[Amps] Tube swap
km1h at jeremy.mv.com
Thu Jan 30 11:26:29 EST 2014
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.
----- Original Message -----
From: "Vic Rosenthal K2VCO" <k2vco.vic at gmail.com>
To: <amps at 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
>>> The instrument used was a new factory-assembled and calibrated
>>> "Almost All Digital Electronics" L-C Meter (http://www.aade.com/).
>>> 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
> Vic, K2VCO
> Fresno CA
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