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:
>>>
>>>>
>>>>
>>>>On Fri, 11 Sep 98 08:20:52 -0800 Rich Measures <measures@vc.net>
>>>writes:
>>>>>
>>>>>
>>>>>The designers rather obviously did not bother to read the RCA
>>>>>Transmitting Tube Manual. In stock config., the amp. is
>potentially
>>>
>>>>>an
>>>>>8122-screen-assassinator.
>>>>
>>>>
>>>>No argument...what was designed was not what Mike Ferber ( National
>>>>Marketing VP) forced on the market.
>>>>
>>>>
>>>>
>>>> > 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" ? I used 2W Allen Bradley carbon composition. This was 10-12
years ago remember.
>
>>Those tests were done about 10 years ago.
>>The amp can be made completely stable by using Johnson, Eimac, etc.,
>>4CX250 screen bypass rings but those items are becoming very hard to
>>find. If you note...RCA specifies those rings in their literature and
>the
>>early NCL prototypes used them. Marketing nixed the idea as too
>>expensive.
>
>A mistake. So is using a too-inductive resistor.
Allen Bradley MIL-Spec are not inductive at HF.
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. I prefer the low
inductance copper strap to ground myself.
>.So is not using at least one resistor per filament pin.
Why filament pins? The 8122 is indirectly heated and has 3 cathode pins
73 Carl KM1H
>
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
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>
>
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