[Amps] resistor loading of cavity resonances

[John T. M. Lyles]

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 at telia.com>
>Subject: Re: [Amps] Grounded Screen 4CX1500B
>To: <amps at contesting.com>
>Message-ID: <003f01c5e3c3$c0d157c0$bc01a8c0 at 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 at comcast.net>
>To: <conrad at g0ruz.com>; <amps at 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
>  >
>