[Amps] Parasitic Suppressor 4-1000A

[R at contesting.com]

On Mar 10, 2006, at 4:23 AM, Steve Thompson wrote:

>
>
> R; Measures wrote:
>>
>> On Mar 10, 2006, at 2:12 AM, Steve Thompson wrote:
>>
>>>
>>>
>>> Saandy wrote:
>>>
>>>> ....yeah! Now, you have arching, like you wanted (HI).
>>>>
>>>> It probably needs more inductance in the suppressor. According to 
>>>> W6SAI
>>>> (blessed his memory), the 4-1000 needs  4 turns, 16 gage, ½ inch
>>>> diameter
>>>> suppressor coil with 2 47 ohms 2Watt resistors in parallel.
>>>
>>> I'm intruiged by this, and I'm wondering if I'm misunderstanding
>>> something.
>>>
>>> As I understand it, the tube doesn't oscillate in isolation - it's a
>>> combination of several factors, including the impedance presented to 
>>> the
>>> plate. At some frequency there's an impedance in the wiring from the
>>> plate to the tune-C and then to ground that allows oscillation. 
>>> Knowing
>>> the frequency and impedance allows you to design a suppressor to 
>>> prevent
>>> oscillation, but the frequency and impedance can vary a lot with wire
>>> lengths, component choices and layout - in which case, how can there 
>>> be
>>> a specific design of suppressor for a particular tube?
>>
>>
>> The optimal suppressor design is that which almost melts down the
>> suppressor resistor at 29MHz,
>
> I can see that gives you a 'standard' design for any given plate load
> impedance - not necessarily for a specific tube.

Heat dissipation at 29MHz is a fair indicator of whether or not it will 
adequately suppress VHF energy.
>
> Depending on the frequency and excess gain to be killed, it might not 
> be
> necessary to cook the suppressor at 29MHz to kill the oscillation.

If a VHF suppressor does not get hellishly hot at 29MHz, it is unlikely 
to absorb energy above 30MHz .
>
>    Adding L increases dissipation at 29MHz,
>> decreases the parallel-equivalent resistance seen by the anode at its
>
> ..increases.. I think.

Z-meter tests show that more L-supp means less VHF RL at the anode, and 
that means less VHF gain at the anode's self-resonant freq. --

For those who wish to calculate suppressor dissipation to within +/- 
10% without integral calculus: April 1989, *QST* has an article titled 
"Calculating Dissipation in  Parasitic Suppressor Resistors".
>
>> VHF self resonance, and that decreases VHF gain at that frequency --
>> hopefully making the amplifier less squirrelly.
>
> Steve
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>



Rich Measures, 805.386.3734, AG6K, www.somis.org





Rich Measures, 805.386.3734, AG6K, www.somis.org