Date   

Re: Borrow an extender in U.K.

 

Hi David,
I'll try, I'll see if I've got his email.

Cheers

Robin

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of David C.
Partridge
Sent: 30 December 2020 15:26
To: TekScopes@groups.io
Subject: Re: [TekScopes] Borrow an extender in U.K.

In Kenilworth any good ?

Though I think Craig Sawyers is closer to you as he lives near Oxford. (He
left the mailing list a while back but I don't believe his email address has
changed).

David


-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Robin_Birch
Sent: 30 December 2020 14:33
To: TekScopes@groups.io
Subject: [TekScopes] Borrow an extender in U.K.

Hi,
Need to give my 7003 and some plug ins a good going over. Is there anyone
in the Cotswolds area (U.K.) who has an extender that I could borrow for a
couple of days ?

TIA

Robin Birch


Re: Borrow an extender in U.K.

 

In Kenilworth any good ?

Though I think Craig Sawyers is closer to you as he lives near Oxford. (He
left the mailing list a while back but I don't believe his email address has
changed).

David

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Robin_Birch
Sent: 30 December 2020 14:33
To: TekScopes@groups.io
Subject: [TekScopes] Borrow an extender in U.K.

Hi,
Need to give my 7003 and some plug ins a good going over. Is there anyone
in the Cotswolds area (U.K.) who has an extender that I could borrow for a
couple of days ?

TIA

Robin Birch


Re: Borrow an extender in U.K.

 

Slip of a finger, it's a 7603

Robin

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Robin_Birch
Sent: 30 December 2020 14:33
To: TekScopes@groups.io
Subject: [TekScopes] Borrow an extender in U.K.

Hi,
Need to give my 7003 and some plug ins a good going over. Is there anyone
in the Cotswolds area (U.K.) who has an extender that I could borrow for a
couple of days ?

TIA

Robin Birch


Re: Mechanism of CRT Double Peaking (UPDATED)

Chuck Harris <cfharris@...>
 

Hi Nenad,

I don't dispute any of that, but rather add one thing,
and that is, ion sputtering can only occur if the CRT is
gassy. I have spent a good bit of time playing with
sputterers used to coat samples for imaging with an
SEM.

My expectation is that double peaking is the result of a
gassy CRT, and not a worn out cathode, per se.

In my playing with double peaking CRT's, I note that you
cannot achieve any sort of sharp focus after the initial
low intensity sharp focus. It only gets worse. Even though
the focus control has a best focus setting that is within its
range... that tends to indicate that the focus grid is getting
the proper bias voltage.

If double peaking was a function of lost emission in the center
of the cathode, you should still be able to "print" a sharp
image of the cathode's emissivity on the screen at any intensity.

The affect of defocusing caused by gas in the CRT is one of
dispersion of the beam as the electrons are deflected by
the gas molecules floating around in the vacuum.

The greater the intensity, the higher the quantity of electrons
streaming through the CRT, stirring up the residual gas.

I doubt we will ever know how the phenomenon works, as it is
undoubtedly a complicated interaction of multiple causes.

And, it is unlikely that anyone with sufficient resources to
fund such research cares about CRT's anymore. They are so last
century...

-Chuck Harris

Nenad Filipovic wrote:

On Tue, Dec 29, 2020 at 06:43 AM, Chuck Harris wrote:
In receiving tubes, that "interface layer" is called Cathode Interface,
and is very true. Look it up.
Perhaps my statement wasn't precise enough, I meant to say "if the interface layer was behind the double peaking phenomenon...", not question the interface layer existence per se.

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.
Oxide cathode is so complex (not entirely understood even to the day) that any plausible mechanism one can think of - probably occurs in it. The question is which of these mechanisms has higher significance for the particular case study. The predominant deterioration mechanism in CRT cathode is sputtering by positive ion bombardment, due to high voltages and concentrated electron beam shape[1, page 116].

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.
Yes in general, but the exact mechanism is slightly different. To the demise of some audiophiles the (activated) oxide cathode is an n-type semiconductor, and a quite sensitive one. To enhance its conductivity and emission, oxide cathodes are doped with impurities in form of reducing activators which are alloyed with the cathode metal carrier[2, page 557]. This metal carrier (e.g. nickel tube in case of indirectly heated tubes) acts as a reservoir of spare activator throughout the life of the tube. Contamination (aka cathode poisoning) consists mostly of oxidizing agents that act as traps[3, page 8][1, page 112], and counters the effects of activation. Funny thing is that both the activator and most contaminants are mobile at the operating temperatures (e.g. can diffuse by electrolysis)[3, page 16]. Some contaminants also become embedded in the crystalline structure of the oxide layer. But contamination is not the only deteriorating effect, there's also sputtering erosion, evaporation and sintering[1, page 115]. The high efficiency of the oxide cathode is in good part due to its high porosity, which significantly increases the effective surface area which acts as an emitter. Sintering solidifies the oxide surface and therefore reduces emission.
During operation of the tube, cathode current forms an electric field in the oxide layer which balances the diffusion of activator, barium (directly related to donors) and contaminants. A natural equilibrium forms which depends on the structural recipe of the cathode and its health state[3, page 35]. The above mentioned deteriorating effects effectively change the structure of the cathode rather permanently, resulting in general conductivity drop[3, page 18]. One artificial way to restore the conductivity is to pump the oxide layer with additional activator. This is accomplished by combination of overheating the filament so that metal base can release the activator, and by running pulse current to stimulate diffusion. Unfortunately the excess barium (its vapor pressure) created in this way is not in equilibrium with the aged oxide layer structure, and will subsequently be lost due to evaporation[1, page 67][3, page 30] in a process known as deactivation. This explains why rejuvenation is short-lived.

In my experience I witnessed rejuvenated CRTs which were bright, but certainly not sharp. This supports the argument that the center of the cathode is mostly lost, and the (temporary) increase of brightness is due to the artificially increased emission of the surrounding area.

Negative resistance and double peaking still remain without clear explanation.

References:
[1] THE OXIDE-COATED CATHODE Vol 1/2; Dr. Ing. G. HERRMANN, Dr. Phil. S. WAGENER; CHAPMAN & HALL LTD. London 1951
[2] Materials and Techniques for Electron Tubes; Walter H. Kohl; Reinhold Publishing Corporation 1960
[3] Electron Tube Design; RCA 1962

Nenad Filipovic






Re: Tek 453A

Arne Buck
 

Tom,
I concur. I've been offered money (not much, though I got it in a bargain
lot including a bunch of other stuff from a couple of guys who gave up
their Colorado garage start-up business trying to turn gold into lead, or
some such) for my ancient Monroe 1655 Scientific Programmable Desktop
Calculator. Genuine Burroughs Nixie tubes, you see. Fourteen, count 'em!
I first used one in the Physics Library at Cal Berkeley luoong-gago. It is
fun watching the Nixies flicker as it calculates the natural log or trig
functions.


Borrow an extender in U.K.

 

Hi,
Need to give my 7003 and some plug ins a good going over. Is there anyone in the Cotswolds area (U.K.) who has an extender that I could borrow for a couple of days ?

TIA

Robin Birch


Re: 7904A restoration questions

Dave Daniel
 

The 7904A has a switching power supply. Using a Variac is not a good idea.

DaveD

On 12/30/2020 7:37 AM, Jean-Paul wrote:
Fantastic find! Use a variac if you want to be cautious on turn on.

a/ Get service manuals DL from TekWiki or BAMA Archive: Check SN range as there are different manual sch etc for various SN ranges.

b/ Clean and exercise all front panel controls. Check CRT focus, for burn in, intensity range.

c/ open the side covers of 7704A, check for dirt, HV carbon accumulations, obviously leaky capacitors.

d/ Plug in the sample then the spec analyzer and test.

ENJOY!

Jon




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


Re: 7904A restoration questions

Jean-Paul
 

Fantastic find! Use a variac if you want to be cautious on turn on.

a/ Get service manuals DL from TekWiki or BAMA Archive: Check SN range as there are different manual sch etc for various SN ranges.

b/ Clean and exercise all front panel controls. Check CRT focus, for burn in, intensity range.

c/ open the side covers of 7704A, check for dirt, HV carbon accumulations, obviously leaky capacitors.

d/ Plug in the sample then the spec analyzer and test.

ENJOY!

Jon


Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio
 

hi Miguel, hi Tom,
great idea, I try to find a TR503, but what value should the crystal have?
I am waiting for the 7613 mainframe to replace the 7603 mainframe, with the 7613 mainframe I should make better use of the SA 7L13.

Thanks and happy new year
Attilio


Re: Mechanism of CRT Double Peaking (UPDATED)

Nenad Filipovic
 

On Tue, Dec 29, 2020 at 06:43 AM, Chuck Harris wrote:
In receiving tubes, that "interface layer" is called Cathode Interface,
and is very true. Look it up.
Perhaps my statement wasn't precise enough, I meant to say "if the interface layer was behind the double peaking phenomenon...", not question the interface layer existence per se.

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.
Oxide cathode is so complex (not entirely understood even to the day) that any plausible mechanism one can think of - probably occurs in it. The question is which of these mechanisms has higher significance for the particular case study. The predominant deterioration mechanism in CRT cathode is sputtering by positive ion bombardment, due to high voltages and concentrated electron beam shape[1, page 116].

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.
Yes in general, but the exact mechanism is slightly different. To the demise of some audiophiles the (activated) oxide cathode is an n-type semiconductor, and a quite sensitive one. To enhance its conductivity and emission, oxide cathodes are doped with impurities in form of reducing activators which are alloyed with the cathode metal carrier[2, page 557]. This metal carrier (e.g. nickel tube in case of indirectly heated tubes) acts as a reservoir of spare activator throughout the life of the tube. Contamination (aka cathode poisoning) consists mostly of oxidizing agents that act as traps[3, page 8][1, page 112], and counters the effects of activation. Funny thing is that both the activator and most contaminants are mobile at the operating temperatures (e.g. can diffuse by electrolysis)[3, page 16]. Some contaminants also become embedded in the crystalline structure of the oxide layer. But contamination is not the only deteriorating effect, there's also sputtering erosion, evaporation and sintering[1, page 115]. The high efficiency of the oxide cathode is in good part due to its high porosity, which significantly increases the effective surface area which acts as an emitter. Sintering solidifies the oxide surface and therefore reduces emission.
During operation of the tube, cathode current forms an electric field in the oxide layer which balances the diffusion of activator, barium (directly related to donors) and contaminants. A natural equilibrium forms which depends on the structural recipe of the cathode and its health state[3, page 35]. The above mentioned deteriorating effects effectively change the structure of the cathode rather permanently, resulting in general conductivity drop[3, page 18]. One artificial way to restore the conductivity is to pump the oxide layer with additional activator. This is accomplished by combination of overheating the filament so that metal base can release the activator, and by running pulse current to stimulate diffusion. Unfortunately the excess barium (its vapor pressure) created in this way is not in equilibrium with the aged oxide layer structure, and will subsequently be lost due to evaporation[1, page 67][3, page 30] in a process known as deactivation. This explains why rejuvenation is short-lived.

In my experience I witnessed rejuvenated CRTs which were bright, but certainly not sharp. This supports the argument that the center of the cathode is mostly lost, and the (temporary) increase of brightness is due to the artificially increased emission of the surrounding area.

Negative resistance and double peaking still remain without clear explanation.

References:
[1] THE OXIDE-COATED CATHODE Vol 1/2; Dr. Ing. G. HERRMANN, Dr. Phil. S. WAGENER; CHAPMAN & HALL LTD. London 1951
[2] Materials and Techniques for Electron Tubes; Walter H. Kohl; Reinhold Publishing Corporation 1960
[3] Electron Tube Design; RCA 1962

Nenad Filipovic


Re: 7904A restoration questions

Tom Lee
 

I second David's advice. If it ain't broke, don't break it.

-- 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 12/30/2020 02:35, David C. Partridge wrote:
Please don't shotgun replacing electrolytics, the odds are you'll do more harm than good. Some of those multilayer boards can be problematic when de-soldering components - you SO don’t want to strip a PTH.

If it works just use it.

David
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of David Campbell
Sent: 29 December 2020 23:05
To: TekScopes@groups.io
Subject: [TekScopes] 7904A restoration questions

Ive ordered all the electrolytic caps to do a shotgun replace. If the scope
works fine, if the plugins work, finer yet!






Re: 7904A restoration questions

 

Please don't shotgun replacing electrolytics, the odds are you'll do more harm than good. Some of those multilayer boards can be problematic when de-soldering components - you SO don’t want to strip a PTH.

If it works just use it.

David

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of David Campbell
Sent: 29 December 2020 23:05
To: TekScopes@groups.io
Subject: [TekScopes] 7904A restoration questions

Ive ordered all the electrolytic caps to do a shotgun replace. If the scope
works fine, if the plugins work, finer yet!


Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Tom Lee
 

That's a great suggestion, Miguel. I went the other direction many years ago to convert a 502 to work with a 492. It was a pretty quick conversion once I was able to find a suitable crystal. So Attilio has an additional option.

-- 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 12/30/2020 01:38, Miguel Work wrote:
You can buy a 503 change the crystal and use the nano to retune the 2nd band pass filter



-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Attilio
Enviado el: miércoles, 30 de diciembre de 2020 1:16
Para: TekScopes@groups.io
Asunto: Re: [TekScopes] Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Hi Dave,
thanks Dave, I'll go read the posts of the nanovna-users group.

--Cheers
Attilio







Scanned by McAfee and confirmed virus-free.
Find out more here: https://bit.ly/2zCJMrO



Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Miguel Work
 

You can buy a 503 change the crystal and use the nano to retune the 2nd band pass filter



-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Attilio
Enviado el: miércoles, 30 de diciembre de 2020 1:16
Para: TekScopes@groups.io
Asunto: Re: [TekScopes] Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Hi Dave,
thanks Dave, I'll go read the posts of the nanovna-users group.

--Cheers
Attilio







Scanned by McAfee and confirmed virus-free.
Find out more here: https://bit.ly/2zCJMrO


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

Roy Thistle
 

On Sat, Dec 26, 2020 at 03:47 PM, Nenad Filipovic wrote:


With this math someone may profit hundreds of $ for a 585 dug up out of some
old man's basement.
No not really ... unless one's reality is "reality T.V. shows." I think, most of the people doing this have a box of old, dusty, and used tubes, sitting in the basement... that will "sell on Ebay, for a bunch, a lot, of money!"... some day... or so they think. They're only dreaming. So disappointing, for them, when Ebay bills them for the ads.


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

Bill Perkins <sales@...>
 

Good, clean data on the 5687/6900 is available here:

https://www.pearl-hifi.com/06_Lit_Archive/08_Tube_Data/Cons_Data/5687_6900_Cons_Data.pdf

Having been thru many 100s of 5687s, as seen here:

https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html

and here:

https://www.pearl-hifi.com/03_Prod_Serv/Cryo/CryoValve_Tech_Info.html

I can say that the Tung-Sol 5687 is the NOS part to use to replace the 6900. But even so they have to be tested, see the reject rate in the Excel spreadsheet.

As nearly as I can tell the Raytheon-branded 5687 was a Tung-Sol part

Bill

Which 500 series was the 6900 used in? (I believe 6900 a twin medium mu triode.) 6AX7/12AX7 was high mu.
Bendix was (their gone) an interesting company, involved in the aerospace industrial military supply. (A common name during WWII and the 50's, and 60s.
The 6900 was a "hardened" tube.. made to withstand high g, shock, vibration, and was supposed to be more reliable. (well ... for at least the brief time a launched missile lasted.)
Unless one is planning on launching one's class A, audio amp, into low earth orbit... one doesn't need Bendix 6900s.


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

Roy Thistle
 

On Sun, Dec 27, 2020 at 08:02 AM, - wrote:


Bendix 6900
Which 500 series was the 6900 used in? (I believe 6900 a twin medium mu triode.) 6AX7/12AX7 was high mu.
Bendix was (their gone) an interesting company, involved in the aerospace industrial military supply. (A common name during WWII and the 50's, and 60s.
The 6900 was a "hardened" tube.. made to withstand high g, shock, vibration, and was supposed to be more reliable. (well ... for at least the brief time a launched missile lasted.)
Unless one is planning on launching one's class A, audio amp, into low earth orbit... one doesn't need Bendix 6900s.


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

 

An enterprising and unscrupulous person would pay for the scope, pull the tubes, sell them on eBay at a premium to the audio-nuts, use the proceeds to repopulate the scope with NOS tubes purchased at reasonable prices, and still make bank on the deal.

Just saying.

-- Jeff Dutky


Re: Tek 453A

Chuck Harris <cfharris@...>
 

I am not sure that you understand what I am trying to say,
so let me be clear:

Whenever the scrap companies I consult for see a 453/454
valued for less than $50, they tear it to bits, and it
becomes gold scrap, aluminum scrap, copper scrap, and plastic
scrap, worth something over $100.

It has nothing to do with storage space, as they don't get
stored beyond what it takes to fill a gaylord box with the
sorted remains to capacity.

I tried for a while to stem the flow, and indeed, I am
storing a pallet full of 453/454's, and I cannot do it. This
group has only one mode: Let me cherry pick your stash, for
less than the scrap value, remove any semblance of order in
your storage space, and leave you with a sore back, and a
disarrayed heap of trash.

So, as I said, if the group wants this stuff to remain in
one piece, then it better start valuing it as if it is more
than worthless trash; it is not, it is very valuable to the
scrap dealers... As scrap. They have no interest in hanging
on to it, and letting the public rummage through their space,
cherry picking the remains. Insurance won't allow it, and
high cost of warehouse space wrecks any value such cherry
picking might expose.

-Chuck Harris



Tom Lee wrote:

I have occasionally looked inside scopes.

Your calculation is correct as far as it goes, but your accounting fails to
comprehend storage costs. I modulate my offering price to achieve a net zero rate of
domestic mass transfer, otherwise the capacitor that is my home will exceed
breakdown. I will tell you, with a straight face, that some scopes are not even worth
$5 to me. Such calculations will, of course, lead to different decisions for those
with different constraints and wants.

As to keeping scopes out of the skip, that's certainly a worthy goal, which is one
reason I have a couple hundred. But again, storage space is a factor. Over the years
I've given away many scopes (and other instruments) to interested students. But the
rate has gone down markedly over the years, as the youngest are accustomed to
handheld battery-operated devices with touchscreens. There is, thankfully, a nonzero
percentage who are fascinated by crts and Nixies, but overall, the percentage has
been decreasing. And I have to be wary of those who want my Nixies merely to make
clocks.

Tom


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

John Williams
 

Thanks Roy. Lots of people out there selling tubes I guess.

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