My Tektronix 310 "Basket Case" Project - Page 1
Forum section: electronics / repair

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 12:38:06 am
content: I found a Tektronix 310 oscilloscope at a garage sale a few weeks ago. It's in really bad shape and was going to be thrown out.Even though I'm a beginner in the electronics hobby, I know we're going to bring this thing back to life!I'm starting with a good cleaning since it's full of cobwebs and over 60 years worth of dirt.The serial number stamped on the faceplate is 1499, and from what I can see, most of the tubes are dated 1956.Let the fun begin

author: xrunner
author_rank: Super Contributor
timestamp: September 07, 2019, 12:44:34 am
content: Cool deal Smokey, please keep the thread going so we can follow!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 01:38:36 am
content: Will do Xrunner!I didn't power-on the 310 because I could see bad tubes through the side panels. The tops of some of the tubes are white and two were cracked.While I was slowly in the process of removing the heavy layer of "mold" from all of the wires, and when I made it to the HV board area, I noticed the same "white" area on a "5642" rectifier tube!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 01:57:32 am
content: While I'm moving along the interior of the 310, I'm checking resistors as I go.Several of the resistors just on the HV board are out of tolerance. Most have silver bands (10%).Now that little black resistor, that's a 1.5 Meg Ohm 1% type, it still measures 1.495 Meg Ohms on my DMM after all of these years!What would be the best choice of replacement resistor for the bad Allen Bradley's that I find?

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 02:39:16 am
content: On Wednesday night, I started to snip all of the wire loom wrap to release the tightly-gripped wires.This allowed me to clean all of the crap easily from the sheathes and bring out all of the colors. I used a small bucket of hot water with dish-washing soap and a little bit of Clorox bleach along with small brushes. Now I can easily trace wires around the chassis.I removed the piano hinge from the back of the case which made access even better.I have 1/2 of the scope cleaned very well and you can see in the last picture where that transition is.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 03:26:31 am
content: I removed the cathode ray tube to gain more access too. It's a Dumont 3WP2.The heater pins are 1 and 12 and I do get continuity.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 07, 2019, 04:28:10 am
content: Quote from: Smoky on September 07, 2019, 01:57:32 amThey're just reasonable power carbon composite resistors, so virtually any comparable resistor will do the job. I'd probably go for thick film or metal oxide 5%s, maybe avoiding wire wound in case there are parasitic inductance issues... maybe look for the ones that best fit the look you want.Worth mentioning that it seems like a lot of the brown half watt or 1W Allen Bradley mil spec resistors drift up over time, so a huge number of even the old stock ones won't be their original value, so I'd probably avoid replacing them with direct replacements.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 07:13:39 am
content: Thank you DaJMasta.I pulled a couple of resistors to test from around the scope. Here's a 2 watt Allen Bradley 33K testing high.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 11:01:18 am
content: I was just sent the 310 schematics from 1955 through 1957Right-click the picture to enlarge them even more. I uploaded the schematics to Imgur.com to save space and to guarantee that they'll be around for a while. These photos are huge!Block DiagramCRTHeater & LV PowerCalibratorPreamplifier

author: bd139
author_rank: Super Contributor
timestamp: September 07, 2019, 11:17:02 am
content: Thanks for writing this up so far. Good to see someone taking care of such a nice instrumentAs for the carbon comp resistors, they always go high. Haven't found any vendor that isn't vulnerable to that...I usually replace carbon comp with the blue TE connectivity metal oxide resistors.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 11:33:48 am
content: ...and the rest of the schematicsAgain, just right-click the photo for an even larger view.Horizontal AmplifierVertical AmplifierSweep GeneratorSweep TriggerSweep Timing SwitchWhat is so nice is that the schematics also identify the wire color in the Low Voltage and CRT circuits!

author: duak
author_rank: Super Contributor
timestamp: September 07, 2019, 04:13:49 pm
content: If you replace the resistors with metal film types, make sure their voltage rating is not exceeded. eg., a 1M0 1/2 W RN65 would dissipate 1/2 W with 707 V across it, but it has a maximum voltage rating of 350 V. This is most likely with the parts in the EHT and around the CRT.Looks like it's cleaning up well. Interesting project - hope there's no show stoppers. I don't think there's anything too biodegradable (ie. self-destructing) like in some modern equipment.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2019, 05:47:41 pm
content: Thank you Duak!I found this chart that converts Allen Bradley resistors to Vishay resistors.It has the voltage information in each column so it's easy to see if that rating is equal or greater.I believe that the Allen Bradley EB (1/2w), GB (1w), and HB (2w) series resistors are in the Tektronix 310....and here are some new tubes I picked up this morning at $1.50 each:And the new 5642 rectifiers tubes under $2 each too.My plan is also to bypass the Selenium rectifiers with silicon rectifiers. I have these 1000VDC Silicon bridge rectifiers from a previous project and I plan to use them. I'll probably fabricate an aluminum heat shield/protective cap/cover for them too. Maybe even mount some of the old rectifier parts to keep the look original. Here is a picture of the Selenium rectifiers in the 310 and the new rectifiers:...and these new tubes have a radiation symbol on the tube and box!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 13, 2019, 11:35:21 pm
content: This weekend I'm going to spend a little time to put together a parts order for Digi-Key and Mouser.For example, here is C722, a 3Kv .0068uf film capacitor from the HV circuit board in the CRT circuit, being tested on the Sencore Z Meter...and a sample of some of the plastic tubular .01uf caps (C612, C613, C639, and C671). All from the LV power supply circuit and reading 5 times higher!...and here's what I'd call The Big Kahuna, C315. The 0.1uf cap on the UHF input jack of the preamplifier. 5.43uf!**Parts are starting to come in. The only resistors I had a hard time finding new on Digi-Key, Mouser, or Newark are R721 on the HV board, R722 on the Intensity pot, and R742 on the Focus pot. These are 2 Watt 5.6 Meg Ohms and a 3.9 Meg Ohm. I'd like to thank Kb4dmf on Ebay. He sent me NOS Ohmite and AB resistors better than 1% tolerance.The original P6017 probe is in really bad shape along with a severed cord. It connects to the oscilloscope through an Amphenol UHF input jack. I recently bought a new P6006 probe from a seller in Chapel Hill, NC for $10 but it has a BNC connector on the end of it. The original UHF input jack mounts to the back of the faceplate of the oscilloscope on two threaded studs. I searched Ebay and I found two new BNC input jacks with the correct mounting flange! It's a Tektronix part number but I'm told they're made by Bendix (131-0279-00)I also read that these 5726 tubes are the same as a 6AL5, so I bought two.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 19, 2019, 09:19:22 pm
content: I was able to accumulate enough parts to start rebuilding the 310. I started last night with the CRT circuit and its printed circuit board.All of the resistors are new Vishay PR01/02/03 and the Meg Ohm are MRS25, all of which meet or exceed the voltage ratings of the old Allen Bradley resistors. The only original resistor that tested excellent was R740 (1%, 1.5 Meg Ohm), which I left intact.The ceramic capacitors are C0G or NP0 and the film caps are metallized PP. The original .0068uf caps were not available in a 3Kv version so I went to a PP .0082uf Panasonic, which I'm told by the Tek Museum folks, is just fine.The reason why I soldered some of the leads of components over the grommets and onto the traces is because the brass grommets are known to lose contact since pressure is all that keeps them in place. I flowed solder to bridge connections that were close. I'm now moving on to the remaining portion of the CRT circuit within the chassis.And what turned out to be a lot of fun was shopping for vacuum tubesThey came from all over the place. All of the sellers were able to test the tubes and match their internal triodes and health. It was cool to find Tektronix "selected pairs" like in the 6BQ7A and 6AU6 types. Other tubes like the 6AN8 were a little harder to find and more expensive. Who knows how all of this comes out in the wash, but I just wanted to have a variety of tubes to experiment with.

author: george.b
author_rank: Frequent Contributor
timestamp: October 20, 2019, 06:59:46 pm
content: Quote from: Smoky on September 07, 2019, 05:47:41 pmhttps://www.orau.org/ptp/collection/consumer%20products/electrontubes.htm

author: SeanB
author_rank: Super Contributor
timestamp: October 20, 2019, 07:50:59 pm
content: When replacing the selenium rectifiers please add a series resistor to the one lead, so that the capacitors it is driving do not get too much inrush current and also have a lower ripple current. Around 33R 2W works for most small ones in valve equipment, though larger higher current ones need a lower resistor value.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 21, 2019, 03:27:14 am
content: Thank you Sean!Here is some good news. Soon after the 310 was on the market, the 310A followed. It is the same oscilloscope but it was built with Silicon rectifiers instead of the Selenium rectifiers.I was able to print the schematics to the 310A's rectifier circuits and it shows the added resistors and values in the legend. They list resistor R601 as a 10 Ohm 1 Watt. Not only that, the capacitance changed for C601. It went from one pair of 40uf caps in parallel in the 310 to three pairs of 15uf capacitors in parallel in the 310A.Here is a shot of the"310A's"Silicon rectifier circuit surrounding C601:

author: Smoky
author_rank: Frequent Contributor
timestamp: October 21, 2019, 03:32:06 am
content: Here is how I rebuilt C601 today.I first gutted the 2 x 40uf can.I purchased six Nichicon 18uf 450v capacitors for the new assembly.In the 310A schematics, C601 is listed as -20%/+100%, so I imagine, going from ~90uf to 100uf is just fine.Ok, I'm now on the Selenium rectifier/power transformer side of the chassis. I'm ready to tackle the removal of the Selenium rectifiers and following the color-coded wires and reading the schematics. Again, it is so nice to have the schematics noting the colors of the wires. It's making tracing the circuit so easy with all of the jumpers everywhere. I found a broken solder joint right on the back of the power socket, it happens to connect with the thermo-cutout switch of the scope!...I also carefully tagged all of the wires and then removed the old rectifiers

author: Smoky
author_rank: Frequent Contributor
timestamp: October 22, 2019, 09:03:00 pm
content: Next up, I went to work on fabricating a mount for the new Silicon bridge rectifiers.I trimmed a length of aluminum angle and carefully milled a "rabbet" on one edge. When the heat sink compound is applied to the backs of the rectifiers, this ledge will keep the assembly from spinning when they're bolted down.Here is the rectifier mount mocked-up in the chassis:I'm also going to make a small cover too that will screw to this mount and hide the wiring connections. I'll probably drill random holes in it too to add to the heat-sink-nessThe hole just above the mount that isn't being reused will be enlarged and a rubber grommet will be installed so that wires can run through.

author: james_s
author_rank: Super Contributor
timestamp: October 22, 2019, 09:47:25 pm
content: Nicely done, that all looks really clean, especially the capacitor.Nice to see an unloved instrument like this coming back together. I probably would have parted it out and scrapped the carcass, I like the outcome you are achieving much better.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 23, 2019, 04:06:23 am
content: Thank you James!Just moments ago I removed the next large can capacitor, C630 (150uf at 250v). This can has its case grounded to the chassis.It wouldn't test on the Sencore capacitor tester so I connected it to a Peak ESR+ meter:I have a brand new Nichicon UCY 180uf at 350V to stuff in it...it measures 160uf on the Sencore, a little more on the Peak:So I cut C630 open and installed the new Nichicon capacitor. This cap was easy, the Nichicon leads reached both the (+) and (-) terminals outside of the can through small drilled holes. I then found a plastic sleeve and glued it inside of the cover:I next put glue around the perimeter of the base and closed up the can. All that is visible is a fine hairline along the base:C660, the 40uf at 450v capacitor, got the same treatment too:

author: Smoky
author_rank: Frequent Contributor
timestamp: October 24, 2019, 03:25:49 am
content: Hey Guys, I'm comparing the early 310 schematics w/Selenium rectifiers to the later 310A which uses Silicon rectifiers.If you notice in the legend of the later 310A schematic that capacitor C661 (.02uf/1400v) was added just after the transformer and before the Silicon rectifier.I read that Silicon diodes can create RF/EMI interference by the way they "switch" in circuit. I'm guessing that C661 is being used as a low-pass filter.The .022uf CDE film capacitor I bought for this purpose is rated at 2KV DC/500VAC.I did notice that one of the ceramic terminal tie strips is cracked, but it seems to be fine and stable since there are so many wire "ties" in that area. None the less, I put a "want ad" out for a used one.*Update*Thanks to T3sl4co1l for sending me a mint-condition 9-notch ceramic stripAlso, I found two original Allen Bradley 2.2 MOhm 1/2 Watt resistors installed in place of, what should have been, a 2.7 MOhm (R506) and a 4.7 MOhm (R519) in the "Calibrator Multivibrator." I bet they didn't have them at the time, so they went with what they had in stock? Well, I installed the correct values as read from the schematics (these resistance values are listed the same in both the 310 and 310A schematics).The new resistors are starting to go in now too!All of the original black 1% precision resistors are still spot-on or maybe reaching just under 2%, so they were tested and left alone.I like jumping forward and checking components around the scope that I haven't touched yet. Get a load of this one, it's C321, a 275uf capacitor on the Preamplifier PC board

author: Smoky
author_rank: Frequent Contributor
timestamp: October 31, 2019, 03:19:05 am
content: I'm digging into the heart of the beastI removed the Vertical Preamplifier board today to get to the hard-to-reach parts. All of the old resistors and capacitors were replaced with new. The old parts are so out of whack!The only part yet to be replaced is the Selenium 100mA rectifier plate (SR321). I compared the Early 310 schematics with the newer 310A schematics. The Selenium rectifier plate was replaced by a Germanium diode (T12G, AKA 1N270) in the newer version 310A scope.I found two NOS Tektronix T12G diodes (part# 152-0008-00) on Ebay and here they areNow, within the 310 and 310A, there are only two resistors that were required to be a "matched" pair. They come off of the preamplifier board (R320 and R401). I put yellow dots on them.So I decided to pull and measure them. They are marked as 1%, 1 MOhm resistors. I tested each one on my Fluke 45 multimeter. Each resistor was given one minute to settle down. One of the resistors measured 1.0144 MOhm and the other 1.0015 MOhm.I purchased four of these Dale .1% CMF60 resistors and put them through the same test.Twoof these resistors settled at 1.0006 MOhm! They're going inHere are the new Silicon rectifiers along with isolated turrets to mount the new 10 Ohm 2 Watt resistors. New PTFE 20 AWG wire is being used to connect the rectifiers to the rebuilt can capacitors. In the background, I bought PTFE 22 AWG striped wire to replace the old wires in the transformer area. I also used the spacers from the old Selenium rectifiers to lift the new rectifier mount off of the chassis.With the hard-to-reach soldering done beforehand, I installed the rectifiers. I drilled out two of the four old rectifier mounting bolt holes and installed rubber grommets to pass the wires through. Next is to wire the transformer back up.Most of the low-voltage section is now back in place with new wires attached. I wanted to repeat what I said about the wires that attach to the back of the power plug socket. I found one with a broken solder joint. It's because the plug is made out of heavy brass bar stock. Tektronix used very little solder. I cleaned the brass on the bench and pre-tinned the brass with ~740 degrees at the solder iron tip. The new joints will be rock-solid for another 50 yearsAfter the large resistors were re-wired, the rebuilt capacitors were installed. The new Low-pass film capacitor (C661) was also installed just above the topmost rectifier too.I'm over to the other half of the oscilloscope now, and working around C250 was no joke. Two soldering irons would've been needed to lift it from the ceramic strip without breaking it, so instead, I carefully removed the old Allen Bradley resistors from below and installed the new resistors the same way.When I got to V150, a 6AL5 tube, I noticed pin 7 wasn't soldered to a lead tying both pins 2 & 7 (the plates of the tube) to capacitor C115. Maybe it had an intermittent problem? I don't know, but it's soldered-in now. C115 is a 5% 180 pf Mica cap, so I measured it. It came out to 200pf, a little high, so I purchased a new 1% Mica. One of the NE-2 neons nearby had rotted a leg off, so I replaced both neons with new ones. David Hess suggests using neons that have a little bit of radioactivity so that they have a consistent strike voltage whether in the darkness or the light in these circuits, so I did.Here's the before and the after of this "quite-busy" Sweep Generator section of the scope...and here's the rebuilt Vertical Amplifier portion. All pairs of resistors on the schematics are matched (under .2%). I really like these new Vishay resistors. Their smaller size fits these tight spaces much better than the AB's.I rebuilt my Sencore Z-Meter last year. This is the most accurate capacitor it has tested so far! A Tektronix can (.01uf/.1uf/1.0uf)!Now on to the cleaning, rebuilding, and lubricating of the switches. Can you see the split in that large tube capacitor...and now the Time Base "trigger" switch is rebuilt and installed into the sea of new red resistors. I flushed and cleaned all switches with Deoxit F5 too. The contacts shine and the movements are smoooooth. The Time/Division switch is next with only just a few caps and resistors left to test/replace. I see the light

author: Smoky
author_rank: Frequent Contributor
timestamp: November 17, 2019, 12:13:21 am
content: Things are going well with the oscilloscope rebuild. I just finished the install of the replacement input jack. I went with a new BNC jack versus the original UHF one. I even use dark red paint from Testors to dab over the reinstalled nuts. The Preamplifier board goes in nextI also went back to the Preamplifier board to install the Germanium diode that is replacing the original Selenium rectifier plate. I bent the leads so that it would be stable once soldered to the copper traces. The anode points to the positive side of capacitor C321, as shown in the schematics.

author: bd139
author_rank: Super Contributor
timestamp: November 17, 2019, 12:20:36 am
content: Looking good. Nice neat work. I am happy to see this scope is in excellent hands

author: Smoky
author_rank: Frequent Contributor
timestamp: November 17, 2019, 12:56:26 am
content: Thank you BD139!Here's the Time/Division switch after it was thoroughly cleaned, and btw, how that big .22uf capacitor (C135D) split in service, is beyond me. The casing appears to be rock-hard epoxy.The small 5% Wima capacitor was what I could find in my stash to replace the smaller 2200pf cap (C135B), none the less, all of the resistors and capacitors for this switch measure less than 1% tolerance. Heck, 99% of all of the parts I put in this scope are less than 1%.I just checked Digi-Key, and they have a long-lead 2200pf PP cap that I may throw into this week's order.Anyway, I'm just having fun!Whoah! scratch that. I was concerned about the short leads on that Wima cap. It pays to take pictures before you disassemble. Here's a shot of the old capacitors in place. Notice how a ground wire was sent down to the first wafer to ground both that small 47pf cap and the large .22uf cap laying flat.It just so happens that the tab for 2200pf cap is next. The short leads on the Wima cap were more than long enough to stretch to both terminals. The two small capacitors don't touch either!...and now good as new and ready to go back homeHere's a shot of the DC Balance and Low Frequency adjustment area.With the Preamplifier board bolted back in place, the soldering of the connections begin. Look at this route in and out of the board of these resistors and capacitors! Many pictures and tags get it back together rightThere are only two resistors inside of this oscilloscope that are required to be a matched pair, R320 and R401 (1 MOhm 1% type). The original resistors measured 1.0144 and 1.0015 MOhm. Here are the new Dale .1% resistors installed. Theybothmeasure 1.0006 MOhmThe wire connections to the preamplifier board are next and the shields follow. Also, I believe the original wire wrapping had shrunk over time. It appears to have been some sort of plastic cord. The wrapping I'm doing isn't choking-tightThe shields are back in and so is the calibrator, but get this, C102 is the big capacitor in the middle. The old capacitor was an 8uf axial that was strapped-in and grounded over to one of the pots. I was able to just fold back up one of the ground loops around V102 since the new cap is a radial type. I put a small ball of Butyl under it to keep it lifted. I used a 10uf 450V Nichicon UPW cap because it measured 9uf on the Sencore. Capacitor C102 is listed as a -20%/+50% 8uf 450V in the parts legend. And on a side note, the Deoxit F5 and D5 sprays really worked wonders on all of the switches and the Allen Bradley pots, even the sealed ones. Super-smooth!All in all, over 240 resistors and capacitors were replacedThe rear portion of the CRT is also complete. I was able to relocate C407 to the upper rear corner and eliminate a wire runner because the new 6.8uf Nichicon UCA cap is a radial.The Time/Division switch is also back in place. You can also see the two NOS Allen Bradley 2 Watt resistors on the Intensity and Focus pots. They are two of the only three new Allen Bradley/Ohmite resistors in this machine. They are not 1%, they are nearly spot on. I can only say this, having followed every trace on the schematics and every solder joint in this scope, I'm in awe of the incredible people of Tektronix of that era that built this thing. I hope I've installed everything correctly so farWell, she's back in one piece!I installed the HV board and completed the wiring to the capacitors. I then bundled the remaining wires and closed the case. It will be this afternoon that the tubes will be installed and the oscilloscope powered-up on the Variac

author: dave_k
author_rank: Frequent Contributor
timestamp: November 17, 2019, 01:30:43 am
content: Great work Smoky! Nice to see such a neat restoration with nice attention to detail. Can't wait to see the final result.

author: bd139
author_rank: Super Contributor
timestamp: November 17, 2019, 10:34:43 am
content: The big tube caps are sprague bumble bee capacitors and are somewhat notorious for pulling that sort of thing. They are paper in oil capacitors so I suspect the electrolyte breaks down the epoxy or moisture gets in and then they expand and crack. Also 1950s epoxy wasn’t that good.If any are still good, sell them on eBay to the guitar lot!

author: Smoky
author_rank: Frequent Contributor
timestamp: November 23, 2019, 06:05:22 pm
content: Whoo-Hoo

author: xrunner
author_rank: Super Contributor
timestamp: November 23, 2019, 06:13:58 pm
content: Outstanding!

author: Smoky
author_rank: Frequent Contributor
timestamp: November 23, 2019, 06:26:33 pm
content: Thank you Xrunner!...she's just sitting here idling while I'm having lunchI'm sure plenty of tuning is in order, and she'll get it!

author: james_s
author_rank: Super Contributor
timestamp: November 23, 2019, 07:55:31 pm
content: Wow, that looks fantastic, practically brand new. Such a cute little Tek scope too.

author: andy3055
author_rank: Super Contributor
timestamp: November 23, 2019, 08:30:24 pm
content: Great job! Congratulations on your achievement!

author: Smoky
author_rank: Frequent Contributor
timestamp: November 23, 2019, 08:39:12 pm
content: Many thanks to you all!I'm measuring voltages right now. The -150 is spot-on, I didn't need to touch the pot.I adjusted the Calibrator pot down from +101.9VDC to +100 volts at pin 7 of V520 as per the manual.I then set the Calibrator to 2VPP and the Time/Div switch to .5 volts. I don't plan to mess with things too muchI just aligned the CRT to the graticule and I'm in the process of feeding it some waveforms right now!...and with the "green" shade over the graticule:

author: james_s
author_rank: Super Contributor
timestamp: November 23, 2019, 11:28:24 pm
content: What's next then? Ready to take on a Tek 555 or 556?

author: Smoky
author_rank: Frequent Contributor
timestamp: November 23, 2019, 11:54:25 pm
content: I need to finish a Leader LBO-302 oscilloscope I started last Fall, and then it is on to a Kenwood TK-55 stereo receiver from 1968, followed by a McIntosh 2205 power amp, MR74 tuner, and a C33 preamplifier

author: moffy
author_rank: Super Contributor
timestamp: November 24, 2019, 01:53:40 am
content: Utterly amazing! Beautiful.

author: ferdieCX
author_rank: Regular Contributor
timestamp: November 24, 2019, 02:04:04 am
content: Beautiful job, congratulations !

author: andy3055
author_rank: Super Contributor
timestamp: November 24, 2019, 03:10:53 am
content: Those traces are so sharp, amazing! Great job.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 24, 2019, 10:50:29 am
content: *Important*If you ever decide to rebuild one of these Tektronix 310 or 310A oscilloscopes, you will want to be aware of this.When I was checking voltages in the scope during the time it was being fed 117VAC on the Variac, the unregulated +450 rail hovered around +446VDC:But when I checked voltages again while the scope was plugged directly into the outlet in my house (~121VAC), the unregulated +450 rail increased to+474VDC:Capacitor C660 is a can cap rated at 450VDC in the parts legend:So if you rebuild one of scopes, you will want to increase the voltage rating of C660 to 500VDC or more.Anyhoo, the scope is running extremely well, and the next step, is to restore the outer metal case and handle.Stay tuned

author: james_s
author_rank: Super Contributor
timestamp: November 24, 2019, 06:13:20 pm
content: Quote from: Smoky on November 24, 2019, 10:50:29 amDid you mean 121VAC?You should post the progress when you start on that vintage audio gear, that looks like some nice stuff. That era was the golden age of HiFi and produced some really nicely made equipment.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 24, 2019, 07:41:23 pm
content: Thanks for catching that James. I made the edit to my original post to correct that. The voltage at the outlets in my house are ~121VAC.Ok, I was thinking about how I'm going to deal with capacitor C660 (40uf). It needs to handle at least 500VDC, but to me, that's not enough headroom to my liking. I did some searching on Digi-Key and there aren't many, if any, 40uf caps or pairs of 22uf caps that go much above the 500VDC threshold.So here's my plan. I dug through my bins again. I found two separate previous orders for Nichicon UCY 47uf 350V capacitors. They're stubby, and I think they'll fit into the cardboard sleeve of the original can.I intend to put two in series to double the voltage and halve the capacitance, then, solder those to pairs in parallel to double the capacitance and keep the voltage the same, ~700. Does this sound correct?

author: james_s
author_rank: Super Contributor
timestamp: November 24, 2019, 07:45:24 pm
content: You have to be careful putting capacitors in series, you can end up with a situation where the voltage is not equally spread between them. You might check Antique Electronic Supply, they sell parts for vacuum tube equipment and may have some higher voltage capacitors. Personally I think 500V is probably adequate though, a little more headroom is nice, but I'd pick a single 500V capacitor over a series pair of 350V capacitors.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 24, 2019, 08:45:30 pm
content: Thank you James, I will find the appropriate capacitor to fit the old capacitor can and circuit.And here it is, an Epcos/TDK 47uf 600v part number B43541B8476M000.And after a minute of being burned-in at 500v, it settled just under 40ufThe new C660 capacitor is installed and the scope is back up to speed with plenty of voltage headroom to spare...and while the new capacitor was warming up under Variac power, I checked about and around the scope and noticed that one of the tubes wasn't glowing. V130, a Raytheon 12AT7 in the Sweep Generator circuit. So I pulled it.Sure enough! I spotted a hair-line crack across pins 1 and 2:Notice how the getter film was depleted due to the lack of vacuum. A new Tung-Sol tube was put in and I'm back in business

author: andy3055
author_rank: Super Contributor
timestamp: November 24, 2019, 09:33:13 pm
content: I was looking at your profile name and thought you had smoke somewhere down the line. But looking at your work, that name does not make justice for you. May be Rejuvenator is a better fit?

author: Smoky
author_rank: Frequent Contributor
timestamp: November 28, 2019, 02:00:14 am
content: With the scope running for about an hour now, I have it and the Siglent SDG-1032X ready for testing. The Tektronix Type 310 cathode-ray oscilloscope is spec'd as having a frequency range from DC to 5Mhz. There are no IC's or transistors in this machine....let's see what she canreallydo!I slowly creeped-up the dial on the waveform generator starting at 1Mhz...I stopped increasing the frequency once the "trigger" controls on the 310 became too touchy...13Mhz!!!...and I forgot to mention, I get a kick out of those built-in waveforms on that SiglentHappy Thanksgiving!

author: andy3055
author_rank: Super Contributor
timestamp: November 28, 2019, 02:11:16 am
content: Very nice, indeed. Happy thanksgiving!

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2019, 06:24:00 am
content: Quote from: andy3055 on November 24, 2019, 09:33:13 pmIt always makes me think of the character Smoky in Big Lebowski, no idea if there's any relation.Regarding the bandwidth, The 5MHz spec is normally the -3dB point, ie the amplitude shown on the scope will be 50% of the true amplitude of the signal. Most scopes will trigger and display waveforms of significantly higher frequency.

author: george.b
author_rank: Frequent Contributor
timestamp: November 28, 2019, 07:37:14 am
content: Quote from: james_s on November 28, 2019, 06:24:00 am50% of the power, yeah? Amplitude divided by √2.

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2019, 08:22:18 am
content: Quote from: george.b on November 28, 2019, 07:37:14 amWhoops, yes you're correct, sorry looks like I got some wires crossed in my head when I wrote that.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 28, 2019, 05:41:09 pm
content: When I measure ripple voltage, I place a large .47uf filter capacitor in-line with the test point to stop all DC voltage from passing through. I set my multimeter to AC and the Millivolt settings.In the service manual, no more than 40mV of ripple is acceptable between the 105-125 range of line voltages. I'm plugged into the house so ~121AC.I'm probing at the positive side of C102 (+300 rail) and I measure 4.7mV RMS. I then went online to convert that value to mV PPK with the result being 13.3mV PPK.Here is that same test point (C102) through my TDS420 oscilloscope with the "zoom" feature on:What I find to be amazing too is, when you look at the waveform, you see that 10-11volt fluctuation, yet when you take your DMM and measure DC volts, they're rock-steady and near spot-on to the schematics. All of that rectifier ripple and noise makes it appear worse than it really is.

author: Colt45
author_rank: Contributor
timestamp: November 29, 2019, 02:53:43 am
content: I don't really think the 11V is accurate. Why not try ac coupling and less attenuation?I'd expect 120hz hum or something, not whatever that is

author: tautech
author_rank: Super Contributor
timestamp: November 29, 2019, 08:37:09 pm
content: Quote from: Colt45 on November 29, 2019, 02:53:43 amYep, this ^Been following Smokey's fun and it's been a good read.Now he just needs to shift this topic into the Repair board using the Move Topic feature that's at the LH foot of the page.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 29, 2019, 09:53:13 pm
content: Thank you Tautech! I didn't know that could be done.I brought out my Tektronix 465B. I use it only occasionally because it doesn't have on-screen measurements.Here it is set at 50V/Div with the probe grounded.And here it is attached to C102 (+300V rail).

author: tautech
author_rank: Super Contributor
timestamp: November 30, 2019, 01:16:13 am
content: Quote from: Smoky on November 29, 2019, 09:53:13 pmYeah well you didn't quite understand what he was pointing out as it's the reason I thanked him.Set the probes input to AC coupled to remove the DC component and V/div to under 1V/div is you want to measure ripple on DC rails. Timebase need be at say 10ms/div or a teeny bit faster to see 120 Hz ripple (2x your mains frequency). Use a DC coupled trigger.Measurements ?Nah, just read them off the graticules.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 30, 2019, 02:21:24 am
content: Thank you Tautech and Colt45!As you can see, I need all of the help I can getI'm not sure how well calibrated my 465B and probes are though.

author: james_s
author_rank: Super Contributor
timestamp: November 30, 2019, 04:38:09 am
content: I doubt my 465B has been calibrated since Reagan was in office, still seems to be pretty darn accurate. Calibration is only really needed when you need traceable measurements that can be certified to a specific accuracy, most decent equipment doesn't really drift much. I don't use mine much anymore either though, I've become spoiled by all the fancy stuff a DSO can do. No digital scope I've tried touches the XY mode of an analog instrument like the 465 though.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 30, 2019, 05:01:23 am
content: Thank you guys for helping me understand all of this stuff!Here again, the test point is capacitor C102 (the +300 rail).On the 465B, the Volts/Div is set to .1 and the Time/Div is 5ms:

author: james_s
author_rank: Super Contributor
timestamp: November 30, 2019, 05:06:09 am
content: That trace looks extremely fat, does it slim down if you enable the BW limit? I guess it could also just be the photo.Looks like 50mV of ripple at most, I'd consider that to be negligible on a 300V rail. Remind me what the spec says?

author: Smoky
author_rank: Frequent Contributor
timestamp: November 30, 2019, 05:23:00 am
content: James, the BW Limit is activated.Tektronix notes a maximum of 40mV tops for ripple on the 300v rail. They show a sketch reflecting ~15mV for the +300V supply.

author: Smoky
author_rank: Frequent Contributor
timestamp: December 01, 2019, 01:23:57 am
content: So I kept the settings the same on the 465B as used above and I move over to the test point next to C240 (the -150V rail)......Holy bolts of lightning Batman!

author: james_s
author_rank: Super Contributor
timestamp: December 01, 2019, 01:37:50 am
content: That looks like high frequency oscillation, you said moving the probe wire around affects things? That doesn't sound right, are you by chance near any radio broadcast antennas? Can you crank up the sweep fast enough to measure the frequency? I suppose it's possible that something in the scope is oscillating.IIRC the readout pin on the Tek scope probes only controls the lights behind the V/div knob scales, so not having the readout pin doesn't actually affect anything, you just have to pretend the other light is lit when reading the setting on the dial. Fancier scopes that have a readout on the display use that pin to scale the number displayed on that but you can mentally account for it. I was using some cheap aftermarket probes on my TDS340 and I'd just mentally multiply the displayed value by 10. A pain in the butt but not a show stopper.

author: Smoky
author_rank: Frequent Contributor
timestamp: December 01, 2019, 03:04:27 am
content: So I'm looking back onto the screen of the 465B. The probe is on C240 (the -150V rail) and we're at 5mV/Div and 5ms/Div:I think to myself, let's start turning some knobs on the front of the 310 to see if it has any effect on what I see. So I start with the Focus knob, next the Stability, nothing, nothing, nothing, until I reach the Calibrator switch. As soon as I turn it one click (to .05V), this pops onto the screen:

author: james_s
author_rank: Super Contributor
timestamp: December 01, 2019, 04:04:10 am
content: I'm slightly confused as to what's going on here. Does the calibrator in the 310 run all the time? Maybe that's causing noise on the power supply rails that also feed it? Moving the wire on the probe should not affect anything, I think you need at least one known good probe to work with. If you want something cheap, I have a set of thesehttps://www.amazon.com/Signstek-P6100-Oscilloscope-Probe-Siglent/dp/B00ENF272Cwith my backup scope and they're remarkable for the price. I mean they're certainly not spectacular but they perform reasonably well and they're dirt cheap. If you want something with the Tek readout pin you can find those for around $40 but I have not personally tested one.

author: Smoky
author_rank: Frequent Contributor
timestamp: December 01, 2019, 04:04:58 pm
content: Honestly, I'm not really sure what's happening. I was just checking to see if the ripple was within reason, and it seems to be since she's running really well.I'm going down the list in the calibration procedure too and I'm trying to figure out a way to turn my Siglent SDG-1032X in to a marker generator sort of thing:I'm trying the "pulse" function and typing in the frequency to match the micro and milliseconds on the Time/Div switch on the scope.

author: james_s
author_rank: Super Contributor
timestamp: December 01, 2019, 05:08:18 pm
content: This might be one of those times to quit while you're ahead and leave well enough alone. Maybe make some notes to investigate some rainy day when you get inspired to poke at it again. I mean the scope seems to be working beautifully so unless you find a functional fault I'm inclined to suspect your other scope is just picking up noise from somewhere.

author: tautech
author_rank: Super Contributor
timestamp: December 01, 2019, 06:28:11 pm
content: Quote from: Smoky on December 01, 2019, 04:04:58 pmYep, it will do it but don't rush into adjusting anything until you have your head firmly around what the Cal procedures mean and the markers required.If you want to be really anal connect it to a 10 MHz reference for better accuracy however I doubt that's really needed for this old Tek.

author: james_s
author_rank: Super Contributor
timestamp: December 01, 2019, 06:38:42 pm
content: It's only gonna be as accurate as your eyeballs on the graticule anyway. Don't go too nuts trying to strive for ultimate accuracy.

author: Smoky
author_rank: Frequent Contributor
timestamp: December 01, 2019, 06:40:51 pm
content: Thanks guys! I used a ramp waveform (for its fine-tip points) just to touch up the alignment to the graticule. For example, here's 10kHz at 100us/Div. I made the ramp as tall and as sharp as possible, but I made it so that it can be lowered to the center horizontal line of the graticule using the Vertical Position knob. I have only turned the "Sweep Cal" pot. The "Sweep Cal" narrows or widens the band of points to line up with the vertical graticule lines.I made no other adjustments....I'm working on matching the hammer-tone paint and repairing the handle. I'll post some pictures soon

author: tautech
author_rank: Super Contributor
timestamp: December 02, 2019, 02:51:42 am
content: Quote from: Smoky on December 01, 2019, 06:40:51 pmMember med6753 over in the TEA thread uses this spray paint for all his Tek touch ups.https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg2427477/#msg2427477Gloss Bahama Sea by Krylon

author: AF6LJ
author_rank: Unknown
timestamp: December 02, 2019, 07:34:58 pm
content: Glad I stopped by, nice rehab on that scope, looks great.

author: Smoky
author_rank: Frequent Contributor
timestamp: December 03, 2019, 12:12:07 am
content: The early 310's had side covers with bends in it similar to old metal ducts to stop any "tin-canning." I could see the bends in my covers but they were flattened over the years and pushed in. I brought the bends back by using my finger brake following the original lines and not going beyond the corners:I gave the side covers a wash then opened up the bottle of rubbing compound to see what it could do. It removed all of the years of grunge. The paint had a baked-on yellow-greasy film that made the overall appearance look awful. It now shines. Don't get me wrong, there are chips and rubs in the aluminum here and there, but nothing that a small bottle of touch-up paint won't fix. Plus, the patina looks really good: