[Boulevardier]

Have you replaced any capacitors in the oscillator circuit? If so, are you sure you've used the correct types? Some of them will almost certainly need to be silvered-mica (or perhaps there's a modern equivalent of s.m).

I can remember a couple of times when I got this wrong. In the first, when we had a recorder on which the oscillator wasn't working at all, I quickly traced the fault to a shorted s.m. cap, and absent-mindedly replaced it with another type, since we didn't have an s.m. small enough to easily fit. No oscillation (still), so I started looking for another fault - until I twigged to the problem. Managed to squeeze in a larger s.m. of right value and all was well. The other case was with a Mullard Type C valve tape preamplifier (truly excellent circuit). I carelessly used a ceramic instead of the specified s.m, and sometimes the oscillator would work, and other times it just wouldn't start - until I replaced it with s.m..

Even if yours still has the original s.m.s and they're measuring OK, it might be worth replacing them - they might be breaking down on load - I'm not familiar with the Ferrograph circuits, but those circuits have to handle quite a bit of power to set up the field in the erase head.

Mike