So I got a 519.
Here it is in a rather compromising position, getting its caps checked.
What’s a Tektronix 519? Arguably the biggest, baddest, ballsiest oscilloscope ever fucking made. Designed over 50 years ago, and built in extremely limited numbers through the 60s and early 70s, it was unsurpassed in its ability to capture extremely fast, transient or one-shot events, as well as repetitive signals of up to 1GHz, in real time.
It is a machine unlike anything Tektronix had ever made, and due to the fact that it was the pet project of a senior engineer working free from the boundaries of the institution’s design team, it bared a only casual resemblance to the rest of their line-up.
Because the variac I have easy access to is only good for 5 amps or so (and gets a bit toasty at that), I decided to just go for it, and hit it with full mains voltage. Side note: I really need to get that 20A variac out of storage and wired up. Nothing.
Checked the fuse, and there was a blown 4 amp slo-blow. Based on the markings, a 4 amp fuse suggests that the unit was being used at 240v, otherwise it would have had a 7 amp fuse for 120v operation. I carefully rolled the unit over to remove the bottom panel and expose the transformer wiring. To my surprise, the transformer was wired for 120v operation. I’m just preying no one tried to power this thing up on 240v, but I suspect not. With the exception of a fine layer of dust, the interior is immaculate, and shows no signs of distressed components. I’m also pretty sure I heard a brief ‘chunk’ of the blower try to start over the heavy click of the switch, so it is possible that it was I who blew the incorrectly installed fuse.
I’m taking this as a sign that I should do a more thorough inspection before firing this thing up for the first time in god only knows how many years. With the chassis still rolled over (I would like to move this heavy, fragile, priceless relic as little as possible!), I went to work testing the supply caps who’s terminals are accessed on the underside of the chassis. These are the ‘low voltage’ supplies, covering about 10 different ranges between -250v through +650v. The high voltage supplies are -4,100v and +20,000v (!!).
Here’s my updated test & reforming rig. My heathkit IT-28 capacitor checker, my trusty old Fluke 83 for measuring voltage across the cap, and a Bell & Howell multimeter for measuring current. This is a kludge to say the least, but it’s what I had on hand. A programmable, high voltage power supply tailored for cap reforming sounds like an interesting next project. In the mean time, this will have to do.
Removing the screws in the GR-874 connector…
And loosening the clamps on the charge line…
…let me carefully pull the charge line out through the front panel.
Here’s the coil that wraps around the charge line and triggers the reed relay within it. It’s also worth noting that the bit of corrosion seen in the photo below represents the only bit of it I’ve found anywhere in here so far.
I started with C613, then moved on to C661,2,3, which is three 125uf caps in parallel. I left the cap fully in-circuit for some of my early tests.
Once I disconnect the + side of the cap, I connect the reforming circuit and start out at 50v and slowly work up to the rated voltage of the cap. As the voltage increases, it takes longer for the current to drop to an acceptable level. As far as what is considered acceptable leakage current, I’ve read a variety of opinions. This site has a handy chart, which suggests that anything under a few mA is acceptable for these beastly 125uf, 450v caps. I’ll move on to the next higher voltage when the leakage current drops below a mA, then hold at the rated voltage until the current levels off. So far, that’s been on the order of a few hundred uA, which is great for 45+ year old caps.
I was dorky enough to record a video. Here it is in all of it’s dark, shaky, glory. Pardon the occasional explicative, I was very excited.
I was able to get a free running trace, at all but one sweep speed. The trace was crisp, and I was able to move it as expected via the positioning controls. It is a shade of blue that I have never seen on a scope CRT before (P11 phosphor). The 24kV accelerating potential made for a staticy, zappy sound when the relay kicked in to power the ‘low’ and high voltage supplies.
I hooked up the rate generator to the input. While increasing the multiplier control, I heard a snap, and saw a white glow in V717, a 77http://paulcarbone.com/blog/wp-admin/post.php?post=409&action=edit34/6GE8 which is part of the +450V supply. This I believe is completely unrelated, but obviously worth investigating.
- Check V717 in my tube tester
- Check the output of the Rate Generator & Step generator with either my 7834, or my 661 (heheheee).
- See if I can get it to trigger on anything.
V717 is a 7734/6GE8, a combo triode + pentode. What claims to be the latest settings sheet for my Heathkit TT-1 tube tester does not have this tube. This is the second time that’s happened this month, and it’s starting to chap my ass. I have a few other testers that are in need of resurrection, but I thought that the TT-1 was the most comprehensive. I’ll have to double check next time I’m back up at ‘The House for Wayward Oscilloscopes’. grrr…. Lets just put it back in and check the 450v line. Perhaps this transient event I witnessed was not actually damaging to the tube.