I'm not so sure. Something is wrong with the way the DC504 counter's front panel at the top looks "Catty-Wompus" either that or the frame of the TM503 is bent. I notice the seller doesn't mention the condition of the DC 504. The rest is a good deal.

Dennis Tillman W7PF

On Thu, 29 Dec 2016 18:29:19 -0200, you wrote:

...

To what extent would
the performance of the buffer >circuit change if the resistor >values were
reduced to 0 ohm?

Strictly answering to your question, this circuit won't work as intended if
source resistors are 0 ohm.
In this circuit's design, the voltage drop at the source resistors is
required because a change in the
Drain-to-Source current translates into a change in the voltage drop that
is fed back into the transistor's gate,
which ultimately is what locks the transistor into the intended bias point.
We can, however, talk about making this value lower and lower if there's a
need for that (e.g. to lower the output
impedance of the buffer) but:
1. It can't EVER be 0 (well, there's no 0 Ohm resistance anyway) and...
2. Its value is not guesswork...It`s calculated in order to have the right
voltage drop at a desired current,
Both voltage drop and current are dependent on the particular
transistor that was chosen for the task.
In this particular Tek 464's circuit, 15 Ohm is probably the best value
that was possible, considering all
the design constraints (the transistor, the operating voltage, the
desired frequency response, etc, etc...)

There are a couple of other things the source resistors affect:

1. Transconductance of a JFET is proportional to the square root
of the drain current and the bandwidth is proportional to the
transconductance so lowering the drain current with the resistors
lowers the transconductance and bandwidth which might be necessary for
stability.

2. Lowering the drain current lowers the power dissipation. Some
JFETs have a high enough Idss that their power dissipation would be
exceeded if Vgs was held at zero volts.

3. The source resistance in the top JFET changes the load impedance
seen at the source which may be necessary for stability. You can find
low value resistors sprinkled here and there for this reason. For
instance the low value gate resistor cancels the negative resistance
at the gate.

I suspect the most important criteria is stability insofar as it
affects transient response.

The numbers are gone too. Doesn't the screen glow normally? I have a vague recollection of how it used to work.
I thought it had a glow visible with the grid ilum dimmed all the way.


Are there diagnostic pins or connectors to test? Something to probe without damaging anything?

Mike,

Where do you see a quick flash? Is it green on the crt? You can at least
check for the -3Kv HV primary. Your unit may have something as simple as a
deflection plate connection loose. What plugins are you using?

jerry

On Thu, Dec 29, 2016 at 3:42 PM, volvoboy242@yahoo.com [TekScopes] <
TekScopes@yahoogroups.com> wrote:

I brought my old 7704 (non A) down from the attic the other day to find
that the CRT is dead.
I see a quick flash upon power down but, other then that, there is no
display.
I am guessing that the HV power supply has kicked the bucket.
I've done no diag since I know the voltage is high and my knowledge
doesn't extend to testing deadly secondary potential.
I've never had the covers off or had any work done (in 20 years).
Is this a serviceable part or do I need to source a known good power
supply?
I'm hoping it's something as simple as a re cap but this might be a bit
beyond me.


If any of you guys would Elmer me through this resto project, I'd be much
obliged!
No rush.


The only other scope I have is an old Velleman hand held that works
occasionally. I have some basic Ham survival tools.
I planned to gear up around this old main frame for radio alignments and
things of that nature.
Overkill I know.


Off topic; Also in my attic, there is an old pre war Allen B Dumont
"oscillograph" I played with when I was a kid.
I'd like to get that one working again some day. Just for fun.


Thanks
Mike
KD2MBG

[Non-text portions of this message have been removed]

Hello Joe,
Congrats for the great scope!
What do you mean with "The screen displays a trace that's vertically wider
than the screen"?
Is it a horizontal trace that is so thick to occupy the whole screen
vertically?
or...
Is it a vertical trace that takes most of the vertical dimension, which
moves horizontally across the screen (and movement is noticeable on slow
sweep rates as you said)?

In either case, it may be vertical noise (or a frequency) that looks like a
thick trace simply because it's not in sync with the sweep. If it's pure
noise (white noise) that is finding its way into the vertical amplifier (or
originating on the vertical amplifier itself), if may be doing so at a
point past the point where the trigger signal is picked-off so she won't
sync on it no matter what.
If it's a particular frequency, even without syncing you may be able to see
waveform by playing with the sweep's Variable control, but if it's pure
noise and not synced, it may be impossible to see it as a waveform at
highest sweeps (and you will see always a "thick" trace) and at slow speeds
you will only see a vertical trace moving horizontally across the screen.

It may also be an unfocused trace (a focus problem), but then at slowest
sweep speeds, the vertical trace will be horizontally thick as well.

Can you post a picture of it? (On the Tekscope's "Photos" area, as the
pictures doesn't get through inside the messages)

Rgrds,
Fabio

If you have the flash on power down then the filament and EHT are probably ok. Either the beam is deflected off screen due to a fault in the X or Y amplifiers (check voltages on the deflection plates with a very slow sweep speed and adjusting the vertical position on the plugin, the plate voltages should move symmetrically in opposite directions) or you have a problem in the z axis circuit which can be more tricky to trace without a second scope.

Regards

Roger

I brought my old 7704 (non A) down from the attic the other day to find that the CRT is dead.
I see a quick flash upon power down but, other then that, there is no display.
I am guessing that the HV power supply has kicked the bucket.
I've done no diag since I know the voltage is high and my knowledge doesn't extend to testing deadly secondary potential.
I've never had the covers off or had any work done (in 20 years).
Is this a serviceable part or do I need to source a known good power supply?
I'm hoping it's something as simple as a re cap but this might be a bit beyond me.


If any of you guys would Elmer me through this resto project, I'd be much obliged!
No rush.


The only other scope I have is an old Velleman hand held that works occasionally. I have some basic Ham survival tools.
I planned to gear up around this old main frame for radio alignments and things of that nature.
Overkill I know.


Off topic; Also in my attic, there is an old pre war Allen B Dumont "oscillograph" I played with when I was a kid.
I'd like to get that one working again some day. Just for fun.


Thanks
Mike
KD2MBG

Hey Joe,

looks like you're well on your way to set her right - sweet!

Mind that the probe compensation signal on the 2465 (et al) changes with
the timebase, maintaining a steady 5 cycles across the graticule up to a
frequency of some 5MHz. You can use this to verify the horizontal
calibration of the scope, as the calibrator is derived from a crystal clock.

Note that the OSD has a separate intensity control pot, and when the pot is
at 12 o'clock, the OSD is off.

If the scope fails self-tests, it stops at a diagnostic screen. To get it
to operate beyond that, you need to press the A/B TRIG button.
If your scope doesn't need that press after power-up, then it's not failing
self-tests.
If it does, then please make note of the state of the LEDs. There are
tables starting around page 6-12 describing how the LEDs relate to the
tests.

Also, if you have her open, you might as well release and re-seat the
hybrids. They do tend to develop poor connections due to oxidation, and
this is an easy thing to do while the cover is off.

Siggi

On Thu, 29 Dec 2016 at 14:41 tatumj1@yahoo.com [TekScopes] <
TekScopes@yahoogroups.com> wrote:

Sorry, I should have included my name. The name is Joe Tatum. After
cleaning and re-seating the connections to the control board it does work
somewhat. I thought the caps on the control board might be bad. I pulled
the board and checked them with my ESR meter and all are .45 ohms. I
measured the voltages at P119 and all are in tolerance. The panel LEDs come
on and change when switched. The screen displays a trace that is vertically
wider than the screen and fills most of the screen. There is no
alphanumeric display. The sweep rate changes when switched and the slower
sweep can be observed. The power supply appears to have been recapped at
least partially. Quite a few of the caps there stand a good 1/4 in above
the board and I do not think they were installed that way by Tektronics.

Hello Goran,
See my replies next to your questions.
Following, I'll try to explain what's the basic idea behind the design.
Brgrds,
Fabio

Hi, I have followed your discussion for quite some time now. I have never
understood the purpose of these two source resistors, 15/20 ohm. Is the
purpose to simplify matching of the two FETs or do they reduce the
input/output offset having not perfectly matched FETs?

Neither!
The source resistors are actually what set the bias point to the JFETs in
this configuration that is called self-biasing.
As for the resistor's values being equal (the top and the bottom), they
don't facilitate anyhow the two transistors to "match".
On the contrary they're only chosen to be equal expecting the transistors
are matched.
Wouldn't the transistors be matched, one or both of the resistors would
need to be made adjustable in order to obtain
0V of D.C. offset, but that would have other setbacks, such as D.C. offset
drift with temperature.

How the whole thing works? I'll explain further down...

To what extent would
the performance of the buffer >circuit change if the resistor >values were
reduced to 0 ohm?

Strictly answering to your question, this circuit won't work as intended if
source resistors are 0 ohm.
In this circuit's design, the voltage drop at the source resistors is
required because a change in the
Drain-to-Source current translates into a change in the voltage drop that
is fed back into the transistor's gate,
which ultimately is what locks the transistor into the intended bias point.
We can, however, talk about making this value lower and lower if there's a
need for that (e.g. to lower the output
impedance of the buffer) but:
1. It can't EVER be 0 (well, there's no 0 Ohm resistance anyway) and...
2. Its value is not guesswork...It`s calculated in order to have the right
voltage drop at a desired current,
Both voltage drop and current are dependent on the particular
transistor that was chosen for the task.
In this particular Tek 464's circuit, 15 Ohm is probably the best value
that was possible, considering all
the design constraints (the transistor, the operating voltage, the
desired frequency response, etc, etc...)

Now, I describe how it works...have the Tek 464 schematic at hand... you
can get it here:
http://w140.com/tek_464_color_schematics.pdf
And be patient please... I don't have the same ability as David to
summarize an idea.

The bottom transistor Q624 forms, with R624, a constant current source. The
transistor's own parameters, along with
R624 sets the current.
At power-up, there's no current crossing R624 and so there's 0V across it,
so it is the Q624's Gate-to-Source (Vgs) voltage.
At 0V Vgs, the transistor is set to full conduction, allowing current to
flow, causing a voltage drop on R624, which is
seen by the transistor's gate as a negative value, which will make the
transistor conducts less and the current will eventually
stabilize at some specific current point, which will be the "bias" point of
the circuit.

In a graph that plots simultaneously the transistor's transfer function and
the source resistor's load line, the bias point
will be where both curves cross.
The resistor's value (and so its load line) should be calculated to assure
that, even if the transistors transfer function may
vary up or down, left or right, that the curves still cross at some point.
If the resistor's value is too high or too low so its load line may fall
outside the transistor's transfer function, then the
lines won't cross and the circuit will either become unstable, or lock down
into cutoff or lockup into full conduction.

There are numerous explanations of JFET current sources... Just google for
"JFET Current Sources".

From the explanation above, it becomes clear that the exact current is not
really established, as it depends on each
transistor's parameters and, especially talking about JFETs, this means
that it can vary quite a lot.
But the beauty of this design is that even though the the exact current
being unknown there's no issue.
As long as the transistors are matched, the circuit will work as expected
no matter the current will end up being 1/3 or 3x the
idealized operating current (there are limits though).

R625//C625 (likewise their upper counterparts R622//C622) don't play an
important role... they're there just to lower both
transistors' Drain-to-Source voltage and possibly to limit the current in
case of overdrive.
During normal operation you can just think of them as a small battery that
subtracts from the -8V (and +8V) supplies.

Continuing... Q622 and R623 are connected as a "Source Follower" (or common
Drain amplifier) in that its "load" is
the above mentioned current source (formed by Q624 and R624).

The upper half of this circuit looks really similar to the constant current
source, but there's a difference.
Q624's gate is connected to the bottom of R624, which integrally feeds-back
R624's voltage (negative) to
Q624's gate and therefore, making it the constant current source that it is.

As opposed, Q622's gate, is not fed-back from its source resistor, but it's
connected to the input signal (via R618)
and only "referenced" to the ground (by R616).

When there's no signal, R616 makes the voltage at Q622's gate to be 0V
(there's no voltage drop on R616 because
under normal operation, a JFETs gate is reversely polarized and there's no
current flowing).

Q622 and R623 are connected in series with the constant current source so,
by definition, they're forced to operate
at the constant current source's current.
Since the transistors are matched (identical) and are being traversed by
the same current, Q622 will call for
the same Vgs that is Q624's Vgs.

Let's assume now the input voltage is 0V... So:
1. Q622's gate is at 0V...(via R618).
2. Q622's current is (by circuit's connection) = Q624's current
3. From point 2. condtion and from Q622 is a matched pair of Q624, then
Vgs(Q622) = Vgs (Q624)
4. From point 1. (gate at 0V) and point 3. Q622's source must be at a
positive value the same as Vgs(Q624) and so, upper side of R623 is at
Vgs(Q624)
5. From R623 is of same value as R624 and they're traversed by the same
current...
then voltage drop at R623 = Vgs(Q624), which is the same as saying that
V@R623 = V@R624
6. Voltage at the bottom of R623 is the voltage at its top minus the
voltage drop of R624 which is,,, the same amount...
7. Therefore Vout=Vin + Vgs(Q624) - Vgs(Q624), then Vout = Vin

Since the transistors are matched (and thermally bonded by a thermal clip),
if Q624's varies its parameters, Q622 is likely
to vary them in the same direction and amount and, given the way they're
connected and R624 and R623 are the same, the
variations will be cancelled out and Vout will remain being = Vin.

Slight mismatches between transistors will not be cancelled out and only
the difference will "show-up" as a D.C. offset of the Output in respect to
the Input.
If we tweak R624 or R623 to compensate for the slight mismatch above, the
D.C. offset may be zeroed for a given condition (i.e. temperature),
but at different temperatures, the D.C. offset may show-up again (and
drift-away) because the transistors are mismatched and so they will drift
apart from each other.

Göran

Here's my folder of 2465 type stuff...a fair amount of resources.
tek 2465a - Google Drive https://drive.google.com/drive/folders/0BxARZnl2qhssZV9FM2hfWHk2ak0?usp=sharing

tek 2465a - Google Drive https://drive.google.com/drive/folders/0BxARZnl2qhssZV9FM2hfWHk2ak0?usp=sharing Drive Sign in Drive My Account Search Maps YouTube Play News Gmail Drive Calendar Translate PhotosMore Shopping Wallet Finance Docs Books Blogger Contacts HangoutsEven more from Google Google apps



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Sorry, I should have included my name. The name is Joe Tatum. After cleaning and re-seating the connections to the control board it does work somewhat. I thought the caps on the control board might be bad. I pulled the board and checked them with my ESR meter and all are .45 ohms. I measured the voltages at P119 and all are in tolerance. The panel LEDs come on and change when switched. The screen displays a trace that is vertically wider than the screen and fills most of the screen. There is no alphanumeric display. The sweep rate changes when switched and the slower sweep can be observed. The power supply appears to have been recapped at least partially. Quite a few of the caps there stand a good 1/4 in above the board and I do not think they were installed that way by Tektronics.

I have the original TEK Service manuals for the 2465A & 2467. If you need a particular close up etc. I can take a pic or try a scan.

Here's the 2465 Service manual online, you'll have ato watch it for a minute while it says 'processing' and then do the dl. I just set it to dl as well....as I have a spare parts 2465 on hand including if u need a board or knob or anything.
TEKTRONIX 2465 Service Manual free download, schematics, eeprom, repair info for electronics http://elektrotanya.com/tektronix_2465.pdf/download.html

http://elektrotanya.com/tektronix_2465.pdf/download.html

TEKTRONIX 2465 Service Manual free download, sc... http://elektrotanya.com/tektronix_2465.pdf/download.html Free download TEKTRONIX 2465 service manual & eeprom info



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Hey Tatum(?),

welcome to the group. The 2465 is a great scope, and likely yours is having
power supply problems, as many of these do by now. Note that there are a
great many differences between 2465, 2465A and 2465B, so it's important to
know which one you have.
The first thing to do is to get the service manual for the scope. I have
the scan from Artek Manuals <
http://artekmanuals.com/manuals/tektronix-manuals/> (search for 2465),
which I can highly recommend. Second only to a paper copy. Looks like Dave
is selling the six volume set for $8.
Alternatively you might be able to find a decent scan for free on the great
Interwebs, though one didn't pop out at me at a quick Google.

It would also help if you could describe how it "tries to start" in more
detail. One common problem mode is the so-called "tick-tick" mode, where
you see lights flicker and perhaps relays click roughly once a second. This
is characteristic of the switch-mode power supply being in some distress,
either due to overload, or else because the electrolytic capacitors are too
far gone for it to maintain regulation.

If it's not in a tick-tick mode, then it's useful to know how far along it
gets in starting. As it's starting up, it counts out the self-tests it's
performing by the front-panel LEDs, and the state of the front panel when
it stops is indicative of the failure it hit.

Does it click relays, display a trace, display the on-screen-display (OSD)?
Does the fan run? You may not hear it, but there'd be a light breeze from
the back vent.

Good luck,
Siggi

On Thu, 29 Dec 2016 at 13:16 tatumj1@yahoo.com [TekScopes] <
TekScopes@yahoogroups.com> wrote:

I am retired but still active as a Ham Operator. My call since 1958 is
K4ZMO. I first encountered Tektronix equipment as an employee of Scientific
Atlanta in the early 1970's. I have used an old Tek 454 scope in Hammond
organ repair since so called retirement. I recently came by a Tek 2465 but
it only tries to start. I found the group and joined hoping to find some
advice in getting it started. Would be much easier to carry around than the
old 454.

I am retired but still active as a Ham Operator. My call since 1958 is K4ZMO. I first encountered Tektronix equipment as an employee of Scientific Atlanta in the early 1970's. I have used an old Tek 454 scope in Hammond organ repair since so called retirement. I recently came by a Tek 2465 but it only tries to start. I found the group and joined hoping to find some advice in getting it started. Would be much easier to carry around than the old 454.

Somebody got a steal! Wow.


--
Joe Laffey

On Dec 29, 2016, at 7:47 AM, mosaicmerc@yahoo.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

TEKTRONIX DM501A DIGITAL MULTIMETER PLUG IN TM504 TM506 TM5006 BENCH TOP TESTING | eBay http://www.ebay.com/itm/142221367884?ul_noapp=true

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no affiliation.




[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

On 12/29/2016 09:10 AM, Kjo kjo@cryden.com [TekScopes] wrote:

Hey Paul, what's a213?

Sent from kjo iPhone

<http://w140.com/tekwiki/wiki/213>

Mark

Hey Paul, what's a213?

Sent from kjo iPhone

TEKTRONIX DM501A DIGITAL MULTIMETER PLUG IN TM504 TM506 TM5006 BENCH TOP TESTING | eBay http://www.ebay.com/itm/142221367884?ul_noapp=true

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no affiliation.

Hi to All,

Just made the Photo Album. The Tek Part Numbers of these Extender Cards are 067-0758-00 and 067-0759-00.


Greetings again,


Egge Siert

Hi Paul,

I don't have a 213, but I have 5 pictures of the 213 Extender Cards (saw them once on eBay).


I can send them directly to you or I can make a Photo Album of them.


I hope you can use them.


Greetings,


Egge Siert