|Subject:||Re: Re: LF: Re: I: Fw: For today the FETs survived...|
|From:||Andy Talbot <[email protected]>|
|Date:||Wed, 31 May 2017 19:39:22 +0100|
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7:19 turns (assuming 50R output) means you have a load resistance of 6.8 ohms which for 180V DC (81 V RSM fund sine) is nearly 1kW I don't think you really mean to go that extreme do you? 13 ohms is more realistic.
As for the tank resonance changing as power increases, that is very wrong. I wonder if the transformer is saturating. Not sure of your core Ae, but lets assume 200mm square, a core of about 16mm diameter.
V = 4.44.F.N.A.B Plugging in 137kHz 7 turns, 200 mm^2 and a Bmax of 0.1 that suggests 85V RMS.
Which is exactlyly what you have. I suggest more primary turns . Before a transformer ratio of 1:2 was suggested, for Rload = 13 ohms
Is the guard circuit in place ? Don't forget, it has to be customised to you exact currents and coil Q. Get teh PA operating to its proper settings foirst - that you can do at low voltage power, it scales perfectly. Only when it it working properly can you add and set up the guard circuit.
When I did teh 700W PA, I had a complete workign (albeit unreliable) unit before even thinking of teh guard circuitry.
On 31 May 2017 at 18:50, [email protected] <[email protected]> wrote:
Hi Andy... me again...
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