[Amps] Question for the tetrode experts

[peter chadwick]

Vic,

Gerald may well have a point about loading. What inductance is the plate choke, what capacitors are there at the 'cold' end of it and what type and is there another smaller RF choke going off from there to the HV supply, with maybe a bypass cap on the HV side of that second choke?

73

Peter G3RZP


========================================
 Message Received: Nov 08 2013, 01:00 AM
 From: "Vic K2VCO" <k2vco.vic at gmail.com>
 To: TexasRF at aol.com, amps at contesting.com
 Cc: 
 Subject: Re: [Amps] Question for the tetrode experts
 
 Gerald,
 
 I have only tested so far on 40 meters. There are no fixed capacitors in the tank on this 
 band...but there is a ferrite choke across the output. I'll check to see if the choke is 
 heating.
 
 I didn't notice a big change in plate current -- I will check this also.
 
 On 11/7/2013 4:46 PM, TexasRF at aol.com wrote:
 > Vic, what frequency? Does the plate current drift?
 > Screen current is extremely sensitive to the degree of loading adjustments. Could it be
 > that there is a capacitor on the output side of the plate tuning circuit that is heating
 > due to rf and changing value?
 > Does the amplifier act the way you described on all bands?
 > 73,
 > Gerald K5GW
 > In a message dated 11/7/2013 5:16:12 P.M. Central Standard Time, k2vco.vic at gmail.com writes:
 >
 >
 >         I've finally applied full drive to my 4CX1000A amplifier. Here is what I'm
 >         seeing:
 >         I have tried two tubes, both pulls. In one case I can run about 1kW out, and
 >         with the other, maybe 1200. What happens when I try to push past this point
 >         is this: when I hold the key down for 10 seconds or so, the screen current
 >         starts to drop, then goes negative, and when it hits -35 mA the screen trip
 >         circuit kicks in. I haven't seen even a flicker of grid current.
 >         The screen circuit is well-regulated at 325v, so this isn't case of runaway
 >         caused by increasing voltage. What it seems like to me is that the screen is
 >         heating up and the secondary emission is rapidly increasing. Screen current
 >         before this happens is reasonable, 20-25 mA, so I am not exceeding its
 >     rating.
 >         I have a couple more tubes to try, but I have a bad feeling that I am going
 >         to end up buying a new tube if I want 1500 watts from this.
 >         Do the experts think my diagnosis is correct?
 >     --
 >     Vic, K2VCO
 >     Fresno CA
 >     [1]http://www.qsl.net/k2vco/
 >
 >     References
 >
 >         1. http://www.qsl.net/k2vco/
 >     _______________________________________________
 >     Amps mailing list
 >     Amps at contesting.com
 >     http://lists.contesting.com/mailman/listinfo/amps
 >
 
 -- 
 Vic, K2VCO
 Fresno CA
 http://www.qsl.net/k2vco/
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