Ampex 60Hz Tape Transports

[Ted]

I have here an Ampex 601-2 that a friend brought back from the US. It one of those old Ampex suitcase 1/4" reel recorders. The electronics needed attention, but I could handle that (putting the correct tubes in got it playing and recording on one channel).

When I tried to play a pre-recorded tape I notice that the thing ran noticeably slow. A quick look at the rating plate - ah. 60Hz. Our mains is 50Hz. The transport motor is synchronous. On browsing the service manual I noticed that Ampex used to offer a 60 to 50Hz conversion kit for the 601 (basically a pulley change).
Ampex Part No 9738....

Now I'm guessing that my chances of acquiring the conversion kit are pretty close to zero. Or even a scrap 50Hz transport assembly. Unless you know different.

So. I need 110V at 60Hz. You can get those 12V->120V converters for running off car batteries. They come in sizes up 2000W. They are cheap(ish). So maybe a 200W one of those, fed with a 240-12VDC regulated supply. On almost all of the ones on ebay it says that the output is a "modified sine wave".
I'm guessing that's pretty close to a square wave. Is that going to be good for a 50 year old motor? Also, like most other products of its era, it doesn't appear to have a lot of protection against high frequency pickup.
Also. Whats the frequency stability/accuracy going to be like on those converters?


Any thoughts?

[Leo_Gnardo]

I don't know much about the modern converters. BUT I have used power amps to drive tape transports for variable speed operation. One of the old standards was the Bogen MO-200A with 8 x 8417 output tubes. It had a 125V output tap - intended for driving distributed PA speakers - but perfect for driving 110 V motors, you just dial down the signal level a pinch. I'm sure, rarer than rocking horse turds in Europe. Or anywhere for that matter. There's one in my attic...

Another solution was driving tape motors directly from a large solid state power amp. Last time I did this, it was an SAE 2500 in bridge mode. You could use any similar modern amp, probably even a cheap class D. The critical part is having an oscillator to drive it that runs rock stable - no drift in frequency. Perhaps one of our MEF boffins can suggest a phase locked loop or similar circuit to do this. Possibly one of the better quality test bench oscillators will suffice. Some are too twitchy to find the exact right frequency, or they slowly change frequency as they warm up. Heck, these days you might even be able to get a usable, tunable, stable frequency off a smart phone.

[Enzo]

I would search ebay for the conversion kit. I know my shop used to have one years ago.

And if it were possible to get measurements on the pulleys needed, they could be turned.

[Ted]

I'd considered that.

So. I tried a phone with a tone generator into an Inter-M 500W PA amp into the 55V winding of a 200VA with the 110V winding driving the power. It kind of works. But it loses something in portability...

[J M Fahey]

Do the simple thing, not the over complex expensive one.

To begin with, I very much doubt there are "50 Hz transports" and "60 Hz transports", I bet the motor is always the same, runs in sync with whatever mains frequency you feed it, then they just adjust linear tape speed by using 2 sizes of capstan, which is the metallic cylinder actually moving the tape, which is pressed against it by a rubber covered roller ... which you will also need to replace, it must already be either cracked crystalized or gooey, rubber has a definite and short life span, a few years at best.

I bet some specialized shop sells both new rollers and *maybe* 50 or 60 Hz capstans.
If the latter is not available, a lathe shop can turn a new one for you, with high precision and at a relatively low cost.
20% larger diameter, of course.

[Leo_Gnardo]

I'd considered that.

So. I tried a phone with a tone generator into an Inter-M 500W PA amp into the 55V winding of a 200VA with the 110V winding driving the power. It kind of works. But it loses something in portability...

Extra points for trying! Agreed, not so portable.

I'm liking Juan's capstan solution. 1984 I wound up doing a similar thing with a Leslie we hauled from USA to London for recording sessions. I inquired with Leslie/Hammond wizard Bill Dunne about 50 Hz motors. Instead he sold me a different pulley for the horn motor, only 5 quid (!). Let the woofer motor run a little slow, so what, nobody noticed.

[Enzo]

He already knows it is a pulley size change, though a different diameter capstan would also work. I think a new pulley would be easier to smoothly achieve than a new capstan.

Some decks had changable capstans. There was a thin central shaft and a capstan sleeve slipped over it. Most capstans are solid shaft, no way to swap out.

I used to work on a lot or TEAC/TASCAM and Fostex, and others. I recall some that had stepped pulleys, and the 50/60 conversion was a matter of slipping a belt from one groove to the groove on the other step.

[Ted]

Fixed. By looking at the manufacturers parts list, there are separate part numbers for 50 and 60Hz drive pulleys and belts. On dismantling further, the drive pulley was stamped with "60". I got a friendly machinist to make me a new pulley with a drive end 6/5 * the diameter of the old one. Add a flat belt from ebay and everything seems to work. Need to get that pulley stamped with a "50"...

[olddawg]

He already knows it is a pulley size change, though a different diameter capstan would also work. I think a new pulley would be easier to smoothly achieve than a new capstan.

Some decks had changable capstans. There was a thin central shaft and a capstan sleeve slipped over it. Most capstans are solid shaft, no way to swap out.

I used to work on a lot or TEAC/TASCAM and Fostex, and others. I recall some that had stepped pulleys, and the 50/60 conversion was a matter of slipping a belt from one groove to the groove on the other step.

The Akai/Roberts had capstan sleeves as I remember. Yep step pulleys in some brands/models. Some even provided the conversion pulley attached by a screw to the cabinet or chassis inside.

[Enzo]

The Akai capstan was a skinny post, and a sleeve slipped over it to set speed. The unit came with more than one, and a small clip was nearby to park the other sleeve. Of course they get lost over time, and then you have to fudge one up if you can't find one.


I had a guy bring me a stepped pulley model once, he had replaced his own capstan belt. Save money and all. Now it runs at the wrong speed. Could I fix it?

Hmmm, take back off, flip belt to correct position, et voila, right on.