Interesting discourse, John. // A Hughes employee told me that their
100kW HF amplifier used some Ni-Cr conductors in the output enclosure to
reduce VHF amplification.
- Instead of using Ni-Cr in a HV-RFC, I use a type-73 ferrite VHF
attenuator bead at the top of the choke when the choke has a resonance
near the anode's VHF resonance. The Henry 3KA and 2K-4 is such an amp.
>The Broadcast Electronics tetrode-based FM broadcast transmitters
>almost all used Nichrome wire in various parasite killers. There was
>a patent issued in early 1980s to them for a particular arrangement.
>What we found was that you could build tuned parasite suck out
>devices (traps) in the big cavities but that as tubes were replaced,
>or the cavity was tuned around the band, they would become
>ineffective. So using the lossy wire de-Q'd them enough to cover
>either the entire 88-108 MHz range, or a portion of it, depending on
>the model. In the big 30 kW rig using the 8990/4CX20,000A variety of
>tubes, the plate choke itself fed a small nichrome coil which then
>connected to the half wave output line. In some versions, there was a
>separate LC trap in the wall, which had nichrome in the L part.
>
>In another company i worked on RF dielectric heating equipment which
>used the 3CW30,000H3, and we changed the plate choke to nichrome, to
>lower the Q, since we needed some impedance over a range (free
>running oscillator from 26-29 MHz). It ran hot from the DC, but
>eliminated having a series R anode transient resistor entirely. I
>believe in Nichrome where you can get away with it.
>
>Now I am making BIG parasitic suppressors for a 3 MW 200 MHz
>amplifier using double ended THALES TH628 tetrode (Diacrode is what
>is is called by the mfr). Since it is a large cavity line circuit,
>cannot use LC circuits that HF systems might use. Since the worse
>parasites come from TE11,TE21 and TE31 modes (400, 800, 1200 MHz
>ranges), the suppressors are high pass absorptive filters, loaded
>waveguides located in the appropiate spots in the cavity. Nichrome no
>good for this. Someday i will publish it and post a note here. Back
>to work....
>K5PRO
>
>
>
>
>>
To: <amps@contesting.com>
>>Date: Sun, 14 Jul 2002 12:25:33 -0400
>>Subject: [Amps] suppressors
>>
>> Are there any commercially built amps currently using nichrome or stainless
>>steel wire for their parasitic suppressors??? Just curious !!!!!thanks!!
>> carl / kz5ca
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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