[Amps] FL2100B

[rgroh at swbell.net]

Another factor that might come into play here is the gain and feedback capacity. Both have a big role in determining the actual input impedance of an amplifier.  That is, the input impedance is a combination of the physical input parameters of the amplifier (tube or whatever) such as input capacity and the parameters that are reflected (via the forward and reverse gains of the amplifier and the feedback impedances of the tube and circuit) back to the input from the output. One impact is that the actual input impedance is a function of the load impedance (although not greatly in the case of a grounded grid amplifier - one of the benefits of GC amps).

Bob, WA2CKY

----- Original Message ----
From: c. <carlseye at tampabay.rr.com>
To: "Amps at contesting.com" <Amps at contesting.com>
Sent: Sunday, January 28, 2007 9:58:23 AM
Subject: [Amps] FL2100B

        I have made an interesting note on the FL2100B input swr VS. 
tubes.!!!
         I have been fighting this amp for a long time now using chinese 
tubes and could never get the input swr down much below 2.5 :1.!!!On 10 
mtrs. I had to add capacity to the input pi-net to get anywhere near 
even 2:1. !!
          I recently acquired a pair of Cetrons, ( 572B/T160L ) , which 
I think was the tube originally used in that amp.
          I tuned the inputs per the original instructions and lo and 
behold, the inputs are almost all well below 1.5:1 swr. the only 
exceptions are the high end of 80 ( 1.55:1) and the High end of 10 ( 
29.4 -29.7 , 1.45 :1 , !!!)  I also had to remove the extra capacitance 
I had added on 10.
           I have to wonder now about the actual  input capacitance of 
the chinese tubes !!!!
     what ever it was that caused the problems on 10 mtrs. I will soon 
see if it has gone away.!!!!!
         Has anyone else had problems with the 2100 on ten mtrs ??
        Just wondering.!!!!


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