Re: Tek 465 Negative 8 volt rail issues

Dave Peterson

Spent a good amount of time yesterday studying available caps and Nichicon documentation. Came across this:

https://www.nichicon.co.jp/english/products/pdf/aluminum.pdf Section 2-9 "Life and Reliability".

"if a capacitor is used ... at the maximum operating temperature or below ... the life doubles for each 10deg C drop in temperature." (Ft)

"The degree that applied voltage effects the life of the capacitor when used below the rated voltage is small, compared to the degree that ambient temperature and ripple current effects life. Therefore, when estimating the life of a capacitor, the voltage coefficient to the applied voltage (Fu) is calculated as 1."

2-9-5 "Ripple Current and Life" is a complex section, but can be summarized as "ripple current causes temperature rise", and this temperature rise reduces lifetime. (Fi)

Section 2-9-6 "Estimated Life" gives lifetime as:

L = Lo x Ft x Fi x Fu

Where Lo = Datasheet lifetime (about 3000h to 10000h for snap-in and radial aluminum electrolytic capacitors). Or:

L = Lo x 2^((To-Tn)/10) x 2^(1-((In/Im)^2)/K) x 1

Fi = 2^(1-((In/Im)^2)/K) is complicated as heck, but note that its value ranges (roughly) from 1 to 2. Suffice it to say, run your ripple current at max at max temperature and Fi approaches 1, but is generally closer to 1.5 to 1.9.

So lifetime, grossly, at worst, is:

L = 3000h x 2^((105-40)/10) x 1 x 1 = 3000h x 2^6.5 = 3000h x 90 = 270,000h = 270,000h / (24h x 365d/y) = 30y

Finally, noted from later in section 2-9-6 "Please note that calculated life time is for reference only and not guaranteed. Typically, fifteen years is generaIIy considered to be the maximum for the estimated life obtained by the above formula." I take this to mean Nichicon does not assure a lifetime of greater than 15 years, in general.

So: given the worst snap cap lifetime of 3000h, run at or below rated voltage, at or below rated ripple current, at approximately 40C (104F) the lifetime of the cap is estimated to be double the guaranteed lifetime of Nichicon caps. You halve the lifetime for every degree above 40C (roughly), and all bets are off if you exceed voltage or ripple current. Run ripple current below rated and you tend to double the lifetime. The "Miniature Type" (U-series) caps do tend to have about double the lifetime and ripple current rating of "Large Can Type" (L-series). But for large cap and voltage values the L-series have more "headroom" with regards to voltage than the U-series.

For the 1200uF, 100v C1513 (the big cap that brought this scope down) I'm going with a snap-cap at 160v. A U-series cap would have been limited to 80v - there's nothing offered in this line above that. The output at this cap is just under 80v, but it's near enough that it gives me pause. And clearly the technology used in U-series is at its limits with this cap, where the L-series is offered in significantly higher voltages. So it doesn't seem as stressed. The big question remains, what is the actual ripple current?

For the 560uF, 100v C1512, the smaller value L-series caps have ripple current specs less than the 2000mA of C1513 above. So I went with a U-series cap for this one. At the lower value this series has a 160v cap available. So why not!? It's ripple current spec is the same, 2000mA, as C1513. The ripple currents for equivalent L-series caps are less than 2000mA.

The low voltage caps are a bit more limited in available capacitance values. The U-series has 5600uF but only at 35v. The L-series has the same at 50v. But then the L-series does not have a 5000uF. It gets complicated going through all the combinations. I found it interesting that in the "465 PS Cap Replacement Guide" used a 5600uF for all three of C1542, C1552, and C1562. I was inclined to do the same as again, the U-series seems to be more against their voltage limits than the L-series. I do wonder about the significance of using a 5600uF cap in place of a 3000uF cap. But these caps are all about biggest C in the space available (at the time), right?

The big unknown that remains is what IS the ripple current to these caps in these supplies? I wonder if I can put together a reasonably accurate simulation. Just to get some sense of order of magnitude.

I didn't come across (yet?) the effect of voltage on the capacitor, besides little to no effect if kept below spec. But common sense suggests a cap operated near its spec is more likely to fail than one that has some head room. The question is what is "some" head room? A good value seems 2x, but it's not well defined. Lifetime suggests no real gain as long as spec is not exceeded and it's just a matter of providing enough head room to ensure spec is not exceeded under all operating conditions.

Here's my final list ordered from Mouser:

C1512, 560uF: UCY2C561MHD, 560uF, 160v, 2130mA, 18mmx40mm, 7.5mm lead spacing.
C1513, 1200uF: LGN2C122MELA40, 1200uF, 160v, 2300mA, 25mmx40mm, 10mm lead spacing.
C1542, C1552, C1562, 5600uF: LGY1H562MELA40, 5600uF, 50v, 2300mA, 25mmx40mm, 10mm lead spacing.

These all fit the adapter boards from the seller on eBay noted above. I bought two sets of both adapters and caps. One as a back-up for my first attempt at installation, and should I succeed without damage I have a second set for my other 465.

This was not as bad to do as I'd feared, and the caps that came out of my "parts" 465 are so bad that I'm kind of a convert now. Leaking is quite evident, though not so much that the A9 board is affected. While I don't have an ESR type meter, I'm able to use the equipment I have to get some kind of capacitance measurement off working caps. It's difficult to impossible to measure the capacitance on the old PS caps as the internal resistance is so high that shorting the leads does not discharge the cap appreciably (C1513 specifically). But the measured cap is less than 1/10th the rated cap. There's a big fat R between the lead and the internal capacitance. I only find it odd that this scope worked at all. I really wish I'd gotten some ripple measurements off the caps of the supplies (before regulation) before it died. I suspect the regulators were compensating until the 55v regulator couldn't take it any more. I'll have to take a look when I get it back working. I wonder if any of the regulator components are affected by the stress.

Sorry for the long write up, but I hope the info is useful to someone down the road.
Dave

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

fiftythreebuick

Probably not a factor in this case, but in some cases we have found that metal film resistors (of the same value/wattage as the original carbon comp resistors) would blow open when exposed to high inrush current transients while carbon comp resistors would live in the same environment just fine. We first discovered this when working on the power supply of a 555. Multiple metal film resistors blew while a used carbon comp from a junker instrument stayed in there just fine.

Just for what it's worth....

Tom

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

kim.herron@sbcglobal.net

Just a note: I have it on good authority that the inventory
that was in the building Stan was leasing has been
moved, sold, or something. It all went out of state, so I've
heard. I have reason to think that it was the property

On 29 Dec 2020 at 10:00, - wrote:

John said: 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.

It was Stan Winston that passed away. I don't know if he had a
brother
or not but I've heard that there is another relative involved that
is
trying to sell the business or sell off the assets. Stan inherited
the
business from his father 20+ years ago so there could be a brother
that's
also part owner. We're all hoping that the business will continue
but it
doesn't look like it will. IMO This would be a good opportunity for
a
foreign investor that wants to own and operate a US business so that
they
could get an immigration visa.

On Mon, Dec 28, 2020 at 3:44 PM John Williams <books4you4@mail.com>
wrote:

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

John Goller, K9UWA & Jean Goller, N9PXF
k9uwa@arrl.net
Leo, IN 46765
USA
1-260-637-6426

Last few new Tek goodies up for Stuff Season

Our stuff season is getting its last additions today, there's still one hard to find 149-0035-00 fan motor (465/475), some blue CRT filters, and some interesting Tek internal bits including a 2335/6/7 sweep switch, 7903/7904 mod kit and other goodies. You can see everything here:

https://www.sphere.bc.ca/test/stuffday.html

There's also a bunch of new LCD and VFD displays going up later today as soon as all the pics are done. Many thanks to everybody that dropped by the Stuff Season page, it wasn't as much fun as having everybody here in person, but for those far away, it was a lot more convenient.

All our best wishes for a better new year,
walter & susan
Sphere Research Corp.
https://www.sphere.bc.ca/test/index.html

Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Dave Daniel

You need to read the group Wiki. I suggest the one on the nanovna-users group.

DaveD

On 12/29/2020 7:28 AM, Attilio wrote:
Hi Tom,
wow fantastic this nanoVNA, I saw that there is also a V2 version, maybe I will buy it, but I didn't understand how to use it with my SA (maybe using it as generator ?).

-- Cheers,
Attilio

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

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

John said: 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.

It was Stan Winston that passed away. I don't know if he had a brother
or not but I've heard that there is another relative involved that is
trying to sell the business or sell off the assets. Stan inherited the
business from his father 20+ years ago so there could be a brother that's
also part owner. We're all hoping that the business will continue but it
doesn't look like it will. IMO This would be a good opportunity for a
foreign investor that wants to own and operate a US business so that they
could get an immigration visa.

On Mon, Dec 28, 2020 at 3:44 PM John Williams <books4you4@mail.com> wrote:

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.

Re: Mechanism of CRT Double Peaking (UPDATED)

Chuck Harris <cfharris@...>

That is probably a miss-memory.

What the designer in GE was talking about is a layer of contamination
that boils up to the surface of the normally highly emissive cathode
material. When the layer covers the cathode material, the emission
drops.

There is good evidence that overheating the cathode, and using the
first grid as the anode of a diode to draw much higher than usual
current from the cathode (using much higher voltages than usual)
will break up the contamination layer, and restore some activity to
the cathode... Indeed, all CRT manufacturers do this to activate the
cathodes of new CRT guns, during manufacture.

Zapping is not really agressive to anything but the cathode layer,
certainly not to the first grid, which is a heavy piece of stainless
steel... way more rugged than the cathode.

Raytronic Beamer, Sencore Rejuvinator, B&K ... there were hundreds
of CRT restorers available to the TV repair shops that all worked the
same way. Each was so magnificent that it was head and shoulders
above all of the rest... Each allowed the repairman to go from gently
(and ineffectually) caressing the cathode to kill'em or cure'em levels
of zapping.

-Chuck Harris

greenboxmaven via groups.io wrote:

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.Â  Apparently, a contaminated layerÂ  canÂ  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.Â  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.Â  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.Â
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.

Â Â Â Â Â Â  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: Mechanism of CRT Double Peaking (UPDATED)

Chuck Harris <cfharris@...>

In receiving tubes, that "interface layer" is called Cathode Interface,
and is very true. Look it up.

-Chuck Harris

If the "interface layer" theory was true then the same negative resistance phenomenon would also be observable in conventional tubes. Personally I've never seen one behave like that, although I curve traced a considerably large and diverse tube graveyard out of curiosity. I witnessed a lot of funny things, but never a negative resistance. Perhaps some more experienced group members have?

For the reason above I believe the phenomenon is related to CRT gun specifics, coupled with the control circuits designed for high impedance on most electrodes. Until someone performs the measurements I proposed previously we'd hardly know in which direction to go.

Re: 485 as a business dependent daily driver?

Chuck Harris <cfharris@...>

Nothing can be made 100% reliable as a daily driver, so no,
your 485 might break, and it might need an expensive repair.

If that is your only consideration, go with something new.

The 485 is a nice scope, but with its tiny screen, and lack
of readout and cursor, most would find it tedious to use as
a daily driver. When the 2465 came out, the 465-485 scopes
disappeared from lab benches very quickly. We were getting
them in government scrap lots by the ton back then.

-Chuck Harris

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) ?

Re: Tek 453A

Chuck Harris <cfharris@...>

Take a look inside of your 453A, make note that gold is almost
\$1900/oz, and tell me, with a straight face, that it is only
worth \$5-10 in a not working condition. Even a broken jug has
\$5 worth of gold in it.

If we want these scopes to remain available, we are going to
have to start offering higher prices than the scrap dealers.

Believe me, the scrappers know exactly what they are worth.

-Chuck Harris (Just say'n...)

Tom Lee wrote:

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

Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio

Hi Tom,
wow fantastic this nanoVNA, I saw that there is also a V2 version, maybe I will buy it, but I didn't understand how to use it with my SA (maybe using it as generator ?).

-- Cheers,
Attilio

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

Jean-Paul

Jared good work! We found the old Bourns trimpots (cermet) are the best, and avail in 3, 5 turns besides one turn.

TEK sampling plugins are interesting but difficult to get working.

Used units can have damaged inputs or hard to find TDs in the sampler.

We have a 7104 mainframe with 7A29 plugins to get 1 GHz response and excellent pulse performance.

Suggest to get some veteran advise on the best sampling PUs for 7704 before plunging in!

Best,

Jon

Re: Mechanism of CRT Double Peaking (UPDATED)

If the "interface layer" theory was true then the same negative resistance phenomenon would also be observable in conventional tubes. Personally I've never seen one behave like that, although I curve traced a considerably large and diverse tube graveyard out of curiosity. I witnessed a lot of funny things, but never a negative resistance. Perhaps some more experienced group members have?

For the reason above I believe the phenomenon is related to CRT gun specifics, coupled with the control circuits designed for high impedance on most electrodes. Until someone performs the measurements I proposed previously we'd hardly know in which direction to go.

Re: Tektronix 1A7 and 1A7A Plug-ins

um-gs@...

Thanks,
but that doesn't solve my request. The 1A7 manual shows the original pre-amp with 4 Nuvistors, and not the modified pre-amp installed in my 1A7 version as described above.

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

 14401 - 14420 of 189686