"Dr. Barry L. Ornitz" wrote in message
...
"Paul P" REMOVE paul @ REMOVE ppinyot . REMOVEcom wrote in message
...

And check all the carbon composition resistors for tolerance.
They tend to drift higher. If you replace any resistors use a non
inductive resistor (carbon compositions) in circuits above....say...18mhz
or less.


Ordinary film resistors, either carbon film or metal film, will work fine.
The inductance is not significant unless the value is below 100 ohms.
Above this value,
shunt capacitance dominates the impedance. A ten ohm resistor starts
becoming inductive around 20 MHz and a 1 ohm resistor starts becoming
inductive over 1 MHz. If your email works, I'll send you some graphs.

73, Barry WA4VZQ


Barry,

Graphs would be good. Graphs would be much appreciated.

I have been on many manufacture's web sites looking for their published
tests. I even emailed Ohmite about their OX line and received a polite
reply about their test tech using their impedance bridge and what he/she
found. But they could (would?) not supply and published data. So I must
take it on their word.
http://www.ohmite.com/cgi-bin/showpa...t=ox_oy_series

I have brought this discussion to other newsgroups to receive comments and
opinions devoid of hard data. Not that I am complaining. I cant seem to
easily put my finger on any myself.

I realize that even carbon comps have inductive qualities at certain
frequencies and at certain lead lengths. Exactly what they are? I do not
have that data either.

I prefer facts to guesses. And guessing and a few bad experiences is all I
have to go on at this time. So I am left with establishing some criteria
for my self that I am sure can be a bit of over compensation.

It is well accepted that wire wound resistors are inductive. It seems to me
that a spiral carbon conductor around a ceramic core would set up an
impedance starting at some frequency. So when replacing resistors in the
front end of a Hallicrafters or Hammarlund that is above 18 MHz (18 MHz
selected because no carbon film resistor has given me any grief in a finicky
Transoceanic) I am not going to take the chance (again) until I see some
welcome hard data or spend the time required doing A/B comparisons and
testing.

And I would like to post your graphs, with permission and due credit, on my
web site for all to benefit.

Thank you in advance for the extra digging,

email: paul at ppinyot dot com.

Paul P.
www.ppinyot.com