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Does anyone know how to tell the difference between an Ampex 350 vs a 351? A friend of mine has a couple of these Ampex pres, and from pictures i've found it obviously one or the other, but there is nothing on either of them to distinguish which model it is. Any help is greatly appreciated.


RemyRAD Fri, 04/07/2006 - 19:21

There is actually a huge difference between the 350 and the 351. There is no difference between the two transports! The difference is in the electronics. The older 350 utilized metal enveloped tubes, that's right, metal tubes like the 12SJ7 Pentodes which were used throughout much of the electronics and only the 6C5/6J5 triode and the 6SN7 dual triode were used in the record circuit driver. The first stage playback head preamplifier tube was also indicated as a special " select" version which all had to be independently tested each for lowest noise before it was appropriate for playback purposes. It also utilized all point to point wiring in the electronics.

The 351 was a huge departure from the old metal envelope tubes which were much more prone to micro phonics, i.e. vibrational noise. The 351 utilized the new 12AX7/ECC83 and the 12AT7 dual triode tubes. They were much lower in noise (as all triodes are in comparison to pentodes) and were in small glass envelopes. They were also mounted on those newfangled printed circuit board thingies!

Some people feel that the 12AX7/12AT7 351 was one of the finest sounding analog machines ever made and the last of the tubes. After that Ampex came up with the "AG" series such as the AG350/354 and others. Those utilized the early germanium transistors. Albeit they were good, they weren't as good as the original 351 tube type. So if you have modular 350 or 351 transistorized electronics, they were still pretty cool but certainly don't have the sweetness in sound compared to their "Thermionic" cousin, the original 351.

The Scully 260 and the original 280 also utilized germanium transistors in their electronics. Germanium transistors are not as robust as their silicon counterparts but they do have a different tonal quality. Many people feel that the germanium transistors are the better sounding transistors and they were not interchangeable with their silicon cousins. They both had different voltage drops, even though later versions of the Scully 280 were updated to the newer silicone versions, they never sounded as sweet as the older germanium transistors had. The Scully 280B were a completely different beast not designed by Larry Scully but designed by another person who worked for the company that purchased Scully, Dictaphone. The designer who created the 280B, committed suicide just prior to AMPRO broadcast products acquisition of Scully. So any technical questions that we had behind the design philosophy was lost forever. The 280B was an all silicone transistor machine that never had any microphone preamplifier's built-in as the original 280 had. There were 2 basic differences between the 280B series in the last of them should have been designated the 280C, but never was. The difference there was basically the 280B, had the same scrape flutter idler roller on the left side of the transport just like the Ampex 350/351/440 had. The last permutation of the 280B, the "C" version had no roller to the left of the head stack but a special motion damped idler arm that was connected to a constant tape tension sensor device and had much better speed regulation and was gentler on the heads.

So if you are looking at an Ampex modular preamplifier, you are looking at the AG350 and although it will add a different flavor to your recordings, I personally feel that they are nothing to really write home about. I think the original germanium Scully 280 had a superior microphone preamplifier in comparison to the Ampex.

Ms. Remy Ann David

heinzbakedbeans Mon, 10/17/2011 - 14:51

to RemyRAD! Further consideration!

Hello to everyone!
this is my first time here, and i know that this is an old thread but i'm intrested in old gear...
i own an Ampex 400a in fully working condition. i even record an album just with and an MX10, no comp/eq and trasfered direct to vinyl.
i really love the sound of this machine but i was looking for a stereo version. i just found an 351 stereo portable version.
i already know the circuit differences between 400/350 and 351, but i never compared the sound.
someone ever did it? who is the best? i'm talking used as a full tape recorder but also just as a microphone preamp.

RemyRAD Tue, 10/18/2011 - 20:48

My mentor Thomas M. Bray had every Ampex, except a model 200. He told me that the 400 was a DOG. I inquired as to why he felt that way since its lineage was similar to the other similar looking machines? He said because it was a pusher and not a puller. The 300/350/351 pulled the tape past the heads. The 400 pushed it across the heads. He said those suffered from greater flutter. Not quite what we would call a nice 3M iso-loop tape path. But all of their machines were built for satellite telemetry loggers. And those used A wound tape as opposed to the B wound Style we've used since the Ampex 300? Anybody remember the difference? No? Oxide out.

Always equipped with inside out information.
Mx. Remy Ann David