[1000mp] MK 5 Driving Amp - a twist?

[John Passaneau]

Hi
Changing the swamping resistor can be done, I did it on my MLA-2500 with 
good results. By the way in my amp the resistor that Denton used was NOT an 
non inductive type. It was your garden type wire wound resistor. I replaced 
mine with a non inductive thick film 50w resistor in a TO-220 style package 
picking a value that gave me a low SWR. Works great! The input SWR is nearly 
flat on all bands.

John Passaneau W3JXP
State College Pa.
w3jxp at arrl.net

----- Original Message ----- 
From: "Rob Atkinson" <k5uj at sbcglobal.net>
To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
Sent: Tuesday, October 24, 2006 9:04 PM
Subject: Re: [1000mp] MK 5 Driving Amp - a twist?


> hi,
>
> is there some reason why the input swamping resistor can't be swapped out 
> for one that's around 60 ohms?
>
> rob / k5uj
>
> On Tuesday, October 24, 2006, at 08:58 AM, Rob Murray wrote:
>
>> I have been following the exciter/amp interface thread with great 
>> interest,
>> and have learned a lot from it, thank you all. I have a Mk 5 driving an 
>> old
>> Dentron MLA-2500 full power amp, and on reading much earlier in this 
>> forum
>> that the Mk5 internal tuner did not add much to the process, discontinued
>> using that tuner.
>>
>> This leaves me with pretty much a permanent SWR at the Mk 5 of about 1.8,
>> independent of band choice; I haven't worried about it much, but have
>> thought it would be nice to get it lower. While the thought of the 20.5 
>> ft
>> coax matching section is most interesting, I had been thinking of simply
>> winding a toroidal impedance matching transformer (say N1/N2 = 1.4:1) and
>> placing it somewhere in the input line of the amp (on the amp input side
>> after the bypass relay). This thinking based on the thought (guess?) that
>> the amp input impedance is pretty well set by the 100 ohm input swamping
>> resistor, slightly reduced by the tube input, ie., about 90 ohms 
>> resistive
>> (generally), consistent with the Dentron specs in the manual.
>>
>> Since none of the discussion has considered such a solution, I must be
>> missing an important point (or two or more...)
>>
>> What am I missing?
>>
>> 73
>>
>> Robert Murray    VA7RMM
>> RR1 S5 C16
>> Edgewood, BC    V0G 1J0
>> Phone/Fax (250) 269-7698
>>
>>
>>
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>
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