[Johnson] Richard Measures

[Gary Schafer]

Burning the band switch in an amp is a common sign that parasitics may 
be present. Parasitics are not necessarily there all the time. Sometimes 
they come and cause very heavy conduction in the tube and very high 
power rf at frequencies other than those wanted in the amp. This can 
cause high voltages and currents across components in the final.

You may be interested to know that Mr. Measures was not the first to 
advocate the use of nichrome wire for parasitic suppressers. If you read 
the chapter on parasitics in Bill Orr's Radio Handbook 17th edition, and 
probably other editions, you will see that he mentions the use of 
nichrome wire for parasitic chokes.

Moving a parasitic to a tubes self neutralizing frequency will do little 
to suppress a parasitic. However if you move your normal operating 
frequency frequency there it will probably prevent self oscillation. :>)

Parasitics can be above or below the self neutralizing frequency of a tube.

Changing the length or size of plate or grid leads will change the 
parasitic resonance of either. Making the plate lead parasitic resonance 
different from that of the grid lead sometimes cures the problem.

As to parasitics being caused totally by external elements of a tube is 
not true. The internal lead lengths of the plate and grid leads are part 
of the circuit just as well as external components are. Screen leads in 
tetrodes too.

73
Gary  K4FMX


Richard Peterson wrote:
> I will throw in the towel about Richard Measures -- I know he has his 
> following. However, engineers are not among them, to my knowledge.
> 
> If you stop and consider what a parastic oscillation is, you will 
> understand that it is cured by bringing its frequency down to the 
> frequency where the tube is self neutralized. The parastic is then 
> killed (suppressed) by loading it with resistance. That's a fact. Using 
> Nichrome wire according to Measure's voodoo concepts a very strange 
> approach, to say the least. Rather, the use of a parallel tuned circuit 
> with decent copper wire is a much more sound approach.
> 
> Now, that said, it is entirely reasonable that a parallel turned circuit 
> using Nichrome wire will work, PROVIDING the parallel tuned circuit with 
> the Nichrome wire just happens to lower the freqency of the parastic to 
> a better point where the existing circuit can deal with it. There are 
> lots of variables. But it is the luck of the draw, it is not sound 
> science, and it is not the best way. And it has nothing to to with 
> Nichrome wire. But if it works for some hams -- Great! I am sincere 
> about that. And Mr. Measures has made some sales, too. It's hard to make 
> a dollar, and I admire his hard work.
> 
> However, I am puzzled by the report in this thread that parasitics had 
> burned up a band switch. That's hard to understand -- unless there is 
> another problem occuring, or the switch were rotated with RF on it .. or 
> maybe even if the rig were being tuned into a reactive load. Amplifiers 
> prefer 50 ohms j0, and I've run into hams loading their finals into all 
> sorts of really wacky loads, which causes a real wreck in the final. To 
> that end, for the folks who are reporting success with the Measures 
> parasitics kits, I would be curious to know what the frequency of the 
> parastic was before the Measures Nichrome modification, and afterward. 
> That would be really useful information.
> 
> By the way, Mr. Measures earned the wrath of Eimac (and I don't blame 
> them) when he alleged that Eimac tubes had internal parastics. Excuse 
> me? That is ridiculous. Parasitics are caused by external elements, not 
> internal. Period.  And it embarassed the heck out of QST.And it should 
> have embarassed them.
> 
> I'm fortunate to have a friend who is an electrical engineer who was so 
> incredulous by the Measures views on parasitics that he even called Mr. 
> Measures on the phone and reprimanded him for foisting that stuff on the 
> amateur radio community.
> 
> In truth, Measures has written some good stuff. But he has also written 
> some bad stuff, and his understanding of parasitics is questionable. And 
> I know of rigs that were really toasted when some Richard Measures 
> modifications were installed. And yet, we have here in this thread some 
> testimony that it worked. That reinforces my belief that some of his 
> improvements DO work, but (like I said ) they work by the luck of the 
> draw. But what works, works!
> 
> I have always wondered if these rigs with the Measures mods really are 
> stable -- if they are completely parasitic free. Maybe yes, maybe no. 
> Not a lot of hams know how to run a rig through its paces to see if it 
> has parasitics.
> 
> But, again, I have no desire to debate this author's view of the world, 
> nor to anger those who have had luck with his approach -- except to say 
> I am troubled by his views on parasitics.
> 
> I will let the matter drop.
> 
> Thanks.
> 
> Richard, WB5NEN
> 
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