RK05 head alignment -- how difficult?

Tony Duell ard.p850ug1 at gmail.com
Mon Jul 24 12:31:37 CDT 2017

On Mon, Jul 24, 2017 at 6:12 AM, Fritz Mueller via cctalk
<cctalk at classiccmp.org> wrote:

>   "OMG, are you nuts, don't take the heads out, you'll never get them aligned,"
> or is it:
>   "Meh, RK05 alignment is not really that tough, and you would be better off making sure your heads are thoroughly clean and intact."
> Any advice appreciated!

I've done it a couple of times. The worst part is that it is somewhat
when you have put the expensive, hard to find, new heads in, load the
rare and hard
to find alignment pack and are about the load the heads praying to the
patron saint
of classic computing [St Chad of Hackforth [1] of course] that the heads won't

Basically, you connect a 'scope to the outputs of the read amplfier,
trigger off the
index pulse, move the heads to the right cylinder (just toggle in a
few values on the
PDP11 front panel) and adjust so that the catseye pattern is even.
There are 2 allen
setscrews for each head. One locks the head in postion, the other
forces the head
out towards the spindle. So what you do is slacken the latter off, put
the head in
as far as it will go, clamp it with the first screw, load the
alignment pack then undo
the locking screw slightly and screw in the pushing screw until the
catseyes look
right. If you overshoot you have to unload the heads, loosen the pusher screw,
push the head in and repeat. ALWAYS have the head locked to the carriage when
loading or unloading.

Head alignment is an interchangeability adjustment. An RK05 with misaligned
heads will format a blank pack and write/read it with no problems. But that pack
won't work in other drives. To get it right you need the alignment
pack (incidentally
neither of my RK05 alignement disks are red, they are the normal white

Now there is a cheat that works some of the time. It goes like this.
Before removing the
heads, screw in the pusher screws until they are contacting the back of the head
mounitng pin. Lock those screws with a drop of nail varnish or an
extra nut. Then
loosen the locking screws and pull the heads out. When you come to
reinsert them,
just put them in until they contact the pusher screws and lock them. They are in
essentially the same position and may well read the old packs fine.

It's up to you if you try it.

[1] St Chad was AFAIK a real saint. Hackforth is a village in
Yorkshire, England.
I don't think there's any connection but the names seem right for
classic computing.


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