[R-1051] Tools, and first assessment (was RE: Intro and WTB: R-1051 cabinet)

[David Wise]

Can anyone give me a correct partial schematic of the Frequency Standard?
Assume that A4's IN and OUT wires were inadvertently swapped.
That would put +28 on Q1.C and R1, and Q1.E and the heater
would be at +17.  But the listed value of R9 puzzles me.
With 18V across it, it can't possibly be 330 ohms - it would
burn up -, but if there were 7V across it, the current would be
21mA, virtually the same as 18V across 820 ohms.  If R9 really
is 330 ohms in modules with A4, then those modules must be
running _everything_ off 17V, not just the heater.  That simplifies
the wiring, but 17V is an awkward value to retrofit.  One user
installed a 7815, but that reduces maximum heater power from
3.5W to 2.7W .  I wonder if that's enough in a cold room.
(And R9 ought to be reduced to 220 ohms.)

Meanwhile, there's another easy target: 19.3V .  Since the
A2A5 module receives +20V as well as +28V, why not just hook
in an NPN emitter follower with base at 20V?  And change R9 
to 430 ohms.

I found a PTC thermistor at Mouser.  Vishay part number TFPT1206L3901JM,
$0.75 each and hundreds in stock.  TC is 0.41% vs 0.43% original.
The only downside is that it's a surface-mount part (1206 size),
which makes it a little harder to use.  I am thinking of mounting
it _inside_ the oven, against the bottom.  Solder it to a little
piece of FR-4, squash it onto a dab of heatsink grease then a mica
sheet then another dab of grease, flip face-down and JB Weld the
whole thing to the bottom of the well.  Solder the lead wires directly
onto J2 pins 1 and 3.  No oven disassembly.  No circuit modification.

What do you think?

Dave Wise

>-----Original Message-----
>From: David Wise 
>Sent: Friday, June 29, 2012 3:35 PM
>To: 'R-1051 Discussion Group'
>Subject: RE: [R-1051] Tools, and first assessment (was RE: 
>Intro and WTB: R-1051 cabinet)
>
>Thanks, Paul, but I want to run it standalone.
>
>My Frequency Standard has an open PTC thermistor.  As far as I 
>can tell from
>the archive, nobody, not even Cecil, has ever found a source 
>or a substitute.
>If I'm wrong, please tell me the recipe!  In the mean time, I'll take a
>whack at it myself.  At least the heater has continuity and 
>doesn't seem
>to be shorted to the housing, and the transistor acts like a 
>transistor.
>
>This Standard is a Bendix 4013399-0701, FSN 6625-078-4718.  
>(By the way, how
>do you figure out the FSN?  The module only has the Bendix 
>part number.  I got
>the FSN from the archive.)
>
>It is wired like Figure 5-6 in NAVELEX 0967-LP-970-9010, 
>except it has no A4 +27V(sic)
>Regulator (actually 17V), and R9 is 820 ohms not 330 ohms.  
>The board under R9
>is discolored.  If anyone has added a 7815 and is satisfied 
>with the result,
>I'd like to hear how you mounted it.  I don't see any place to put it.
>And did you hack it in like A4, or did you cut into the wire 
>at J1 pin 1?
>My idea is to mount it on the mainframe, and bring in +15V on 
>one of the
>spare J1 pins.  I'm also thinking of an LED to indicate how 
>much current
>the oven is using.
>
>I noticed that S1 is different.  The schematic labels the positions
>EXT, INT, and COMP, but my module is INT/COMP, EXT(NORMAL), 
>and EXT(OVEN STBY).
>Does anyone have a schematic that matches this?
>
>>-----Original Message-----
>>From: r-1051-bounces at mailman.qth.net 
>>[mailto:r-1051-bounces at mailman.qth.net] On Behalf Of paul
>>Sent: Friday, June 29, 2012 11:14 AM
>>To: R-1051 Discussion Group
>>Subject: Re: [R-1051] Tools, and first assessment (was RE: 
>>Intro and WTB: R-1051 cabinet)
>>
>>Good news is if there is an issue with the 5mc osc you can run it 
>>externally from a 5 mc source.
>>I run my 1051 externally with a rb reference compared to GPS
>>Regards
>>Paul
>