G3RZP wrote:
>
>Andy said:
>
>>My current power supply project has been built with a tuned filter on the
>>negative rail of the DC, tuned to 100hz (i.e. 2xmains hz)
>
>Have you checked the actual resonant frequency? My understanding of the
>tuned choke filter is that it should be tuned slightly higher in frequency.
>This makes the circuit look like a very much bigger inductance, so that a
>smaller bleed resistor is needed to keep the inductance above the critical
>value. Actually hitting resonance can give some very nasty voltages, as
>Tom, W8JI, can tell you. From your nominal values, the resonant frequency
>(nominal)is 102.7Hz. This means the effective inductance is 38.08 Henries,
>which should be OK, but if the tolerances are such that the resonance is
>far off, you could be seeing problems. Typically, the choke will probably
>be around 10% and the cap is probably no better than 5%. I'd suggest you
>start by measuring the real resonant frequency.
Since this circuit relies on being critically close to resonance, but
absolutely never hitting resonance, it would be very unsuitable for use
with a generator whose speed can vary (just a thought, since some of
Andy's amps do go out in the field).
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
|