Revox PR99 - anyone know how to set ZENITH??

[C4audio]

I just popped new heads on a second PR99 i have - the first went ok but fraught with complications. The second was MUCH easier and I've done most of my head alignment except now it seems that my zenith is a bit off (that is to say both R and PB heads are a bit 'tilted back' and giving uneven contact patches relative to the tape). It seems from what i can tell that the center screw in front of each head is used for both height AND zenith so you can dial ONE in but not the other - unless you get lucky as i did on the first deck.


anyone have any insight into this? thanks.
This is my first post here

 

[tapetech]

The rear screw is zenith (Tilt). Adjust that screw so that head face is parallel to the capstan (for play head). Then adjust same screw on the record head so that face is parallel to play head face or erase head face.

Set azimuth (middle screw on the side) on both heads. Use azimuth tape for play head. Record mode (10KHz) for record head.

Next is head height. Mark position of all three screws. Adjust all three screws exactly the same amount until you have the correct height. Use the marks to determine how much you turn the screws.

Re-check azimuth both head.

Re-check zenith both heads.

Next is wrap. Coat the head face with a black sharpie pen. Play a back-coated tape with the tape reversed so that the back of the tape faces the head. Now see if the head gap is in the center of the wear pattern. Twist the head if not and repeat the test until it is.

Re-check azimuth both heads.

 

[GPS16]

Hi,

I have replaced heads on Revox machines only and removed the head block in all cases. For a B77 and C270, there is some dismantling to be done to disconnect the wiring. For an A700 it is easy peasy as the head block is removed after removal of 3 screws. All wiring is on a plug/socket.

I have clear leader tape which I use to set up the head height. I have spliced a loop of it which I can lay over the head block with the heads facing upwards. I dangle a 5" reel in the loop for a bit of tension. The height is then set to put the head central in the path of the leader. To set the Zenith, I have cut pieces of old credit cards which are slid down between the Rec and Play heads to sit on the machined base of the head block. The edge which is 90 deg to it is then used to set the tilt. With the head block between a strong light source and eye, the zenith is adjusted until the whole of the surface of the head appears at the same time with small movements of the head block. The Play Head is best with the credit card reference. The Rec head may be set to the erase head as Tapetech has said. Which ever is easiest. If the top or bottom edge of the head appears first then adjustment is required. The clear leader (front screw) and credit card (back screw) are repeated until no further improvements can be achieved. The Azimuth is kept with them but only by eye looking directly from the front. Bear in mind that any error in Zenith will force the tape to creep either up or down as the tape will be trying to run true on a ramp. So an error in Zenith may enforce an error in height as the tape slides down or up the slope. Hence the repeat till no better!!

So far this has been successful for me as the wear pattern has not yet been trapezoidal. It can be time consuming BUT this is the reference/starting point for the whole machine alignment. Errors here may render the following electronic set up procedure a complete waste of time as it will not work. The final Azimuth MUST be done with a reference tape!!

Bear in mind I am doing this as a hobby and I am prepared to put in the time involved with this. Also I do not do it often!! Azimuth and cal may be done on a reasonably regular basis but these two adjustments a really "New Head Initial Set Up" and should last for the life of the heads in question.

Hope this helps. Thanks to Tapetech for his professional view for us hobbyists.

Cheers.

GPS16

 

[C4audio]

The rear screw is zenith (Tilt). Adjust that screw so that head face is parallel to the capstan (for play head). Then adjust same screw on the record head so that face is parallel to play head face or erase head face.

Set azimuth (middle screw on the side) on both heads. Use azimuth tape for play head. Record mode (10KHz) for record head.

Next is head height. Mark position of all three screws. Adjust all three screws exactly the same amount until you have the correct height. Use the marks to determine how much you turn the screws.

Re-check azimuth both head.

Re-check zenith both heads.

Next is wrap. Coat the head face with a black sharpie pen. Play a back-coated tape with the tape reversed so that the back of the tape faces the head. Now see if the head gap is in the center of the wear pattern. Twist the head if not and repeat the test until it is.

Re-check azimuth both heads.

GEEZ - you're saying that by leaving the zenith for last i have to re-do everything ??? (sad face)
i didn't know there was a specfiic sequence to do these in but maybe it makes sense.

anyway -ok thanks for affirming which screws do what.

yeah i found my own little technique for checking the contact patch (as i call it) - just using translucent white leader tape and alcohol - it gives a very telling 'patch' where the head meets the tape (while under tension) so i was able to set the wrap etc quite accurately - that's HOW i know the zenith is off - the contact patches are non-rectangular ... narrower at one end than the other.


WEIRD THING IS though that the contact patch on the RECORD head is MUCH larger (6mm wide) than on the play head (Where it's maybe 1.5-2mm) - I THINK the record head is sticking out a bit too far ... it has nothing to do with wear pattern obviously - since both heads are brand new.

 

[C4audio]

Hi,

I have replaced heads on Revox machines only and removed the head block in all cases. For a B77 and C270, there is some dismantling to be done to disconnect the wiring. For an A700 it is easy peasy as the head block is removed after removal of 3 screws. All wiring is on a plug/socket.

I have clear leader tape which I use to set up the head height. I have spliced a loop of it which I can lay over the head block with the heads facing upwards. I dangle a 5" reel in the loop for a bit of tension. The height is then set to put the head central in the path of the leader. To set the Zenith, I have cut pieces of old credit cards which are slid down between the Rec and Play heads to sit on the machined base of the head block. The edge which is 90 deg to it is then used to set the tilt. With the head block between a strong light source and eye, the zenith is adjusted until the whole of the surface of the head appears at the same time with small movements of the head block. The Play Head is best with the credit card reference. The Rec head may be set to the erase head as Tapetech has said. Which ever is easiest. If the top or bottom edge of the head appears first then adjustment is required. The clear leader (front screw) and credit card (back screw) are repeated until no further improvements can be achieved. The Azimuth is kept with them but only by eye looking directly from the front. Bear in mind that any error in Zenith will force the tape to creep either up or down as the tape will be trying to run true on a ramp. So an error in Zenith may enforce an error in height as the tape slides down or up the slope. Hence the repeat till no better!!

So far this has been successful for me as the wear pattern has not yet been trapezoidal. It can be time consuming BUT this is the reference/starting point for the whole machine alignment. Errors here may render the following electronic set up procedure a complete waste of time as it will not work. The final Azimuth MUST be done with a reference tape!!

Bear in mind I am doing this as a hobby and I am prepared to put in the time involved with this. Also I do not do it often!! Azimuth and cal may be done on a reasonably regular basis but these two adjustments a really "New Head Initial Set Up" and should last for the life of the heads in question.

Hope this helps. Thanks to Tapetech for his professional view for us hobbyists.

Cheers.

GPS16

yes that's what i did (in terms of removing the head blocks etc as you describe) - and the leader tape bit too.(see above)

Yes - i'm doing the head swap now because I was about to start all the electronic alignment stuff ... i've even replaced the trimpots etc after redoing all the electronics throughout the deck .. it was a bit of an odyssey and a learning experience!!

 

[GPS16]

Hi C4audio,

we all seem to find our own ways when doing these sorts of tasks. Keep going as a PR99 is a machine that is worth spending the time on.

You will now have a sequence of steps to follow now which will save lots of time when compared to the first go!! I do spend a lot of time listening to the HiFi as the quality of the content on TV leaves a lot to be desired!!! No matter how many channels.

I have quite a library of tapes to go at, some of them from the 70s when I had my first recorder, the RT707. I don't know what I would do without my Reels!

Cheers

GPS16

 

[Chip Chester]

Another approach for height is to use a white china marker -- like you use to mark your edit points. Using any old tape, color the edges of the tape where it meets the head, on the top and bottom edge. Pull the tape away, and see where it sits in relation to the head gaps. Measure (if you have the spec), adjust, clean and re-mark to see your results.

C4's alcohol method is good for including 'wrap' in the equation.

Locating a head in free space is a 3D wonderland.

 

[tapetech]

For 4-track height, I use a Tandberg height tape. You adjust height for min signal.

Genn labs also makes a height test tape for both 2-track and 4-track heads.

For zenith, I use a small precision ground SS bar. Put one end on capstan and adjust head zenith so that it is flush with bar.