question...

    I've been sourcing out components to put together an Ampex 351 recorder. So far I've got a line on a 351 transport with ag440 electronics which I'll probably use in the meantime until piece together the 351 electronics. The transport can be used as a 4 track or a 2 track because it has switchable guide posts. If anyone has any info on this configuration please let me know. Was it a reliable setup? I like the idea of having the option using either 1/4" or 1/2" tape depending on the project.

    As for the electronics, I've sourced some 351 slave units. The catalog number is 30750-9 which I can't find any info on. I know that certain numbers correspond to being used with either 7.5ips/15ips transports or 15ips/30ips transports. Or does it really matter? Will any 351 work with any transport? Any info on these particular model numbers would be appreciated.

    And final question... If I wanted to put together a four track, how many master and slave units would I require? Would just one master work with 3 slave units?

    Thanks in advance for any and all replies! Cheers!
  2. Boswell

    Boswell Moderator Distinguished Member

    One for McMurphy....
  3. DonnyThompson

    DonnyThompson Distinguished Member

    Uhmmm.. I'm confused here... the 351 was/is a mono/single track recorder.... the guide posts would only help using different tape widths, you'd need a 2 or 4 trk head stack, and the electronics are mono.... :confused:
  4. DeVille

    DeVille Active Member

    As far as I know the 351s were available in mono or stereo versions.

    We also see plenty of 350/351 4 track machines out there. Whether that was a factory option or if it was a common aftermarket thing that was done, I don't know.

    Not sure how the machine I'm interested in started its life, but it currently has a 1/2" 4-track head stack. The seller also mentions that the guideposts are dual purpose and it can therefor be used with 1/4" tape. Not sure if this means that the tape would then just pass across 2 tracks of the heads, or if one would have to switch out the headstack. If the former were true and it functioned well, then I'd be interested in this machine. Seems pretty cool.

    Aparently it was modified in the early 80s. To what extent, I'm not sure. Im only aware of the 440 electronics, and the multipurpose guide posts as being non original. I have yet to get details from the seller about other potential mods that were done, but I thought I'd get educated here first before wheeling and dealing.

  5. rmburrow

    rmburrow Active Member

    DeVille: If the Ampex electronics uses miniature tubes (12A*7 type), has the large Simpson VU meter, and has a SO-230 coax jack on the back of the electronics for bias coupling, you can use one master electronics and the rest slave electronics. You need to sync the bias or convert over to bias amplifiers in the slave units. I have a 351 with a manual so I will look up the schematic...the electronics was probably used on the later Ampex 300 multitrack units also....
  6. DeVille

    DeVille Active Member

    Thanks rmburrow... very helpful!

    This sounds like the ones I'm looking at. I thought I read somewhere that a "-9" in the catalog number meant they were used with 300 transports. Should work fine with 350/351 transports though?

    They also look like they've been modified to be able to make adjustments via holes on the front. Would this be the bias amp conversion you mentioned?

    I'll attach what pics I received from the seller.


    Attached Files:

  7. rmburrow

    rmburrow Active Member

    Deville: It appears you have the electronics interchangeable with the later 300 series and the 351 series Ampex recorders. The VU meter looks like the older Burlington meter but the printed boards, etc. look very familiar. I see the Ampex input transformer in the picture taken oblique from the rear of the amplifier. I was looking for the Amphenol SO-239 coax connector that is probably labeled "Bias Couple" on the amplifier. (This is a single pin coax connector.) You can use standard coax (RG-59 type) and tee connectors to interconnect the bias if you don't have the Ampex cables, but remember the slave amplifiers must be synched in frequency or converted to bias amplifiers (to avoid objectionable artifacts on recordings)...
  8. DeVille

    DeVille Active Member

    Cool! Thanks again for the great info!

    What's involved in converting to bias amps(in layman's terms)? Any advantage in doing this over syncing?

    I have yet to grasp the concept of this but I assume the bias adjustment would be the simpler route, just more time consuming if regular adjustments need to be made. Correct in my uneducated guess?

    Am I also correct in assuming the holes in the front of these were made as part of a relocation of the high/low speed frequency controls?

    I'm very grateful for the time you're taking with these questions! Cheers!

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