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On Thu, 1 Mar 2018 at 15:59 Malcolm Hunter <malcolm.r.hunter@...>
wrote:

It can be done. I've 3D printed feet for the 465 based on this model I
"designed" based on the original feet:
. Printed in PLA, they are
functional but I wouldn't bank on them holding out for every day use.
Someone with a bit of 3D modelling ability and an original foot should be
able to craft a suitable replacement for the 335 too. Printed in something
a bit more durable would work and even if they weren't as good as the
original, you could have plenty of spares.

There are now services that'll demand-print and ship items, like e.g.
ShapeWays, which will print in a variety of materials. It'd be nice to have
a stash of 3D models for Tek replacement parts cataloged someplace, and/or
to have them listed on these print services.

I modeled the PCB bracket I needed for my FG504, but the PLA prints I got
from the 3D printer I have access to delaminated as soon as I put a screw
to them. The ShapeWays nylon print, however, worked just fine (see <
>),
and I know other people have had luck with the same print.

I priced out your thing on Shapeways, and the two materials/methods that
look likely are:

- Strong & Flexible Plastic Black (Selective Laser Sintering): $8.98.
- HP Nylon Plastic Black (Multi Jet Fusion): $17.96.

though perhaps it'd be possible to bring down the per-item cost for e.g. a
set of four by optimizing the design...

Toby,

Documentation is just a notebook, a few pics before disassembling anything important.
Analog computers are two Comdyna GP-6. FWIW, the system could modeled in MatLab, Mathematica, or even MathCad. This project is modeling some audio transfer functions - it will be quicker for me to optimize by seeing and hearing the residual errors. For the display a vintage Tektronix 503 will do; has identical X and Y amplifiers so additional scaling circuitry and their effects is eliminated.
Also checking out Rolynn's suggestion of a 602 or 604 monitor.

Thanks, Ron

On 2018-03-02 12:25 AM, Ronald Carlson wrote:

Anyone have a Tek 503 that's looking for a new home?

The 503's specs fit nicely as an output display for an analog computer project I'm working on.

I'm curious about your analog computer. Are you
documenting/blogging/video'ing this anywhere? What is the goal?

I'm also working on circuits to drive X-Y displays, but at a very basic
level since I'm an electronics beginner.


--Toby

Or, perhaps there's a better, newer model the group could recommend?

The identical low frequency response horiz and vert amplifiers with a
square display make it initially an interesting option.

TIA, Ron

It is made on laser engraver. I have a friend that work on this machine and I make a corel with outlines and what need to be on scale.
it is made from black PVC foil past on Plexiglass.
First cut the foil on low power to remove the foil only and after this cut outline on big power.
I'm not sure which one will illuminate better, but will test all 3 before to choose one. Think this one with black foil back will be better then other because will illuminate only the scale on top of the LED.
I hope in next week to find a time to go to make the knob and will make some pictures with all installed.

I have been refurbishing some late 70s-early 80s HP gear and I only replace bad capacitors per ESR or Q meter readings. A schematic helps in making sure there are no other elements in parallel that would skew the results. Many power rail caps are in parallel so I just lift their one end and measure that way.

I have found several bad tantalum slug capacitors - I replace those with modern equivalents that often have similar part numbers and look very similar or identical. Those are not particularly cheap and I always replace the hermetic ones with new hermetics, not the cheaper yellow plastic encapsulated ones.

If a given type of a capacitor has failed more than once in a given instrument, I replace all - if there’s less than 5 or 6 total. Otherwise I do a judgment call based on circuit types and the stress the part is likely to experience.

The failure mode for tantalums that I checked was almost always high ESR or high DF, and capacitance changes were secondary and not always present.

I also test all electrolytics after 24hrs of preforming/burn-in at room temp. They seem to fail randomly and I also shotgun those that see lots of stress if any compatriots have failed. For me, they almost always fail with both ESR/DF and capacitance changes. I would still advise having a good ESR meter in addition to capacitance meter.

In some units there is a lot of failed electrolytics, in some others - few if any. I don’t have enough experience to see a clear pattern there yet.

Kuba

The LO input to the mixer is also dead. It comes into the mixer through a cable/plug and it's still dead while unplugged. There are several test points on the LO circuit . The manual has a few reference wave forms I can check. In summary, both the LO is dead and the mixer's output transformer isn't even passing the basic AF wave by itself. But the transformer isn't open. I'll dive into these over the weekend and see what I can find.

Sounds good. I terminated it with 600 ohms and now it's perfect. Thanks for pointing me in the right direction.

Rick

Dennis' suggestion of using add and invert mode on the oscilloscope
works well depending on how much sensitivity you need.

If you have a 7000 mainframe, then a 7A13 combined with standard x1
probes may be acceptable. Standard x10 probes have the problem of not
having matched attenuation which spoils the common mode rejection.

Another alternative I have occasionally used is to build the probe
into the circuit using a fast instrumentation or difference amplifier.

Dave,

Thanks, yes a couple of them sold that would be just fine. Repair project is OK. I'm standing by and eventually I'll be providing one a new home and tlc. Either private party, hamfest, or the 'bay.

Ron

To second Dennis, this is exactly what we do, and we’re a professional audio archive lab.

George

Massdrop had one a week ago for $140.



I was actually quite surprised to see such a specialized piece of equipment
show up for sale there.



If it's not available now, be patient, it'll come up again.



Menahem

Dave-

You might consider going to ham radio swap meets. A really great FET differential probe is the Tek P6046. I picked up one for less than $50 if I remember correctly and it is perfect. Many people do not know what they are and that accounts for them selling so cheaply. It takes some time to find one but at least you'll be rewarded with a great tool once you do.

Phil

There were some selling very reasonably on eBay not too long ago; they
still might be on there. Have you checked?

Dave Casey (who is not currently selling any scopes on eBay)

On Thu, Mar 1, 2018 at 11:25 PM, Ronald Carlson <
ronald.carlson.54@...> wrote:

Anyone have a Tek 503 that's looking for a new home?

The 503's specs fit nicely as an output display for an analog computer
project I'm working on. Or, perhaps there's a better, newer model the
group could recommend? The identical low frequency response horiz and vert
amplifiers with a square display make it initially an interesting option.

TIA, Ron

Anyone have a Tek 503 that's looking for a new home?

The 503's specs fit nicely as an output display for an analog computer project I'm working on. Or, perhaps there's a better, newer model the group could recommend? The identical low frequency response horiz and vert amplifiers with a square display make it initially an interesting option.

TIA, Ron

There is no such thing as a cheap differential probe. They have to be matched across a wide frequency range to have good CMRR. If you want a cheap CMRR the solution may be on your scope. All dual trace scopes have an ADD function for both traces. They all haave a way to invert a trace on one of the channels. So switch to Add, Invert one channel, and use the gain knob of one channel to adjust the trace to a straight line when you put a signal in through two same number probes - any two will do as long as they are the same (two P6109 probes for example).

Voila, a poor man's Differential probe.

As long as there isn't too much of a voltage difference between the two channels the waveform will stay on the screen where this will work OK. It isn't much but that is probably the best you are going to get when you require "cheap"

Dennis Tillman W7PF

A giant rubber band also works to hold the plugin in to the connector. Hobby stores sometimes sell them.

There may be something wrong with your TM501 connector if the extender card falls out. I can't recall ever having a problem with this style of connector in over 40 years of using them. The original design is by Cinch. I think Tek used Edac brand connectors but the design is the same. All of the green Cinch connectors I ever used hold on to a PC Board of the right thickness very tenaciously. The nominal board thickness is 0.061 inch. Check that your extender card is that thick. If it still falls out take a careful look at the green connector.

I stripped my TM501 down to the bare bones. Just removing the cover gave me access to some of the plugin but the side frames kept getting in the way to I cut the entire side frames off right back at the connector PC Board with a hacksaw. If I were to do this again I would have allowed about an extra inch forward of the connector because the two pass transistors are mounted down at the bottom by the connector and this way you won't have to move them.

I use this completely open frame supply all the time when testing or building TM500 plugins. There are problems with my "hack job" which you should be aware of:
1) When the TM501 power supply section is upright the front of the plugin needs a small support of 1/4". PostIt notes work perfect because you can peel off a 1/4" stack from the rest of the pile for this purpose.
2) When the TM501 is on its side the front of the plugin has to be supported with a 1" spacer if the supply is on its left side or 1/4" spacer if the power supply is on its right side.
3) You may want to move the power switch since the pull switch is in an awkward position after you make these changes. I used a small C&K DPST switch mounted on a bracket on one of the screws holding the transformer in place. It was handy and it was up top. I also put a pilot on it so I know when power is applied to the TM500 and its plugin.
4) If I was really smart (apparently I'm not since I only realized this years after cutting up my TM501) I would also cut down the cover so that it completely covered the power supply section from wandering hands. I haven't yet been shocked from my open frame TM501 supply but it's only a matter of time before I am reminded that I am not nearly as smart as I think I am.

Was I a bad person for desecrating a TM501?

Dennis Tillman W7PF

I'll cite one example of a mod not having a 2-letter identifier. On at
least some of the 7L12, 13, and 14 spectrum analyzers, before Option 39 was
available the same effect could be had as "Mod 139U" or something similar.
I can send a picture of the label if you don't believe me.

Dave Casey

Hi H?kan,
All of the instruments that I know of which have been modified have a Tek label that says something like "MOD WN". The MOD is always identified by two letters on every plugin that has a mod. I have never seen MODs listed by Tek part numbers.

In fact until now I didn't know there were part numbers for the MODs at all. Brian Henry put a copy of the Tek Modified Products list (June 1978) in the archives some years ago. It is at

/g/TekScopes/files/%28Modified%20Products%29.pdf


You can see from Brian's Modified Products list that there was almost no consistency in how MODs were numbered. I understood from talking to several people that the MODs were not well "controlled" by some centralized authority. As a result a lot of documentation relating to the MOS was lost. Your list with the standard part numbers suggests otherwise. Maybe there was a system after all and someone was responsible for issuing these part numbers (Deane Kidd?). Is there a way to cross reference a MOD identifier from Brian's document such as "MOD WN" to a 040-xxxx-xx number from your list? Your list gives very little information about what the MOD does compared to Brian's document.

Good luck getting your Microfiche copier repaired. Bummer that it broke!

Dennis Tillman W7PF

Hi Velik,

You did a great job! These look as good as the original skirt from Tek.
I am very impressed with how all three dial's turned out.

There are many times when members need to make replacement skirt's with scales on them for their equipment.

Would it be possible for you to write up a step by step procedure for how you did these lovely scales for your curve tracer. As you write it keep in mind that other people may have a different number of choices on the skirt of their dial, different size skirts, and/or different settings on the skirts. I can help with the final edits if you need to finish the step by step directions on how you did it.

Dennis Tillman W7PF

Sadly, nothing under ?100 on fleaBay :-(

Anything in the DIY arena ??

Dave