Date   

Re: Remove adhesive from old Tek aluminium cabinet covers

Colin Herbert
 

I couldn't agree more, Carsten. My wife and I have been members of CAMRA for more than 20 years.
Cheers, Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Carsten Bormann
Sent: 17 December 2020 14:30
To: TekScopes@groups.io
Subject: Re: [TekScopes] Remove adhesive from old Tek aluminium cabinet covers

On 2020-12-17, at 14:00, Colin Herbert via groups.io <colingherbert=blueyonder.co.uk@groups.io> wrote:

4% ethyl alcohol in water
Americans call that “a beer” (Miller, Coors, …).
(In Germany, beer has to fulfill some additional requirements.)

Grüße, Carsten


OT SDR, DDR1 DDR2 RAM for free

 

For Shipping cost only, about $30 from Israel to US/EU
Paypal only.

About 30 pieces, all OK, name-brand memory. Micron, Crucial and others.
And a Seagate 160GB Laptop HDD

Especially for the older equipment.
Not worth my selling on epay, and I thought to offer them here, before recycling them.

Please contact me off-group if interested
yachadm ^T Gmail^COM


Re: So how does this hobby work now?

Jeff Kruth
 

Like any other hobby or endeavor of man, scarcity leads to speculators wanting to cash in.  In the 1980's when I was buying govt surplus buy the truckload, no one wanted 500 series scopes. They fell from $500-$1000 apiece retail to $50-$100. This was because there was no more commercial market, only hams and a few hobbyists.

In the mid  '80's, I used to see tube guys buying 585's for $10.00 at the Gaithersburg MD hamfest, pulling the tubes and leaving the carcass near the trash barrels.Its like anything else. Now if you want the stuff, you have to travel to where it is and make a deal, then lug it home. Or pay a high price to those who are remarketing on eBay etc. There you are paying for the convenience of sitting on your duff, ordering off the computer then waiting for it to be delivered at your door. How easy!  I used to drive all over Hells half acre chasing stuff down.  But now, the pickins are slim and the low hanging fruit is gone. Things like 519's were immediately scrapped by anyone who bought them because who wanted a scope with no vertical sensitivity and a few centimeters of deflection.... People valued the 4X150s and sockets more than the rest of the scope! No one cared about 1 GHz BW, they looked at the size and said UGH. I recently passed (2018) on 1500 pounds plus of old Tek scopes because it was not worth my time to struggle with moving, storing, then trying to find a home for 'em then getting the shipping money out of any potential customer. Since the fuel surcharge of the mid 2000's UPS has steadily raised their prices to absurd levels. At one time junkyards were full of model T's. Now original parts from one are quite pricey. Same with the old Tek scopes. Of course as the old timers kick off, some stuff ends up available for a song. The widow just wants the basement clean again.... Due to the way govt accounting worked, excess equipment hit a HUGE peak in the late 80's early 90's. Stuff was available by the pallet load for CHEAP. But there was no market for it then, so off to scrap much of it went. I personally saw Cadisco and US Surplus in Baltimore, both BIG dealers, sell their inventory to scrap metal dealers when they closed their doors. It would make tears come to the eyes of many on this list. I always made it a point to get it when the getting was good. The only problem is moving it, storing it and caring for the stuff over the years. Adds a lot to the value.When guys would approach me after the govt auction, I would sell stuff off the pallet pretty cheap. I didnt have to move it store it and fix it. All adds to the cost. Oh well. Who would have thought that in 2020, there would be a internet list of Tek addicts! Still storing all that stuff until now would have been a showstopper. And, no offense intended, but there is still no money in it, so why would someone bother?I mean, people beef about paying $100 for something, when in reality $100 doesnt buy hardly anything of value anymore. Its like $25.00 back in the late 70's when this stuff was available. $100 is 20 Big Mac meals, nothing really. Yet people back then would pay $25-50 for a 1A4 with all the nuvistors in it. Even then, the tubes were worth more than the plugin.No one wanted the sampling stuff at all. Too much work to fiddle with. YMMVJeff Kruth  In a message dated 12/18/2020 1:30:17 AM Eastern Standard Time, snapdiode=yahoo.com@groups.io writes: Now that it appears that there is a much smaller offering of 500 series stuff on eBay, where do people get stuff now? There hasn't been a 1S2 listed in years AFAICT. The single 1S1 that's on now has been re-listed several times at 280$. Spectrum analyzer plugins, 1A5, test units, Type O, etc So how does one ascertain the value? Where to get one? I mean there's a Type O for 200$. Who would buy that?


So how does this hobby work now?

snapdiode
 

Now that it appears that there is a much smaller offering of 500 series stuff on eBay, where do people get stuff now?

There hasn't been a 1S2 listed in years AFAICT. The single 1S1 that's on now has been re-listed several times at 280$.

Spectrum analyzer plugins, 1A5, test units, Type O, etc

So how does one ascertain the value? Where to get one? I mean there's a Type O for 200$. Who would buy that?


Re: 475A Chop Blanking and a Theory Question

 

Well, what I can't solve by intellectual effort (a humbling experience for me), I have managed to solve by brute force (so to speak).

I checked Q348 with my multimeter's diode function and it appeared to be open between all pins (not what I expected) so I figured I had another blown transistor in the Z-axis circuit (which wouldn't have been surprising after what I found in the Z-axis amp). I pulled Q348 and tried it in my component tester, but it tested fine (identified as a PNP transistor, Hfe = 205, Uf = 678 mV), so I put it back. Then I buzzed out the circuit backwards from the emitter of Q348 toward U340 (the 4700). I found connectivity to R348, and R348 measured as the correct value (~330 ohms), but I could not find connectivity from R348 to any pin on U340 (R348 is supposed to be connected to pin #8 of U340).

Further inspection revealed that there was connectivity to the pad under pin #8 on U340, so I pulled U340, cleaned its pins with IPA (they were a bit dirty, but not terribly so), and reinstalled U340 in its socket. Now the CHOP blanking is working as expected.

On one level I am very pleased with my diagnostic skill, but on another level this feels too easy. Even if I'm not quite up to speed with the underlying circuit theory, I feel like I need more of a challenge. At the same time, I'm pretty sure that I'm not quite up to diagnosing some of the less well defined problems I have with my father's scopes (e.g. a "drifty" channel on the 2213 that seems to clear up if I keep the scope running for any period of time, or the odd wiggles in channel 2 on the 475 that were visible in the CHOP test).

I guess I'll just keep soldiering through the performance checks on the 475A and see what comes.

-- Jeff Dutky


Re: 475A Chop Blanking and a Theory Question

Carsten Bormann
 

On 2020-12-18, at 05:40, Jeff Dutky <jeff.dutky@gmail.com> wrote:

what is the purpose of Q348
I didn’t look at the schematics, but your description sounds like it is a level shifter from the positive-to-ground TTL signal to a negative-to-ground input to the Z-axis amplifier.

»The current gain of a common-base amplifier is always less than 1. The voltage gain is a function of input and output resistances, and also the internal resistance of the emitter-base junction, which is subject to change with variations in DC bias voltage.«
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/common-base-amplifier/

Grüße, Carsten


Re: 475A Chop Blanking and a Theory Question

Dave Peterson
 

Yes, it's a PNP.

I think I see better now. The description for Z-axis amplifier for the 475 Service Manual, page 3-19 says:

"The current signals from the various control sources are connected to the emitter of Q1338 and the algebraic sum of the signals determines the collector conduction level."

One of those signals coming in is Ice (that's collector/emitter current) of Q348 in the chop blanking circuit.

I suspect the -2.5v in the schematics is a nominal voltage level, but the injection of current from Q348 will raise the voltage at the emitter of Q1338 probably cutting off the forward bias of it's base/emitter junction.

The wiki page for Bipolar Junction Transistors has a nice image of the current amplification that goes on in a BJT. The current from the forward biasing of the base/emitter junction triggers a large current between the collector and emitter. I think the purpose of Q348 is to provide current drive to the Z-axis amplifier Q1338. The output of U340 is likely not able to provide that current drive.

All this examination of these scope circuits is rekindling my fundamental circuits classes, but I know how much I don't remember. So I don't mean to speak as an expert. I'm sure there are plenty on this forum who can explain this better. I hope my explanations help.

Dave


Re: 475A Chop Blanking and a Theory Question

 

Dave,

I understand every word you said, individually.

The symbol for the transistor shows an arrow pointing to the base, that's a PNP transistor, right? And the emitter is the connection with the arrow, right?

Well, the connection with the arrow is connected to the output of the chain of inverters (U340, a 7400, elements A, B, and C), and the base is connected to ground. When the inverter signal is positive we have forward biased the emitter base junction, and most of the current will flow through from the emitter to the collector, right?

When the output of the inverter chain is low then we will (I hope) have the voltage on the emitter close enough to ground (it's TTL stuff, so it only really needs to drop below something like 1.5 V, I think) that the transistor will be in "cut off", right?

When the transistor is in "cut off" it's basically an open circuit, so it's not pulling the collector side in either direction: the collector side will do whatever it was already trying to do. This raises a further question: what is the purpose of Q348? It's not amplifying anything. Is it just there to provide a high impedance input to the Z-axis amplifier system? (I used a big word, "impedance" that I don't think I fully understand. I hope I used it right. I meant that Q348 seems to be there to make it very hard for the collector side to have any affect on the emitter side)

I'm also a little fuzzy on how the beam intensity signal works, but looking at the schematic, the beam intensity pot drives between -8V and +15V. I don't recall if -8V is high or low beam intensity.

My ability to read a schematic falls far short of what is required to reason about what is going on in the Z-axis amplifier, and how it will affect the mesh voltage in the CRT, but I think a high mesh voltage should suppress the beam.

I'm going to set up the 475A for investigation over the weekend. I figure that whatever I don't understand it theory will become clear in practice (I may not be able to read a schematic, but I can read a multimeter value or a scope trace just fine). This also gives me a chance to use my just-fixed 2236 for it's intended purpose.

-- Jeff Dutky


Re: 475A Chop Blanking and a Theory Question

Dave Peterson
 

I'm a bit rusty on my discrete xtor education, but I believe Q348 should be passing the +5v output of the inverters.

The forward biasing of the Base-Emitter junction of a Bipolar Junction Transistor results in a Emitter to Collector current path, not Collector to Base.

Dave

On Thursday, December 17, 2020, 07:37:05 PM PST, Jeff Dutky <jeff.dutky@gmail.com> wrote:

I've been going through the performance check process with my recently repaired 475A, partly to get familiar with what will be needed to do a calibration, but also to verify that the device is in fact fixed, and I've run into a few snags. The one I'm concentrating on at the moment is the chop blanking: when I did the chop performance check I was clearly able to see the traces joining the channel 1 and channel 2 signals, so there's still a problem in the beam intensity system. I know that the problem isn't the beam intensity amplifier, because I don't see the horizontal retrace anymore, and that makes me suspect the chop blanking signal that feeds into the beam intensity amplifier.

So I'm looking at the vertical channel switching schematic, and I find this chain of inverters (U340) that feed the emitter of a PNP transistor (Q348) whose collector then feeds into the beam intensity amplifier, but whose base is connected to ground.

This is called a common base configuration?

It looks to me as if the signal coming out of U340 is forcing Q348 to sink current to ground from the beam intensity amp, but the diagram seems to indicate that the voltage on the collector side is -2.5 V, so I'm confused.

Maybe this isn't a problem for diagnosing or fixing this circuit, but I really don't understand how this is supposed to work, and that bothers me.

(DISCLAIMER: as I've said before, I'm almost a complete amateur in electronics, and transistors are still in the realm of myth and magic as far as my understanding of them goes)

-- Jeff Dutky


475A Chop Blanking and a Theory Question

 

I've been going through the performance check process with my recently repaired 475A, partly to get familiar with what will be needed to do a calibration, but also to verify that the device is in fact fixed, and I've run into a few snags. The one I'm concentrating on at the moment is the chop blanking: when I did the chop performance check I was clearly able to see the traces joining the channel 1 and channel 2 signals, so there's still a problem in the beam intensity system. I know that the problem isn't the beam intensity amplifier, because I don't see the horizontal retrace anymore, and that makes me suspect the chop blanking signal that feeds into the beam intensity amplifier.

So I'm looking at the vertical channel switching schematic, and I find this chain of inverters (U340) that feed the emitter of a PNP transistor (Q348) whose collector then feeds into the beam intensity amplifier, but whose base is connected to ground.

This is called a common base configuration?

It looks to me as if the signal coming out of U340 is forcing Q348 to sink current to ground from the beam intensity amp, but the diagram seems to indicate that the voltage on the collector side is -2.5 V, so I'm confused.

Maybe this isn't a problem for diagnosing or fixing this circuit, but I really don't understand how this is supposed to work, and that bothers me.

(DISCLAIMER: as I've said before, I'm almost a complete amateur in electronics, and transistors are still in the realm of myth and magic as far as my understanding of them goes)

-- Jeff Dutky


Re: Finding good homes for older Tektronix equipment (547, plugins, 454A)

Mark Vincent
 

Jeff,

I am interested in getting items from you. I would like to know what you have, working condition, willingness to ship and prices. Thanks.

Mark


Re: Looking for accessories for 2400 series scopes.

Roy Thistle
 

On Thu, Dec 17, 2020 at 04:17 AM, Lawrance A. Schneider wrote:


If anyone wants them
So much heartbreak avoided... and so much of your time not wasted... if only you would say I'm located in Kalamazoo, or Timbuktu... and I would, or would not, ship to you; because, your located in Uttar Pradesh or Arkhangelsk.


Re: Alcohol (was: Re: [TekScopes] Remove adhesive from old Tek aluminium cabinet covers)

 

Dave,
TOO FAR OFF TOPIC.
Please stop this nonsense.
Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dave Seiter
Sent: Thursday, December 17, 2020 11:16 AM
To: TekScopes@groups.io
Subject: Re: Alcohol (was: Re: [TekScopes] Remove adhesive from old Tek aluminium cabinet covers)

Waaayyyy off topic, but what I was fascinated by was the data from toilet paper manufacturers that stated the the *average* TP use was 1/3-1/2 roll per person, per day. Who uses that much?! Around here, we go through a roll in about three weeks per person. (I actually started keeping track) Of course, these are the large Costco rolls, but still...
-Dave
On Thursday, December 17, 2020, 07:43:53 AM PST, Jeff Dutky <jeff.dutky@gmail.com> wrote:

Many of the COVID-caused supply shortages are just demand shocks: just-in-time manufacturing and delivery is very good if the demand is predictable, but when demand doubles or triples (as happened, for example, with toilet paper) it can take quite a while for supply to readjust. I suspect, however, that another factor in the ongoing shortages is that many manufacturing operations have very little excess labor capacity, and that only a few people out sick is enough to bring entire operations to a halt. It's one thing if you have to cover for one person out sick for a week or two, but when 10% of your staff is out for two weeks you probably don't have enough cross-trained people to cover all positions. Now multiply that across dozens of companies involved in any supply chain and you get massive shortages of all kinds of things, even things that are not directly being demanded by the crisis.

None of this is to say that I completely understand the supply shortages caused by COVID, I just think it's a fascinating example of how complex systems can fail under unexpected conditions.

-- Jeff Dutky











--
Dennis Tillman W7pF
TekScopes Moderator


Re: Looking for accessories for 2400 series scopes.

 


Re: WTB: 3B4 plug in for RTTY

Brenda
 

Hello Bruce,

I do have not 1 but 2 Tektronix 3B4 time bases that I would be willing to part with. 1 of them is functional as far as basic use goes. I am not a professional by any means, so I don't fully understand everything about all the features. But last time I used it, it does trigger very well and has a "NOS" 7119 tube for the amplifier according to the flea bay seller which I had to drop $100 for 1 of those tubes. (People are greedy when they see the Amperex logo....) The other one is a parts unit and is in better shape cosmetically that I have been holding onto for the working time base. I think I did throw some tubes in it and tried it out, and the sweep was all wonky, but it did seem to trigger if memory serves me right, been a few years since I have piddled with the time base. I am pretty sure that I have a hard copy of the manual as well.

If you are still interested, I could pull out that time base and check it to the best of my knowledge. Granted, they are not calibrated.

Brenda


Re: Tektronix 317

Bob Albert
 

Well if you like I can take a look.  I'm in the San Fernando Valley.
Bob

On Thursday, December 17, 2020, 02:22:45 PM PST, <brockkoren@gmail.com> wrote:

I turn it on and it gets power, but there is no trace on the CRT. I move both position knobs and AC coupe it but still can't see a trace.  I open it up and there does not appear to be any lose wires or connections. It was pretty clean and I used compressed air to clean it out more. The fan kind of works, it spins really really slow. The tubes all appear to glow but after the 317 is on for 30 minutes it starts to make some noise so I turn it off for fear of cooking something.


Re: Tektronix 317

 

I turn it on and it gets power, but there is no trace on the CRT. I move both position knobs and AC coupe it but still can't see a trace. I open it up and there does not appear to be any lose wires or connections. It was pretty clean and I used compressed air to clean it out more. The fan kind of works, it spins really really slow. The tubes all appear to glow but after the 317 is on for 30 minutes it starts to make some noise so I turn it off for fear of cooking something.


Re: WTB: 3B4 plug in for RTTY

widgethunter
 

Look at 2B67; hor in without tunnel diode triggering and often available for nothing.The 3B4 is much more rare and my personal favorite, but may be overkill for your application.

-----Original Message-----
From: greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io>
To: TekScopes@groups.io
Sent: Thu, Dec 17, 2020 9:46 am
Subject: Re: [TekScopes] WTB: 3B4 plug in for RTTY

I want to be able to display other signals as well as the  common RTTY
X-Y tuning indication without needing to exchange the modules.

      Bruce Gentry, KA2IVY


On 12/17/20 12:38, widgethunter via groups.io wrote:
why not use another vertical plug-in for external hor input?
 
 
 
-----Original Message-----
From: greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io>
To: TekScopes@groups.io
Sent: Wed, Dec 16, 2020 8:37 pm
Subject: [TekScopes] WTB: 3B4 plug in for RTTY

I am going to use the 561B rack mount scope I have restored in an RTTY
setup.  The time base I have does not offer an external horizontal
input. A 3B4 or perhaps 3T4 does have it. Does anyone have one to spare?
Thanks,

Bruce Gentry, KA2IVY












Re: WTB: 3B4 plug in for RTTY

greenboxmaven
 

That won't be a problem. There is plenty drive available and at low impedence, the signals for X-Y will be at low frequency. A 3B4 will do the job fine, and allow observation of other signals conveniently.

Bruce Gentry, KA2IVY

On 12/17/20 16:00, widgethunter via groups.io wrote:
That could be problematic; the hor input isn't cal'd and it probably won't match the vertical plugin's impedance or gain. For symmetrical x/y displays of equal bw you will likely need 2 identical vertical amps, cal'd to the input sensitivity of the mainframe.
-----Original Message-----
From: greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io>
To: TekScopes@groups.io
Sent: Thu, Dec 17, 2020 9:46 am
Subject: Re: [TekScopes] WTB: 3B4 plug in for RTTY

I want to be able to display other signals as well as the common RTTY
X-Y tuning indication without needing to exchange the modules.

Bruce Gentry, KA2IVY


On 12/17/20 12:38, widgethunter via groups.io wrote:
why not use another vertical plug-in for external hor input?
-----Original Message-----
From: greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io>
To: TekScopes@groups.io
Sent: Wed, Dec 16, 2020 8:37 pm
Subject: [TekScopes] WTB: 3B4 plug in for RTTY

I am going to use the 561B rack mount scope I have restored in an RTTY
setup. The time base I have does not offer an external horizontal
input. A 3B4 or perhaps 3T4 does have it. Does anyone have one to spare?
Thanks,

Bruce Gentry, KA2IVY




















Re: WTB: 3B4 plug in for RTTY

widgethunter
 

That could be problematic; the hor input isn't cal'd and it probably won't match the vertical plugin's impedance or gain. For symmetrical x/y displays of equal bw you will likely need 2 identical vertical amps, cal'd to the input sensitivity of the mainframe.

-----Original Message-----
From: greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io>
To: TekScopes@groups.io
Sent: Thu, Dec 17, 2020 9:46 am
Subject: Re: [TekScopes] WTB: 3B4 plug in for RTTY

I want to be able to display other signals as well as the  common RTTY
X-Y tuning indication without needing to exchange the modules.

      Bruce Gentry, KA2IVY


On 12/17/20 12:38, widgethunter via groups.io wrote:
why not use another vertical plug-in for external hor input?
 
 
 
-----Original Message-----
From: greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io>
To: TekScopes@groups.io
Sent: Wed, Dec 16, 2020 8:37 pm
Subject: [TekScopes] WTB: 3B4 plug in for RTTY

I am going to use the 561B rack mount scope I have restored in an RTTY
setup.  The time base I have does not offer an external horizontal
input. A 3B4 or perhaps 3T4 does have it. Does anyone have one to spare?
Thanks,

Bruce Gentry, KA2IVY











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