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Hello Benedikt ,

A 1L5 was my big project for a while in the '90's. I operated it in a Type 132/133 power supply unit.

I mostly re-designed and rebuilt the frequency setting and sweeping circuits for improved linearity, center-frequency, and lower drift. Was happy with the results.

Also added an op-amp sweep generator mounted inside for autonomous operation. I used it with a TDS340A which allowed noise filtering with the scope averaging, and of course storage of slow sweeps.

Am now thinking of an external wide range sweep box with better accuracy to work with 1L5, 1L20, and equivalent-time sampling units working into a DSO.

Karl G

Hey Karl,

you don't have anything documented about your project, don't you? I'm highly interested.
I am currently trying to optimize some steps of the adjustment procedure first with access to modern equipment, like adjusting the 3 MHz IF filter externally with a Network analyzer or the 1st LO output filter with the Oscillator output at a spectrum analyzer.

I plan to use the analyzer in a more "natural Environment" in my 549 I recently overhauled.
But having better stability and linerarity as well as a calibrated Log display would be really nice. I know it was even back then considered a low cost SA, but with modern tech I think there should be many points which can be improved without much effort.

regards
Benedikt

Hello Benedikt,

I'll try scanning the notes and marked-up schematics I did. I'm afraid my documentation isn't very organized. Can I email them to you?

I can also explain what I was trying to do. I also was interested in doing a more precision log amplifier, but never got to it.

Karl G.

Hey Karl,

yes sure,
just send it to my email when you can finish it. Any excplanation would also be a nice thing.


Benedikt

Hi Benedikt,

I'll start scanning my notes and schematics.

Karl

Hi Benedikt,

I've scanned about 10 pages of pencilled schematics and notes about the 1L5 modifications. I'm trying to make them useable and add schematic refs.

I still want to do some explanations as well.

Can you email me so I can get your email? I can't use the Tekscopes link; it's in Outlook, which I don't have.

Karl G

You could also upload them to TekWiki at .

Regards,
Dave Wise
________________________________
From: [email protected] <[email protected]> on behalf of Karl Goedecke <karl@...>
Sent: Sunday, May 5, 2024 2:56 PM
To: [email protected] <[email protected]>; [email protected] <[email protected]>
Subject: Re: [TekScopes] Experiences / Improvements with 1L5

Hi Benedikt,

I've scanned about 10 pages of pencilled schematics and notes about the 1L5 modifications. I'm trying to make them useable and add schematic refs.

I still want to do some explanations as well.

Can you email me so I can get your email? I can't use the Tekscopes link; it's in Outlook, which I don't have.

Karl G

Hey Karl,

hope you are well. Did I miss your mail od did you not find the time yet?

regards
Benedikt

Hi Benedikt,

I'm actually re-doing the discriminator and oscillator schematics in Kicad. My pencilled notes were just too sketchy and smudged.

I might try uploading to a group file sheet by sheet.

Karl

:D I understand.
Take your time. And uploading them also to the tek wiki is a really good idea.
Then they will not be lost.

Regards
Benedikt


-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von Karl Goedecke
Gesendet: Montag, 20. Mai 2024 16:11
An: [email protected]; [email protected]
Betreff: Re: [TekScopes] Experiences / Improvements with 1L5

Hi Benedikt,

I'm actually re-doing the discriminator and oscillator schematics in Kicad. My pencilled notes were just too sketchy and smudged.

I might try uploading to a group file sheet by sheet.

Karl

Hey Karl,

hope you are well.
I'm just curious about any progress you made.

regards
Benedikt

I have a couple questions about the 1L5
I have a 556 scope and acquired a 1L5 that appeared in very nice condition.
But didn't seem to be working. Feeding it a sine wave from a generator all I could see was a flat line with one small blip
and then something smoked (using the left bay). I shut it down and pulled it out. I couldn't see anything on an initial inspection that looked smoked on the 1L5 and
Other plug ins seem to work fine yet. I have replaced the lytics on it checking the old ones out of circuit as I went along, and none tested bad.
Also, I have checked all the plugin transistors including the FET on a Heathkit IT 121 semiconductor analyzer and all appear to be good.
At the time didn't have an extension cable to do any live checking. I have since gotten one and have a manual as well. Also I didn't realize that the 1L5 had a sweep selector switch on the back that had to be set depending on what scope you used it in.
It was all set aside but I would like to troubleshoot it going forward. The scope has had no problems with any other plugins.
So, could I have smoked something by having that switch in the wrong position?


Just wondering if there are somethings I should specifically target that anyone might suggest for the smoke issue and the signal issue when I get back to this? (Of course now that I have that extension cable, I'll check various supply voltages)
Is there something in the scope that would connect to this 1L5 that doesn't on many other plug ins that might have smoked?
I have not dug into the scope back plane to see if something hidden back there might have smoked there but again it seems to operate normally.

I would like to get this going as it should and then would be very interested in playing with some upgrades to improve it.
Thanks for any advice!

Hi Benedikt,

I will send you an intro document by e-mail listing the different circuits I worked on and the types of changes made, and a list of schematics I'm cleaning up.

Karl G.

Hi Bill,

There's not a lot of power used in a 1L5. The only high power resistor is R459, mounted off the back panel. It supplies current from the +75V supply to run the 1L5's +10V supply.

It shouldn't matter which position the back panel switch is in, from a safety standpoint. The 556 horizontal sawtooth output is probably 0-100V, not 0-150V. Even if it were 150V and the switch was set for 100V there's nothing that would be damaged.

Which electrolytic caps did you change?

Karl G.

Kind of thought that would be the case for the switch position. Thanks for verifying
It's been a while since I looked at it but as I recall there were about half a dozen small caps in the 1L5 that I changed.
As I haven't seen anything charred (yet) I still don't know if the smoke came from the 1L5 or the scope.
It didn't happen immediately on plugging in the 1L5, it was plugged in for several minutes while I was trying to get it to display something and then there was smoke from that bay (left side).
I assumed that it came from the plug in as I hadn't had any previous problems with the scope itself nor have I had any since.
But that doesn't mean that one of the can caps in the supply didn't vent or something. Scope has never been recapped.
I didn't see anything then that looked fried in the 1L5 but I didn't spend a lot of time in as I didn't have the manual or the extension cable at the time.
I've seen a lot of discussion of tantalums going bad in various Tek equipment. Didn't note any in that but may have missed it.
Just figured I'd get some thoughts on it before I pull everything out and get back to it. It's a project that has been on the back burner for some time now. But now I have a couple audio projects that I'd like to try it out on.
Guess I'll have to do some basic troubleshooting starting with some voltage checks. And maybe open up the scope enough to see if there is anything going on in the supply area too. That should probably all be recapped but I've just been keeping my fingers crossed and running on the, 'if it works don't fix it' plan.

Hey Karl,

I received your mail without issue, however my reply got lost in the void.

The first thing I indeed want to modify is the oscillator you completely overhauled.
Do you have a good suggestion for the RC tanks components? I think low thermal coefficient thinfilm resistors and ceramic caps would be best right?

regards
Benedikt

Hi Benedikt,

Yes, I agree that a rebuilt oscillator would give the best immediate improvements to the swept frequency source linearity.

It should directly reduce or eliminate 2nd harmonic content, but should be combined with a good low-pass filter to reduce the higher harmonics too.

If I were doing it again, I think I would put it on an SO-8 "Schmart patch" stick-on proto-typing board, available from Digi-Key. In addition to mounting the chip, there should be room for some SMT resistors and capacitors. The 5 or 6 components for a 3-pole filter can also be SMT chips and could maybe go on another Schmart board, which could be cut from a larger one with scissors. The two trimpots could mount in now-empty locations on the 1L5 board.

Looks like I owe you more values for the oscillator design.

I used an LM6361 op amp I happened to have, but I'm sure there are plenty of others, the AD847 for one.

Karl