On Thu, 25 Mar 99 11:19:55 -0600 Jon Ogden <jono@enteract.com> writes:
>
>OK, I had promised to report back on this subject, so here goes:
>
>Back a month or two ago, I said that I was going to simulate the
>impedance of my 4-1K's cathode by using two 220 Ohm resistors from
>each
>cathode pin to ground and by leaving the tube in socket (driving
>impedance is 110 Ohms). I could then use my MFJ-259 to tune my input
>
>pi-networks.
>
>Several people here said they didn't think that would work and that
>you
>couldn't simulate the complex impedance of a tube with a couple of
>resistors.
>
>Well, I have to tell these experts and the rest of us that they were
>not
>correct. The simulation worked VERY well.
That is very good info Jon. It also is very timely since I just bought a
MFJ-259B and havent even opened the box yet.
After designing the input
>
>circuits this way, and after using the amp for a while, I am pleased
>to
>report that simulating the input impedance of a tube using a couple of
>
>resistors DOES INDEED WORK!
>
>My SWR on all bands with the exception of 10M is nearly 1:1 in at
>least
>some portion of the band. On 10M, the SWR is about 1.3 or 1.4:1,
>which
>is still fine (it's probably off because the inductance in the leads
>of
>the resistors is probably significant at 28 MHz). 20M might be 1.2:1
>or
>so. On 40M and 15M, the SWR is absolutely flat and on 80M it is very
>
>good as well (perfect in some spots, but the tuning bandwidth is
>considerably less than the higher bands).
>
>So folks, it does work. Don't let the so called experts fool you.
>Logic
>and common sense told me it would and it does.
I vaguely remember those discussions but kept out of them due to a lack
of experience. I also swore that I would never buy anything from MFJ
again but all the good comments about the 259 forced my capitulation!
73 Carl KM1H
>And by the way: all my caps are fixed. The only thing I can tune are
>my
>inductors.
>
>73,
>
>Jon
>KE9NA
>
>
>------------------------------------------------------------------------
--
>Jon Ogden
>
>jono@enteract.com
>www.qsl.net/ke9na
>
>"A life lived in fear is a life half lived."
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
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>Problems: owner-amps@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
>
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