Aaaargh, my active crossover is buzzing like a mofo

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Hi chaps
I've built up a 3 way 2nd order active tube crossover based on the Morgan Jones design in his latest edition of Valve Amplifiers.
The design is based on 12SN7 cathode followers which are actively loaded with triode-strapped EF91/6AM6 pentodes. Each section has an input buffer, then the filter, followed by an output buffer (just like the Jones design).
The power supply is bipolar 225V (which is not decoupled for any stage). The 12SN7s have a DC power supply, while the EF91s are AC.
The thing buzzes and hums like you wouldn't believe. Imagine a chainsaw being operated a foot from your ears. I use AC on all my pre and power amps, and I've never had *any* hum before. This has me baffled. It measures perfectly on the scope. The buzz is still present (although greatly reduced) when the B+/- is removed.
Is there some trick to working with CFs? Are feedback circuits prone to oscillation? I have 2k grid stoppers on all the 12SN7s. Do the EF91s need grid stoppers? What about DC heating for the EF91s? Should the 12SN7s have stoppers anywhere else, or should the grid stoppers be bigger?
Any suggestions appreciated. Cheers. Doug

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Topic - Aaaargh, my active crossover is buzzing like a mofo - Doug Flynn 20:47:14 08/18/06 (5)

Re: Aaaargh, my active crossover is buzzing like a mofo - EC8010 16:54:33 08/20/06 (0)

Yikes - BlackPlasticSound 09:49:01 08/20/06 (1)

Re: Aaaargh, my active crossover is buzzing like a mofo - Chris O 06:18:02 08/19/06 (0)

Re: Aaaargh, my active crossover is buzzing like a mofo - fatbottle 00:52:09 08/19/06 (0)

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