PG506 of solid gold

Nenad Filipovic

I'd appreciate the enlightenment why somebody dished out >$500 for a PG506:
A few months ago I was the second highest bidder at around $130, not sure what to think now.

Nenad Filipovic

Re: Update (was RE: [TekScopes] TDS510 or TDS460A or 485 scopes as upgrade)


On Sun, Feb 21, 2021 at 08:13 PM, Tom Lee wrote:

I've never tried that before.
Applied by using a finger, which makes the butter very soft. Since most dirt stuck on the front of these buttons is greasy, it works very well and preserves the text.


Re: P6021 Noise Problem?


The 100 MHz noise can be parasitic oscillation, rather than power rail lack of bypass

The Ft of the transistors can shift over the decades.

One tip-off is if the 100 MHz changes amplitude or disappears as the DC level is changed.

Another test is apply a low frequency small amplitude Signal and see if the noise is just adding to the signal or affects the 100 MHz.


Re: Update (was RE: [TekScopes] TDS510 or TDS460A or 485 scopes as upgrade)


On Sun, Feb 21, 2021 at 08:13 PM, Tom Lee wrote:

I wonder what other foods might be useful in restoring equipment...
Do you think cooking my wife's favorite meal in exchange for extra time to spend on restorations would count?


Crud (was: Re: [TekScopes] 3T77 tunnel diodes (again)

Brad Thompson

Tom Lee wrote on 2/20/2021 9:25 PM:<snip>

....You could make them in dirtyrooms (take a look at early die photos of ICs -- you can see all sorts of crud; apparently, the industry then relied on cigarette ash as a dopant)....


Allegedly true story (secondhand): an engineer  who worked at National Radio during the 1950s
told me about a piece of equipment which relied on sliding contacts. The contacts resided in a box
that when sealed, prevented maintenance and lubrication. The contacts developed intermittent
problems, but applying various lubricants didn't solve the problem.

By accident, an assembler dropped some cigarette ashes into one of the boxes.
Rather than taking the time to remove the ashes, the assembler sealed the
box which astonished the design engineer by passing its life test without
developing intermittents.

"What did you do differently?" asked the designer. The assembler confessed to
contaminating the box with ashes which apparently were acting as a mild abrasive
and scrubbing the contacts. "Keep it up," said the engineer, and henceforth every
box contained a sprinkling of cigarette ashes.

Until the government inspector arrived and happened to witness the
assembler taking a drag on his cigarette and then tapping the ashes into the box.

The inspector raised  hell as only a government inspector can, and
after some intense negotiations allowed the process to continue--
provided that the
assembly instructions were edited to add a specification for "cleaning agent, Camel
cigarette ash, one-half inch."


Brad  AA1IP

Re: 454 HV transformer

Paul Amaranth

You sure it's the transformer?

I had the 2n3055 go bad in the HV oscillator when I was restoring a 454.
They don't build those transistors like they used to and not all of them
will work in the circuit. I had to sort through my pile to find one
that worked.

Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows

Re: 454 HV transformer

Joel B Walker

The 454 HV transformer part number is 120-0471-00. None on eBay, none at Qservice, and not listed at Sphere. You might want to email Walter Shawlee at Sphere and see if he has one that isn't listed. He is a member here.

Re: 2467B TEST 04 FAIL 02

Michael W. Lynch

On Sun, Feb 21, 2021 at 02:40 PM, Chuck Harris wrote:

Anyway, my major point was they went to an awful lit of work
to make a square wave, when all they needed was some zero
crossings. A sine wave will do.

Yes, I understood your point about the sine wave. That all made perfect sense to me. I am actually starting to understand some of this stuff.

Although I do not own a 2465 series instrument, I find your comments about calibration are always helpful. What I took from this was a method to pair the TG501 and any one of a number of PG50x Pulse generators to obtain other more useful and desirable signal characteristics. I might just start looking for a 2465 as a "project".

Funny part about this, and what caught my eye was you saying that these Option 1 TG501's were "rare as hens teeth". I have three TG501's, and all are Option 1 and they all work. I even built a 4th "Option 1" unit from a "junk parts" box that I bought and which I later sold on E-bay.

Thanks for the verification!


Michael Lynch
Dardanelle, AR

Re: 3T77 tunnel diodes (again)


The 5.6k (carbon comp) resistor was indeed completely open. It looked perfect, no cracks or swelling, other than some whitish oxidation on the leads. Replaced it with a modern resistor and resumed work on the 3T77A.

The display is garbled - can't get it to trigger properly on a nice 6 MHz square wave from my 114 pulse generator. The "pull to sync" mode won't give me the 9 pulses before holdoff, either. It's either 2-3 pulses or it free runs with no holdoff.

Meanwhile, the trace decided to move vertically offscreen (down) and can't be brought back on. Pulling the invert switch on the 3S2 sends it offscreen (up). This is the behavior I first saw when the staircase & sweep weren't working at all. But they are fine, and the 3T77A is sending the proper (sampling strobe) pulses back to the 3S2. Whatever the latest problem, it doesn't appear to be in the time base plug-in (although I will still have an interesting time with the triggering before it will be useful). Could be the 3S2... or the S-2 head...

That's it for now - I have to go out of town for a week and I'm tired of messing with things that break while you're looking at them.

Re: P6021 Noise Problem?


This. It does sound like external interference may be the problem. For a
while I had an office from whose window the tower of the infamous "Palace
of Culture and Science" building in Warsaw was visible about a mile away.
It housed a whole load of FM radio transmitters. They got in to
*everything* analogue. I had to use bandwidth limiting on the scope most of
the time, and just get used to the awful fuzz on the traces if I was doing
any higher-speed work.


On Sun, 21 Feb 2021, 18:41 Leon Robinson, <>

The clue, moving your hand. A number of years ago I was working with some
fast pulses and depending on the placement of the 50 ohm probe cable the
scope display changed a lot. I got some of the clipon ferrite beads and
put them on the probe cable. Problem solved.

Leon Robinson K5JLR

-------- Original message --------
From: Chappy <>
Date: 02/21/2021 11:03 AM (GMT-06:00)
Subject: Re: [TekScopes] P6021 Noise Problem?


Thank you for picking up on the error in my title, my probe is the 6201
900MHz FET probe. After working on the issue some more I think I have
narrowed down the problem. Shielding all of the parts with tinfoil
grounded to the chassis did not change anything. However, holding onto the
probe lead did.

With a 1Mhz, 5mVpp square wave signal I am able to see a roughly 100Mhz
oscillation riding on the square wave. As I carefully move the probe lead
around while grasping the probe lead with my entire hand I am able to
reduce the oscillation amplitude from 2mVpp to approx 1mVpp. So my main
problem is not random noise but a distinct separate signal.

I had another look at the +/-15v supply rails on my power supply and the
scope trace for the negative rail is slightly thicker than the trace for
the +15V rail on a 5mv/div setting. I am going to investigate this further
with my 7A22 plugin with it's greater sensitivity. Once I get this issue
resolved I will then look at those capacitors that you have mentioned if
the problem still persists. Perhaps I have a small high frequency
oscillation in my power supply that is working its way up into the probe
head and back, further compounded by degraded electrolytics in the probe

Thanks to all who have replied with advice and insight so far.


Re: What years were tunnel diodes designed into Tek instruments?

Ed Breya

A few decades ago, I used to have a Tek 661 sampling system (actually it was my first Tek scope). As I recalled, the trigger and time-base circuits were loaded with TDs. I just looked it up, and it appears it does have TDs, and it was introduced ca 1961. So, viable, commercial ones must have existed - or had preliminary data and samples - by say 1959 or earlier. It makes sense that TDs would have been used first in the highest speed, state of the art stuff, before triggering applications in regular scopes, which were gradually getting faster and faster, thanks in part to TDs. The earliest, fastest, usable versions of TDs probably cost a fortune, but allowed the high speed triggering for samplers, and pulsers for TDR, etc to work. They were always expensive and finicky, so as soon as better alternatives emerged, they disappeared from general use, contrary to the glorious predictions of the TD makers. Remember too, that Ge transistors and diodes were disappearing, so Ge TDs were kind of on their own, as specialty items and processes, not able to take advantage of the advances in Si.

Anyway, if there's another sampler older than the 661, it may set the clock back another year or two.

I think the last use of TDs at Tek would have been in some of the 7K series time-base plug-ins - I know the 7B92A has some. The S-52 TDR pulser also falls into 7K, but it actually showed up much earlier, I think in a 3-series TDR plug-in.


Re: 2467B TEST 04 FAIL 02

Chuck Harris <cfharris@...>

Yes, that is the one. They are out there, but really not
all that stable, and certainly overkill for the usual timing
calibration of scopes.

Anyway, my major point was they went to an awful lit of work
to make a square wave, when all they needed was some zero
crossings. A sine wave will do.

-Chuck Harris

Michael W. Lynch via wrote:


An enlightening explanation, as always. As a point of education for me, is the "Extended Accuracy TG501" an instrument with Option1, the 5MhZ temp compensated Oscillator?

locked Slightly OT: How can I dissolve Potting Compound? FOLLOWUP


Thank you one and all for your suggestions on removing the potting. Your
suggestions fell into two general categories:
1) Nasty chemicals which I decided had to be avoided at all costs based on
your advice.
2) Heat. This seemed like a slightly better approach than the chemical one.

But before I get to what happened when I applied heat I learned many new
things along the way thanks to a few of our members and especially, Ed
Breya. Ed's comments explained in detail how these HV potted power supplies
worked. That led me to an amazing web site that has a staggering amount of
information on them about every aspect of lasers of all kinds including
their HV Power Supplies. If anyone is interested the site is
I have to caution you that I spent hours roaming around in all Sam had to
say. He is an incredible resource for anyone who owns a laser. I found many
different power supply circuits and details about laser HV modules which is
what I apparently blew out that prompted me to ask about removing the
potting in the first place.

With suggestions from Ed Breya I tried using the other more powerful potted
HV laser supply I had. It was going to try and force too much current
through the spectrum tubes so I added additional ballast resistors and
connected it to a Variac so I had some control over the High Voltage and the
constant current With this arrangement I was able to test every one of the
spectrum tubes (I have over 20 different ones each containing a different
gas) to determine their breakdown voltage and their steady state current
requirements. That told me what I should be looking for to replace the Laser
HV supply that I blew out.

In Sam's web site I found the design and schematic for a power supply
designed by the legendary Jim Williams of Linear Technology. It was a
universal design capable of powering every one of the spectrum tubes I had.
I ordered the parts to build it.

I still wanted to see what I might learn from removing the potting of my
failed HV Laser supply so for $15 I bought a toaster oven at a thrift shop.
I set it up outside, set the temp to 200F (93C) for 30 minutes and poked it
with a sharp tool. Nothing happened. At 250F (120C) it got a little softer
and a few cracks appeared. At 300F (150C) I was able to chip off the bottom
and see the solder side of the PCB. A few of the sides also chipped off.
This was starting to work.

Since the oven was on the ground it was hard to see the temperature knob
from the angle I was standing but I raised the temperature once again by the
same amount.

30 minutes later when I checked on it, it was smoking. I would rather not
say what the reading on the thermocouple was but I will tell you it was way
over 260C (500F). When I touched the potting the PC board fell away from the
rest of the potting. I knew immediately that was to be expected since solder
melts at a lot less than 260C. The parts fell away from the epoxy, by
barely touching them but of course there was no way to know what they used
to be connected to anymore. The entire thing was a mess.

It did teach me some things. Heat is definitely safer than chemicals to
remove potting but realistically even with carefully controlled heat potting
is not going to give up its secrets easily or cleanly. I now have an "oven"
I can use for soldering surface mount parts with whenever I find something I
can't build with a through hole parts.

In the end TekScopes members led me to a solution for an excellent HV Power
Supply for my Spectrum Tubes in the form of the Jim William's Linear
Technology Application Note 49, August 1992, titled "Illumination Circuitry
for Liquid Crystal Displays". His design is shown in Appendix D.
"Figure D1: Laser Power Supply is Essentially a 10KV Compliance Variable
Current Source".

Thank you Ed and many others who offered their suggestions

Dennis Tillman W7pF

-----Original Message-----
From: [] On Behalf Of Dennis
Tillman W7pF
Sent: Saturday, January 02, 2021 6:19 PM
Subject: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF

Dennis Tillman W7pF
TekScopes Moderator

Re: What years were tunnel diodes designed into Tek instruments?

Tom Lee

Thanks, Kurt. So far, then, 1961 seems to be the earliest Year of the TD, with the 519 and 661.

-- Cheers,

Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

On 2/21/2021 12:13, Kurt Rosenfeld wrote:
As far as I know:
- The 661 makes extensive use of tunnel diodes and was designed in 1961.
- The 585 started using tunnel diodes in 1962.

Re: 2467B TEST 04 FAIL 02

Michael W. Lynch


An enlightening explanation, as always. As a point of education for me, is the "Extended Accuracy TG501" an instrument with Option1, the 5MhZ temp compensated Oscillator?

Michael Lynch
Dardanelle, AR

Re: What years were tunnel diodes designed into Tek instruments?

Kurt Rosenfeld

As far as I know:
- The 661 makes extensive use of tunnel diodes and was designed in 1961.
- The 585 started using tunnel diodes in 1962.

Re: 2467B TEST 04 FAIL 02


Chuck, perfect information as always, and very useful to those who suffer with an ornery CTS option.

Bon Journee,


454 HV transformer

michel soldevila

I own 2 "type 454" scopes togetre with a "type 491" spectrum analyser. The high voltage transformer (T1430) of one of the scopes is dead.
Who could tell me where to find one, and at what cost? An important detail: I live in France.
Mike (F1GOC)

Re: Update (was RE: [TekScopes] TDS510 or TDS460A or 485 scopes as upgrade)

Tom Lee

Thanks for that suggestion, Raymond. I've never tried that before. I wonder what other foods might be useful in restoring equipment...

-- Cheers,

Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

On 2/21/2021 06:42, Raymond Domp Frank wrote:
On Sun, Feb 21, 2021 at 03:41 PM, Raymond Domp Frank wrote:

On the 4xx scopes never use IPA as it will take the lettering off the
...Nor use (anything containing) water! I usually take some butter(!). Works
very well!
Applies to the plastic buttons only...


File /067-0513-00 Tunnel Diode Pulse Generator.pdf uploaded #file-notice Notification <noreply@...>

The following files have been uploaded to the Files area of the group.

By: Dennis Tillman W7pF <dennis@...>

The Early Use of Tunnel Diodes at Tektronix Notes from Dennis Tillman and John Addis

4861 - 4880 of 183706