B77 Tape Drive PCB and Guide Bearing Questions

[supwiddiss]

I have taken ownership of a very nice 1 owner B77 quarter track, 3 3/4 - 7 1/2ips machine. I have all of the original brochures, owners manual, sales receipt, QC sheet...etc. I'm a very happy individual indeed! I've wanted a machine like this for years. I've been around tape equipment since I was very young. The B77 was owned by an electronics engineer and has been very well serviced. It's in awesome condition. That said, I have a few questions to ask. Looks like this is the place to ask them.

Is it correct for the right guide (with the stud to hold the head cover) to have a non-turning spacer? I see the left guide uses a roller bearing. Has anyone ever substituted a roller bearing for the solid spacer? What would be the disadvantage of a bearing in it's place?

I notice a slight but audible 60hz vibration from the take up reel motor. It goes away as the motor is allowed to spin up with no tape loaded. The supply reel very slightly has the same 60hz vibration but is significantly lower in amplitude. The service manual does not have the schematic for the Tape Drive PCB, only the block diagram and PCB layout. Could it be an old capacitor failing? Is there a schematic for the Tape Drive available?

Could someone steer me in the right direction please? I haven't opened the deck yet to look inside.

Also, If I were to buy a PR99 how difficult would it be to convert it to a slow speed quarter track machine? Is it even possible? Consideing I had all of the resources to perform the conversion, has anyone reading this ever attempted to do so?

All of the open reel media I have is either store bought or recorded at 7 1/2 ips on my old A77 mkIII. I figured it was time to give the old girl a rest.

[Tim]

2. Line-frequency related flutter:  If you lightly put your finger on the reel motor as it was turning in play mode, you could feel the motor housing vibrating at 60Hz.  You could also feel this vibration on the tape and it would be introduced as a flutter into the audio.  I believe I traced it down to a defect motor control Triac.  It was so long ago that I can't remember if that was it for sure.  Anyway, I saw that defect several times.

[supwiddiss]

Yes. Thank you. I read that from a previous post. Schematic anyone? I can probe the board with a 'scope and isolate the component causing the hum.

[ironbut]

Hi supwiddiss (btw we use our real names here),
Welcome to the forum.
I don't think that you'd have a tremendous amount to gain by getting a PR 99 for playback of 1/4 track, 7 1/2 ips prerecorded tapes and considering that you've already got a minty B77. Converting a PR99 would be a good bit of cash too (the new heads would be a good bit just by themselves).
Here's a link to the service manuals, schematics etc. All you need to do is register with the site to download them for free.

http://www.hifiengine.com/manuals.shtml

Once you get it running perfectly, you may consider upgrading the playback electronics if you're handy or know some else who's willing to do the work for you. Arian Janzen has a step by step on his pages at the Los Angeles Orange County Audiophile Society web page.

[microstrip]

Although we can find several Revox service manuals at the hifiengine site - I have downloaded  and uploaded a few to this excellent site - if you have a good internet connection you can download them from the Studer site 
ftp://ftp.studer.ch/Public/Products/Revox/Revox_B77/
The files are much larger, but they usually are of much better resolution.