Karl-Arne and Jim and others:
I have seen those floating end resistors in Continental FM b'dcast
rigs, and can attest to their functionality. I recall that RCA also
used some similar 'half-connected' Globar (Carborundum) resistors in
some of their old tube PAs for 100 MHz - if my memory serves me
correctly.
While visiting the French Thales company a few years ago, I was shown
a large Megawatt PA that had similar resistors in the HV compartment
before the feedthough to the anode of the tetrode. They called them
Candlesticks (in French).
You can get similar effects with chunks of Eccosorb or other
microwave absorbing material to dampen the dimensional resonances of
a box, but its simple to use Globars, as they have standard mounting
brackets/caps and the value of 'bulk' R is given.
73
John
K5PRO
>Date: Mon, 7 Nov 2005 18:50:34 +0100
>From: Karl-Arne Markstr?m <sm0aom@telia.com>
>Subject: Re: [Amps] Grounded Screen 4CX1500B
>To: <amps@contesting.com>
>Message-ID: <003f01c5e3c3$c0d157c0$bc01a8c0@speedbox>
>Content-Type: text/plain; charset=iso-8859-1
>
>Have also seen this used in the Granger 172-2 MF/HF 5 kW amplifier.
>
>Two 100 ohm Globar resistors were placed near the anode cooler of the P-290A,
>with one end grounded and the other end "floating".
>
>The designer's motivation for these resistors was that they were
>supposed to damp
>out a tube dimension related parasitic resonance in the high VHF range.
>
>73/
>
>Karl-Arne
>SM0AOM
>
>----- Original Message -----
>From: "Jim Tonne" <tonne@comcast.net>
>To: <conrad@g0ruz.com>; <amps@contesting.com>
>Sent: Monday, November 07, 2005 3:14 PM
>Subject: Re: [Amps] Grounded Screen 4CX1500B
>
>
>>
>> Conrad:
>>
>> Regarding a resistor in the PA cabinet, absorbing harmonic
>> energy: it is not anedotal! Quite true, being used at
>> Continental Electronics.
>>
>> But the position is important and has to be done by cut and
>> try methods. This technique was used for both stabilization
>> and for VHF/UHF harmonic control.
>>
>> - Jim Tonne ex-Continental guy now enjoying retirement
> >
>
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