[Heathkit] Parasitics and neutralization definitions

[jeremy-ca]

> Carl,
>
> I submit that unless you have had a PhD, *and* wrote reference material 
> during the '30s and '40s, that your last paragraph is indicative of *your* 
> interpretation.
>
> Reference F. E. Tereman, July 1933 and also "Radio Engineers' Handbook", 
> 1943, pp 500 - 503.  Specifically referring to *Low-Frequency parasitics*.


The proper spelling is Terman since you have a proclivity for nitpicking. I 
still have the 1955 edition from school in 59.
One of my sons is a MSEE and going for his PhD at MIT as did Terman, he 
never heard of Terman except in passing or as a footnote'



>
> You may *not* be enamored with the name and description - However, it is 
> indeed the terminology used to describe them.  William Orr simply 
> continued this terminology.


Terminology changes as the technologuy matures. Sophisticated test equipment 
and circuit analysis programs did not exist in the 30's. Today I can create 
an amplifier circuit on my PC and vary parameters to create and prove its 
performance. Then build it and have it work the first time. I do it 
regularly at microwave frequencies for business and "play" with it for this 
ham hobby..

I prefer to call it an oscillation since the circuitry is outside of the 
tube. It is simply a Tuned Grid No Plate oscillator since the HF pi network 
looks like a piece of wire to LF. A pi network is a low pass filter.


>
> My reference to the aluminum rod had NOTHING to do with LF parasitics, it 
> instead *is* the neutralizing capacitor used in Heath radios. I only added 
> that for S & Gs.


Yeah sure and I believe Al Gore also.....


>
> The Heath applicability in regard to *Low-Frequency parasitics*, shows in 
> the DX-60 where the dual triode 6DE7 modulator has had its cathode taken 
> to ground to resolve this issue in an audio stage.


What frequency did this occur?


> I'm sure that this will show up in other Heath designs, and in many other 
> tube equipment used and or built by hams from the 60s on.
>
> This was *never* meant to get into a knowledge contest or argument.


I was not in a juvenile contest. I was simply trying to explain in very 
simple laymans terms the facts as relating to parasitics and neutralization 
versus pseudo engineering blather.


 It
> simply seems that you and I have a proclivity to butt heads, as this *is* 
> the second time that this has occurred.  The other being over painting 
> methodology.


Nothing that I remember nor care to address since it is off topic.

Carl
KM1H
National Radio 1963-69
Member of the NCL-2000 Design team




>
> 73!
> Bob - N0DGN
>>
>> LF parasitics are usually caused when the grid bias choke and its 
>> associated bypass capacitor create a resonance that is able to pass thru 
>> the anode circuit with little attenuation. This was very common in 
>> amplifier stages of the 30's and 40's where bypass capacitors were highly 
>> inductive. For this reason many designers did away with the choke and 
>> replaced it with a carbon resistor of 1K Ohms or thereabouts. A ferrite 
>> bead over the grid lead will also help suppress that oscillation. Ive 
>> used a combination of ferrite and low inductance ceramic capacitors to 
>> tame notoriously unstable RF and IF amps in late 20's to mid 30's 
>> receivers. An amplifier at any power level, from milliwatts to serious 
>> QRO can be unstable; the higher the gain the more likely it becomes.
>>
>> Before responding with further confused statements I suggest that you 
>> read up on some 30-50's application notes from RCA, GE, Philco and others 
>> that address LF oscillation, it really should not be called a parasitic 
>> since it is not created inside the tube or the anode tank circuit.
>>
>> Carl
>> KM1H
>
>