Date   

Re: Yet another 'replacing carbon resistors with metal film' question....

Jared Cabot
 

Well, after replacing a couple faulty trimpots (it looks like they were already replaced with some cheap rubbish in the past) it seems to work as well as I can measure on my TDS210 and HP 34461A.
Tonight I'll replace the temporary trimpots I used for testing with some nice Bourns trimpots I picked up today in Akihabara, and after a gentle clean of the switches and stuff I'll call it done.

Next I'll need to get some sampling plugins for my 7704 to really get this thing (and my other TM500 modules) dialed in properly...


Re: 485 as a business dependent daily driver?

redarlington
 

Depends on what you need to do. Completely inadequate if you need to take
data with a computer.

I used one for years doing ultrasound preamp and power amp design work. 2
channels right there on the table was really handy, and it was portable,
and it did everything I ever needed it to do in the ham radio world at the
time. The vertical gain switches need to be worked periodically (as do
probably the rest) or it can be somewhat finicky. Not an issue if it's a
daily driver, but mine has taken a back seat to a Tek 7854. For gross
signal checks it's a great scope up to about a GHz. It does get fired up
occasionally as it did this week to verify my 10MHz reference clock was
still choochin'. It was closer to me than the other.

-Bob N3XKB

On Mon, Dec 28, 2020 at 1:27 PM Ondrej Pavelka <info@vintageaudiorepairs.eu>
wrote:

Hi folks,

I scored 485 with few missing knobs and very blurry trace. It was for
about $30 so I didn't expect much from it.
I have 2445B as a main scope I rely on for my everyday work as a vintage
audio repair business. I did bump on a few occasions into 200MHz bandwidth
limit of the 2445B and 485 is really tempting with its smaller size and
higher bandwidth.
Would you say if I invest the time and money into the 485 I can bring it
to state where it can be 100% reliable dependable instrument?
Otherwise I will pass it onto a friend who will repair it to have it as
his only scope but if this has the potential to take the place of the 2445B
(as much as I will miss the cursors) ?






Re: Tek 453A

Tom Lee
 

Hi Maurice,

These contain no proprietary ICs (no ICs!). The only sort-of unobtainium parts are the tunnel diodes used in the trigger circuits. These scopes are highly repairable as long as the jug isn't dead. But not showing a trace could mean anything from a bad filter cap to a bad crt, so you're taking a higher than average risk. I'm infamously cheap, and wouldn't pay more than $5-$10 for one in that condition. I might stretch that to double that amount if the crt showed some kind of glow and if the scope were complete and in good cosmetic shape.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 12/26/2020 20:57, Maurice Smulders wrote:
I can obtain a Tek 453A locally, but it doesn't show a trace, so I have no idea yet what is broken. What would be a good offer for it, and is it usually repairable?

- Maurice




Re: Tek 453A

Phillip Potter
 

Hi Maurice,

I got my 453 for $10 and it turns out it was only needing a cleaning... I'd pass on a non-working one, unless it was (essentially) free, like mine.

Phil

On 12/26/2020 8:57 PM, Maurice Smulders wrote:
I can obtain a Tek 453A locally, but it doesn't show a trace, so I have no idea yet what is broken. What would be a good offer for it, and is it usually repairable?

- Maurice




Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Tom Lee
 

Hi Attilio,

One other option you may wish to take a look at is the nanoVNA. It's small and portable, and for the price, it's hard to beat. I've done a lot impedance matching and filter tuning with it. Great for checking frequency response (and you get phase information, too, which you don't get with the noise source setup).

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 12/28/2020 16:54, Attilio wrote:
Hi Tom,
thank you very much for the explanations, in fact I was looking for a TR502 Tektronix tracking generator but I can't find it, so for now I will have to settle for a noise generator NF-1000 with all its limitations.

-- Cheers,
Attilio




Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio
 

Hi Tom,
thank you very much for the explanations, in fact I was looking for a TR502 Tektronix tracking generator but I can't find it, so for now I will have to settle for a noise generator NF-1000 with all its limitations.

-- Cheers,
Attilio


Re: 485 as a business dependent daily driver?

Leon Robinson
 

Ondrej,

I have seen an intermittent problem with the Ch1 & Ch2
BNC input connectors.
I think it is where the center pin connects to the PCB.It wasn't my scope but a scope at work, I don't know if they
ever got it fixed, I doubt it.

Leon Robinson    K5JLR

Political Correctness is a Political Disease.

Politicians and Diapers should be changed
often and for the same reasons.

On Monday, December 28, 2020, 6:15:05 PM CST, Tom Gardner <tggzzz@gmail.com> wrote:

On 28/12/20 20:27, Ondrej Pavelka wrote:
Hi folks,

I scored 485 with few missing knobs and very blurry trace. It was for about $30 so I didn't expect much from it.
I have 2445B as a main scope I rely on for my everyday work as a vintage audio repair business. I did bump on a few occasions into 200MHz bandwidth limit of the 2445B and 485 is really tempting with its smaller size and higher bandwidth.
Would you say if I invest the time and money into the 485 I can bring it to state where it can be 100% reliable dependable instrument?
Otherwise I will pass it onto a friend who will repair it to have it as his only scope but if this has the potential to take the place of the 2445B (as much as I will miss the cursors) ?
What does your business need?

Two benefits of the 485 are not having calibration constants stored in a fragile
ROM, and having a proper 50ohm input (not 50ohm//15pF).


Re: 485 as a business dependent daily driver?

Tom Gardner
 

On 28/12/20 20:27, Ondrej Pavelka wrote:
Hi folks,

I scored 485 with few missing knobs and very blurry trace. It was for about $30 so I didn't expect much from it.
I have 2445B as a main scope I rely on for my everyday work as a vintage audio repair business. I did bump on a few occasions into 200MHz bandwidth limit of the 2445B and 485 is really tempting with its smaller size and higher bandwidth.
Would you say if I invest the time and money into the 485 I can bring it to state where it can be 100% reliable dependable instrument?
Otherwise I will pass it onto a friend who will repair it to have it as his only scope but if this has the potential to take the place of the 2445B (as much as I will miss the cursors) ?
What does your business need?

Two benefits of the 485 are not having calibration constants stored in a fragile ROM, and having a proper 50ohm input (not 50ohm//15pF).


Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Tom Lee
 

Hi Attilio,

It's important to understand the limitations of a noise source used as a substitute for a tracking gen. Depending on what you plan to measure, a noise source may be just fine, or it may be useless. Only you can make the decision.

Advantages of a noise source: They're cheap and small.

Disadvantages: Low precision, probably poor long-term stability.

You lose a huge percentage of the dynamic range your spectrum analyzer has. If you plan to characterize the stopband attenuation characteristics of a filter, you may find that a noise source is inadequate. For passband measurements, you'll be fine as long as you are not fussy.

Another problem is that the avalanche characteristics of ordinary diodes do not age at all gracefully. I do not know the specifics of the diodes used in these cheap sources, but the price tells me that these probably use more or less standard microwave diodes that have not been designed or characterized for long-term avalanche stability. You may find that the ENR and spectral flatness change over time and with temperature. If you care about these parameters, you may be disappointed. If your planned measurements are relatively insensitive to these concerns, then forge ahead!

My understanding (never verified) is that diodes specifically designed for service as noise sources are of the buried-junction variety (similar to what lives inside the LM199), and then subsequently aged, then characterized for ENR vs. frequency. A typical microwave Schottky is not a buried structure, so its avalanche noise properties are likely to be somewhat unstable.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 12/28/2020 13:20, Attilio wrote:
Hi Nenad,
i am going to buy the NF-1000 noise generator, what do you think?

Greetings to all
Attilio





Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio
 

Hi Nenad,
i am going to buy the NF-1000 noise generator, what do you think?

Greetings to all
Attilio


Re: Rescuing 500s from tube snatchers/scavengers - how much is it worth

John Williams
 

This is very sad news. Do you know which one of the brothers it was? Sad to hear, they have been very helpful in the past with reasonable prices and good shipping practices. I hope the business will carry on.


485 as a business dependent daily driver?

Ondrej Pavelka
 

Hi folks,

I scored 485 with few missing knobs and very blurry trace. It was for about $30 so I didn't expect much from it.
I have 2445B as a main scope I rely on for my everyday work as a vintage audio repair business. I did bump on a few occasions into 200MHz bandwidth limit of the 2445B and 485 is really tempting with its smaller size and higher bandwidth.
Would you say if I invest the time and money into the 485 I can bring it to state where it can be 100% reliable dependable instrument?
Otherwise I will pass it onto a friend who will repair it to have it as his only scope but if this has the potential to take the place of the 2445B (as much as I will miss the cursors) ?


Re: 465 Scope AC Gnd DC Coupling Switch

Ananda
 

That is a great write up indeed! if one follows this with the instructions in the manual, it should be a piece of cake.


Re: Mechanism of CRT Double Peaking (UPDATED)

greenboxmaven
 

Some years ago, I had a very fine conversation with a picture tube designer at General Electric here in Syracuse. One phenomena that could explain the double peak you see is the electrical interface between the cathode material and the metal cup it is applied to. Apparently, a contaminated layer can build up that carries current well up to a point, then passes it poorly until there is enough current demand to develope a voltage across the layer and cause it to break down. This effect is far more detrimental for television than it would be for an oscilloscope where the beam intensity is usually on or off. Decades ago, there was a rejuvinator called the Raytronic Beamer that was supposedly superior in breaking down this layer. They were so effective they raised a great deal of controversy because people would zap dim jugs and sell them as excellent used or even rebuilt. I have had mixed success zapping scope jugs, it made a small improvement for a very dim 453, but worked well for 5UP1s and other older ones. One thing about zapping a jug must be kept in mind- it usually enlarges the aperture in the first grid, which enlarges the beam spot. That does help brightness, and is usually OK for black and white television, but would certainly reduce clarity and resolution on a scope or color television.

Bruce Gentry, KA2IVY

On 12/25/20 8:53, SCMenasian wrote:
This is a very complex subject and the correct explanation of what is going on depends critically on what type of cathode is involved. I do not know exactly what types of cathode Tektronix used. They probably used several in various generations of tubes. Two types, in addition to coated cathodes come to mind. Both can respond to higher than normal heater current.

The first is the dispenser cathode, familiar to many experimental atomic physicists. These cathodes (which are extended in nature and probably not suitable for CRTs) are consist of a pellet of sintered material in which the active electron emitting oxides are actually in the body of the cathode. The must be "activated" by raising the temperature high enough to diffuse the active material to the surface. If, for example, Tektronix developed a dispenser cathode in which, initially, the activated surface was only a tiny point and, in which, subsequent overheating would cause active material to diffuse, not only to that point, but to the entire anode facing surface, the behavior might be as described.

Another cathode material, often used in vacuum tube filaments, is thoriated tungsten. In this material, thorium is, initially, distributed through the body of the material and initial (and subsequent) heatings serve to diffuse the thorium to the surface, with, possibly, similar results.

Stephen Menasian





Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Nenad Filipovic
 

On Sun, Dec 27, 2020 at 09:18 AM, Thomas Garson wrote:
However, even if it is only a "flat" white noise source, I can see the
utility it offers.
...
I never considered using a broadband noise source as an alternative to
the tracking generator. From your post, it appears that you have done
so, with at least acceptable results.
The eBay ad is a mess but the device is decent, well worth it but won't do wonders for $20. It's a white noise source, just a plain Zener diode hooked to a wideband amplifier. Reference (average) level is approx -30dBm, my specimen has a broad bump of +3dB at around 1GHz and then continuously drops to -5dB at 1.8GHz. However the curve is rather smooth; I mostly use it for spans of just a few MHz and in that case it's virtually flat. For wide spans I use a 7854 program to record a sample of a "flat" reference, and then subsequently apply the inverse of it to correct the actual measurements.

I also have a TR502; its generous output level adjustment is superb and it provides much better SNR in any measurement compared to the noise source. But sometimes funny things happen if you hook it to a DUT which is far from 50ohm, resulting in bumps and tilt of the bandpass curve. I empirically concluded that (this particular) noise source is more resilient to that, so I always try both devices. During Covid lockdown in spring I calibrated the IF of a B/W tube TV receiver from the 60s, and ended up using the noise source. The result was like from a textbook.

Best regards and Happy Holidays,
Nenad Filipovic


Re: Tek 465 Negative 8 volt rail issues

Dave Peterson
 

Thanks Toby and Barry,

I'm becoming partial to Nichicon, not because I think their documentation is better, but I am becoming more familiar with it. And their capacitor series. I've found their Series charts very useful: https://www.nichicon.co.jp/english/products/alm_larg/index.html But I enjoyed reading and learning more about the large power supply cap types. So thanks for the app notes.

I am a bit concerned that the lifetime specs are so much less than the U** series caps, but I see that the "Large Can" types are intended for higher voltage. It's difficult to find a 1200uF, 100V U-series cap, but the "Large Can" L-series can handle that easily. But at a cost of lifetime/ripple current?

LGN2C122MELA40: 1200 uF, 160V, 25/40mm, 3000 hour lifetime @105C, 2300mA ripple current.
UHW1K122MHD: 1200uF, 80V, 16/40mm, 10000 hour lifetime @105C, 3500mA ripple current.

The application is a 465 C1513 which is filtering the unregulated 55v supply. Schematics, and measurement, shows this output is really in the range of 70+ volts. So very near the limits of U-series cap. The existing cap is a 100v cap, so we'll say that's the spec? But the U-series cap above has significantly better lifetime and ripple current. Which is the more important selection criteria here?

And then for the lower voltage, but higher value +15v, +5v, and -8v: the U-series again has significantly higher lifetime and ripple currents at the expense of a lower voltage rating, but still greater than the application. For example: UHE1E562MHD (5600uF, 25v, 10000h, 4200mA) vs. LGY1H562MELA40 (5600uF, 50v, 5000h, 2300mA)

The 1200uF cap seems a little on edge at 80v for U-series. But, within voltage spec, doesn't lifetime and ripple trump the ratio: spec voltage/operating voltage?

Dave


Re: Yet another 'replacing carbon resistors with metal film' question....

Jean-Paul
 

AHA! Yes PG502 is a fine unit, the back term 50 Ohm is handy. I have several, neither has ever has any problem.

For scope cal, the really fast rise pulses are from PG506 and Leo Bodnar's 40 pS pulser

As a general use PG with fast capability PG502 is best.

The resistors you highlight are not critical to the performance and even a 5% value should not affect it.
I dont recommend Removing, testing and replacing the parts if its performing satisfactorily.


Enjoy,

Jon


Re: Tektronix 1A7 and 1A7A Plug-ins

bobkrassa
 

The 1A7A manual is on the Tekwiki site.

Bob Krassa ACØJL


Re: Yet another 'replacing carbon resistors with metal film' question....

Jared Cabot
 

I have the PG502 250MHz Pulse Generator in front of me now (I also have a PG506 to look over but that is another project for another time).

I guess I'll see how the unit performs with the minimum of modifications to get it functional and make a decision once I see what it says as to further repairs.
I've found a lot of these types of resistors have drifted high in a number of pieces of test equipment I've worked on in less critical applications, hence my thoughts on replacing them in this unit, but I guess if it works, then no point fixing it until it breaks.... :)


Here are the schematics with the Allen Bradley style carbon composite resistors in my unit highlighted:
https://i.imgur.com/8WiK5b9.jpg
https://i.imgur.com/g3KXKlN.jpg
https://i.imgur.com/geXFOIK.jpg


Re: Tek 465 Negative 8 volt rail issues

n4buq
 

Regarding snap caps, the leads are bent into a crook so as to allow inserting processes to push the leads into the PCB holes and grip the cap in place until soldered. Otherwise, they're like their ordinary radial-leaded cousins.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: toby@telegraphics.com.au
To: TekScopes@groups.io
Sent: Monday, December 28, 2020 9:25:25 AM
Subject: Re: [TekScopes] Tek 465 Negative 8 volt rail issues

On 2020-12-27 11:10 p.m., Dave Peterson via groups.io wrote:
Paul,

I'm putting together a Mouser project for 465 PS caps. I pulled all 5 as
they appear to have been leaking, it was going to be necessary to get at
the suspected C1513, and once I got going it wasn't that bad, so might as
well do all of them. I also have the adapter boards ordered and waiting
for USPS to get them across country.

I was searching for radial Nichicon caps as I'm pretty happy with the
order I made for C1419 replacements. I didn't catch your earlier reference
to "snap" caps, and I see that these come in higher capacitance and
voltage values than radial. Not that radial's aren't available, it just
appears snap caps are inherently larger?

I've never heard of snap caps before. Aside from the obvious lead
difference, what is the purpose/difference between radial lead caps and
snap caps?
Nichicon publishes app notes and press releases like these:

https://www.nichicon.co.jp/english/products/pdfs/e-al_gui.pdf

https://www.nichicon.co.jp/english/lib/new133.html
https://www.nichicon.co.jp/english/lib/new135.html
https://www.nichicon.co.jp/english/lib/new141.html

via https://www.nichicon.co.jp/english/lib/index.html

Hope some of that is helpful.

--Toby

Dave









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