Oscilloscope Porn

Discussion in 'The Projects Forum' started by tindel, Jan 13, 2013.

  1. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    I've been looking for a scope for a while so I've been scavenging craigslist and ebay... Picked up this scope for $5 off of Craigslist. I don't think it works, but I've never owned a analogue scope, so I don't know what to expect or what all of the controls do. I'm going to need a working scope to get this thing up and running probably.

    Specs:
    Hewlett - Packard 130BR
    circa 1959
    A mind-blowing bandwidth of 300kHz!
    1mV to 150V per div
    .2us to 15s per div
    2Mohm input impedance
    Original list price $650 USD (about $5k USD in 2012 dollars)

    First thing's first - the power light doesn't work.
    Second - I need probes... judging from the spec, I just need banana cables with alligator clips. I was thinking something like this: http://www.newark.com/mueller-electric/bu-3070-c-24-0/connector-assy-banana-plug-black/dp/90F5728


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    CIMG0188_sm.JPG
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    OMG. What IS this? :D
     
  3. JingleJoe

    Member

    Jul 23, 2011
    185
    10
    mmm lovely device you have there, mind if I probe it? ;) no need to worry about discharging all that built up static charge into it, those old valves can handle anything you've got ;)
    Enough of this nonsense :D
    You may have some broken tubes, that's allways possible but also the old caps may be "fermented" for want of a better word, along with any high value resistors; they can drift way off although 1959 should be more advanced, perhaps they won't be so bad as my old scopes- 1940's! :p
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,006
    3,232
    Touch you finger to the scope vertical input (don't touch the oscilloscope ground or chassis). If the scope is working, with adjustment of the vertical sensitivity and the horizontal sweep rate, you should see a ratty image of the 60Hz power line frequency sinewave.
     
  5. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    crutschow - I did what you said, and there was a repeatable signal at ~14ms - or 71Hz... The timebase may be off a bit so, I'm guessing it was really 60Hz - I'm sure it hasn't been calibrated in over a decade, maybe two or three. The scope is actually in a pretty decent condition for not having been used for so long. There's very little rust... the board interconnect wires are a bit sticky, due to the crappy insulation and heat. I might replace the wire at some point.

    As I said before, something didn't quite seem right about the scope, and sure enough - It's missing a power supply tube - 6DJ8 / ECC88 - which regulates the +585V rail. It's not even there - someone probably needed the tube for something else, is my guess.

    Anyone have a cheep and reliable source for tubes? I know nothing about tubes... anything I need to know before I purchase one, or should I just buy one, plug it in, and go? I also need one for a guitar amplifier I have... I'll get both at the same time, I hope.

    My DMM only supports up to 500V, any ideas on how to measure those high voltage lines to find out what the voltages are? A high resistance voltage divider (1M/1M)?, as to not load the line? There's also a -2550V rail that I'd like to measure... maybe a different method is in order?

    Also, during my probing, I found that I was having a hard time breaking through the oxidation layer of the traces. I'm wondering if a little rubbing alcohol would break through easily to help make testing easier. Thoughts?
     
  6. RamaD

    Active Member

    Dec 4, 2009
    254
    33
    A high voltage probe is better. To provide isolation with a voltage divider, hmmm, is too much of a problem. Just a word of caution in case of voltage divider, you need to use high voltage resistors, yes, the resistors are rated for voltage too. HVR68 series from Phoenix Passive Components can withstand 10000V DC and 7000V RMS, and they are expensive! 1M/1M could be too low with high power dissipiation. About one and a half Watts in each when measuring 2500V. 10M/1M with the meter side connected to 1M is better. You need to take into account the input impedance of the meter, which is normally 10M! Assuming it is 10M, 9.1M/1M will give almost 1/10th the voltage into the meter!
    That oxidation layer could be conformal coating. Rubbing alcohol does not remove it easily. A paint thinner works well, but I am not sure about its availability there.
     
  7. tindel

    Thread Starter Active Member

    Sep 16, 2012
    568
    193
    RamaD - thanks for the info on the resistor voltages... I think I'll probably end up just getting a high voltage tester with applicable probes. I hadn't realized that resistors are voltage rated as well, rather than their power rating (v^2/R).

    It's definitely not conformal coating as it is only on the traces - there isn't any conformal coating on anything that I can find... it's definitely trace oxidation.

    I realized today that I should probably be testing with a isolation transformer.

    I also found a coworker that has a tube tester so I can test most of the tubes!
     
  8. tindel

    Thread Starter Active Member

    Sep 16, 2012
    568
    193
    I tested the tubes with my buddy and found 4 tubes were bad and 1 tube that was missing (585V bus regulator). I got the new tubes in the mail last night, so I tested each of them to verify they were good.

    Then I plugged the new tubes into the scope... turned it on... and... SMOKE! :eek: Coming out of the HV rectifier box! :eek::eek: I did this all just before bed so of course, I couldn't sleep trying to figure out what was wrong in my head and if I had smoked the HV transformer (literally, pun intended).

    I finally fall asleep, and I wake up at 3:30am, local. I proceed to figure out how to discharge the CRT correctly. Then I start taking apart the HV rectifier box. Oil... my heart sinks thinking that it is an oil cooled transformer (I didn't know for sure). I get the box apart and the transformer appears to be ceramic heat sink cooled... I breath a little sigh of relief.

    I continue doing some inspecting and I find some ceramic caps that are in need of replacement - there are three caps in there that are cracked near the leads... one is measuring 460ohms on my meter... I can only imagine that this is the cap that let it's smoke out. This should be an easy fix.

    So what caused the smoke in the first place? I think it was the fact that I had installed a new tube with higher gain... and the Cathode was higher voltage than the old dead tube and in turn let the smoke out of the cap.

    I'm still curious where the oil came from... I did find a HV paper cap that appeared that there might be some oil on it... but I wiped off the oil and it looked fine. I have no idea where this thing has been so, it is possible that it's been in somebodies garage and oil was dripping onto the scope. It is also possible that the primary transformer (which sits right next to the HV transformer in the chassis) is oil cooled and it has developed a leak. The ONE place I've seen any rust is just a little bit on the main transformer lid. Maybe it's coming from there slowly.

    Anyway - I do have a question about the tubes on this guy - The owners manual calls out in the tube replacement chart a 6DJ8/6BQ7 (I believe that it was originally designed with 6DJ8's in mind). So I ordered the 6BQ7 (they were cheaper) and received 6BZ7's, which are almost identical to 6BQ7, per the datasheet.

    The pinnouts of all three tubes (6DJ8/6BQ7/6BZ7) are all exactly the same so I'm not worried about that, but what I am moderately worried about is that this tube is used to regulate the 585V bus with a nominal voltage of 470V on Plate #2. The spec says a maximum of 300V in a cascode configuration (which this isn't a cascode config, if I'm reading the schematic correctly, and my education isn't failing me). The 6DJ8 datasheet says maximum plate voltage of 130V, but a plate supply voltage of (Ib = 0mA) of 550V - so what is the difference? Are the 6BZ7 going to fail on me prematurely?

    Note: I have powered on with the 6BZ7's, and they appeared to be working okay for the 30-45 seconds they were on. I figured I'd be okay since the 6BQ7 and the 6BZ7 datasheet maximum are exactly the same. But I thought I'd try to get some thoughts here.

    6DJ8:
    http://www.vt52.com/ftp/data/iht small signal/6DJ8.PDF

    6BQ7:
    http://www.datasheetarchive.com/dataframe.php?file=DSA8180002118.pdf&dir=Datasheets-X&part=6BQ7A#

    6BZ7:
    http://www.datasheetarchive.com/ind...ns-008&keywords=6Bz7&database=user-highscore#

    Schematics (pgs 54 & 55, V314)
    http://www.hparchive.com/Manuals/HP-130B-Manual-SNprefix-201.pdf

    Sorry if I sound as giddy as a school girl - it's because I am - this has been such a fun project so far!
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,788
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    I can't tell you anything about your tubes, but I would like to suggest something to remove the oxidized surface layer of the traces you mentioned.

    An eraser(pink or white) will do the job quickly. I prefer the white ones which are supposed to be used on ink, not pencil. They are slightly more abrasive...
     
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  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,031
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    We're you able to find the vintage, high voltage caps you need for that boat anchor?

    Be careful, old transformer oil contained PCBs (toxic).

    Also, there is a lot (mostly) point-to-point wiring on those old things. Keep your hands safe and expect more smoke as the insulation properties of the wire tends to drop off after 40 or 50 years. Finally, you might want to replace the power cord right away and ground the chassis - you likely have a 2-wire plug.

    Stay safe and enjoy your porn.
     
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  11. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    Kermit - Thanks for the tip! That's what I was looking for!

    Gopher - I haven't really looked for caps yet - I've been trying to see if I can get the thing to work properly first. I'm not a huge fan of just replacing parts because I can. I like to know there's a reason first. I will probably look for new-old-stock when it come to it though. I like to keep things as original as possible. I'll only replace caps that need it. No sense in sending something to the recycle bin or trash if it doesn't need to be there.

    Well, the cap wasn't the problem after all, it was actually the new tube! There is a RF oscillator that regulates the HV with a feedback loop. Similar to the MOSFET/pwm/opto-isolated flybacks we use commonly today. After hours of troubleshooting, I put the old tube in and the whole box works perfectly!

    Lesson learned - only replace one tube at a time so you know where to go back to!

    So, this thing is working great! Check it out -

    In order of appearance
    #1 - This is the internal calibration square wave - the scope isn't calibrated, so I haven't even tried to see how accurate it is yet.
    #2 - DC input (5V/div) - my DMM says 18.somethingV The scope is saying 15V, obviously something is out of cal - my guess is the scope. ;)
    #3 - Here is the AC off of the same DC regulator (I just removed the filter cap and rectifier from the DC trace). Beautiful - I couldn't ask for better. It says it's at 49.0Hz, so I'm guessing the time base needs some calibration work too. No surprise there.
    #4 - this is the same sine wave on the vertical amplifier with the calibration signal on the horizontal amplifier. I'm not use to using x-y coordinates yet - having used high quality digital scopes my whole life, but maybe someone knows what's going on... and can explain it to me.
    #5 - Guitar snobs have NOTHING on me! :p 25 tubes a glowin' - there's gotta be a song in there somewhere.

    What's next? A through cleaning with IPA and some white pen eraser. And some obvious repairs. The CRT mounting cushion needs replaced, the HV lines are cracked and need replaced, there is vibration isolation on the vertical and horizontal amplifiers that have deteriorated over time, and any other little things I find along the way. I'm still debating on if I should replace all of the wiring or not. It all seems fine, they used very high quality hookup wire - even by today's standards.

    This scope is truly a piece of art, and is in immaculate shape for it's age. I may see if a museum wants to display it for a while. My research has shown that these were produced in Colorado Springs, so there may be a local museum down there that would like it for a little while. My wife won't let me display it in the dinning room much longer!

    So far I've been very happy with my $28 investment. Hours of fun, frustration, and learning. My goal is to get everything replaced and in tip-top shape for under $100 - barring a large amount of old-school electrolytic caps needing replaced, I think this is extremely doable.
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Excellent work.

    I am not a fan of replacing caps "just in case" either. I was just assuming you needed one based on the blown cap theory of one of your earlier posts.

    Remember, if you put it in a museum, you won't be able to use it.

    Also, the knobs on front panels have maroon colored calibration knobs that are expected to be adjusted on an hourly or daily basis in the old tube scopes. Unfortunately, even the internal calibration signal drifts a bit.

    Good luck.
     
  13. MrChips

    Moderator

    Oct 2, 2009
    12,440
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    This is a vintage scope. Great that you got it to work. I wouldn't spend must more time or money to fix it up or try to calibrate it. If you can use it for simple audio testing that would be great otherwise just use it to enjoy the pretty pictures. Lissajous figures are always fun to watch.
     
  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Could you imagine what pride the engineering design and manufacturing teams from HP would have if hey knew their product would still function and be used in 2013. Especially when they were phasing out tubes for the emerging transistor technology at that time. Orwell's book was already out 10 years when this scope was made and 1984 seemed like a very far off year to them. Now we are approaching 30 years beyond Orwell's book and that scope still works... and, just as amazingly, somebody is interested in repairing and using it!

    That is like us designing a product that will be around until 2067 and someone caring to refurbish and use it. Doubtful!

    Cheers to the scientists and engineers at HP in 1959.
     
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  15. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    Gopher - So true... I just can't believe that this thing has made it 54 years and it works with NO adjusting of any internal pots. The engineers should certainly be proud. They are probably in their 80's or 90's if they are still with us.

    Mr. Chips - yeah - I'll probably start using it soon. I have an amplifier that is popping speakers that I want to get to the bottom of and sell it - this scope will be perfect for that, with no adjustments. IMHO, it would be a shame in my eyes to not clean it up and calibrate it to some extent. It doesn't have to be perfect, but I figure I can at least use my CPU sound card to dial it in a bit more than it is now.
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    I am still waiting to see the porn but it is not allowed here.
     
  17. MrChips

    Moderator

    Oct 2, 2009
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    What? You've never seen a SPICE model here before?
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    SPICE models are too skinny. I like a woman to look like a woman, not look like a young guy. The SPICE GIRLS had curves and looked fine.
     
  19. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
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    Hi,

    I've owned one that looks just like it for about 20 years. Been a long time since I fired it up.
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    After 20 years I would imagine a SPICE model would be very out of date and frigid by now.
     
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