Having used several of the "older" Ten-Tec rigs, my feeling is that 98% of
the time I am much happier using an audio filter in the rig than a crystal
filter. The audio CW filter makes them sound like "real Ten-Tecs" to my
ears.
If you choose to fabricate an audio filter, it is important to put it into
the circuit as the rig is originally designed. The AGC voltage in the rigs
is generated from audio. If the filter does not appear before the AGC
sampling point, signals outside the passband can still "pump-up" the AGC
voltage. This is true of external audio filters, too.
73, Mike N4NT
----- Original Message -----
From: "Curt" <rhulett1@consolidated.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Cc: "Marty Hartwell" <mhartwe@gmail.com>
Sent: Tuesday, December 14, 2010 10:37 AM
Subject: Re: [TenTec] Replacment cw filter
Hello Marty,
Having the same problem you did trying to find a 245 for a 544 I bought,
used the 245 from my 540 as a pattern. All the components are still
available, so had a PCB fabricated using my 245 as a pattern. Did a less
than perfect job of duplication, had to redrill holes for the 7 vector
pins
used to connect the board to the rig.
A lot of time and trouble for what might just as easily be accomplished
using an outboard audio filter, just to prove to myself that could do it.
Anyway, it works perfectly, just same as the 245 in my 540. It isn't very
complex, just two dual op-amps and some resistors and caps. Somewhere I
have the TT documentation, pictures, parts list, schematic, pattern of the
PCB.
Building one on vector board is certainly feasible, and maybe easier than
dealing with a PCB.
GL & 73, Curt
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