[TenTec] This Old …Rig” – Tonight’s Proj ect: Replacing the Corsair II PTO with a DDS VFO

[Barry N1EU]

Indeed, congrats Dave on pursuing and succeeding in a noble endeavor.
I too count myself as a big fan of the Corsair II.  One of these days
I've got to go DDS.

My only real issue with the Corsair II is easily solved by routing the
AF around most of those umpteen noisy op-amp stages.

73,
Barry N1EU

On Thu, May 24, 2012 at 11:27 PM, Wilford D Lindsey <qrpnut5 at gmail.com> wrote:
> Dave:
>
> I just gotta send you a note of congrats and kudos on your successful completion of this fantastic project with your Corsair II.  Man oh man am I ever jealouw just thinking about that fabulous rig you now have sitting front and centre in your shack!  Wow!  The Corsair II is IMHO truly one of the finest receiving rigs I have ever used.  It really can allow you to dig down thru layer after layer of noise and get that really weak one down below the the noise level.
>
> So congrats again, and many happy QSOs.
>
> 73,
> Doc/K0EVZ
>
>
> Sent from my Verizon Wireless BlackBerry
>
> -----Original Message-----
> From: David and Dianne on Comcast <dhhdeh at comcast.net>
> Sender: tentec-bounces at contesting.com
> Date: Thu, 24 May 2012 18:53:36
> To: Ten Tec Reflector<tentec at contesting.com>
> Reply-To: Discussion of Ten-Tec Equipment <tentec at contesting.com>
> Subject: [TenTec] This Old …Rig” – Tonight’s Proj
>  ect: Replacing the Corsair II PTO with a DDS VFO
>
> I seem compelled to return to the Corsair II. Its
> appearance, simplicity, and receiver performance
> always draw me back. In the mid-1990’s, I bought
> and sold several CSII’s attempting to find the
> ‘perfect one’…which I did...and then foolishly
> sold it later.
>
> Last fall I decided to see if another Corsair II
> might be in my future. While they are for sale
> from time to time, most are getting pretty long in
> the tooth. Many are mechanically worn out.I was
> very lucky to acquire an excellent CSII from a W6.
>
> For me, the CSII, with its fine receiver design
> along with its pure analog sound, creates an RX
> audio quality that is unmatched in most digital RX
> designs of today. It’s a warm, unprocessed sound
> that is very pleasing to listen to for long
> periods without fatigue. Unlike many, I also
> really enjoy the ‘hang’ AGC on SSB. I have always
> replaced both stock SSB filters with INRAD 2.8 KHz
> SSB filters for improved SSB audio while a TT 500
> Hz filter is my choice for CW. Many believe that
> the CSII is primarily a CW rig. True, but this is
> the only rig from which I get unsolicited
> compliments on my SSB audio using only an
> unequalized electret microphone. The radio remains
> a pretty darn good performer for a one designed in
> an era pre-dating DSP and today’s sophisticated
> microprocessors.
>
> Much of the CSII’s receiver performance can be
> attributed to its front-end design coupled with
> the use of an electrically quiet, mechanical
> PTO.But the PTO is prone to problems over time due
> to the lubrication hardening in its drive bearings
> along with considerable thermal drift in some
> units. The PTO also has a stiffer feel than with
> modern VFO encoders.
>
> Both G3TXQ-Steve and N4YG-Joe have each designed
> excellent DDS VFO replacements for the CSII PTO.
> Both are different. One is a ‘drop-in replacement’
> design and the other is a more significant
> modification to the basic implementation of the
> features set of the CSII. Both have received
> excellent user reviews.
>
> I went back and forth on which to choose. I
> ultimately chose the design of G3TXQ-Steve Hunt,
> (http://www.karinya.net/g3txq/corsair_pto/) as I
> wanted to keep the CSII as true to its original
> design, appearance and functionality as I could,
> while reserving the (unlikely) option to easily
> bring the CSII back to ‘stock’ condition. I also
> wanted to undertake a building challenge without
> step-by-step instructions.
>
> The electronic fabrication (short of programming
> the PIC and winding two toroids) is fairly simple.
> I needed to acquire a custom PCB board from
> Express PCB along with the requisite electronic
> components including two toroids, a PIC, a quality
> encoder and the usual resistors, caps, transistors
> and Molex connectors etc. to build a board
> containing the PIC controller, RF buffer, LPF and
> 5V regulator. All parts/components (with the
> exception the PIC and toroids) are available from
> either Mouser or Newark. Info on the PCB board’s
> design/layout and the PIC code is available from
> Steve’s web site above.A pre-assembled DDS
> daughter board comprising an AD9851 chip and 30MHz
> reference oscillator (the core component of this
> DDS VFO) plugs into the board described
> above.Readily available from eBay, its cost is +/-
> $25.00.
>
> The most difficult part of this project for me was
> the metal fabrication involved in constructing the
> enclosure box and a dial shaft adapter (so that
> the original CSII tuning knob and logging scale
> skirt can still be used). The VFO box is actually
> a section of 2 X 3 X 1/8 inch rectangular aluminum
> tubing. It must be drilled and tapped (#4-40) to
> match the mounting holes of the original PTO box
> to the CSII chassis. The new VFO encoder shaft is
> too short and too large in diameter to accommodate
> the original CSII knob assembly which I wanted to
> preserve intact. It needs a custom shaft adapter
> to be fabricated. All of this metal work,
> especially the shaft adapter, was the real
> challenge for me. In the end I did it all with a
> hacksaw, file and hand drill.A couple of early
> tries were a disaster, but finally it all came
> together after five attempts.
>
> The results have been fantastic including silky
> smooth tuning with an incremental tuning speed
> feature for rapid band excursions, excellent
> frequency stability with little thermal drift from
> start-up, a “drop-in” replacement design and no
> more PTO rebuilds. I just completed conversion of
> my CSII external VFO with identical results. I
> suspect this DDS VFO replacement would easily work
> in most other Ten Tec rigs using PTOs.
>
> My thanks to Steve Hunt-G3TXQ for sharing his
> design and answering my many questions and to
> Jerry Haigwood-W5JH for his mentoring and hands-on
> assistance during this project. Jerry has been a
> frequent resource and advisor to me through all
> phases of this project. Thank you Steve and Jerry.
>
> Next Project….G3TXQ’s PIC replacement for the CSII
> MPU display/keyer board.
>
> With apologies to PBS, there is new life for….
> “This Old ...Rig”.
>
> 73 de N1LQ-Dave
>
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