[AMPS] Question on reforming caps NCL2000

[km1h@juno.com]

On Sun, 13 Sep 98 09:32:01 -0800 Rich Measures <measures@vc.net> writes:
>
>>
>>
>>On Sat, 12 Sep 98 18:44:33 -0800 Rich Measures <measures@vc.net> 
>writes:
>>>
>>>>
>>>>
>>>>On Fri, 11 Sep 98 13:23:18 -0800 Rich Measures <measures@vc.net> 
>>>writes:
>
>>>>>>
>>>>>> > If you are interested, I can mail you a copy 
>>>>>> of a schematic with needed changes.
>>>>>>
>>>>>>I tried them...they dont work. 
>>>>>
>>>>>You tried the RCA Transmitting Tube Manual recommended cathode 
>>>>>feedback resistors and they don't work?
>>>>
>>>>
>>>>That is correct....they do not work in the NCL2000's I tried and 
>the 
>>>amp
>>>>goes wild on 10/15M. The problem can be traced to the marginal 
>screen
>>>>bypassing that is used, only 500pf per pin coupled with the 2W 
>>>cathode
>>>>resistor lead lengths. 
>>>
>>>Are you saying that was with resistors supplied by us?    
>>
>>
>>Who is "us" ?  
>
>Me and my biz partner/helper, who recently graduated from nursing 
>college 
>and now has a real, fulltime job in Santa Barbara.  
>
>>I used 2W Allen Bradley carbon composition. This was 10-12
>>years ago remember.
>>
>We were selling kits in 1988.  


Beats me, I never saw any ads back then. I just read the RCA spec sheet.
Actually, come to think about it, it was more around 1983-84 that I tried
it. The HF NCL-2000 was retired from active duty in 1986  (still have it
on the shelf) when I used the PT-2500A.




>>:.......
>>>A mistake.  So is using a too-inductive resistor.
>>
>>Allen Bradley MIL-Spec are not inductive at HF.
>>
>Every conductor and every superconductor in the universe is inductive. 
> 
>Four inch silver strap is inductive at LF, MF, HF, VHF, on and on.  My 
>
>guess is around 100nH per foot.  #10 wire is inductive - and not that 
>much more inductive than 4" silver strap thanks to the logarithmic 
>relationship between width, length and L.  .  


I forgot about your propensity to nit-pick. I should have said those 
Allen Bradley  resistors will exhibit negligible inductance at HF and the
lead lengths were the most likely problem.....end of subject.


>
>> > So is using too much lead length.  
>>
>>You have to use some lead length, I had them as short as possible.
>>I suspect that even with proper screen bypassing using the resistor 
>in
>>the cathode method would lead to instability at VHF. 
>
>Svetlana recommends cathode feedback R .  RCA recommends cathode 
>feedback 
>R.  Eimac recommends cathode feedback R.

Yes they do for an improvement in IMD but show me one example in a
commercial amp. Maybe the Alpha 91b or QRO ?  Do the Europeans use this
resistor in all the Eimac and Svetlana tetrode amps? Is it stable at VHF?
 Or is the mfg recommendation for audio and HF only?

Inquiring minds want to know.

Cheers   Carl  KM1H


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