Re: Intermittent no trace / sweep.
On Thu, Apr 26, 2018 at 07:03 am, Fabio Trevisan wrote:
there's a last problem which I won't be able to solve... the CRT is worn out
:-(
Have you tried boosting the filament voltage ? I have had good luck with that in TVs and now did a scope and it came out fine. It is just a matter of either jumping out a resistor or usually adding a turn to a winding on the HV transformer. Anyway, back to the topic here. I am pretty adept at boosting CRTs so if you want details contact me, unless you don't want/need to.
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Re: Intermittent no trace / sweep.
Hi,
This is a group, not a forum.
Many members (most?) access this group using the email
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Further, most members that use the email option, delete,
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As a result, each message, with a given subject line, has
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To help others understand what you are writing about, it
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Trim out any quoted text that doesn't apply to your reply,
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Because many new members do not follow the conventions of
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vaclav_sal via Groups.Io wrote:
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Sorry, perhaps me posting my first one wrong way.
Why is there even a need for attachment?
I did not indicate that in both of my posts.
I think I am capable carrying on a discussion without pictures - if that was reason you mentioned attachment.
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TM504A differences from TM504
I'm finally getting around to fixing, updating and working on my 500 plug in collection.
I have a, apparently, rare TM504A chassis that was modified by a previous owner so not all modules work in all slots and sources do not talk to destinations. It also has an oscillation in the power supply that I need to fix (Classic issue with how they did the feedback on the power supply). It is finally time for me to understand the back programing header and how to use it so that say my freq counter can read the oscillator or the volt meter read the power supply though the back plane while still being able to swap out modules.
I have been unable to find a manual or schematic for this unit, but there are plenty for the TM504. Is there any real difference other than the addition of a fan and switch location? Is the TM504 service manual good enough or if not where can I hunt down a TM504A one?
I sure wish there was a modern version of the 500 modules. I have some great modules with no current product options. I use the filter/pre-amp all the time at work and once I updated the op amps it works better than the current version by another vendor. But these things sure are getting old and I wonder if it is worth my time to keep them working for bench work any longer. For now I'll keep trying.
Thanx,
Hawker
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Re: Intermittent no trace / sweep.
Hello Vaclav, Please see my answers just after your questions: Rgrds, Fabio Sorry, perhaps me posting my first one wrong way. You're welcome... don't need to apologize. Why is there even a need for attachment?
I did not indicate that in both of my posts. My mistake... I just assumed there could be a picture because your original message doesn't explain what is the problem that you want help for and because it's so common for newcomers to paste or attach pictures to their first messages. Since the pictures don't get through to the forum, the messages quite often look like yours, with an open question but without an indication of what the problem is. I think I am capable carrying on a discussion without pictures - if that was
reason you mentioned attachment. No bad feelings... One thing you will see in this group is that people from all levels of knowledge (some are really rocket science high level, believe me) and all levels fluency are welcome and treated fairly. B.T.W. One thing that really *do* annoy many in the group is when people reply to a previous message without quoting the original question or doubt. Ah... In time, I have myself a 464 that took me about a year to solve all problems... and still there's a last problem which I won't be able to solve... the CRT is worn out :-( Rgrds, Fabio
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Re: BNC Installation Tool
I just uploaded some pictures of the tool.
Mine has the numbers -0755- hand engraved in the handle so the P/N is 003-0755-00. I added the page from the Tools Catalog to the album. /H?kan
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Re: Intermittent no trace / sweep.
Sorry, perhaps me posting my first one wrong way.
Why is there even a need for attachment?
I did not indicate that in both of my posts.
I think I am capable carrying on a discussion without pictures - if that was reason you mentioned attachment.
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Re: Tek 7623A - Readout omits 2nd zeroes while cold
Fabio,
I have looked at the pins you mention on U2232, particularly at pin 12, C1 which is involved in adding zeros. The behaviour of all the pins is consistent with a logic low of around 0.5V and a high level around 3V. The high level has a lot of switching noise looking like analogue ramps with an amplitude of close to 1V and the low level is clean but of very short duration so that you may not see it depending on your sweep speed and trigger settings. The narrow spikes carry the readout information and move and disappear when you change eg from 500mV to 1V per division, the 'noise' on the high logic level is largely unchanged.
Have you tried removing U2232 (and maybe U2244 and U2185 the row and column decoders) and cleaning pins? You may have the notorious TC IC sockets which are very prone to corrosion problems.
Regards,
Roger
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Hi Albert,
There are a good few on eBay.co.uk.
Most are in Germany which should be handy for you..
Plenty in the States as well.
Regards
jim
Ei2BB
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On 26 April 2018 at 09:18, Albert Otten <aodiversen@...> wrote:
Does anyone have any data on Nuvistors (miniature metal-envelope
tubes), or have any to sell? I could use an 8056, and have some
7586s...
A useful site is Frank's Electron tube Pages, and
its mirrors.
The 8056 pdf for instance via :
.
Albert
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Used to have some many years ago.?Will check just in case any are still in the drawer but pretty sure I sold mine to someone on eBay. www.cwgsy.net/private/mandoline "Error 008472. Horrible bug encountered. $Deity knows what happened." On Thursday, 26 April 2018, 09:18:14 BST, Albert Otten <aodiversen@...> wrote: > ? ? Does anyone have any data on Nuvistors (miniature metal-envelope
tubes), or have any to sell?? I could use an 8056, and have some
7586s...
A useful site is Frank's Electron tube Pages, and its mirrors. The 8056 pdf for instance via : . Albert
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Does anyone have any data on Nuvistors (miniature metal-envelope
tubes), or have any to sell? I could use an 8056, and have some
7586s...
A useful site is Frank's Electron tube Pages, and its mirrors. The 8056 pdf for instance via : . Albert
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Re: Notes on bringing up an old Tek 570
Hi John:
I have refurbished two 570 scopes and your suggestions are exactly the procedure I followed, but did not document. I replaced all the can electrolytic caps with modern high voltage tubular electrolytic models and mounted them under the chassis. I left the original canned caps in place but removed the hot leads.
I am sending a list of the parts I ordered to do the job.
Value (uF) Volts Quantity Substitute Jameco P/N Price each
1) .047 400 9 .05@1KV 332507 .59
2) .01 300 6 .01@1KV 97375 .19
3) .015 400 1 .02@1KV 332487 .55
4) .0047 400 2 .01@1KV 97375 .19
5) .001 500 5 .001@1KV 332436 .12
6) 15/20 450 12 22@450 331433 1.95
7) 80 500 3 120@400 2158426 1.95
8) .0068 3KV 3 .01@6KV eBay
9) .01 2KV 3 .01@6KV eBay
10) .005 4KV 1 .01@6KV eBay
11) .015 3KV 1 .01@6KV (use 2) eBay
Good luck, they are fantastic pieces of equipment and well worthy of an investment in time and money.
Reed Dickinson
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On 4/25/2018 9:51 PM, John Atwood wrote: A friend of mine just purchased an old Tek 570 Vacuum Tube Curve Tracer that hadn't been used in decades. He is a competent technical guy, but wasn't too familiar with old tube scopes. I made up a list of things to change and check, so I thought I would pass it on to the group.
Note starts here >>>
I've owned a Tek 570 for over thirty years and have tested thousands of tube on it. It is from around 1958 and has rounded corners and the black and white plastic meter. Here are my recommendations for initial bring-up and potential weak spots to address:
1. Before turning on, either: a) carefully reform the electrolytic capacitors or b) plan on replacing all electrolytic with new ones. This can be done by wiring them under the chassis and leaving the old cans in place. For reforming the capacitors, I recommend using a high-voltage adjustable power supply and slowly increasing the voltage across each capacitor until it draws 10 mA. Only after this decreases can the voltage be increased - eventually reaching the maximum rated voltage. A series resistor from the power supply can also be used to limit current.
2. Change all tubular paper capacitors. This is especially important if they are the black color-striped capacitors - these are notoriously bad. Regular mylar caps are a good replacement. Make sure to change the high-voltage capacitors in the CRT power supply, unless they are ceramic.
3. Check all the tubes on a tube tester and replace any weak tubes. Luckily all types are common. In later models the 6BQ7s were replaced with 6DJ8s. You could go back to using the 6BQ7, or you can use the Soviet 6N23P, equivalent to the 6DJ8/ECC88.
4. Spot check the resistance of the carbon-composition resistors. In some years they had a tendency to drift with age, always upwards in value. Replace any that are out of tolerance. About 1/5 of all my resistors had drifted out of spec.
5. Make sure to use silver-bearing solder on the ceramic terminal strips.
6. Lubricate the switches and pots with a drop of oil on the shaft and grease on the detents. I've found that military rifle grease works well here. A brief spray of DeOxit will clean the switches and pots. Use lightly. Also lubricate the fan.
7. I don't recommend changing the tube rectifiers to silicon - this will stress the rest of the system. Plus, the tube rectifiers used are common and cheap. If you want to replace the 5642 HV rectifiers with silicon, use only high-speed rectifiers.
8. The CRT is the same type as used in the Tek 575, so if there is a problem with the CRT, find a 575 parts unit. They are infinitely more available than the 570. The CRTs seem to be quite reliable, though.
9. In my 570, the readings were erratic at low current settings of the VERTICAL MA/DIV switch. It turns out that the current-sensing resistor string on this switch is grounded to the frame of the switch. If there is any corrosion where the switch is mounted to the front panel an erratic voltage drop is created. Running a wire from the switch frame to a ground point under the chassis solved this problem.
10. The step-generator circuits use some very high impedances. You may have to try several different 6AN8 tubes in the V8 and V38 sockets to get linear steps. It is helpful to use an oscilloscope on the step generator output to check for linearity.
Manuals and factory calibration procedure are available at:
end of note.
- John Atwood
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Re: Notes on bringing up an old Tek 570
Hello John
Both you and your friend are lucky guys to have got hold of a 570 each! They are rare as hen's teeth.
Only one comment. Silver-bearing solder could be confused with lead-free solder. Best to clarify with
tin/lead solder with 2-4% silver (I think the Tek original was 3%).
Craig
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Notes on bringing up an old Tek 570
A friend of mine just purchased an old Tek 570 Vacuum Tube Curve Tracer that hadn't been used in decades. He is a competent technical guy, but wasn't too familiar with old tube scopes. I made up a list of things to change and check, so I thought I would pass it on to the group. Note starts here >>> I've owned a Tek 570 for over thirty years and have tested thousands of tube on it. It is from around 1958 and has rounded corners and the black and white plastic meter. Here are my recommendations for initial bring-up and potential weak spots to address: 1. Before turning on, either: a) carefully reform the electrolytic capacitors or b) plan on replacing all electrolytic with new ones. This can be done by wiring them under the chassis and leaving the old cans in place. For reforming the capacitors, I recommend using a high-voltage adjustable power supply and slowly increasing the voltage across each capacitor until it draws 10 mA. Only after this decreases can the voltage be increased - eventually reaching the maximum rated voltage. A series resistor from the power supply can also be used to limit current. 2. Change all tubular paper capacitors. This is especially important if they are the black color-striped capacitors - these are notoriously bad. Regular mylar caps are a good replacement. Make sure to change the high-voltage capacitors in the CRT power supply, unless they are ceramic. 3. Check all the tubes on a tube tester and replace any weak tubes. Luckily all types are common. In later models the 6BQ7s were replaced with 6DJ8s. You could go back to using the 6BQ7, or you can use the Soviet 6N23P, equivalent to the 6DJ8/ECC88. 4. Spot check the resistance of the carbon-composition resistors. In some years they had a tendency to drift with age, always upwards in value. Replace any that are out of tolerance. About 1/5 of all my resistors had drifted out of spec. 5. Make sure to use silver-bearing solder on the ceramic terminal strips. 6. Lubricate the switches and pots with a drop of oil on the shaft and grease on the detents. I've found that military rifle grease works well here. A brief spray of DeOxit will clean the switches and pots. Use lightly. Also lubricate the fan. 7. I don't recommend changing the tube rectifiers to silicon - this will stress the rest of the system. Plus, the tube rectifiers used are common and cheap. If you want to replace the 5642 HV rectifiers with silicon, use only high-speed rectifiers. 8. The CRT is the same type as used in the Tek 575, so if there is a problem with the CRT, find a 575 parts unit. They are infinitely more available than the 570. The CRTs seem to be quite reliable, though. 9. In my 570, the readings were erratic at low current settings of the VERTICAL MA/DIV switch. It turns out that the current-sensing resistor string on this switch is grounded to the frame of the switch. If there is any corrosion where the switch is mounted to the front panel an erratic voltage drop is created. Running a wire from the switch frame to a ground point under the chassis solved this problem. 10. The step-generator circuits use some very high impedances. You may have to try several different 6AN8 tubes in the V8 and V38 sockets to get linear steps. It is helpful to use an oscilloscope on the step generator output to check for linearity. Manuals and factory calibration procedure are available at: end of note.
- John Atwood
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Re: Tek 422 ac/dc power supply issues
"glad to hear the DC/DC converter is working that should be a relief. so why is the Ac-Dc linear causing an issue??" I found out it's not. It's the voltage. "The Chopper xsistor is not too important which were my original thoughts prior to over thinking a replacement. It appears the venerable 2N3055 should be fine." I tend to concur now that I know how slow they chop. I don't know about a 3-55 but hell, it might. What I don't see is an easy way to mount a TO-3 in there, maybe a TO-3P or whatever, some sort of flat pack type should be fine and they are available now with specs just as good if not better. A TO-220 would be great as long as one can be had with good enough specs, perhaps a 2SD401 ? We used them for just about anything. Not real fast but we apparently don't need real fast. Either way, switching time is not causing the excess current drain, and neither would high saturation voltage. Now listen to my latest conclusion on mine, the waveforms : At ~16 volts in; 50 uS /g/TekScopes/photo/44484/2?p=Name,,,20,1,0,0 ~17 mS /g/TekScopes/photo/44484/3?p=Name,,,20,1,0,0 Now at ~30 volts in; 50 uS /g/TekScopes/photo/44484/4?p=Name,,,20,1,0,0 ~17 mS /g/TekScopes/photo/44484/5?p=Name,,,20,1,0,0 At 16 volts in it runs cool. At 30 volts in the heat builds up fast. In both cases the AC transformer was completely disconnected and out of circuit. The 16 volt readings were using a full wave rectified source running into 10,000 uF external filter, in a Kelvin type connection. About 1 volt P-P ripple. The 30 volt readings were using a full wave rectified source running into 1,500 uF plus the 2-1,300 uF in the Tek PS itself. About 3 volts ripple. No heat buildup at 16, fry eggs at 30. Looking a the waveforms, at 30 volts there is so much disturbance at the collector of Q 1174 the scope won't sync. At 12 volts it syncs fine. The "slo" waveforms were with the sweep down to match the ripple. At 12 volts you can see an aberration at 120 Hz, at 30 it seems to be random and looks like arcing actually. (I am familiar with that look from the TV days) If I were you I would look for similar aberrations in the waveforms in that unit. It is a simple matter of slowing the sweep. You can take it to some factor of 16.67 mS if 60 Hz where you are, or 20 mS if 50 Hz. This allows you to isolate the ripple and the error correction involved. Just rock it in free running. If you see what I saw at 3- volts in, your problem is similar at least. However I can't call it an arcing T 1201 yet. The drive has top be ruled out and I am not sure how to do that. The base waveform is no doubt susceptible to the Miller effect and that will even affect the waveform at the primary of T 1171. (in an HOT or LOPT circuit the effect is very profound) I think that means the ripple is responsible for the aberration in the chopper waveform at 16 volts input, especially since it reduces when the 10,000 uF is bridged in parallel with the input. T 1201 is still a prime suspect, the voltages going to the drive circuit are regulated, (have to make sure of that of course) while the voltage into the primary of T 1201 is allowed to vary with the input. Unfortunately I think I am going to find T 1201 bad, and I think the chances of getting one are about the same as me winning the gold medal in Women's gymnastics. It might be a DC only scope now...
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I popped out the transistor pair in the downstream A trigger view circuit and the voltages didn't change, so that leaves out that circuit as causing problems. So I did like Fabio said and pulled out the preamp transistor pair, and biased the input to the chip with two parallel 100 ohm resistors to ground. Now we're getting somewhere. The input was close to zero (don't remember now exactly) and 1 and 16 were -.755 volts. So it seems the chip works. Ohmed the transistors but that didn't tell me anything specifically about their condition. So since the B trigger side has an identical pair of preamp transistors, I swapped those into the A trigger side. Voltages were -30 mV on the input to the chip, and -.755 at 1 and 16. Tested the trigger and now I can get a trigger! I also have the A trigger view. The chip isn't coming out unless it were to turn out to be bad. It's very soldered complete with solder fillets. So somehow the original preamp transistors are bad, or at least one is. I just need to source them, which so far the internet is telling me they are obsolete (of course). Any ideas anyone? Manufacturer part number: SF50031, which comes back to 2N5245 N channel JFET, which is obsolete. It's late and I haven't tried to cross reference that yet. As a side effect the trace seemed to have some ac coupled into it. It hasn't done that before but I'm wondering if it's because the case is off? Thanks Fabio and everyone else! Hello Lorn,
I also own a 464 and mine also had a problem triggering... And while looking at your description I looks like deja vu to me. On mine one of the FET transistors of the input circuitry were leaky...(it had about 200kOhms impedance between source and gate, while reverese biased. The good ones measure Infinite, or very high Megohms. The leak developed a voltage drop on the 1M resistor at their gates and make the output voltage to have a huge offset of... wow! 70mV...(that's 1/10th of what you're getting). 70mV offset was enough to take the preamplifier IC so off that trigger would only work by adjusting the level potentiometer near its end of range and, still, after warming up, the offset would grow just a bit more and then even taking the Level potentiometer to the end was not enough to make it trigger. On yours it seems the offset is some 0.7V, so no wonder why it doesn't trigger. Your course of action is exact and removing the FET transistors will allow you to rule-out if the positive offset is coming from the IC, or if it's coming from the buffer stage into the IC. It's likely, however, that if you just leave pins 2 and 3 opened, as they will get when FETs are removed, you will be fooled by false voltage readings at pins 2 and 3, due to the input pins need some biasing. So, after you remove the FET ICs, connect a resistor of - say - 51R between pins 2.3 of the preamp IC to ground. The impedance at the other side of this balanced input differential amplifier is roughly 50Ohm, so biasing pins 2,3 with 50Ohms will make the input perfectly balanced. In this condition, pins 2 and 3 must read a low voltage, close to 0V. By no means it can be more than 50mV... as I told, my 464 had 70mV and that was enough to screw up the triggering. Alternatively, you can check the FET input buffer's offset, by taking the IC out and measuring voltage directly at pins 2.3 of the IC socket... Don't worry, taking the IC out is safe... nothing that's past of the IC will burn because the IC isn't present. (I had this same doubt back then). Set the Trigger input to EXT, coupling to DC, and ground the Ext. input, so that you're sure that you're not feeding DC into the input buffer, and its output should be very close to 0V. If the transistors are perfectly matched and thermally even, in theory, the DC offset of this input buffer is exactly ZERO. Good luck, Rgrds, Fabio
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I think this one is 6CW4 , if interested where do I mail it?
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464 intermittent trace / sweep
I would like someone to help me to figure out why my trusty 464 won't keep the sweep going.
I do have shop manual.
The scope been sitting on my desk , unused for over two years.
As far as I can tell the CRT works OK.
The only visible / mechanical problem is that the delay sweep knob pulls out but has no indentation.
So the scope MAY be in "delay sweep" mode - but I cannot really tell.
I will provide more details when I get a reply.
Vaclav in Houston
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Re: BNC Installation Tool
That's the same one from the ebay link - same vendor and manufacturer too.
Vince.
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On 04/25/2018 07:59 PM, Glenn Little wrote:
First find from my friend Google.
On 4/25/2018 3:18 PM, Larry McDavid wrote:
Someone here mentioned a BNC installation tool. I took that in context
to mean a tool that holds a chassis-mount female BNC jack while
tightening the backside nut but I don't find any such tool when
searching, only tools to disconnect mated BNC connectors.
Did I misunderstand what was suggested for straightening bent BNC
connectors or can someone point me to such a tool?
--
Michigan VHF Corp.
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Re: BNC Installation Tool
First find from my friend Google.
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On 4/25/2018 3:18 PM, Larry McDavid wrote: Someone here mentioned a BNC installation tool. I took that in context to mean a tool that holds a chassis-mount female BNC jack while tightening the backside nut but I don't find any such tool when searching, only tools to disconnect mated BNC connectors.
Did I misunderstand what was suggested for straightening bent BNC connectors or can someone point me to such a tool?
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
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Re: BNC Installation Tool
And here's one covering the installation tool.
Vince.
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On 04/25/2018 05:59 PM, Ed Breya via Groups.Io wrote: I just stumbled across this about BNC repair:
Ed
--
Michigan VHF Corp.
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Jeff Urban
Fabio Trevisan
zenith5106