[Amps] Oldie but Goodie MLA2500 questions

[Clark Turner]

When you see coils have bunched up, The choke took a heavy hit of 
current and the wire expanded with heat.  I know because I have an amp 
here that likes to do that to the Ameritron plate choke. I have been 
through 3 of them. One single arc over of the output tank and the 
winding's will bunch up at the base.  If you go out of resonance while 
tuning one time, The choke is toast.


C


On 6/1/2016 6:14 AM, charlie carroll wrote:
> 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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