When I first looked at the choke, the winding seemed to have slid down
the core and somewhat bunched up at the bottom. There also appeared to
be some discoloration over the winding. I eventually pulled the choke
and took a closer look. No breaks in the wire and no burn marks. There
is some discoloration, but maybe that's more perception on my part. The
best I recall, the amp worked fine during the 2007 contest trip to
Dominica.
There is some slight bunching of a couple turns at the bottom of the
choke, right above the circular insulator. My best guess is this is an
artifact of the original manufacturing. Yesterday I received a private
e-mail with some data on the choke. Based on that info, it looks like
the person that did the original 3CX800 conversion also removed some
turns from the top of the choke. Again, best guess, 4-6 turns. The
discoloration, the removed turns, plus the bunched turns at the bottom,
contributed to my "worn" conclusion.
FWIW, after I removed the choke, I measured it on my network analyzer.
I did find two resonances, 18.3 and 25.7 MHz. Good enough for non-WARC
operation.
BTW, the individual that did the conversion also replaced the single
500pF plate bypass disc cap with a 1000pF doorknob. I'm going to try to
shoehorn in a couple of additional disc caps of different values.
73 charlie, k1xx
On 5/29/2016 5:18 PM, Carl wrote:
What do you mean by "a little worn" Charlie? They all look scruffy
after 30+ years and unless there are obvious burn marks at the top
they should be fine. The same choke was used over a wide range of
Dentron models.
The choke will smoke the top turns when run on 11 and 12M. Unwind 4
turns and its OK.
Carl
KM1H
----- Original Message ----- From: "charlie carroll" <k1xx@k1xx.com>
To: <amps@contesting.com>
Sent: Wednesday, May 25, 2016 5:32 PM
Subject: [Amps] Oldie but Goodie MLA2500 questions
About ten years ago I acquired a 2500 that had been backfitted with a
pair of 3CX800s. The amp has been sitting in a shipping box since we
returned from our last trip to J7 in 2007.
I'm finishing up some refurbishing (caps, diodes, step start, etc.)
before giving the amp to one of the locals. This morning I noticed that
the RF plate choke is looking a bit worn.
1. Does anyone have an original MLA2500 plate choke lurking at the
bottom of their junk box? The original choke is pretty small (3" tall),
so I haven't been able to find a commercial replacement.
2. If I have to rewind the choke, does anyone have the value and/or
design info? All the manual says is "Choke Plate." I've gone through
the amps archives and done a bit of googling looking for info.
thanks
73 charlie, k1xx
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