[R-1051] R-1051 Digest, Vol 50, Issue 6
paul swed
paulswedb at gmail.com
Wed Oct 31 12:48:15 EDT 2012
Well thats a tough one. It can be in many places. If every frequency is off
by a linear amount look at the freq standard. By the way you can go
external and grab the 5 mc from another unit.
If its just some frequency its most likely the frequency translator and
those pesky crystals.
I have seen lots of components drift in that unit. Adding caps to vcos to
bring them back inline stuff.
Don't know if anyone fixes them. These days the shipping is a killer.
They are great boxes I have a 1051 and another transmit rcv unit don't
recall the number. RT 914.
Regards
Paul.
On Wed, Oct 31, 2012 at 11:35 AM, Terrence Harvey <terrencelharvey at yahoo.com
> wrote:
> Hello Dave and group;
>
> I am an swl with and addiction to the 1051s. I own 4 in various
> states of operation except for the "fully operational" mode! Mostly I seem
> to have frequency error probs on the three that fire up. (unit # 4 is
> non-op with all modules being suspect) Indicated freq is actuallu 2-4 kc
> off actual freq as measured on my R8B. One of my nicest cosmetic units goes
> silent after 5-10 minutes of on time. It has a label indicating was from
> Naval post Grad school in Monterey CA. Another, the nicest, has a pale
> green front panel that might indicate was from an officers suite,
> shipboard. Anyway, sorry for the ramble. Any tips or suggestions on
> frequency error fix would be appreciated. One last thought, does anyone
> on/off the list service these?
>
> Thanks and Regards,
>
> Terry Harvey,
>
> Crystal lake, IL
>
> 815 455 7872
>
> off list, terrencelharvey at yahoo.com
>
>
> ________________________________
> From: "r-1051-request at mailman.qth.net" <r-1051-request at mailman.qth.net>
> To: r-1051 at mailman.qth.net
> Sent: Tuesday, October 30, 2012 12:00 PM
> Subject: R-1051 Digest, Vol 50, Issue 6
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> Today's Topics:
>
> 1. Frequency Standard NTC Thermistor Retrofit FINAL (David Wise)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 29 Oct 2012 16:49:39 -0700
> From: David Wise <David_Wise at Phoenix.com>
> Subject: [R-1051] Frequency Standard NTC Thermistor Retrofit FINAL
> To: "'r-1051 at mailman.qth.net'" <r-1051 at mailman.qth.net>
> Message-ID:
> <FFF45F8A4E2B6F4CA4920B3B028CE73D01EA82B9EF at SCL-ExchMB.phoenix.com>
> Content-Type: text/plain; charset="us-ascii"
>
> INTRODUCTION
>
>
>
> The R-1051 series Frequency Standard is a high-failure item. There are a
>
> lot of dead ones around. Usually they have a bad thermistor. Leaded PTC
>
> thermistors like the original are hard to find, but an NTC thermistor can
> be
>
> used instead. It's easy and cheap, and it works fine.
>
>
>
> If anyone expresses interest, I'll post photos and sketches on SkyDrive.
>
>
>
> Warning: This mod is not applicable to the early R-1051 plain frequency
>
> standard, P/N 666231-006, which uses an oscillator and rectifier in the
>
> oven control instead of a DC amplifier. If you have one of these, you're
>
> on your own, and good luck!
>
>
>
> DISCUSSION
>
>
>
> This mod replaces fixed resistor R13 with an NTC thermistor, and replaces
>
> PTC thermistor R2 with a fixed resistor.
>
>
>
> I used a 100K thermistor. At the time I wrote this, October 2012, eBay
> members
>
> "tayda2009" and "taishopetc" were selling a pack of 5 for $0.99 including
> shipping.
>
> It's made by a Taiwanese company called Thinking; it's part number
> TTC05104.
>
> The TTC05 datasheet is available at
> http://www.thinking.com.tw/documents/en-TTC05.pdf .
>
> There is nothing special about this part; it has about the same R-T curve
> as most
>
> TC thermistors. They don't put the curve on their website, but they'll
> send you a
>
> pdf if you ask. I have it too.
>
>
>
> You have to modify circuit board A2A5A1, but it's easy and reversible.
>
> While working, refer to the A1 schematic, Figure 5-6 in NAVELEX
> 0967-LP-970-9010.
>
>
>
> NTC thermistors are much more sensitive than PTC. An NTC thermistor placed
>
> directly into the old bridge circuit will provide too much gain, causing
> the control
>
> circuit to oscillate. We work around this by adding a resistor in series,
> to reduce
>
> the percent change of the total. This also makes the rate of change vary
> with
>
> thermistor resistance Rt, but a second fixed resistor in parallel with Rt
> makes
>
> the total approximately linear near operating temperature.
>
>
>
> Temperature trimpot R15's adjustment range is (5.3K/10K - 4.3K/9K)*10V or
> about 500mV.
>
> The original thermistor together with upper leg R13 puts out about
> 6mV/degree.
>
> That's about 80 degrees of adjustment range, or 5 degrees per turn. (It's
> a 15-turn pot.)
>
> This is really twitchy, and the slightest drift will throw it way off.
>
>
>
> It's possible to eliminate this problem. If you increase your thermistor
> output,
>
> the degrees per turn go down correspondingly, but you have to change
>
> R23 to keep the loop stable. 4.7K/15K/11K makes about 30mV/degree instead
> of
>
> 6mV/degree, which makes R15 about 1 degree per turn.
>
>
>
> This resistor set is for R16 = 4.3K . If you have an R-1051H module
> (3.9K),
>
> use 4.7K/18K/10K instead.
>
>
>
> My calculations said I had to change R23 to about 240K if it was 1.2M
> before,
>
> but testing showed that 330K is optimal for my 4013399-0701 with mains
> regulation
>
> upgrade (see below). This should be good for all versions where R16 is
> 4.3K* .
>
> For the R-1051H, I'd try 220K or 270K.
>
>
>
> * The NAVELEX schematic labels R2 as 3.9K but that's at 25 degrees. It's
> around
>
> 4.7K at 85. The R-1051H schematic also labels it 3.9K but that can't be
> right
>
> because R16 is also 3.9K; it must be a different thermistor, one that's
> about
>
> 4.3K at 85.
>
>
>
> PROCEDURE
>
>
>
> 0. Determine your crystal's turnover temperature. The manual says 85
> degrees but
>
> mine was 82.
>
>
>
> 1. Connect a 3" to 5" cable to your new thermistor, which I call R913c.
>
> Try to arrange for the cable to be away from the crystal and
> oscillator area when
>
> A1 is reinstalled in the oven. This will make sense after you have
> read the entire
>
> procedure.
>
>
>
> 2. At the other end of the cable, put a connector, which I call J92. I
> used a 2-contact
>
> socket that mates with the popular 0.1"-spaced square pins.
>
>
>
> 3. Arrange thermistor R913c in the bottom of the oven near the abandoned
> R2.
>
> Make it lie flat and out of the way. The connector must reach the
> upper left
>
> corner of board A1 when viewing the component side. Seal it in place.
>
> I used JB Weld.
>
>
>
> 4. Cut a piece of double-sided plated-through padboard, 1.0" long and 0.3"
> wide;
>
> 10 pads by 3 pads. (You can use single-sided if you're careful
> soldering.
>
> Arrange it with the pads up.)
>
> Solder square pins P92 at one end, extending off the board and
> parallel to it.
>
> P92 will point toward the bottom of the oven after installation, and
> thermistor
>
> connector J92 will mate to it.
>
>
>
> 5. On the padboard, tack three resistors, R913a (4.7K), R913b (15K), and
> R902 (11K).
>
> Arrange R913a near A1 centerline, R902 near A1 edge, and R913b in the
> middle.
>
> R913b goes across P92.
>
> One end of R902 goes to P92 pin 2 with the other end uncommitted for
> now.
>
> One end of R913a goes to P92 pin 1 with the other end uncommitted for
> now.
>
>
>
> R902 replaces thermistor R2 in the lower-left leg of the bridge, and
> the R913 trio
>
> replaces fixed resistor R13 in the upper-left leg, with R913a the
> series element,
>
> R913b the shunt element, and R913c the thermistor itself. R913b and
> R913c
>
> are in parallel, and R913a is in series with them.
>
>
>
> 6. Prepare the top surface of R15, and glue the padboard to it. I used
> super glue.
>
>
>
> 7. Remove R13 (4.7K) and P2 pin 3 (which goes to old thermistor R2).
>
>
>
> 8. Run a wire from R902/P92 to the left pad where R13 used to be.
>
> This pad also goes to where P2 pin 3 used to be. This is the
> temperature
>
> sensing node.
>
>
>
> 9. Run a wire from the uncommitted end of R902 to ground, which is
> available
>
> at an unused pad next to the top pin of R15.
>
>
>
> 10. Run a wire from the uncommitted end of R913a to the right pad where R13
> used to be. This is +10V.
>
> 11. Remove R23 and replace with 330K. (220K-270K if R-1051H.)
>
>
>
> 12. Slide A1 partway into the oven, connect J92, then slide A1 in the rest
> of the way.
>
>
>
> 13. Adjust R15 for the proper temperature.
>
>
>
> TESTING; USING A DIFFERENT NTC THERMISTOR
>
>
>
> Transient response is important. General Dynamics selected R23 to control
> this.
>
> R23 determines the gain of the amplifier, excluding the output
> transistor. In older
>
> A1's where Q7's (2N697) collector load resistor R24 is 2.2K, the nominal
> value was
>
> 1.2M, which gives a transconductance of about 230mA/V . The latest A1 for
> the
>
> R-1051H is 1.2K and 820K, giving about 280mA/V,making up for the lower
> output
>
> of their 3900-ohm thermistor. Larger values tighten control but increase
> ringing,
>
> while smaller values reduce ringing but degrade regulation.
>
>
>
> The resistor values I provided above are okay for the Thinking TTC05104.
>
> Other parts may need different values. There are three goals:
>
>
>
> 1. Control loop is stable,
>
> 2. Setpoint is achievable within R15's trim range, and
>
> 3. Bridge voltage vs T is linear around the setpoint.
>
>
>
> Ask the manufacturer for your thermistor's R-T table; they don't usually
> put
>
> them on their websites. With that and a programmable calculator, you can
>
> come up with usable values. Although you can assess stability with just a
>
> VOM, a storage or digitizing scope or a chart recorder makes it MUCH
> easier.
>
> You need an extremely slow sweep rate. I used a triangle-wave function
>
> generator set to .00002Hz as X input. That's 250s/div .
>
>
>
> Monitor Q7 collector during the transient you get when switching from
>
> operate to standby. (It's less stable in standby, because the higher
>
> supply voltage increases system gain.) Your amplifier may have more
>
> gain than mine, or less. Watch the scope trace and you'll be able to tell
>
> what's right for you. Keep the insulating lid of the oven in place;
> otherwise
>
> you'll choose too much gain.
>
>
>
> MAINS REGULATION UPGRADE - 4013399-0701 ONLY
>
>
>
> What a fascinating journey. My particular Frequency Standard (P/N
> 4013399-0701)
>
> does not have a preregulator, and R24 is referred directly to unregulated
> +28V.
>
> This gets away from the R-1051B's embarrassing "dead oven in standby"
> problem,
>
> but it makes the oven sensitive to variations in the power source. If the
> mains voltage
>
> rises, so will the temperature. However, I discovered that, on a shorter
> time scale,
>
> this ciruit actually creates negative feedback, above and beyond what's
> obvious in the
>
> schematic. Let's say the oven temperature is rising. The amplifier will
> pass less current
>
> to the heater. With less load, the +28V line rises, increasing the
> current through R23,
>
> which increases heater current. I discovered this when I tried to improve
> the temperature
>
> regulation by reducing mains sensitivity. A simple way to accomplish that
> is to add a
>
> resistor from +28 to the thermistor side of the bridge, so the supply
> appears equally in
>
> both bridge arms and thus cancels out. When I did this, the oven went
> unstable, because
>
> I had eliminated a hidden source of negative feedback. I could have
> reduced thermistor
>
> gain, but why bother since I'm already changing R23?
>
>
>
> With 330K in R23, 820K is appropriate for compensation.
>
>
>
> PRESERVING ORIGINAL R23
>
>
>
> If you want to leave R23 alone, you can scale your new thermistor's output
> back
>
> down to the original level with a different choice of scaling/linearizing
> resistors.
>
> The disadvantage is a twitchy R15, same as it was originally. I don't
> know why
>
> you'd do this just to preserve one 1/4W carbon comp resistor, but...
>
>
>
> I calculated some combinations to save you the work. They're for TTC05104,
>
> with R16 = 4.3K . If you are doing an R-1051H with 3.9K, bump R902 down
> 10%.
>
>
>
> Resistors mV/degree
>
> a/b/902
>
>
>
> 22/10/27 8.5
>
> 24/9.1/30 7.2
>
> 27/9.1/33 6.5
>
> 30/9.1/36 6 <--- worked for me
>
> 33/9.1/39 5.5
>
>
>
> SUMMARY
>
>
>
> Thinking TTC05104, scaled and linearized by 4.7K/15K/11K, with 330K
> feedback,
>
> and (4013399-0701 only) 820K compensation. This should work for all
> modules
>
> originally using a 4700-ohm thermistor. You can even reuse your old R13
>
> for R913a.
>
>
>
> For the R-1051H, which uses a 3900-ohm thermistor, I'd try 220K or 270K,
> but I
>
> don't have hardware to try it.
>
>
>
> Dave Wise
>
> SWL in Hillsboro, Oregon
>
>
>
> ------------------------------
>
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>
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