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Reel to Reel Tape Machines / More Revox mods
« on: November 08, 2008, 05:41:03 AM »
I also just received today a high speed Revox B77 with half track heads, which appears to be in decent shape, although the heads could use a relapping. Other than it being an NAB deck, it's set up correctly for TP tapes. I also found some spare B77 audio boards on fleaBay which should be readily modifiable for IEC 15ips (the PCBs are the same per the service manual, so all I have to do is swap out a few resistors and caps). Is the reason you haven't been recommending Revox just that the high speed half track configuration is hard to find, or is that only part of it?
Hi bobschneider,
As far as Revox B77 PCB's go, the playback amps are all the same and you can change components for IEC 15ips. But of all the record amp PCB's, the only one which isn't the same is the NAB 7 1/2 - 15ips board. You can't make the mod to IEC without cutting up tracks. This is a pity - the NAB high-speed record amp board is rare, I wouldn't cut it up. I would rather find a secondhand 3 3/4 - 7 1/2ips NAB record amp board and modify that to IEC.
Most B77's sold were NAB 3 3/4 - 7 1/2 ips 1/4 track machines as this had become the de facto consumer standard in the 1970's. It's easy enough to modify a B77 to 1/2 track by changing heads - but nowadays that's expensive. It's also easy to modify the electronics to 7 1/2 - 15ips IEC.
But it's much less easy to modify the mechanicals from 3 3/4 to 7 1/2 ips. To do it the Revox way, you need a different capstan shaft and a different support casting that shifts the motor so the tape path geometry stays the same with the thicker capstan shaft. That casting is the heart of the machine. The capstan motor, pinch roller arm and head block all bolt to it. Replacing it would be a big job, even if you could get the part from Revox, which I doubt - it's not a wearing item so it's unlikely they still stock it.
There is also Arian Jansen's published method for modifying a B77, which spins the motor at double speed by modifying the motor control electronics. I haven't tried that myself. Both the B77 Mk.II's we have here are original high-speed machines, they only needed the mod from NAB to IEC. I am curious to try it, though, and I do have a wow and flutter meter so I could easily check its performance against a factory high-speed machine. All I need is a standard-speed B77 to try it on. If I do try it and test it I will of course let the forum know.
With best regards,