The old adage "if it ain't broke don't fix it" applies here. I wouldn't go recapping it or rebuilding the scope unless it was absolutely necessary. The only problem I had with my 556 was the dreaded HV transformer rot. The 556 has two of them and they are located where they are not easy to remove and replace. Once you've dealt with that you can consider yourself invincible!
Morris
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Hi Bill. As owner of some 556 scopes I have had some experiences during their restoration. They are pretty well engineered and I would say ultra reliable. The only area I would caution about is the tunnel diode sweep triggering. I had one unit that I just could not get to trigger and wound up parting it. The other thing might be to get some spare tubes. There are a couple of unusual ones in there that are unique to this scope. A final word of advice would be not to drop it on your foot. Otherwise good luck.
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Lots of Tek 155-series ICs getting posted shortly
I made a deal to buy up the Tek spares stock of a closed service center in europe last month,
in order to get some hard to find 155 and early 156 parts. I have gone through them, and will be posting them up to the stuff page shortly, we're busy photographing all of them now.
Some of the parts include these hard to find 155 items: 0064-00, 0082-00, 0085-00, 0085-01,
0091-00 and 0244-00/01.
there's also some VERY early 156 parts, including Fairchild RTl, with these low numbers: -0001-00,
0010-00, 0011-00.
and lots of dual PNP high beta transistors, 151-0354-00. all the items will go very cheaply, as we got a good deal on the parts, hopefully it will bring some good gear back to life!
it will all be here by monday:
all the best for Easter,
-walter (walter2 -at- sphere.bc.ca)
sphere research corp.
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Re: Odd +55v source to 465 CH1/CH2 Vertical Assembly.
Cool Tom. Thanks for that, though I'm still only understanding about half (generous) of what you're saying. It will contribute as I continue to study though.
The insights to the purpose of the compensation are really the answer to the question, and makes me feel better about just jumpering in the +5v needed to operate the circuit. Full frequency calibration would take place in situ. And this is only for benchtop functionality testing.
E.g. CH2 is not only non-functional, the scope remains displaying CH1 while CH2 is selected. So obviously it's a switch issue. I have another 465 with odd noise at the top of the deflection of CH1 only. Despite a thorough cleaning. I'm 99% certain it's still a dirty contact as it is volts/div setting dependent. I want to be able to clean, test, repeat. Having to re-install would be beyond a pain. Now I don't feel like I'm gong to kill the board or components with a test jig.
I find these implementation particulars fascinating as an engineering solution given the constraints of the state-of-the-art at the time. I get the need for BW and temperature compensating components, but the available documentation doesn't get into the why of things like this interesting bias supply. The need for cold temperature operation isn't something I would have thought of. Pitying the techs operating in the Artic/Antarctic regions - or Minnesota.
Dave
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On Saturday, April 3, 2021, 01:26:51 PM PDT, Tom Lee <tomlee@...> wrote: Hi Dave, That network provides temperature compensation of bandwidth. A peaking capacitor (a trimmer) already exists across the emitter degeneration to boost bandwidth. The varactor in parallel (effectively) with that peaking cap allows the boost to increase with temp, to compensate for the drop in bandwith that would otherwise occur as the amp heats up. You want enough voltage to guarantee that the current source diode acts like a good current source under all conditions. As to "why 55V", remember that the scope is spec'd down to -15C. Replacing 55V with 5V would fail even at room temp, because that would leave nothing across the diode. 15V is enough at room temp, but at -15C, the varactor would need too high a voltage to keep the diode happy. So, 55V. The amp doesn't need that network to function, so if you power up the temp. compensation part of the circuit with 5V in the way you propose, that would be fine. You can proceed with troubleshooting. --Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 4/3/2021 12:22, Dave Peterson via groups.io wrote: Can someone here explain the purpose of the +55v source to this circuit?
I'm am trying to see if I can power the vertical assembly on a bench. I have a very dysfunctional vertical assembly, and would prefer to work on it in a bench environment where I have access to all components, switches, etc. I'd like to develop this as a regular bench setup as removing and installing the vert. assembly is a pain. It'd be nice to validate the assembly before putting it back in place.
It looks like I would be able to do this with -8, +5, and +15 volt sources, which I have in a recent bench power supply acquisition. I do also see +120v going to this board, but it appears to only power the "uncal" light, so I can live without that.
It looks like +55v only goes to the bias supply of the CH1/CH2 first stage amplifier. It is immediately stepped down to about +5v by an interesting set of components. I don't understand why this needs to be powered by the +55v source if +5v is already available.
What is the purpose of taking +55v, stepping it down through CR39 (JFET, 1mA, 1N5297) to about +5v (measured) and across RT39?
In writing this I've studied it a bit and taken some measurements. There's a deleted resistor, R34, that used to tie this node to +5v by 430k ohm. Watching the voltage at the node it starts at about 6v when powered on, and drops to 5v as the scope warms up. Makes sense: it's a temperature compensation to the first stage. Still, I find it odd that it's powered by +55v. Fifteen volts is also readily available.
I'm sure this wasn't implemented on a whim. Any insights to why +55v, and can I safely use +5 jumpered to the output of the divider to drive the first stage for testing? Perhaps through a 430k resistor to mimic its original implementation?
Thanks,
Dave
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I would do that, except for one small problem.? I'm using EAGLE 7.x with a hobby style license.? I am specifically prohibited from selling the boards.? Now, if I could guarantee that nobody would make the boards and sell them, that might be fine.
As to the design, it's essentially trival for anyone with another PCB program (other than EAGLE) to use.? For EAGLE, easy enough to make and do, it's the license that's the problem.
Harvey
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On 4/3/2021 4:45 PM, Ke-Fong Lin wrote: For those who did not see, I am offering two boards per person, all you
need to is contact me off list, and send an SASE (self addressed,
stamped envelope) with enough postage to get the boards back home.? The
boards are free. Hi Harvey,
If you're not considering selling them, have you considered to just make the gerber files available online (let's say github)?
A lot of people now regularly buy PCBs from JLCPCB or pcbway. They can basically just "batch" these boards in one order.
Best regards,
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Re: what's the market for newly produced tunnel diodes?
Right side of the scope, A8 board. There are 4 right in the middle of the board. You should probably be able to see the silk-screen notes for (top to bottom): B FIRE, B ARM, A FIRE, A ARM along with the typical tunnel diode schematic symbol. They are the gold cans about 3 mm in diameter and length (eyeball guess). Staring at a set right now while studying trigger waveforms. Trying to grok these little gems myself.
Dave
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On Saturday, April 3, 2021, 01:40:15 PM PDT, DaveH52 <ac2gl.dave@...> wrote:
I've got a 465 and I didn't know there were any tunnel diodes in it. Where should I go looking for it?
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For those who did not see, I am offering two boards per person, all you
need to is contact me off list, and send an SASE (self addressed,
stamped envelope) with enough postage to get the boards back home.? The
boards are free. Hi Harvey, If you're not considering selling them, have you considered to just make the gerber files available online (let's say github)? A lot of people now regularly buy PCBs from JLCPCB or pcbway. They can basically just "batch" these boards in one order. Best regards,
|
Re: what's the market for newly produced tunnel diodes?
I've got a 465 and I didn't know there were any tunnel diodes in it. Where should I go looking for it?
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Re: Odd +55v source to 465 CH1/CH2 Vertical Assembly.
Hi Dave,
That network provides temperature compensation of bandwidth. A peaking capacitor (a trimmer) already exists across the emitter degeneration to boost bandwidth. The varactor in parallel (effectively) with that peaking cap allows the boost to increase with temp, to compensate for the drop in bandwith that would otherwise occur as the amp heats up.
You want enough voltage to guarantee that the current source diode acts like a good current source under all conditions. As to "why 55V", remember that the scope is spec'd down to -15C. Replacing 55V with 5V would fail even at room temp, because that would leave nothing across the diode. 15V is enough at room temp, but at -15C, the varactor would need too high a voltage to keep the diode happy. So, 55V.
The amp doesn't need that network to function, so if you power up the temp. compensation part of the circuit with 5V in the way you propose, that would be fine. You can proceed with troubleshooting.
--Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
toggle quoted message
Show quoted text
On 4/3/2021 12:22, Dave Peterson via groups.io wrote: Can someone here explain the purpose of the +55v source to this circuit?
I'm am trying to see if I can power the vertical assembly on a bench. I have a very dysfunctional vertical assembly, and would prefer to work on it in a bench environment where I have access to all components, switches, etc. I'd like to develop this as a regular bench setup as removing and installing the vert. assembly is a pain. It'd be nice to validate the assembly before putting it back in place.
It looks like I would be able to do this with -8, +5, and +15 volt sources, which I have in a recent bench power supply acquisition. I do also see +120v going to this board, but it appears to only power the "uncal" light, so I can live without that.
It looks like +55v only goes to the bias supply of the CH1/CH2 first stage amplifier. It is immediately stepped down to about +5v by an interesting set of components. I don't understand why this needs to be powered by the +55v source if +5v is already available.
What is the purpose of taking +55v, stepping it down through CR39 (JFET, 1mA, 1N5297) to about +5v (measured) and across RT39?
In writing this I've studied it a bit and taken some measurements. There's a deleted resistor, R34, that used to tie this node to +5v by 430k ohm. Watching the voltage at the node it starts at about 6v when powered on, and drops to 5v as the scope warms up. Makes sense: it's a temperature compensation to the first stage. Still, I find it odd that it's powered by +55v. Fifteen volts is also readily available.
I'm sure this wasn't implemented on a whim. Any insights to why +55v, and can I safely use +5 jumpered to the output of the divider to drive the first stage for testing? Perhaps through a 430k resistor to mimic its original implementation?
Thanks,
Dave
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Re: Odd +55v source to 465 CH1/CH2 Vertical Assembly.
On Sat, Apr 3, 2021 at 09:59 PM, Raymond Domp Frank wrote:
CR39 is a constant current diode, @ 5 mA.
That should have been 1 mA. Raymond
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Re: Odd +55v source to 465 CH1/CH2 Vertical Assembly.
On Sat, Apr 3, 2021 at 09:22 PM, Dave Peterson wrote:
It looks like +55v only goes to the bias supply of the CH1/CH2 first stage
amplifier. It is immediately stepped down to about +5v by an interesting set
of components. I don't understand why this needs to be powered by the +55v
source if +5v is already available.
What is the purpose of taking +55v, stepping it down through CR39 (JFET, 1mA,
1N5297) to about +5v (measured) and across RT39?
In writing this I've studied it a bit and taken some measurements. There's a
deleted resistor, R34, that used to tie this node to +5v by 430k ohm. Watching
the voltage at the node it starts at about 6v when powered on, and drops to 5v
as the scope warms up. Makes sense: it's a temperature compensation to the
first stage. Still, I find it odd that it's powered by +55v. Fifteen volts is
also readily available.
I'm sure this wasn't implemented on a whim. Any insights to why +55v, and can
I safely use +5 jumpered to the output of the divider to drive the first stage
for testing? Perhaps through a 430k resistor to mimic its original
implementation?
CR39 is a constant current diode, @ 5 mA. It needs the headroom to do its thing. 15V wouldn't be enough. Together with RT39, it supplies a temperature-dependent voltage, which is used to achieve temperature compensation for frequency behavior, through varicap CR34. Raymond
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Re: Odd +55v source to 465 CH1/CH2 Vertical Assembly.
CR39 is a 1mA current regulator, or constant current diode. It is a high impedance device
and will not function at (15 - 4.2 = 10.8v). It supplies bias to CR34, a vari-cap that is part of the
temperature-dependent frequency compensation. Powering this from anything but 55v may wreck
the frequency response, so I would not make any frequency compensation adjustments this way.
Dave
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Show quoted text
What is the purpose of taking +55v, stepping it down through CR39 (JFET, 1mA,
1N5297) to about +5v (measured) and across RT39?
In writing this I've studied it a bit and taken some measurements. There's a
deleted resistor, R34, that used to tie this node to +5v by 430k ohm. Watching
the voltage at the node it starts at about 6v when powered on, and drops to 5v
as the scope warms up. Makes sense: it's a temperature compensation to the
first stage. Still, I find it odd that it's powered by +55v. Fifteen volts is
also readily available.
I'm sure this wasn't implemented on a whim. Any insights to why +55v, and can
I safely use +5 jumpered to the output of the divider to drive the first stage
for testing? Perhaps through a 430k resistor to mimic its original
implementation?
Thanks,
Dave
|
Odd +55v source to 465 CH1/CH2 Vertical Assembly.
Can someone here explain the purpose of the +55v source to this circuit?
I'm am trying to see if I can power the vertical assembly on a bench. I have a very dysfunctional vertical assembly, and would prefer to work on it in a bench environment where I have access to all components, switches, etc. I'd like to develop this as a regular bench setup as removing and installing the vert. assembly is a pain. It'd be nice to validate the assembly before putting it back in place.
It looks like I would be able to do this with -8, +5, and +15 volt sources, which I have in a recent bench power supply acquisition. I do also see +120v going to this board, but it appears to only power the "uncal" light, so I can live without that.
It looks like +55v only goes to the bias supply of the CH1/CH2 first stage amplifier. It is immediately stepped down to about +5v by an interesting set of components. I don't understand why this needs to be powered by the +55v source if +5v is already available.
What is the purpose of taking +55v, stepping it down through CR39 (JFET, 1mA, 1N5297) to about +5v (measured) and across RT39?
In writing this I've studied it a bit and taken some measurements. There's a deleted resistor, R34, that used to tie this node to +5v by 430k ohm. Watching the voltage at the node it starts at about 6v when powered on, and drops to 5v as the scope warms up. Makes sense: it's a temperature compensation to the first stage. Still, I find it odd that it's powered by +55v. Fifteen volts is also readily available.
I'm sure this wasn't implemented on a whim. Any insights to why +55v, and can I safely use +5 jumpered to the output of the divider to drive the first stage for testing? Perhaps through a 430k resistor to mimic its original implementation?
Thanks,
Dave
|
Re: A6302/P6302 current clamp questions and parts.
On Sat, Apr 3, 2021 at 08:26 PM, Jared Cabot wrote:
OMG, I am a happy panda!
I connected the wires as below and it works! Not bad for a $160 gamble on this
probe. :)
Congratulations Jared. Important quality aspect is lack of noise in the most sensitive DC ranges. Well, being not that good in color distinction I asked my wife for assistance., I'm glad we didn't make mistakes! Maybe also good to mention in your overview that the ground strip should make contact with the body. IIRC my P6302 had no groundstrip (yet). Albert
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Re: Persuading a 7S12 to play nice with a 7934.
Both effects are present in my opinion, shift between alternate sweeps and chop noise. I added a picture "A17 noise" that might convince you. The noise frequency corresponds tp the chop rate (judged by eye, line A5 signal). With the 7704A there was a third "noise" source", the interdot blanking pulses. I don't understand why interdot blanking periods in my 7S12 last so long, some 10 us. The manual says 3 us but that might have changed with the new Q690 etc. circuit.
The alternate and chop choice might be due to bad noise immunity in the main frame "Display Right" circuits.
I'd like to postpone further comments (on your previous findings) and investigations until I can place the 7S12 on extenders. I still have 2 kits somewhere.
Albert
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On Sat, Apr 3, 2021 at 02:50 PM, Richard Steedman wrote:
I re-checked the voltage level of the B7 input and you are correct - It's not
-0.4V at all, rather it's shifting between -0.66V and -0.7V. I must have
mis-read the display when I first looked at it. I'm pretty sure it's shifting
levels on alternate sweeps rather than from chop signal noise. The shift
occurs every 250?s and the timebase in the 7934 is set to 20?s/div. The
chop frequencies of a 7934 are roughly 1MHz for vertical and 200kHz for
horizontal.
I really appreciate the time you're spending to verify my observations. It's
reassuring to find that this behavior is not unique to my mainframe.
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For those with a 2465A (or maybe B) version; I just received a 2465. Very clean and good looking inside; probably heavy usage, though, considering the status of the blower: noisy.
Another thing I noticed (didn't mention that actually works normal - up to a point) is that adjusting intensity it goes in a de-focus state; partially adjustable, but you don't want to do that every time you go from low frequency to higher. Could be a CRT issue or something in the control circuits; have to do some verification.
The first issue is the one I need some help with: the blower's motor is a Siemens device that's beyond repair and I'm considering the idea of changing the whole blower with a regular fan and some mods in the path of airflow; that if there is a kind soul that could take the trouble to provide a picture of the fan in a 2465A; from SM I take it might be not a blower, but a regular fan; I might be also wrong.
Regards
TT
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Re: A6302/P6302 current clamp questions and parts.
OMG, I am a happy panda!
I connected the wires as below and it works! Not bad for a $160 gamble on this probe. :)
Luckily my coax (The clear-ish wires) weren't broken so I didn't have to worry about those being reversed.
Also, my serial number is B071921 for the record.
A - Red/White
B - N/C
C - Orange/White
D - Black/White
E - White
F - Yellow/White
H - Brown/White
J - Gnd strip (For Coax from Pin 1 of CT, common with K)
K - Gnd strip (For Coax from Pin 7 of CT, common with J)
L - N/C
M - Coax from Pin 1 of CT
N - Coax from Pin 7 of CT
Thanks again Albert for the help and risking your probe's well-being for my sake. :)
I'll have to make a little diagram of the late version pinout and upload it to TekWiki.
Jared
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On Sun, Apr 4, 2021 at 01:20 AM, Albert Otten wrote:
A red/white
B NC
C orange/white
D black/white
E white
F yellow/white
J gnd strip
K gnd strip
L NC
M, N both blank plastic
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Re: A6302/P6302 current clamp questions and parts.
Wow, thanks for that! There's no way I would have got it correct.....
I saw your picture at TekWiki and mine matches there, so I'll rewire my Amphenol plug to match yours and see what happens.
Many much thanks! :)
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Bill,
My recommendation would be to, after due deliberation, decide if you are going to Repair, Rebuild, or Restore. They are very very different in terms of how long you and your 'scope will be out of commission.
cheers
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Re: A6302/P6302 current clamp questions and parts.
Nasty surprise Jared: in my A6302 S/N B76170 all colors are different! With magnifier glass I feel quite sure they are as follows:
A red/white
B NC
C orange/white
D black/white
E white
F yellow/white
J gnd strip
K gnd strip
L NC
M, N both blank plastic
The ground strip end gets located between body and the inserted boot part.
M and N wire type looks exactly the same. That's problematic since these also determine polarity.
It's easy to verify that the lock switch is wired between C and J.
You can see some colors arriving inside the probe in my picture "component" view at Tekwiki.
Albert
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John Williams
Dave Peterson
DaveH52
Raymond Domp Frank
Jared Cabot