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Fwd: [AMPS] Tuned input

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Subject: Fwd: [AMPS] Tuned input
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Date: Fri, 13 Jul 2001 08:16:58 EDT

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Jim, I ran into a similar problem with a Dentron DTR-2000L linear amplifier. 
The DTR-2000L does not have a tuned-input circuit and was causing excessively 
high SWR when driven by my solid-state transceiver (Yaesu FT-840) . I built a 
small external pi-network tuned-input circuit using a double-pole rotary 
switch to switch in different value toroid inductors and fixed mica 
capacitors for each band in addition to 365pf air-variables permanently wired 
across the input and output sides of the circuit for fine-tuning. I used #2 
mix (red) toroids about 1" O.D. size and #18 magnet wire for each toroid. 
These will easily handle 100-150 watts of RF at the relatively low impedance 
levels for a tuned input circuit. The whole circuit is mounted inside a small 
aluminum mini-box and connected to the amplifier input thru a 1 ft length of 
RG-213 coax. The values for the toroids were fine-tuned after basing their 
values on a handbook article using the 8877 tube. This arrangement keeps both 
the exciter and amplifier happy. I recommend always keeping an SWR meter in 
line between the exciter and amplifier at all times to monitor the condition 
of match between the two, as well as a second SWR meter to monitor the output 
match to the amplifier. Hope this may help. 73 Todd Roberts WD4NGG .

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Date: Mon, 09 Jul 2001 13:09:16 EDT
Subject: [AMPS] Tuned input
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A friend of mine recently purchased a Dentron MLA-2500.  In the archives I 
noticed some one had asked about this amp before, but I could not find the 
answer to this question.  Since the MLA-2500 does not have a tuned input what 
percautions are necessary to use it with a solid state rig.

As you can probaly guess I am not very familiar with amplifiers or their 
construction, but am planning to rectify that with some studying on the subject.

    TNX & 73,

      Jim KM8I

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