Bryan keeps harping on this subject even tho they perform as expected in
parasitic suppressors for many users.The only claim made by Ohmite is they
are replacements for a carbon composition.
I used them yesterday in a Command 2500 Magnum that self destructed by being
tuned into a shorted coax. At 2700W on 10M they ran cool.
Carl
KM1H
----- Original Message -----
From: "Vic Rosenthal K2VCO" <k2vco.vic@gmail.com>
To: <amps@contesting.com>
Sent: Wednesday, January 29, 2014 10:32 PM
Subject: Re: [Amps] Tube swap
The AADE meter cannot measure the stray inductance of a resistor. From the
instruction manual: "Inductors must have a reasonable Q for their
value and negligible distributed capacitance for their value." A resistor
has very low Q!
It also has trouble with large tubing coils due to the distributed
capacitance. And it is not good for toroids on cores where the
permeability varies with frequency.
Given those limitations, the AADE meter can be very useful.
On 1/29/2014 6:01 PM, William Turner wrote:
Please keep in mind two things:
1. The AADE meter measures inductance at a very low frequency. At VHF
the inductance can be considerably different due to distributed
capacitance between windings. The best tool is an impedance analyzer
which applies the actual VHF frequency and costs about $10k. I don't
have one either. It was that or a house. :-)
2. There is no such thing as "non-inductive". Even a short straight
piece of wire has inductance. If someone tells you a resistor is
non-inductive, they are prevaricating.
73, Bill W6WRT
------------ ORIGINAL MESSAGE ------------
On 1/29/2014 5:31 PM, Bryan Swadener wrote:
I measured new Ohmite pn OY470KE (47ohm/2W) resistors at 1.6uH
inductance.
The instrument used was a new factory-assembled and calibrated
"Almost All Digital Electronics" L-C Meter (http://www.aade.com/).
According
to the manufacturer, it compares closely to several high-end L/C/R
instruments. I verified mine, compared to a few other pieces of HP
gear that
I trust.
Before making any measurements, I first nulled the internal inductance
with the terminals shorted, using a 1" length of 14ga wire (about 17nH).
A NOS Allen-Bradley 47 ohm/2W carbon composition resistor then
measured 20nH, and a 3-1/2 turn 14ga parasitic suppressor inductor
(Heathkit SB-220) measured 80nH. The OY "resistor" measured 1.58uH.
The datasheet for the Ohmite OX/OY resistors
(http://www.ohmite.com/cat/res_ox_oy.pdf) says only:
"The OX/OY resistors can often replace carbon composition resistors
which can be difficult to source."
They make NO claim that they are without inductance. In fact,
nowhere in the datasheet is the word "inductance" or "reactance"
used, or inferred.
eBay seller "bigsmythe74" always seems to have
A-B Carbon Composition resistors available for reasonable prices.
I have no connection with him other than as a customer.
vy 73,
Bryan WA7PRC
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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