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
----------------------------------------------------------------------
Date: Tue, 28 Jan 2014
From: Carl
Subject: Re: [Amps] Tube swap
For 4-1000's and 30-40 years ago I was using a 50 Ohm Globar when I could
find one, or 3 150 Ohm 2W carbons in parallel.
These days 3 of the Ohmite OY series work well or use a bulletproof 25-50W
Carborundum type from fleabay. Value can be roughly 50 Ohms +/- 30% or so.
If you are pushing the power over 1200-1500W then use strap or small tubing
for the inductor.
[snip]
Carl
KM1H
----- Original Message -----
From: Bill WA4LAV
Sent: Tuesday, January 28, 2014 2:48 PM
Subject: Re: [Amps] Tube swap
Many years ago I got one of his kits for my single 4-1000A amp and the
suppressor went with a bang. I went to normal suppressor. The point is
to simply introduce loss, lower the Q, of VHF parasitic resonances that
can exist in the plate circuit of the amplifier.
73
Bill WA4LAV
________________________________________
From: Karel VA3KO
Sent: Tuesday, January 28, 2014 2:36 PM
To: Don W4DNR
Subject: Re: [Amps] Tube swap
Sorry, I met him over internet right after his write-up for AR Handbook
was
rejected and that was a long time ago. I brought up his name here once
before and got slapped for it, sorry, I should know by now. I owe cup of
coffee to all. Hopefully we will meet some day.
I still have his suppressor package for two 4-1000A 's to be installed.
Without bringing his name out again, can someone warn me about using it?
I installed his suppressor package on my friend's Henry 2K. It lasted few
years, but his plate transformer croaked recently, I wonder if the
suppressor had anything to do with that.
Karel VA3KO
----- Original Message -----
From: Don W4DNR
Sent: Tuesday, January 28, 2014 10:56 AM
Subject: Re: [Amps] Tube swap
Quoting Karel VA3KO:
Hardy,
yes I made myself a Hi-pot tester as well. I forgot the specs, but I
believe I can go up to 20 kV. (It may be one of Richard Measures
designs).
Don W4DNR
------------------------------
Date: Tue, 28 Jan 2014 20:44:20 -0800
From: Bill W6WRT
Subject: Re: [Amps] Tube swap
What does thickness of the grid leads have to do with VHF parasitic
frequency? It would seem that thin leads, having less capacitance to
everything else, would tend to raise the frequency, if anything.
73, Bill W6WRT
On 1/28/2014 6:14 PM, Carl wrote:
Old tubes will have their parasitic down at low VHF, often right
around 6M due to long thin grid leads.
------------------------------
Date: Wed, 29 Jan 2014 02:03:14 -0500
From: Roger K8RI
Subject: Re: [Amps] Tube swap
On 1/28/2014 6:11 PM, Carl wrote: The handbook has a good section on
designing them, but after you get all the info, and calculations, you
have to take into account stray inductance and capacitance. IE, they
give you a base design that likely will need to be modified to fit the
layout of the amp and tube, or tube. So as Carl says, pick an amp with
the same tube and similar layout and build a supressor like theirs and
it'll likely work with little or no modification.
73
Roger (K8RI)
Suppressors are usually tube and layout/construction dependent for the
inductor part.
Look at commercial and good HB ham amps that have the tube you want to
use and go from there.
Having a quality brand of GDO helps a lot as an economical tool..
Carl
KM1H
----- Original Message -----
From: Karel VA3KO
To: Carl; Don W4DNR
Sent: Tuesday, January 28, 2014 5:53 PM
Subject: Re: [Amps] Tube swap
Thanks Carl,
I just have to figure out what the factory design should be. I will
definitely use ceramic resistor. Any suggested lead to better
suppressor setup?
Values, arrangement? Thanks,
Karel, VA3KO
----- Original Message -----
From: Carl
To: Karel VA3KO; Don W4DNR
Sent: Tuesday, January 28, 2014 4:26 PM
Subject: Re: [Amps] Tube swap
Stick to factory designs, they work fine for decades without problems.
The Ohmite OY series of ceramic resistors do well in place of out of
tolerance carbon composition.
Sell the voodoo crap on fleabay to a CBer
Carl
KM1H
----- Original Message ----- From: Karel VA3KO
To: Don W4DNR
Sent: Tuesday, January 28, 2014 2:36 PM
Subject: Re: [Amps] Tube swap
Sorry, I met him over internet right after his write-up for AR
Handbook was rejected and that was a long time ago. I brought up his
name here once before and got slapped for it, sorry, I should know
by now. I owe cup of coffee to all. Hopefully we will meet some day.
I still have his suppressor package for two 4-1000A 's to be
installed. Without bringing his name out again, can someone warn me
about using it?
I installed his suppressor package on my friend's Henry 2K. It
lasted few years, but his plate transformer croaked recently, I
wonder if the suppressor had anything to do with that.
Karel VA3KO
----- Original Message -----
From: Don W4DNR
To: <amps@contesting.com>
Sent: Tuesday, January 28, 2014 10:56 AM
Subject: Re: [Amps] Tube swap
Quoting Karel VA3KO:
Hardy,
yes I made myself a Hi-pot tester as well. I forgot the specs, but
I believe I can go up to 20 kV. (It may be one of Richard Measures
designs).
Don W4DNR
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