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Rebonjour

Probes, as mentioned the P600x series was used at the time.

The later probe's had wider BW but lower compensation C range.

A point of history...Stanley Kubrick's 2001: A Space Odyssey had a scene of astronauts David Bowman and Frank Poole, troubleshooting the AE -35 LNA, with a Tektronix P600x probe. No scopes though

Recommend 1980s Tektronix circuit concept books
Oscilloscope Probe Circuits and
Probe Measurements

536: a unique scope, used throughout the 1960s. So, at Marantz, Sid's , tube amp, preamplifier, tuners, 1,5,7C, 10B, were designed using 536. I was assisting Sid, later at Sequerra, I marveled at the simplicity of his technique.


Jon

“According to George Lydeck on this group, the Tek 535A is the best scope ever for tube audio work.”

Did I really say that?

I think what I meant to say is a good tube oscilloscope, like the 535A, is a good choice for dealing with the high voltages encountered in, let’s say, an audio tube amplifier since it is a little more bulletproof than a solid state scope. Although I have original probes for my 535A I tend to use more modern probes as they are less cumbersome.

Cheers and Happy New Year,

George KD6NEW

On 12/31/24 22:47, Jean-Paul via groups.io wrote:

Sid would display a lissajous of the input audio vs the output or distortion product of a distortion analyzer.

That's a fine looking 10 x 10 equal grid on the CRT face of the 536 on tekwiki.

I see how that would be the analog purist's favorite with 11 MHz bandwidth.
Much finer than a 602 monitor...and with number and letter plugins with the T timebase, (which I had never noticed before), it's better than a 504 503 or anything else without a 10 x 10 measuring grid on the CRT, (like the 535).

As an EE, you may have been taught the term like I did in school 'it's broke'. The class and instructor laughed. A bit of New Year's humor.

Likely you have at least one d-c restorer diode that is open or shorted. Replace ALL of them with 1N4937. In the schematic on page <13> these are to the right of the 'focus' control and have CR16xx. The schematic is found by looking up 'tektronix 485' online then looking for the w140 page. There will be pdfs of schematics and information, . You can find a paper manual online. I prefer a paper manual over a digital one. I did replace the two 22meg bleeder resistors in the d-c restorer circuit with Vishay VR37 series. The original 1/4w carbons will be well high in resistance. The symptom of these being too high is a bright trace when turned on then dimming after 15-20 minutes without touching the intensity knob. I did replace R1745 with a 1/2W in the Z circuit. C1748, in mine, are 47mfd 25V Nichicon ULD types. UHE will work fine also.

There is a 13V supply with a 15V tantalum used. Replace this with a 25V type. I used the ULD in mine. Also, in the front end, there is a 100mfd that should be changed to a higher voltage. I do suggest making the mod for the higher s/n types to protect the input IC from damage when switching from 1meg to 50 ohm. This is shown in the schematic. I did this to my earlier s/n model.

Check all of the 0367 transistors! These are known to be bad from C to E checking as a diode. The early ones are a bit larger in body size with round leads that will be tarnished. Mid types will be normal size with square leads that may or may not be bad. The last ones made with a blue tinted face will likely be good. Only in the 7D15 will the number be 0402 for these. They are the same transistor. I used KSP10BU as replacements. Other models and plugins have the 0367s in them. If you find ones that are bad, replace all in the piece. I have seen this number cause problems such as triggering not being right.

I did replace some resistors with higher wattage and mounted them a bit off the board to allow for better air flow and to make any probing easier. The tantalums are also suspect. Seeing 15V on a 25V tantalum will be alright. If the tantalum is rated at 20V, raise the voltage. Using good quality electrolytics, low ESR, high temp and long life types, with a higher capacitance works. If a tantalum is working fine and the voltage of it is high enough above the voltage across it, it is not necessary to change it.

I chose to restuff the two main filters in the power supply with Nichicon LGR types of higher capacitance. I wanted new in mine to make sure age would not be a problem.

Mark

One thing to look out for is bad IC sockets. The low profile ones used in this and other models use contacts that make contact with the sides of the pins. Little contact. The best replacements are ones by Augat or MilMax machine types that use round contacts that are firm. Second choice are the better ones that have a dual wipe.

Hello John, fabulous offer - have messaged you.

(I haven't seen a copy of my sent message in my email client, so not sure where that may have gone?).

I have a Tek 485 that I have had and used lightly for 20+ years with no issues.? That is until last night.? I hadn't used it in couple of months. After turning it on I went to adjust the Intensity and it went totally bright and stuck there.? The Intensity flickers when the control is moved, but when left in any position, it's always stable on high.? A second symptom simultaneously appeared.? The retrace of the beam is not blanked.? So, both issues point to a problem with intensity modulation of the beam.?


I thought I had the service manual for this, but I am unable to find it.? I am sure the first thing I need to do is get a copy of this.? What is the best source for this?? I am a retired electronic engineer, so I have no problem digging into the scope.? But I only have one, so I hope I don't need another to troubleshoot this one.


Any suggestions on what areas of the circuitry to look at would be appreciated.

On Fri, Dec 27, 2024 at 01:26 AM, Richard Kelly wrote:

understand the potential issue with the silver deposit ceramic strips and have
electronic solder to hand that is 95% Tin, 3.8% Silver and 0.7% Copper

According to Tektronix (back in the day)...
The solder they used... for the metalized ceramic strips (the notches were metalized with silver.. and dip coated with the solder)
The solder they used was 60% tin, 37% lead, and 3% silver.
The flux used was rosin.
Solder with 60% tin, 37% lead, and 3% silver has a melting range of approximately 179–183°C (354–361°F).
This composition is close to the eutectic solder alloy of 63% tin and 37% lead, which melts at a fixed temperature of 183°C
Eutectic solder... or near Eutectic solder... melts more fully... and solidifies more fully, in a shorter temperature... and time... range than non-eutectic solder.
That's good for a couple of reasons.
With 63/37 the silver can dissolve, to a small extent.
Most of the silver loving part of the solder is the tin.
More silver would get 'dissolved' at higher soldering temperatures... and times
So lead free, " 95% Tin, 3.8% Silver and 0.7% Copper" solder would not be 'ideal.' ... more on that later.

Anyway... I reckon the concern was dissolving the silver... sufficiently... from the ceramic strip notches... causing mechanical instability... in the soldered joint... supported by the notch... of the ceramic strip.
So, when using these old 500 series... with the ceramic strips... shipboard... or airborne... the military types would have scrutinized that... for reliability.

Anyway... I reckon further... that unless you are gona take your ceramic strip series 500... for a ride on New Sheppard... or with you and Elon (hopefully) to Mars...
I wouldn't worry about it.
--
Roy Thistle

Bonjour à tous

In 1960s Sidney S Smith was the audio and analog engineer at Marantz, Dick Sequerra was the RF genius.

In 1971, I had the good luck to work with them at their newly formed Sequerra Co.

Sid taught me a lot about hifi and analog circuitry.

His favorite scope was the 536, which had excellent 11 Mhz XY bandwidth.




Sid would display a lissajous of the input audio vs the output or distortion product of a distortion analyzer.

Just a walk down memory lane....

Jon

The P31 conversion is done and looks great. Both CRTs are in very good shape and bright, with no burns at all. Still working on the other stuff. Will report next year.

Ed

Hi Richard. I have plenty of these. PM me your mailing address and I will send you a set of four. Do you need all parts for each one ie the screw, plastic part, and the little metal thingy?

Hi Jim. To be frank, it seems a bit premature to look for probe information when you don’t have a scope, and maybe don’t know what you are going to use it for exactly. It might be better to look for some help choosing and acquiring whatever type you decide on, and how you are going to get it. There are a few 535’s on eBay, but no indication of working or not. Prices seem to be around the $400 mark plus shipping. As far as probes go, I pretty much stick with the P6006. I have never had a use for 100x probes. When I was selling scopes I brought in a quantity of Chinese probes. They were pretty much the same as the Tek ones. Quality was good and they were quite inexpensive. I always use 4 foot ones, the six and nine foot cords always seemed to get in the way and snagged on everything on the bench. If you have one scope, a couple are all you need anyway.

Ed,
My first thoughts after reading the descriptions are switch contact issues in the selector switches and or something in the routing logic that is on the back plane of the mainframe. If I remember correctly there are 3 IC's on the back plane that handle signal selection and routing. It sounds like one of those might not be receiving the correct signals or not outputting correctly for signal switching.

Zen

I have this last 7904 up and running as explained previously. It showed several problems including readout loss, severe vertical compression, A-horizontal failure, and supply crashing when control lighting is turned off. I swapped in another readout board, which got that working about right. I'll have to slog through the rest.

The vertical problem is very strange, and depends on the plug-in type, apparently. When I first fired it up, I put in a 7A26, 7A18, and 7B53 - the very same ones I had been using in the 7613 for diagnosing the PS for this unit. The compression was evident immediately, and I blamed the mainframe, but after some swapping around of plugs and holes and other 7A18s and 7A26s, I started to blame the 7A18, thinking it may have just crapped out coincidentally (this kind of thing has happened before). After enough combo trials, I realized the 7A18s were OK and confirmed their proper operation in the 7613. The 7A26s worked in both 7904 verticals, while both of the 7A18s had the same symptom with the line stuck near the bottom of the screen, barely affected by input signal or position controls.

After more checkout, it seems the vertical display and triggering are fine in both slots using the 7A26s, and only the B-horizontal works properly. When "A" is selected, it crashes something and the display goes crazy, looking collapsed kind of like in beam-find mode, and missing parts.

At this point I know the supplies seem OK, and the display looks good, with full control of intensity and focus.

Has anyone seen things like these in a 7904? As I mentioned before, my notes from 2012 and also 2019 indicate that this was kind of a junker, with multiple problems existing or swapped into it, including the bad PS. Now that that's fixed, I get to revisit all of it together. The notes include stuff about the readout, the vertical and horizontal interface boards, suspecting one side of the differential signals missing, and that some plug-ins like 7D01 worked OK, while others didn't. Unfortunately, I didn't make very precise notes, so all I can tell is that these were some of the issues involved, but there's nothing about resolution of any problems.

The strangest part I think is why certain plug-in types would work just fine and others not.

Ed

A CORRECTION
I gave the wrong links for the "Radiotron Designer's Handbook". I gave links to the table of contents only, the full text is available, it is:

Radiotron 4th Edition:
<>

Radiotron 3rd Edition:
<>

Sorry for this, I didn't notice until I reveiwed my post later.

On 12/30/2024 9:12 PM, Richard Knoppow via groups.io wrote:> wave response. Beside scope specs also see the catalogs for probe specs.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Anita Abranovic <anita.abranovic@...> added the photo album JFETs substitution for 12au6s in 575 curve tracer ( /g/TekScopes/album?id=299769 ) : Both horizontal and vertical amplifiers have these instead of matching 12au6s

In very good mechanical condition, lights up when plugged in, controls and buttons seem to work.
$100 and I'll ship free (from Austin) CONUS only please.
I can't guarantee it since I don't have any probes / scopes that are compatible as far as I can tell.
Email if you want a picture.
Thanks!

A few things to consider when selecting probes:

Check the probe's compensation range against the input capacitance of the scope input.

For work in tube circuits check the max input voltage spec of the probe. Also consider how safe the probe is for high voltage circuits.

Lastly consider the attenuation of the probe against the v/dev range of the scope against the voltages in the circuits you're working on.

The Tek P6006, P6008, P6009 should be considered. The first two are 10x. The latter is 100x.

Mark,
I listed the Multiplier and knob on eBay.

Barry

Hi Joel,

Sorry to say, they are already spoken for. I will let you know if that changes.

Regards,

Barry