[Amps] 4CX250 IMD

[Richard]

>
>
>-----Original Message-----
>From: Richard [mailto:2@mail.vcnet.com]
>Sent: 02 July 2002 02:06
>To: g0ruz@btinternet.com; AMPS
>Subject: RE: [Amps] 4CX250 IMD
>
>
>
>
>>
>>
>>-----Original Message-----
>>From: amps-admin@contesting.com [mailto:amps-admin@contesting.com]On
>>Behalf Of Richard
>>Sent: 01 July 2002 23:34
>>To: AMPS
>>Subject: Re: [Amps] 4CX250 IMD
>>
>>
>>
>>
>>>
>>>
>>>> Compared to poor regulation, yes.  Compared to a well-engineered zener
>>>> shunt screen regulator, probably not a significant improvement.  To
>>>> arrive at good linearity with a 4cx250B/R/BC/7203, load for less screen
>>>> current, use maximal anode supply V. and add c. 5-ohms of RF-NFB R in
>the
>>>> cathode (Rk).  See Fig 10 on my Web site.
>>>>
>>>> >G3SEK is vacationing in the states at the moment, but he gets
>>significant
>>>> >improvement in IMD suppression with the tube by holding the screens
>>>within
>>>> >millivolts using active regulation.
>>>
>>>You might take a look at his website, he compares the active regulator to
>>>the active regulator with an 150 ohm series resistor to raise the
>impedance
>>>of the regulation, (Probably no worse than the Z of VR tubes or zeners)
>and
>>>a zener string with 100 uF to stabilize the transients (By far the worst
>of
>>>the three tests).
>>
>>**  Would you trust a stock buy recommend from a brokerage that gave
>>salesmen a commission on stock sold?
>>
>>
>>Huh what does that mean?
>>
>**  I built a 2 x 4cx250 2m AB1 amplifier with a conservatively run zener
>shunt screen regulator.  It was as clean as Eimac claimed.  //  It means
>that foxes should probably not be entrusted with hen-house security
>evaluations.
>> ...
>
>I trust the data provided by John Nelson GW4FRX who has no pecuniary
>interest in publishing the data as far as I am aware, why do you feel it
>necessary to disregard his measured data when you have only tried the zener
>regulator? 

1.  Because most designers assume that a 5w zener can work well at 5w. 
2.  A spectrum analyzer is not the right measurement tool.
3.  Such a test should measure p-p screen V - with voice-mod - vs total 
IMD observed on a double-filter receiver using a step-attenuator to 
measure relative signal strengths.  

>John measured both methods and the improvements were worthwhile
>in his opinion and in the opinion of many other mid 80's VHF ops in Europe.
>Have you actually read the article?
>
no.  I built amps and I realize that peak cathode current varies as the 
3/2 power of screen potential. 

>If I have the inference of your riddles correct you are suggesting that we
>should not trust the  advice of either GW4FRX or G3SEK because they have
>been involved with the development of the tetrode boards provided by Ian. 

I trust in doing one's own measurements.


>  I find that utterly preposterous because as well you know from your own
>various retrofits nobody gets rich selling amp bits to radio amateurs.

Indeed.  I make less than zero money from the business.  My two helpers 
are 13 and 16 yr old neighbors that we have known for over a decade.  My 
wife and I do not need the money.  They do. 

>People occasionally do us all a service, there are many examples of this out
>there. Indeed I do it myself, regularly passing on parts to others and
>merely meeting costs.
>
This is good.  The issue is whether super-regulation is better than good 
regulation.
The 723 based regulator shown in Figure-8 on my Web site is a screen 
super-regulator and yet the on-the-air improvement is/was insignificant 
over a +/- 1% trog 2-transistor regulator. 

>I really wish that you would try speaking in plain English, It's my native
>tongue and even I can't understand you, what have foxes got to do with
>amplifiers :-)

RR

cheers, Conrad

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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