Old school Tek porn - Page 1
Forum section: electronics / projects

author: GK
author_rank: Super Contributor
timestamp: July 19, 2012, 09:30:28 am
content: Had a couple of days off work with a cold and decided to use the time to get my three big Tek's up and running. From left to right they are model 575 transistor curve tracer, model 545B dual timebase oscilloscope and model 551 dual beam oscilloscope with seperate power supply unit.The 575 and 545B had a few minor faults that were easilly rectified. I performed a full calibration on each and they are now entirely fault free and calibrated to factory specification. I've fixed a CRT circuit issue with the 551 (HV rectifier tube with broken heater wire, replaced with solid sate), but now have a DC balance fault to track down in one of the distributed vertical amplifiers (which is causing the beam for this channel to remain deflected off screen).I was expecting to have to compile a shopping list of HV electrolytic capacitors to buy, but amazingly all of the original units seem to be perfectly OK. The calibration section of the service manuals for these machines actually specifies the p-p ripple amplitude for the electronically regulated rail voltages, and they all measure within specification.

author: digsys
author_rank: Unknown
timestamp: July 19, 2012, 01:20:27 pm
content: You've kept these in damn nice condition. A place I'm working at has a lot of test equipment from that era, they were(may still maybe) going to set up a reference / test lab one day. Are you collecting vintage test gear? We're inBayswater Melbourne, what city you in? Maybe we can do some deals :-)

author: olsenn
author_rank: Frequent Contributor
timestamp: July 19, 2012, 01:26:11 pm
content: Nice curves

author: w2aew
author_rank: Super Contributor
timestamp: July 19, 2012, 07:51:57 pm
content: +100!!Absolutely beautiful!

author: tekfan
author_rank: Frequent Contributor
timestamp: July 19, 2012, 08:02:09 pm
content: Wow, just wow. Those are really in pristine condition.Does the 551 have P11 phosphor and is that a Tek 310 in the corner?

author: anotherlin
author_rank: Frequent Contributor
timestamp: July 19, 2012, 09:27:17 pm
content: There's a huge amounts of tubes inside, how many of them ?

author: Short Circuit
author_rank: Frequent Contributor
timestamp: July 19, 2012, 10:30:23 pm
content: Oldies p0rn... pervert

author: jh15
author_rank: Frequent Contributor
timestamp: July 20, 2012, 01:57:34 am
content: I have a 575 in great shape, I was hoping some day to use it on vacuum tubes...Also have a 535a and a Hickok clone of a tek 545. The hickok is about to be parted out.

author: MickM
author_rank: Regular Contributor
timestamp: July 20, 2012, 02:25:25 am
content: Hi;Nice - they look very clean.I used to have a 535.I believe it had some matched Tektronix vacuum tubes in it.That is, they were made or specially selected by Tek.They had the Tek logo on them.Now here (Seattle), you cannot find ANY vacuum tubes.Stores used to have testers in them - all gone.You can get them for Marshall Amps from music stores, but HF matched sets?Hamfests have some tubes, but that is about it.Not to mention the lights dimming when you power that sucker up.Plus it took maybe half an hour to settle down.Still cool to look at though.Mick M

author: GK
author_rank: Super Contributor
timestamp: July 20, 2012, 08:24:11 am
content: Quote from: digsys on July 19, 2012, 01:20:27 pmHey, I'm in Adelaide, but always interested in old Tek stuff and spare parts. If there is anything interesting, just send me a photo or two.

author: GK
author_rank: Super Contributor
timestamp: July 20, 2012, 08:27:07 am
content: The little scope on the shelf is a 422. Dunno what the 551 phosphor is, I'd have to look it up. The 551 has a lot of tubes. Dunno how many, have not counted.

author: saturation
author_rank: Super Contributor
timestamp: July 20, 2012, 02:59:53 pm
content: Very nice! and great photos. Where were you able to get replacement tubes? or gasp, are theyoriginal?

author: digsys
author_rank: Unknown
timestamp: July 20, 2012, 03:03:13 pm
content: Quote from: GK on July 20, 2012, 08:24:11 amWe're in the process of moving 2 factories full of old stuff to 2 new factories (100M away), then I'm going through ALL theboxes to sort out what lives and what dies :-) I'll take photos then.

author: SeanB
author_rank: Super Contributor
timestamp: July 20, 2012, 03:17:23 pm
content: Would love to find a curve tracer........

author: GK
author_rank: Super Contributor
timestamp: July 22, 2012, 11:07:57 am
content: Quote from: saturation on July 20, 2012, 02:59:53 pmI'm pretty sure all of the tubes are original. I haven't found any evidence of previous tampering or servicing in any of the three machines either. Each of these machines still has the original (and untouched) spool of silver-containing solder inside, that Tek provided for servicing purposes. I've got quite a few spare tubes, but they are still not hard to find NOS if you need them. In fact a number are still in current production and can be bought new from various on line audio parts vendors (eg 6DJ8, 12AT7, 12AU7). But anyway, there isn't much reason why most if not all of the current tubes shouldn't last my life time.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 06, 2012, 07:06:18 pm
content: Nice! I still use my 545B almost every day. IMO, it's the pinnacle of analog scope design at that bandwidth. Also use my 575 opt122 curve tracer quite often.

author: wkb
author_rank: Super Contributor
timestamp: August 07, 2012, 08:50:49 am
content: Beautiful kit!

author: GK
author_rank: Super Contributor
timestamp: August 14, 2012, 06:48:04 am
content: Unfortunately I'm a bit too preoccupied with other things to power mine up almost everyday, but I’ve got these repaired, calibrated and set up on my bench and endeavour to use them as often as practical. Despite the limited performance (a bit more than -3dB at 30MHz) they’re perfectly adequate for the shortwave and HF radio stuff I mostly play with. The clarity of modulated carrier / envelope waveforms on the large, bright CRT is second to none, particularly for the 545B.

author: GK
author_rank: Super Contributor
timestamp: February 18, 2013, 10:28:53 am
content: Here is another little Tek toy, that I picked up recently on Ebay - a Type 280 Trigger Countdown unit. Probably not quite as exciting as one of the glowing-tube-packed mainframe oscilloscopes, but cute nonetheless.The name of the unit is actually a little misleading. It doesn't do anything as sophisticated as counting. What it basically is, is a nominally free-running pulse generator that can be synchronized, if desired, with a much higher frequency signal source. The operating frequency range is from 15MHz to 50MHz, adjustable with a pair of pots on the front panel ("coarse" frequency and "fine"). The external synchronization signal can be up to 5GHz!The intended function of the unit is to provide timebase triggering pulses when using a plug-in GHz-bandwidth vertical-channel sampling amplifier in a low frequency mainframe. GHz frequency signals are beyond the capabilities of the triggering circuits of these oscilloscopes. The idea is you feed the GHz-frequency signal under examination into both the vertical-channel sampling amplifier and the Type 280 "sync" input, via a t-piece adapter. The synchronized, low frequency pulse train from the 280 is fed to the external triggering input of the oscilloscope.The Type 280 will reliably sync so long as the free running frequency is patiently adjusted to be close to an exact sub multiple of the GHz signal under examination. However it's handy just as a variable high frequency pulse generator on its own.The case disassembles into two halves. One half contains the power supply while the other half contains the simple oscillator circuit. Everything is extensively shielded, including the mains power input. The variable oscillator is a negative resistance type based on tunnel diode D12.The unit didn't work when I first applied power, but the problem was quickly tracked down to an issue I have not yet encountered in any other piece of Tektronix gear of this era - completely buggered electrolytic capacitors. Both halves of the power supplies main filter cap, C612 were pretty much completely dried out. The actual waveform on each end of R612 was a full-wave rectified sine without any smoothing whatsoever! Capacitor C613 was also faulty, but leaky instead, pulling the base of Q614 down to only 2V.To temporarily get the unit running I just soldered a new 470uF in parallel with C612A and disconnected one end of C613 from circuit. Other than those issues, everything seems to be quite fine.

author: SeanB
author_rank: Super Contributor
timestamp: February 18, 2013, 04:26:49 pm
content: Only unobtanium part there is that diode on the input circuit.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 18, 2013, 06:21:03 pm
content: GK, thanks for the pictures and the explanation. I absolutely love chassis mounted systems like these (that is why I have been in love with vacuum tube equipment since I started electronics in the 80's).

author: GK
author_rank: Super Contributor
timestamp: February 19, 2013, 11:36:14 am
content: You're welcome. Here are some more pics. With a bit of tag strip I managed a neat enough fix for the faulty capacitor replacement. Interesting wire mesh RF shielding on the input/output sockets. The 2nd and 3rd pictures show the free-running trigger pulse outputs while the 4th picture shows the unit successfully synced to a ~100MHz input signal, the unit oscillating at 1/6 the frequency.

author: GK
author_rank: Super Contributor
timestamp: April 09, 2013, 01:43:10 pm
content: Just finished a preliminary clean up and test/fault find on another Tek toy, recently acquired - a "Type 1121 Amplifier". It's basically just a fixed gain (x100), general purpose ac-coupled preamplifier with a bandwidth of 5Hz to 17MHz. The input impedance is 1M to suit standard CRO probes and the signal is fed through a turret attenuator before being amplified by 100. With the input shorted to ground and the attenuator set to the straight through (x1 position) the output noise is approximately 4mV rms, which works out to an input-referred noise of less than 10nV square-root-Hz, which isn't too bad.It didn't work at first due to some dodgy wires. The components for the preamplifier are all mounted on the upper shelf (tubes upside down), which is rubber shock mounted to minimize microphony. The bottom shelf contains the power supply components and the electronic voltage regulators. There are four regulated rail voltages provided for the preamplifier, of -150V, 150V, 130V and 225V.The rail voltages are brought up to a ceramic terminal strip mounted directly above the front panel mounted turret input attenuator. Short lengths of looped hookup wire link this terminal strip to the shock-mounted preamplifier chassis. All but one of these wires had fatigued and snapped due to movement of the preamplifier chassis. One flying wire to the front panel-mounted potentiometer for calibrating the gain had also snapped due to fatigue, as had an earth braid from the preamplifier chassis to the turret attenuator body. Clearly not a very robust design, wiring wise! But anyway, once all of those wires were reconnected to where they were supposed to go, the unit seemed to work quite fine.Here are the pics:

author: BiOzZ
author_rank: Regular Contributor
timestamp: April 09, 2013, 03:45:38 pm
content: damnit man ... i liked these pants

author: GK
author_rank: Super Contributor
timestamp: November 16, 2013, 09:19:56 am
content: Picked up another toy today. Spent the late afternoon cleaning it up and started fault finding. It's a "Tektronix 502 Dual Beam Oscilloscope", originally introduced in 1958. Its one of Tek's low-end models from the time and doesn't accept plug-in vertical amplifier(s). It's a little smaller than the plug-in 500 series mainframes, but similarly still has a 5" diameter CRT.The (identical) vertical amplifiers have differential inputs and 200uV per division/cm sensitivity, though bandwidth is dependent on the sensitivity setting and is quite low at 200uV - 100kHz.The thing initial reeked or cigarette smoke and the build up of (conductive) cigarette tar in some unusual places has been causing problems. I initially could not get anything up on the CRT. The first thing to sort out was the low voltage regulated supplies. There are three LV regulated rails; -150V, 100V and 350V. The -150V rail is adjustable and is the reference to which the other rails are regulated. As a consequence if the -150V rail is out of order, so are all of the others. The -150 rail was well out of whack, with about 80% mains ripple and an average output of ~-175V. The electrolytic filter capacitors were dried out. I made a temporary fix by soldering a new electrolytic capacitor across the tag terminals of the chassis mounted filter capacitor for the -150V regulator and the -150V rail then came up good. The other rails came up within specification, voltage wise, but still with excessive ripple, though still passable for preliminary testing. The 3 regulated rails are derived from their own transformer secondary windings and filter capacitors.The next step was to get something up on the CRT, which at that point was still blank. I started by checking the static deflection plate voltages to rule out the beams being deflected off screen by either a pair of defective vertical amplifiers or a defective horizontal amplifier. They all came up fine and they sit at approx 230V nominal/mean. I then adjusted the vertical and horizontal position controls for 0V between each respective pair of deflection plates (thus ensuring that the beams are centered on screen). However the CRT was still blank. I then checked out the -2900V regulated rail for the CRT cathodes and that came up OK, but the fault was eventually tracked down the the grid supply. The 2M intensity potentiometer measured ~300 ohms and as a consequence grid bias to the CRT remained in a state of beam cut-off. Upon opening the pot I found it to be full of stinky yellow cigarette tar, but otherwise look quite OK. Giving it a good clean out with electrical cleaning solvent restored it to 2M and I then got some nice and bright traces on the CRT, though the focus was badly out and the front panel controls had no effect. Turned out to be the same issue - the two 5M focus pots initially measured ~400k each but came good after a clean out.The scope now appears fully functional, with the exception of a timebase triggering fault, which can be seen on the odd display generated when triggered on a 1kHz sine, as shown in one of the attached photos. The fault appears to be induced by excessive mains ripple on either or both the 100V and the 350V regulated supply rails, which are still operating with their original dodgy electrolytic filter capacitors. Before progressing any further with the fault finding / calibration / restoration I will have to replace all of the electrolytic capacitors in the power supply.The scope has some weird packaged plug-in transistors. There is a total of 3 transistors in the scope and one selenium rectifier, forming a fully solid-state regulated PSU of 6.3V to supply the heaters of the input stage tubes of the vertical amplifiers only. This measure was taken due to the high sensitivity of the vertical amplifiers, to prevent any significant mains hum being induced into the desired signal via heater to cathode coupling.A pretty straightforward resurrection, this one. The scope is also in great shape - the front panel is almost flawless.

author: GK
author_rank: Super Contributor
timestamp: November 16, 2013, 09:21:13 am
content: .

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2013, 09:58:54 am
content: Old point contact transistors...... As well as the TO3 adaptor plate on the power device.

author: GK
author_rank: Super Contributor
timestamp: November 17, 2013, 12:42:12 am
content: The obsolete package for the units in sockets (2N214's) is TO22, according to an old reference.

author: edavid
author_rank: Super Contributor
timestamp: November 17, 2013, 02:28:16 am
content: GK, how do you get this equipment so clean? It looks great!

author: robrenz
author_rank: Super Contributor
timestamp: November 17, 2013, 03:12:33 am
content: Yes, it looks very nice indeed

author: GK
author_rank: Super Contributor
timestamp: November 17, 2013, 09:06:27 am
content: Lots of cans of electrical cleaning solvent, a rag, a towel, a bucket of warm soapy water and a little patience.

author: GK
author_rank: Super Contributor
timestamp: April 05, 2014, 07:33:03 am
content: Just spent the past couple of hours cleaning up an running some preliminary checks on my latest toy - a 7904A 500MHz mainframe oscilloscope with plug-ins. Half a can of cleaning solvent later and all of the controls are now noise free and everything (with a minor triggering fault on one of the timebase plug-ins) appears to be in order. Just checking everything out before I go to town on it replacing all of the electrolytic capacitors and giving it a full factory-spec calibration.Second only to the 1GHz 7104, this model is right up there at the pinnacle of analogue oscilloscope design/performance. The jitter performance of the 7B85 timebase is pretty impressive, as shown in the 1nS/division screen photo. The 7B85 can trigger up to 400 MHz and has a maximum sweep speed of 10nS/division. 1nS/division is achieved with the x10 multiplier switched in. The majority of the jitter shown can be attributed to the phase noise performance of my ancient vacuum tubeAdvancemodelE2signal generator, providing the 100 MHz test signal. The intensity control for the 1nS picture is only about half way up. This scope has a VERY bright CRT.Like the 7104A, the vertical deflection amplifiers feature custom amplifier IC's mounted on micro strip printed circuit boards with custom chip carriers. This scope and the plug-ins have been given the "option 3" treatment, which is EMC screening.

author: GK
author_rank: Super Contributor
timestamp: April 05, 2014, 07:42:32 am
content: Here is the 7A19 vertical amplifier plug-in. This one is rated at 600MHz and the 7904A mainframe delivers its rated 500MHz bandwidth when equipped with this plug-in. There is also a direct-to-deflection-plates passive vertical amplifier plug-in available for this scope, which delivers a 1GHz -3dB bandwidth, but with the limitation of a fixed vertical sensitivity.The input to this plug-in is fixed at 50 ohms.

author: GK
author_rank: Super Contributor
timestamp: April 05, 2014, 09:27:32 am
content: Here is the other vertical plug-in, type 7A24. This one is a dual channel but is only rated to 350MHz. With this vertical plug-in installed into the mainframe along with the 7A19, I can have 3 traces on the screen.Like the 7A19, the input impedance is fixed at 50 ohms and the minimum vertical sensitivity is 1V division. There is also no AC input coupling option.

author: robrenz
author_rank: Super Contributor
timestamp: April 05, 2014, 11:09:04 am
content: A thing of beauty

author: lapm
author_rank: Frequent Contributor
timestamp: April 05, 2014, 01:25:12 pm
content: Just found this thread... Now that's some beauty equipment... Some looks like they might have manufactured just yesterday... Nice condition..

author: megajocke
author_rank: Regular Contributor
timestamp: April 05, 2014, 01:31:05 pm
content: True to the title of this thread!

author: GK
author_rank: Super Contributor
timestamp: April 05, 2014, 01:56:15 pm
content: LOL. I think one thing I am going to have to make for myself in the future is a multichannel, 1M input impedance, high frequency buffer amplifier so that I can use standard x10 probes with the 50-ohm-input vertical amplifier plug-ins.

author: GK
author_rank: Super Contributor
timestamp: April 06, 2014, 12:34:21 pm
content: The timebase plug-ins. Huge 10uF and 1uF capacitors in the 7B70 that a first glance appear to be polystyrene. I couldn't imagine what replacements for those would have cost back in the day.

author: Neganur
author_rank: Unknown
timestamp: April 06, 2014, 04:00:28 pm
content: Very pretty.I haven't opened my 7104 at all ever since I got it. Maybe I should!

author: lowimpedance
author_rank: Super Contributor
timestamp: April 07, 2014, 04:19:20 am
content: Also impressive in its own 'vintage' way is your still functional E2 !!. Dare I let on that I had used one in the distant past.And of course the TEK gear is enough to give any collector a woody. Such nice condition too

author: GK
author_rank: Super Contributor
timestamp: April 07, 2014, 08:29:11 am
content: Here are some photos so you can reminisce. For me these were, essentially, hand-me-downs. I haven't done anything to them but they still work OK. The dial frequency calibrations are all dead on.

author: Rigby
author_rank: Super Contributor
timestamp: April 07, 2014, 02:41:13 pm
content: No one ever regrets taking higher-resolution photosimgur.com will host them for free, and there's no BS when you link the file into a forum, so don't be afraid to go big.high-res porn is always better than low-res porn.

author: BravoV
author_rank: Super Contributor
timestamp: April 07, 2014, 02:59:14 pm
content: Quote from: Rigby on April 07, 2014, 02:41:13 pmRight, until one day imgur.com's (or your others favourite "free" image hosting sites) management decided that every picture they hosted will be embedded with ads with boobs and tits courtesy of porn industries.A very nice example, just watch what happened at the "photo" in the 1st post at one of the biggest thread in this forum ->Here

author: Rigby
author_rank: Super Contributor
timestamp: April 07, 2014, 03:41:26 pm
content: Quote from: BravoV on April 07, 2014, 02:59:14 pmI've never heard that... There are images hosted at imgur.com which create terabytes of traffic per day that don't ever get modified. in fact I think any modification or deletion would be a prank by the person that uploaded the image. imgur has never ever modified or deleted an image to my knowledge, and the owner is available and contactable all the time. if there's anything that makes a company more trustworthy than having an owner that is contactable has vowed may times to keep it as a BS-free image hoster, and has kept the promise for many years, I don't know what it would be.I am more than willing to be proven wrong, though.

author: BravoV
author_rank: Super Contributor
timestamp: April 07, 2014, 03:50:43 pm
content: Quote from: Rigby on April 07, 2014, 03:41:26 pmNothing to argue there, just check few of your old posts, I guess probably your photos aren't worth to see say in few days after they've been posted, so understand your circumstances and also I guess nobody will bother anyway if they're gone.

author: N2IXK
author_rank: Frequent Contributor
timestamp: April 07, 2014, 03:56:32 pm
content: Quote from: BravoV on April 07, 2014, 02:59:14 pmBoth boobs AND tits? Didn't know there was a dividing line between the 2...

author: Rigby
author_rank: Super Contributor
timestamp: April 07, 2014, 04:09:14 pm
content: I think I hold a record for the most threads derailed in the shortest amount of time.sometimes I wonder if I'm a net good on the planet, honestly.

author: G0HZU
author_rank: Super Contributor
timestamp: April 07, 2014, 10:14:56 pm
content: My first scope was very similar in appearance and was the big old Tektronix 585 (85-100MHz) with the type 82 dual plugin. I bought it in the 1980s when I was a student. I still have it and it has been lugged to every address I've lived at since. It's in pretty good condition but not as tidy as these scopes. It still has the original little pocket handbook and the probe notes in the little top flap.I bought another scope and stopped using the 585 over 20yrs ago and it is stored in a quiet corner gathering dust. I guess I should check how clean the fan filter is at some point.But it still works!... See below

author: old gregg
author_rank: Regular Contributor
timestamp: April 08, 2014, 10:42:40 am
content: looks like there's a lot of tube in the tek 545Bmust be really hungry for power

author: jh15
author_rank: Frequent Contributor
timestamp: April 12, 2014, 04:30:42 am
content: Thanks for keeping the Tek Porn thread active. At one point I was going to part out my Tek sturf on ebay to help out collectors/restorers, but now I think I will clean up my 535, in perfect operating condition but icky inside, figure if I should keep the Hickok Tek clone for parts, sell it, or restore it from my 535,. Also the 535 era thing I can't make out on the top shelf in my garage.. has tunnel diodes, maybe pull them (I had to design a tunnel diode oscillator in college) and play with them.I might have a 545 kicking around...

author: GK
author_rank: Super Contributor
timestamp: December 20, 2017, 09:53:53 am
content: More porn. I decided to re-cap and calibrate my Type 127 power supply unit today. The 127 allows a pair of 500-series plug-in units to be used independently of a mainframe oscilloscope. For example a vertical amplifier plug-in can be used as a stand-alone measurement/laboratory amplifier.The signal path in the 127 is fully differential for both channels and the output signals from the respective plug-in amplifiers are provided via PL259 connectors on both the front and the rear panels of the unit. The design is a bit weird though in that the 12AT7 triode parallel-connected cathode-follower pair for each output does not deliver a low enough output impedance to terminate a 50 ohm coax. The 127 signal amplifier outputs were therefore specified to drive 170 ohm terminations. The manual for the 127 specified a Tek part number for the 170 ohm terminators but says absolutelynichtsabout the type of coax to use. My Type 1121 amplifier (showcased earlier in this tread) drives 93 ohm terminators via RG62A coax, which has a characteristic impedance of 93 ohms.I don't have or know of any coax type with a 170 ohm characteristic impedance, nor have any 170 ohm terminators, so for the time being as a temporary (maybe) compromise I calibrated my Type 127 to deliver the correct signal gain and optimal pulse response into a 1m length of 50 ohm coax unterminated. The 127 terminated into 170 ohms is supposed to give a rise time better than 20nS. Testing my 127 with my TU7/1M1 Pulse/Load Calibrator plug-in, which delivers a ~3nS rise-time high frequency square wave, the best I can tweak into my 50 ohm unterminated lengths without over shoot and with a flat square wave response is in the order of ~48 nS.Anyway, the 127 comes in handy when you need more traces on your single plug-in mainframe, as shown in an attached photo. Here I have a Type CA dual-trace plug-in inserted into my Type 545B mainframe. A pair of 1A1 dual-trace plug-ins inserted into the Type 127 provide signal inputs for four independent signal traces. I used my analogue chaos computer as a signal source and all of the plug-in amplifiers are operating in the "alternate" dual trace mode.The four independent traces on the 545B are a bit tricky to set up though. You actually have to use both timebases of the mainframe oscilloscope. On the rear panel (why not conveniently on the front panel too I don't know) the Type 127 is provided with a binding post for each plug-in amplifier which serve as the bistable trigger inputs for any dual-trace plug-in amplifier (Type CA, 1A1, etc) which has the "alternate" trace function.In the 545B mainframe, this trigger input of the plug-in amplifier is internally wired to the "+ Gate A" signal output binding post. This signal is a pulse that occurs at the end of each sweep of Timebase A; so when you set the plug-in amplifier to operate in the "alternate" mode, the plug-in's signal output is alternately toggled between CH1 and CH2 at the termination of each horizontal sweep.Now here is where is gets to be a bit of a pain getting 4 traces to display with a pair of external dual-trace amplifiers. The external plug-in amplifiers, for obvious reasons, must not alternate at the same rate as the internal plug-in amplifier, but at 1/2 (ideally) or less the switching rate. To achieve this you connect the external trigger input for Timebase B to the "+ GATE" output of Timebase A, and set Timebase B's sweep duration to double that of Timebase A. The "+ Gate" output binding post for Timebase B is then wired to the trigger input binding posts at the rear of the type 127 (this is the yellow wire in my set-up photo). This basically sets Timebase B to operate synchronously with Timebase A, but at half the frequency, and this half-frequency "+ Gate" pulse from Timebase B is used to toggle/alternate the external amplifiers. Timebase A is obviously set to be the displayed timebase.Because this, in addition to accessing the trigger input binding posts at the rear of the 127, is a pain, I'm currently building a 1U 19" rack patch panel, to breakout the trigger inputs, which will mount in the rack either above or below my 127. This patch panel will also incorporate a bistable/toggle flip-flop and driver circuit to drive the 127's trigger inputs. This will provide the half-frequency alternate trace switching function, thus eliminating the need to use Timebase B at all and permitting the same trace number expansion method to be used on oscilloscopes without dual timebases (for example a 6-trace setup with my 551 mainframe).

author: GK
author_rank: Super Contributor
timestamp: December 21, 2017, 05:01:03 am
content: Okay, a prototype flip-flop knocked up on the breadboard and I have six traces on the 551. In theory, if I had a pair of 1A4 plug-ins in the 127 and another in the upper beam slot of the 551, I could have as many as twelve traces.