Changing the clock frequency slightly (PDP-11)?

[Tony Duell]

> 
> After pulling out my hair for a while trying to get my PDP-11 to
> talk to me, I finally discovered that the master clock (26.667 MHz
> crystal oscillator) is dead. (KDF-11BA CPU board).
> 
> Those metal-package oscillators are very common and inexpensive
> (around $2), but I can't find one in that exact frequency. 25,
> 25.175 and 27 MHz units are available. Semi-custom ones aren't
> terribly much more expensive (~ $15) but have longer lead times.
> 
> Is there anything in the circuitry that can't be run a little
> slower (or 1.2% faster, 27 MHz)? I'm not worried about squeezing
> every last MIPS out of it.

I've not actually worked on this machine, but I know that the old Unibus 
11's have nothing that depends on the exact freqeucny of the Xtal. I 
would be suprised if any of the ones you mentioned wouldn't work fine.

-tony