[Scott Dorsey]

gareth magennis wrote:
I posted earlier that 100 ohms in series with around 2nF produced full blown oscillations.
I was scoping the ringing at the time, didn't have audio monitoring connected, and didn't notice that it was motorboating at a few Hz as I didn't want the unit to be oscillating like that for long.

So this recreates the symptoms. Full blown oscillations of around 100kHz and 60v pk to pk dumps the power supply and it motorboats.

This would explain motorboating into long cables. It's not related to the
transformer ringing (except in that it also might be a consequence of crappy
transformers). But when it motorboats, you see the it ring, because it rings.

The ringing is at the same frequency.

You have multiple serious design problems here. Send it back, get a real
Pultec.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."