[Amps] Oldie but Goodie MLA2500 questions

[Carl]

Since the resonances change when in circut it should still cover WARC's; I 
have no problem with my MLA 2500 backup amp. Nor the Clipperton L and 
DTR-2000L here that use the same choke with 3-4 turns removed and mostly 
used on AM including WARC.

I also use a pair of 2200pf 6KV discs as the choke bypass; makes a noticable 
improvement on 160 (along with other changes) plus Dentrons are notorious 
for blowing filter caps, likely from some RF getting into them.

Carl
KM1H



> 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 at k1xx.com>
>> To: <amps at 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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