A 1950s Ampex Tape Recorder Microphone Preamplifier Restoration

So often when we read of a modification on a classic piece of tube electronics we prepare to wince, as such work often results in senseless butchery of a well-preserved survivor. With [Frank Olson]’s work on a 1958 Ampex 601 tape recorder though we were pleasantly surprised, because while he makes a modification to allow its use as a stand-alone microphone preamplifier he also performs an extremely sympathetic upgrade to modern components and retains it in substantially the form it left the Ampex factory.

The video below the break is a satisfying wallow in pre-PCB-era construction for any of the generation who cut their teeth on tube, chassis, and tag strip electronics. We can almost smell the phenolic as he carefully removes time-expired capacitors and fits modern replacements complete with period features such as sheathing over their leads. The larger multiway can electrolytics are left in the chassis, with their modern miniaturised equivalents nestling underneath them out of sight. We all know that electronic components have become a lot smaller over the decades, but it’s still a bit of a shock to see just how tiny even a high voltage electrolytic has become.

The Ampex would have been a very high quality tape recorder when new, and while this one has a problem with its mechanism it’s that quality that makes it easier for him to do this work in 2020. There’s every chance that this one could be returned to service as a tape recorder if someone was of a mind to fix it, and meanwhile it will give Frank excellent service as a high quality pre-amp. This is how resto-mods should be done!

Ampex are very much still in existence making digital storage products, but back in the 1950s they were at the forefront of analogue magnetic tape technology. We’ve written in the past about how Bing Crosby had a hand in the development of high quality tape recorders, and also about Ampex’s part in the gestation of the video recorder.

12 thoughts on “A 1950s Ampex Tape Recorder Microphone Preamplifier Restoration

    1. Modern? XLR is much older than 1958. Balanced mic’s were common long before then.

      I have a model 600 with the half-track mono option (allowed flipping tapes) with the same set up. Still works, but has had difficulty holding stable drive speed for 40 years and I have never fixed the clutch. Eventually I might, as I have roughly 120000ft of recordings from the 1950’s and 60’s.

    2. I worked in Broadcast Engineering since 1956. The 3-pin XLR came in shorly after that, mainly in portable equipment, then everything. There was a 1930’s round 3-pin connector, the type P, followed in the late 40’s by the type UA, with gold plated pins which was used in many broadcast stations through the 70’s.

      1. There were a lot of oddball microphone connectors that were used up until the 60’s. It is interesting getting an old mic and having a crazy hard time getting a connector for it. I keep thinking this would be a really good use for 3D printing.

  1. Argh, weather to wrestle the wire out of the terminal or just clip and splice onto the cut wire and have two solder joints close together and one gets weakened as the new one is formed nearby. I have in storage 2 of the first generation decks and electronics.

  2. Feel like I do/don’t want to work on something like that.. Can’t make it any messier while ‘fixing’ it but PCB’s seem so much tidier.. Not sure if the larger component rats nest is easier to trace trouble on than a PCB with narrow traces and SMD’s either..

    Nice fix, and good to see attempts to make good mechanical join before the soldering for that durable connection.

    1. Double sided PCB, single sided PCB with lots of straps, cordwood style, manhattan style, veroboard, free form, none of it matters at all if you think in nodes. Wiring is just wiring. Leave worrying about the shape of them until you’re messing with UHF or so, and that won’t be because of how it looks.

      1. Indeed, its just nice if its neat enough to follow so it can be debugged fixing a free form wire ratsnest is tricky – is that thin yellow one or the other the one you want?

    2. I was having similar thoughts while watching this. He did an impressive job, but damn that does not look like a fun bit of kit to work on. Contrasted to Tektronix scopes of the era, which are generally a great joy to work on.

  3. kind of strange that he opted to let the resistors stay in place. from my experience, those old high ohm carbon resistors tend to drift in al directions over time and some are really noisy. but oh, he is content and that is what counts.

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