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

Fri May 25 07:25:34 PDT 2012

Hi Gary

Re-read your post and chuckle at the typo.

Ron
K3MIY
(owner of a couple TT rigs)

Quoting GARY HUBER <glhuber at msn.com>:

> Great piece.... I'm still using my original Corsair II (#2576) purchased 
> 10-21-88 along with a 961, 263G, 282, 288, and 705 from Amateur Electronic 
> Supply (Milwaukee, WI) for $1925.90.
> 
> Absent replacing the meter bulb, and some parts on the display board, there 
> have been no other repairs.
> 
> I worked a lot of CW and SSB DX during the late eighties and all the 
> nighties with my Corsair II.  And like others I preferred it over the 
> Paragon-II I bought for MARS work in Desert Storm.
> 
> When I bought a new OMNI-VI+, the Corsair II became my PSK-31 and RTTY 
> radio.  Now with a new OMNI-VII, the Corsair II is still used daily for 
> PSK-31 and occasional DX.
> 
> Like others I find the Corsair II with its great audio, PTO with no PLL or 
> digital artifacts to be the ultimate (at least for me) analog rig. I've 
> purchased the parts to keep the digital display going and hope to keep this 
> great little radio running as long as I'm able to talk into a mike, send CW,
> 
> or type.
> 
> 
> 73 ES DX,
> Gary -- AB9M
> -----Original Message----- 
> From: Wilford D Lindsey
> Sent: Thursday, May 24, 2012 6:27 PM
> To: Discussion of Ten-Tec Equipment
> Cc: WD Lindsey K0EVZ
> Subject: Re: [TenTec]This Old 
Rig” – Tonight’s Proj ect: Replacing the 
> Corsair II PTO with a DDS VFO
> 
> 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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