Date   

Re: Q122/222 Jfet J300 subs for 2215A scope ?

Ed Breya
 

Oops - I meant to say Vds here, not Vgs:

The Vds should be fairly constant since the required output excursion is only about +/-100 mV.

Ed


Re: Q122/222 Jfet J300 subs for 2215A scope ?

Ed Breya
 

Yup, I see it. I finally looked at the schematic for the 2215A. Looks like the quiescent drain current should be around 11 mA, and the source at Vbe.I'm looking at the J310/J309 data sheet here:

https://www.mouser.com/datasheet/2/308/J309-D-109346.pdf

If I'm interpreting Fig. 1 properly, the lower curve set is for the J309, and the Id is about right for Vgs= -Vbe. The upper curves for the J310 are about 3 X higher - too far out there for the nominal circuit conditions, although Q15 could probably pull it hard enough to DC balance (but things would start getting weird). The JFET runs with Vds about 8V, so pretty close to the 10V used in the specs. The Vgs should be fairly constant since the required output excursion is only about +/-100 mV.

This circuit reminds me of the ones in all the other 2200 series, and may be essentially exactly the same. More info may be discerned by looking at those others to see what JFETs were used. The 2N5486 keeps sticking in my brain.

Ed


Re: Tektronix 7D13 and 7A42 wanted

 

What did you use for a battery?

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ed Breya via groups.io
Sent: Wednesday, November 18, 2020 2:18 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tektronix 7D13 and 7A42 wanted

The cleaned up 7A42 is still working OK. I'm calling this one fixed and done, ready to go back on the shelf. Hopefully it will still be good whenever I need it.

Ed







--
Dennis Tillman W7pF
TekScopes Moderator


Re: Tektronix 7D13 and 7A42 wanted

Dan G
 

I was lucky that I caught the leaking NiCd battery in my 7A42 back in 2016, when
it was still in the early stages. Surprisingly, the only damage was to the nearby
jumper plugs, many of which had seized and became encrusted with blue crystalline
deposits. This damage was not immediately obvious -- one had to examine contacts
inside the black plastic plug housing.

Amphenol still makes identical jumper plugs today (Mini-Jump p/n 65474).

I should note that I had decided _not_ to replace the battery, as any new NiCd
battery will just cause more of the same damage if allowed to run empty.
(And, depending on the quality of the replacement battery, possibly much
sooner than the original part made by Saft.) This is not suitable for a unit that
only sees occasional use, and where the hope is to preserve it for many years
into the future.

If the battery is not replaced, then it is important to move the BE (Battery
Enable) jumper to the open position, to stop the plug-in from attempting to
initialize the front panel settings from invalid memory contents. With the BE
jumper in the closed position, and no battery, the plug-in can occasionally
lock-up during power-up.


dan


Re: Q122/222 Jfet J300 subs for 2215A scope ?

Tom Lee
 

Yes, a J310’s IDSS range is centered high for this particular circuit. The J309’s IDSS range is actually about right, as the buffer circuit aims to operate the FET at a VGS of -0.6 (to compensate for the VBE of the bipolar follower that the FET drives), so the drain current for a J309/J310 is perhaps 8-10mA lower than IDSS, assuming a typical gm of 15mS.

AFAIK, the J309 and J310 come from the same process recipe.

—Cheers
Tom

Sent from my iThing, so please forgive typos and brevity.

On Nov 18, 2020, at 1:53 PM, Ed Breya via groups.io <edbreya=yahoo.com@groups.io> wrote:

For some reason I've been referring to the original working JFET as a J310, but looking back all the way to the OP, I'm not sure what it is - all kind of parts are floating around this thread. So Charles, can you identify the one official, working JFET that I've been referring to?

The reason I ask is that I looked up the J310, and found it is a very heavy beast - VHF/UHF, with Idss 24-60 mA - way too big and fast for this little scope amplifier, and way too big for Tom's estimated max of 30 mA for circuit operation. The correct part must be something else more "normal," among many possible choices. The J309 may work, but even it seems a bit much.The J300 seems about right, and the J210 or preferably J211 may be a good option. Also, I mentioned the 2N5485 and 2N5486 earlier, which I'm pretty sure were used a lot under various Tek part numbers. I think especially the 2N5486 was used extensively in scope input amplifiers.

Anyway, there are types that it could be, and types it shouldn't be.

Ed






Re: Another A5 board repair attemp - help needed

Rogerio O
 

Hi Folks,
The parts arrived from Mouser.
I replaced U2101 (DAC), U2521 (4051) and U2420 (TL084) as well as all the 0.47uF capacitors connected to the U2521 just in case.
I though I read somewhere the the capacitors in this circuit may be the cause of having low +1.36V/-1.25V values, as I was experiencing (is it true??).
Anyway, I have now the error changed to TEST 4 FAIL 2 but voltages' prior to DAC adjustment are +1.4V and - 1.28V !!!
It seems I will be possible to execute the DAC calibration and move on to the other calibration steps.
Unfortunately I have to travel tomorrow and will only br able to work on the scope on next Monday.
Thanks to all of you that have helped me to get to this point.
Roger


Re: Tektronix 7D13 and 7A42 wanted

Dave Daniel
 

Hmmmm...electrolytics?

DaveD

On Nov 18, 2020, at 17:17, Ed Breya via groups.io <edbreya=yahoo.com@groups.io> wrote:

The cleaned up 7A42 is still working OK. I'm calling this one fixed and done, ready to go back on the shelf. Hopefully it will still be good whenever I need it.

Ed





Re: Tektronix 7D13 and 7A42 wanted

Ed Breya
 

The cleaned up 7A42 is still working OK. I'm calling this one fixed and done, ready to go back on the shelf. Hopefully it will still be good whenever I need it.

Ed


Re: 7L5 Res shaft encoder

Dan G
 

On Tue, Nov 17, 2020 at 05:25 PM, Nenad Filipovic wrote:

Today I attempted disassembly of my Resolution/Freq. Span knob and got halfway
there, photos (album name "7L5 Knob Repair Attempt"):
https://groups.io/g/TekScopes/album?id=256833&p=Name,,,20,1,0,0
Hi Nenad,

Your photos encouraged me to attempt to disassemble my own res/freq knob assembly.
I was hoping to be able to tell you whether my L-shaped insert also appears glued, but
interestingly, I could not even get that far. The best I could do was to remove the black
plastic resolution knob/ring.

My 7L5 s/n is >B090000, and therefore has the 263-0064-00 encoder. In this version,
the hollow cylindrical centre of the (die cast?) metal base seems to extend all the way
through the frequency span knob as a single piece, rather than being made up of
two fluted interlocking parts. Hence, the resolution and frequency span sections do
not come apart when the resolution knob/ring is removed.

Peering down the length of this cylindrical opening toward the underside of the
frequency span knob, I believe I see the bottom of a machine screw, but I cannot be
certain.

It would appear that different disassembly procedures are needed for
260-1693-0x and 263-0064-00 encoders. I don't think that I will attempt any further
disassembly, for fear of damaging or marring a perfectly working pristine unit.

Perhaps someone with an older 260-1693-0x assembly (and more courage) will be
able to make further progress.


Good luck,
dan


Re: Q122/222 Jfet J300 subs for 2215A scope ?

Ed Breya
 

For some reason I've been referring to the original working JFET as a J310, but looking back all the way to the OP, I'm not sure what it is - all kind of parts are floating around this thread. So Charles, can you identify the one official, working JFET that I've been referring to?

The reason I ask is that I looked up the J310, and found it is a very heavy beast - VHF/UHF, with Idss 24-60 mA - way too big and fast for this little scope amplifier, and way too big for Tom's estimated max of 30 mA for circuit operation. The correct part must be something else more "normal," among many possible choices. The J309 may work, but even it seems a bit much.The J300 seems about right, and the J210 or preferably J211 may be a good option. Also, I mentioned the 2N5485 and 2N5486 earlier, which I'm pretty sure were used a lot under various Tek part numbers. I think especially the 2N5486 was used extensively in scope input amplifiers.

Anyway, there are types that it could be, and types it shouldn't be.

Ed


Re: Delayed Timebase on a Tek 2215A

 

Raymond and Leo, thanks for the correction, it was ENTIRELY operator error and misunderstanding. I see that the same thing can be achieved on the 475 by selecting the B trigger source as "STARTS AFTER DELAY" even though the 475 does not offer the more pleasing ALT horizontal display mode.

I know that this is shallow, but I just wanted to be able to see the two signals one above the other rather than stitched together vertically with a sliding transition from one timebase to the other. I don't have any real use for the feature, which is part of the reason that I didn't understand how to use it, but as this is just my hobby, being able to play with a cool looking feature is basically the only requirement.

-- Jeff


Re: Q122/222 Jfet J300 subs for 2215A scope ?

dave G8SFU
 

Sorry I got the impression from earlier in the thread that these were a totem pole pair of fets .
My bad
Must be more careful to look at the manual.

Regards dave

⁣Sent from BlueMail ​

On 18 Nov 2020, 20:19, at 20:19, Tom Lee <tomlee@ee.stanford.edu> wrote:
Ed,

I’ve analyzed the circuit. Any IDSS below about 30mA will satisfy the
loop, as I’ve noted twice before. If much lower than that, dynamics may
suffer, but the upshot is that there’s a very wide window.

It’s that accommodating nature that leads me to suspect that the OP may
have other problems.

Tom

Sent from my iThing, so please forgive brevity and typos

On Nov 18, 2020, at 12:15, Ed Breya via groups.io
<edbreya=yahoo.com@groups.io> wrote:

There may be some confusion over "selecting" versus "matching," due
to the different input amp topologies also included in the discussion.
In this case, it's an opamp-stabilized system, with only one JFET up
front, for each channel. There is no need for matched JFETs, but
apparently there is a need for the JFETs used to fall in a narrower
Idss range than the generic part types they come from. It looks like
the official Tek part number used is provided by the vendor from J310s
or similar, selected for some range of Idss according to Tek's spec for
this part. The problem is that we don't know the selection criteria
applied, but we do know the one good original J310 found in the circuit
appears to work, so finding another VHF JFET that has similar Idss
should work too. We don't know if the original is an ideal example - it
may be at an edge of the desired range, or right in the middle, but at
least getting close to whatever it is should be in the ballpark.

Ed






Re: Q122/222 Jfet J300 subs for 2215A scope ?

Tom Lee
 

Ed,

I’ve analyzed the circuit. Any IDSS below about 30mA will satisfy the loop, as I’ve noted twice before. If much lower than that, dynamics may suffer, but the upshot is that there’s a very wide window.

It’s that accommodating nature that leads me to suspect that the OP may have other problems.

Tom

Sent from my iThing, so please forgive brevity and typos

On Nov 18, 2020, at 12:15, Ed Breya via groups.io <edbreya=yahoo.com@groups.io> wrote:

There may be some confusion over "selecting" versus "matching," due to the different input amp topologies also included in the discussion. In this case, it's an opamp-stabilized system, with only one JFET up front, for each channel. There is no need for matched JFETs, but apparently there is a need for the JFETs used to fall in a narrower Idss range than the generic part types they come from. It looks like the official Tek part number used is provided by the vendor from J310s or similar, selected for some range of Idss according to Tek's spec for this part. The problem is that we don't know the selection criteria applied, but we do know the one good original J310 found in the circuit appears to work, so finding another VHF JFET that has similar Idss should work too. We don't know if the original is an ideal example - it may be at an edge of the desired range, or right in the middle, but at least getting close to whatever it is should be in the ballpark.

Ed





Re: Q122/222 Jfet J300 subs for 2215A scope ?

Ed Breya
 

There may be some confusion over "selecting" versus "matching," due to the different input amp topologies also included in the discussion. In this case, it's an opamp-stabilized system, with only one JFET up front, for each channel. There is no need for matched JFETs, but apparently there is a need for the JFETs used to fall in a narrower Idss range than the generic part types they come from. It looks like the official Tek part number used is provided by the vendor from J310s or similar, selected for some range of Idss according to Tek's spec for this part. The problem is that we don't know the selection criteria applied, but we do know the one good original J310 found in the circuit appears to work, so finding another VHF JFET that has similar Idss should work too. We don't know if the original is an ideal example - it may be at an edge of the desired range, or right in the middle, but at least getting close to whatever it is should be in the ballpark.

Ed


465M Wave Forms

Harrison
 

Need some basic clarifications and guidance. I want to view some wave forms of a 465M scope with a 460A digital scope. The manual for the 465M tells you to run a 50 Ohm cable between the "A EXT Trigger of the test scope (460A) and the "+A Gate" of the scope under test (465M). The 465M markings are clear. In the case of the "A EXT Trigger" of the 460A, would that be the EXT clock BNC on the rear of the scope?
I am a bit confused. If I have the bnc cable hooked up as indicated above, is the probe attached to channel 1 of the 465M or is it attached to the 460A. Or, am I all wet on this. Thank you
Harrison N1FAM


Re: Q122/222 Jfet J300 subs for 2215A scope ?

Tom Lee
 

Hi Dave,

I earlier posted that I doubt very much that any detailed selection went on, other than a crude sort for IDSS. The whole point of that design was precisely to eliminate the cost and bother of matching!

-- Tom

Sent from my iThing, so please excuse the terseness and typos

On Nov 18, 2020, at 6:12, "dave G8SFU via groups.io" <djk302=zoho.com@groups.io> wrote:

Hi Tom, my thinking went thus::

I understood from previous posts that there were a pair of identical fets. I similarly understood they were "selected".

If these two statements are correct I stand by my original suggestion.
I should admit I have not worked on a 2215 and base my opinion on reading the thread, not looking at the actual circuit.

Regards dave
⁣Sent from BlueMail ​

On 18 Nov 2020, 10:17, at 10:17, Tom Lee <tomlee@ee.stanford.edu> wrote:
Hi Dave,

Keep in mind that this is a 60MHz scope, and that the circuit in
question is a simple buffer. I don't see how adding a new constraint of

matching helps to fix it. I still think that the OP either has a
collection of JFETs that Murphy has arranged to have extremely off-spec

IDSS (hence my advice to simply measure it; it's trivially easy to do),

or hasn't gotten the pinouts quite right (there is not a single
standard
pinout). It is also possible that there is a separate hardware problem
that is making one channel excessively finicky. It's straightforward to

eliminate or verify possibilities 1 and 2, so if it's neither 1 nor 2,
the OP should move on to 3. It's not hard to debug the bias loop, so if

he eliminates 1 and 2, getting through 3 should be fairly quick.

Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 11/18/2020 01:55, dave G8SFU via groups.io wrote:
Can I add a further thought to Ed Breya's suggestions.
By all means use Ed's procedure to get the best possible spec for the
required fet.
But then try and match a pair of new ones. It seems to me much more
likely to work than matching a 40 year old one with a 'new' one.
Regards. Dave.

⁣Sent from BlueMail ​

On 17 Nov 2020, 20:58, at 20:58, "Ed Breya via groups.io"
<edbreya=yahoo.com@groups.io> wrote:
It may be good to rethink and summarize what's going on with these
parts. Here's my take on it, presuming I haven't missed something.

1. There is one "good" original J310 that works properly in either
channel. This indicates the circuits for both are likely OK, as long
as
the "right" JFET characteristics are present.

2. The main issue is finding another JFET - a J310 or similar one -
that has the "same" characteristics as the good one. Alternative
part
trials so far have been unsuccessful.

3. The input circuit of the 2215A is of the opamp-stabilized type,
so
should be quite tolerant of JFET DC characteristics.

4. The "proper" part is 151-1124-00 = Siliconix J2400, which
apparently
is not a standard commercial part.

5. You have to get the pinout right, and we're assuming a TO-92
package.

6. Measuring Idss

Recommendations:

1&3. You can be pretty confident that both channel circuits are OK.
However, it's possible that one may have a minor fault or part out
of
tolerance such that it's OK with the good J310, but another part
that's
close and should work, doesn't quite. For now I think it's safe to
say
both are OK, and can be determined once a "right" part is found.

2. All along, the discussions have been mostly about getting Idss
right
- this is still the case, for DC conditions, one way or another. If
you
can find a VHF-class JFET (more on this in #5) that you can select
to
be close to the good J310, then it should work.

4. Let me explain a little about Tek and selected parts. In the old
days, when particular characteristics were needed, if they could be
selected out from stocks of generic parts at reasonable yield, Tek
often did this in-house, and a dash-number was assigned to the base
part number. This assumed also that the generic parts were used in
sufficient quantity that those not selected out (usually the -00)
would
be used up elsewhere. Later, as the real cost of all the in-house
selection and inventory and tracking complications became evident,
there was a big push to reduce this sort of stuff. One way is to
have
the vendor pre-select for the desired characteristics, out of their
much larger volumes, and assign a custom part number. This can be
done
if you're a large enough customer, and you pay a little more for the
parts to cover the vendor's cost of doing it. The benefit is that
you
get what you need, under a single part number, and you know the true
arm's-length cost. So, the supposition that J2400 is a custom part
number is likely correct - it's selected by the vendor from one of
their generic types, and sold only to Tek.

5. The pinout is important - more than just getting it connected
right.
What you want is a TO-92, with the source lead in the middle. VHF
parts
typically have this arrangement to minimize proximity and
capacitance
between gate and drain leads. The exception is if it's for
common-gate
topology, where you'd ideally want the gate in the middle, and it's
RF-grounded, and shields the drain from source. So, in choosing
possible candidates for substitution, first they should be listed as
"VHF amplifier" in the application highlights. Then look at the
pinout,
and pick only those with the source on the middle pin. The drain and
gate on the outside don't matter - you can always flip them around,
but
of course be sure what's what when installing.

6. For Idss, the easiest is to use a curve tracer and measure the
original good one - it's the gold standard, so take good care of it.
If
you don't have a curve tracer, you can rig up a simple bias circuit
for
checking and comparing. The best would be to measure the DC bias
conditions in the actual working circuit. The gate is assumed at
zero,
so all you need are the source and drain voltages, and you can
estimate
the drain current. Then set up a resistor bias scheme that gives the
same conditions if the same JFET were present. Note that this is not
an
Idss measurement (unless the source happens to also be at zero) -
it's
even better - an actual in-circuit test that can be done on the
bench
to sort the best parts to try in the real thing. In reality, the
vendor
likely sorted for a certain Idss range at a certain drain voltage,
which you don't know, but an in-circuit equivalent should be as good
or
better. There is a simple proxy for Idss, that you can use to
pre-sort
parts, rejecting those that are very unlikely to land close. Just
measure the "on" resistance of the drain-source (with gate tied to
either), with an ohmmeter, compared to that of the gold standard. I
think you'll find that the switching type JFETs will be quite low
(10-50 ohms), and the small, slow ones (like for high-Z DC
amplifiers)
quite high (over about 200 ohms). The VHF and HF ones are typically
in
the mid-range around 50-200 ohms.

The idea of putting in a temporary socket is good too, but a little
awkward working down in the guts. That will certainly tell what
works
and what doesn't.

That's all for now. Good luck.

Ed










Re: Tektronix 7D13 and 7A42 wanted

Tim
 

Thanks for bringing this up Ed.
My pristine 7A42 had just started to show some battery leakage and was able
to clean the liquid on the board.
Had some green on the power supply jumper pins but it cleaned up ok.


On Tue, Nov 17, 2020, 23:00 Ed Breya via groups.io <edbreya=
yahoo.com@groups.io> wrote:

Nevermind - I found it. The 7D20 has "EAROM" to store settings only - no
waveforms. No battery is mentioned. Ed






Have some free Tek probe parts and 475 delay lines, etc.

 

Digging through our many parts bins, I found a stash of oddball NEW probe parts we have no use for, so they can be yours free if you can use them. This includes:

2 ea. P6040 50 ohm probes (has GR874 to SMB, I think for CT1-CT2 current probes.
2 ea. 0415-1170-00 P6108A Compensation box (the part of the probe that fits on the scope, less the cable).
7 ea. 0013-0107-02 push on probe grabber (like a witches hat, but no brim). Don't know what they fit.
9 ea. black push-in probe tips (I think for P6106/6108 type) has only partial number: 206-023, also has the insertion tool. These have a long gold tip and a short one, and just push into the end of the probe body for easy replacement.
4 ea. boxes of what I think are differential probe tips, 1 ea. p/n 016-1781-00 (saver), 1 ea. 016-1885-00 (variable spacing adapter), and 2 ea. 016-1884-00 (square pin adapter).
I can provide pics of these on request.

We also have two used 475 delay lines (good pulls), and some misc. peltola jumper boards.

I will post all the items to the FREE section of the Stuff Season page:
https://www.sphere.bc.ca/test/stuffday.html

later today if no immediate takers. lots of other Tek goodies there including an assortment of the most common BNC connectors (including indicating ones) Tek used going up later today. There's a pile of great 11K frame spares there, open to any good offer, they are just taking up space here.

let me know if you can use these items, email me directly if possible:
walter2 -at- sphere.bc.ca

regards,
walter
sphere research corp.
https://www.sphere.bc.ca/test/


Re: Special Offer from Peter Keller to TekScopes Members: The Cathode Ray Tube, Technology, History, and Applications"

 

Hi Richard,
If you are still at 2612 Virginia Rd I added you to the order list for Peter's book. If this isn't your current address please let me know.
Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Richard in Edenton NC via groups.io
Sent: Wednesday, November 18, 2020 6:37 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Special Offer from Peter Keller to TekScopes Members: The Cathode Ray Tube, Technology, History, and Applications"

Hi Dennis, is it too late to get one? I have been busy with a sick relative and not reading emails lately.

Thanks and 73

Richard W4MCD







--
Dennis Tillman W7pF
TekScopes Moderator


“High Bandwidth Transient Capture,” Tektronix Publication 1991

Christian
 

I've been unable to find anything more than bibliography references to this document (in an ESD context). Does anyone happen to have a copy?

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