Test Equipment Anonymous (TEA) group therapy thread

[cyclin_al]

OK so here is the 502A ! 

....snip

The handles. Yep, those old leather handles rot and fall apart. Luckily Tek later went to much more durable plastic handles. I had the same issue with my Type 535A. Nothing left but the rusty inner frame. I bought some leather strips and a leather tool kit and made new ones utilizing that inner frame. It came out decent and secure enough to be able to easily lift the scope.

I could salvage plastic handles from another scope for sure, but I don't find plastic very qualitative or sexy... my idea, long term, for my collection of glowing Tek scopes, is to try to reproduce the original leather handles, to make it look as good and sexy as possible. I could take a rotten handle and remove the stitching to unfold the leather piece so I can use it as a template to cut a new piece of fresh leather. Sawing it would be difficult I guess, without the appropriate equipment, unless they are just hand stitched like a steering wheel, I don't know. So I would spend some time  learning a bit about the basics of leather craftsmanship on the web, see how it's done. Would then try to find some local "leather club ", probably full of grand  ma's making hand bags and whatnot... so they can help me out do a good job of it.  I would get the metal / bright work sand blasted and sent out to get refinished / re-plated so it looks like new.
Once I have figured all this out and am happy with the result, I would then be able to make a small batch of handles to cater for my many scopes.

Then with a repainted cabinet and new screws.... overall should make for a nice sexy looking cabinet ! 


Your leather handle sure looks beefy ! That's one chunky strap and heavy duty rivets, should hold up ! 
Seeing these rivets reminds me of work... inspecting millions of rivets on the aircraft.  So I can't help but notice that the third rivet from the left is not acceptable !    Way too close to the edge. I don't know for leather, but for aluminium rule of thumb is the axis of a fastener should be at least 1.5 times the diameter of the fastener, away from the edge of the part. If you have a whole bunch of rivets holding the parts together, as is often the case, you can afford to have a few of them closer to the edge than normal, like x1 instead of x1.5, but you need to do the paper work / "concession"  and send it to the R&D bureau, for acceptance (or not...).

I think the LCF (low cycle fatigue) on a scope handle is much less than for an aircraft!  Nonetheless, you are correct.

Working with the leather is rather easy.  You should be able to cut it with a hobby knife and a straight-edge.  Start with a fresh blade, and will probably need to also change the blade after you are done.
There are also large shears used for leather.  They have blades that look somewhat similar to "tin snips" or "aviation snips" but slightly larger, with longer handles.

You should be able to buy a small bottle of dye in the appropriate colour and apply it with a cotton rag or small brush.

[factory]

OK so here is the 502A ! 

Sorry for not posting yesterday when I got it. Was too tired once back home.

So I now know a bit more about this "transformer" shit on his ad, where he claimed the transformer was used for tube amps and was selling for parts just for that...

Actually turns out he has not one but TWO 502A ! He gave me the best one and opened it up for me spontaneously to show what condition it was in inside, and that no part was missing.

Is the cover for the HV transformer missing, or did you remove it to investigate the TF?


The less said about mine the better, last time I worked on it it keep destroying diodes in the trigger circuit, followed by the transistor.

David

[cyclin_al]

In the german area i come from they say: "They go in the cellar to laught" about people who are always angry.

That explains a lot... I don't have a cellar!

I could tell you some Dad-jokes ...

 

Please. I´ll add them to my dad-a-base.

I am sure the distinction between bad jokes and your dad-a-base will be quite apparent 

[factory]

Also tried out a the UV lamp and remote for IR (was no good, needs removing to run without flashing).


David

Ah well it was worth a try. Did you manage to try the method someone else suggested, using a graphics manipulation tool?

I ran out of time yesterday, maybe have a play at the weekend.

I've had another look at the hp 745A AC calibrator this afternoon, testing with the Tek THS reveals no problems with the output (34401A DMM didn't like it when tested last week).

...snip

That's the one thing my little (?) collection of TE lacks. A good AC calibrator. And finding one that works, and won't break the bank.

And maybe not a hernia producer like mine, weight of the 745A is about 29kg, the 746A high voltage amplifier companion is another 34kg, might be a while before I find one to add to mine (only one available is collection only in the US).

Also tried out a the UV lamp

Believe.

Thanks for that  , I think that is pretty much what can be seen with the UV, but I couldn't tell the which was the blue or black line, with either normal light or UV though.

David

[Vince]

Working with the leather is rather easy.  You should be able to cut it with a hobby knife and a straight-edge.  Start with a fresh blade, and will probably need to also change the blade after you are done.
You should be able to buy a small bottle of dye in the appropriate colour and apply it with a cotton rag or small brush.

Yeah cutting a new piece sounds like the easy and fun part. As for dying not even sure I would have to go there, as I think I would prefer mat black liek some of my Tek scopes do. Not all handles are blue...
so I guess any leather is available in black...

No the part that sounds the trickiest / most intimidating to me, is the sewing/stitching however it's called, to put it back around the metal work..... make something that looks good/tidy/straight, and is strong/does its job...

Also does one perforate the leather piece before hand, to make way for the sewing needle, or does the needle do its own hole as you along...
If need to perforate before hand, I guess you need some kind of appropriate tool to make it look good and have holes with an even consistent diameter, looks and spacing/pitch... 
All basic newbie questions so I am sure when the time comes, it should not be too hard to find the answers and have a go at it...
Good thing is, a handle necessitates so little leather, that it's cheap, so I can afford to make 2 dozens trials/experiments if need be, until I manage to get a result worthy of the original, that I would be satisfied with...

[Vince]

OK so here is the 502A ! 

Is the cover for the HV transformer missing, or did you remove it to investigate the TF?


The less said about mine the better, last time I worked on it it keep destroying diodes in the trigger circuit, followed by the transistor.

David

Yep the cover is missing !!!   

I just noticed it earlier today while looking at my pics !
That's why one 502A is not enough, one needs at least TWO of every model !
Luckily my other 502A does have both its HV covers in place, so I am covered 

Hmm.... recurrent trigger problem ? Interesting... maybe mine suffers the same and that's why I have no sweep... maybe sweep itself is working fine, just never triggered...
I would have hoped though, that at least in "AUTO" mode, it would trigger the sweep.. but no.

[Vince]

Vince I feel your pain...[/b][/i][/color] there were times when I wished for 56K speeds... 

Welcome to my world...

That said... [..] I had myself set up with 1GB/1GB service for $66/mo,

That sounds like a deal... your suffering was not long enough for it to have any meaningful impact on your view of the internet world... you need to suffer much longer than that. Like me, 2 years and counting.

I have more BW than I know what to do with.

Just gimme 5% of that 1GTB, will be plenty enough to make me happy and you won't even notice the loss.. but I sure will appreciate the gain on my end ! 

[med6753]

Mother Nature left a reminder note last night. 

Yeah, same here. 24 degrees Funkenkopft and 1.5 inches on the roof of the car when I got up at 6 am... crawled into my wellies and did the usual morning snow-belt dance ritual so it would be ready for my wife's first day at the new job.

As I was bringing the thawing pot and snow shovel back inside, of course then the most pertinent question popped into my head...

"Why the fuck didn't I park in the garage last night...?"

mnem
You may all now point and laugh at the silly ol' dwagon...

That is all you got?  Woosses 

We had a drift 2 feet deep on the driveway.  Barely got out with the truck, even with the 4WD on.  Had to get the kid to school sort of on time...
Came home and shovelled by hand for 2 hours.  Moved a lot of snow from the driveway over to the side to cover up the green grass where there was no snow drift 
A couple of hours later it rained and melted all the snow away.  All that shovelling was for naught 

Now we have a couple of inches.  Just enough to drive back and forth with the truck to pack it down.  Sounds lazy?   Not at all.
It is necessary to pack down the first layer of snow so that the snowblower can be used for subsequent snowfalls.  If not, then the snowblower becomes a gravel blower, which is to be avoided when one has vehicles and windows.  Plus, the house has windows too...
Okay, I am lazy and p***d off by all that shovelling.

-- GWN version of masochism

We typically don't see large snow amounts until after Christmas but there are rumbles and rumors of a potentially big storm next week. I say bring it. 

[factory]

OK so here is the 502A ! 

Is the cover for the HV transformer missing, or did you remove it to investigate the TF?


The less said about mine the better, last time I worked on it it keep destroying diodes in the trigger circuit, followed by the transistor.

David

Yep the cover is missing !!!   

I just noticed it earlier today while looking at my pics !
That's why one 502A is not enough, one needs at least TWO of every model !
Luckily my other 502A does have both its HV covers in place, so I am covered 

Hmm.... recurrent trigger problem ? Interesting... maybe mine suffers the same and that's why I have no sweep... maybe sweep itself is working fine, just never triggered...
I would have hoped though, that at least in "AUTO" mode, it would trigger the sweep.. but no.

I don't know, mine did have a sweep, I can't remember if that was before or after sorting the broken intensity control, it also had three white toobs, one of which was the neon voltage reference. It was rescued from a local house clearers stall at a vintage agricultural steam/yesteryear show for £20.


This diode failed twice on the Timebase mode switch (looking at the picture now probably needs the neon replacing too), then this transistor was found deceased (maybe due to open circuit neon indicator causing over-voltage), it's currently in storage.


Edit: First image below shows the top view, but correct picture of front in full size, that's a new one. Had to upload it again. 

David

[Vince]

502A : it just got its quick clean on the front panel. Well "quick" still means 30/45 minutes, as there are so many  nooks and crannies to clean patiently in so many knobs.... but it's quick in that I don't remove the knobs.. I only remove the CRT bezel and the associated bits and pieces, so I can give them a good clean as well, clean the face plate behind and... well if you don't remove all that, water ingresses in there, it's a mess and you end up having to take everything off to clean the mess anyway... so might as well do it from the get go.

It cleaned up really nice, not much greasy fingers prints to deal with, pretty much only saw dust as expected, but that's all.
Also happy with the way the red knobs turns out. They looked kinda dark red at first, which I hate, but once cleaned they are now a much brighter/ more vibrant red. Makes them look so much fresher, not crusty at all.
Also, another thing that makes the front panel look good, to me at least, is that the UHF connector don't have the usual crusty semi-transparent, vomit brown dielectric piece in them. All my scopes do... not this one. Somehow the dielectric piece still looks brand new, sparkling, snow white. Weird. The outer / threaded part still looks old an crusty, but the dielectric piece no, it's like new.  Maybe Tek had different suppliers for these UHF connectors... or maybe the 502A having out of the ordinary specs compared to the general purpose models, called for different UHF connectors specs ? Don't think so... as my other 502A has the ugly brown dielectric, not the white one...

One thing I noticed while taking the CRT bezel apart, is that although it does not have a colour filter... it still has a plastic piece on top of the graticule, where the colour filter would go. Plastic is strange, never seen one like that. It's very thing and flexible, not like your colour filter that's very thick/rigid plastic.
Also, even though it looks transparent, you can kind see some tint to it, like it was dirty or something, but it's not, I cleaned it well....
Also, there are words engraved into it ! It says "THIS SIDE OUT " . Which means it matters that this transparent piece goes one way and not the other ?! 
Weird... so I am thinking, it all looks like maybe it could be some kind of polarizing layer or something ?! In the 50's / early '60's ?!
Whatever it is, I found it interesting... will dig a bit more into it I think...

Also CRT related... the bezel is missing its 4 rubber washers/spacers that go onto the studs to keep the bezel from contacting the face plate directly.
Instead, I found bits of folded paper held in place with sticky tape ! How charming ! I removed all that crap, cleaned as well I could... and will be putting 4 washers that I will steal from some donor scope...

Anyway, looks real clean and nice now, kinda motivates one to go further with the troubleshooting ! 
Now when you look at it you are attracted to it and want to play with all the knobs and switches, whereas before, the instinct was more like "Fuck me I am not touching this thing, gimme gloves and a breathing apparatus !!! " 

A few "BEFORE" pics, then after.... hopefully you will see a difference ! 

[tautech]

Also does one perforate the leather piece before hand, to make way for the sewing needle, or does the needle do its own hole as you along...
If need to perforate before hand, I guess you need some kind of appropriate tool to make it look good and have holes with an even consistent diameter, looks and spacing/pitch... 

Yep, with a Pricking wheel....look it up. 

[Neper]

77 knots east of Newfoundland. Now, that's what I call a decent breeze...

[vk6zgo]

It was a 12AT7 tube, V474 on the upper beam sub-assembly. Looked it up in the schematics, it's the tube that drive the lower deflection plate. Tek scopes seldom use the 12AT7, have very few of them... ended up pulling one from my other 502A (which I know works). Need to buy a new tube now then, of course. Hopefulyl they are cheap and I can buy two or 3 of them to have spares.

In our part of the world it's ECC81, and it is common in guitar amps. Still being made. Expect to pay about 15€ for it. Or 45€ if you are a man⁰ with small genitals, a very unscientific stereo system, and want NOS. 


Footnote 0: I could be modern and say "person", but since the people who "want to believe" are overwhelmingly self-identifying as cis men I will not. Any female audiophool who feels left out: Sorry, not sorry. You should know better; because this shit is where cis men lose themselves. Don't get dragged down to their level.

12AT7, 12AU7, 12AX7, etc are as common as dirt over here. And cheap as dirt too as long as you stick with RCA or GE. But if you want the "ECC" version of these tubes which are far superior and sound better (Yea, right) then audiophool pricing takes effect. 

If they are so cheap send me a dozen of them so I have some stock here !

ECC is just the European designation for the 12A-X/Y/Z , it's the same tube as Mansaxel said. Hell even that audiophool website I mentioned, is honest enough to admit it upfront ! They do say though, indeed, that the audio guys often are hesitant to buy the tube under its ECC / European designation, thinking it would sound different (worse) somehow !

https://humbuckersoup.com/ecc83-vs-12ax7-tubes-difference/

There is a little bit of "method in their madness".

In the twilight of the tube era, there were a number of minor European brands which had a rather poor reputation.
There were also "pretend" brands which bought tubes from all over & relabelled them----"Zaerix" comes to mind!

The problem was that even "reputable" companies started doing this, notably Mullard.
In Oz, if you bought from Philips, you often got a mix of their own tubes & Mullard (or whatever) devices, so this needed watching.

Back then, we found that, during those years, in terms of reliability & meeting initial specs, the list read:-

AWV-----consistently exceeded specs
RCA-----consistently met specs
Siemens------consistently met specs
Sylvania------consistently met specs
GE------usually met specs
Philips------usually met specs
Mullard------usually met specs, with some "really battling"
Brimar,------usually met specs (just)

with the others making up a gaggle of "also rans">

[vk6zgo]

I could salvage plastic handles from another scope for sure, but I don't find plastic very qualitative or sexy... my idea, long term, for my collection of glowing Tek scopes, is to try to reproduce the original leather handles, to make it look as good and sexy as possible. I could take a rotten handle and remove the stitching to unfold the leather piece so I can use it as a template to cut a new piece of fresh leather. Sawing it would be difficult I guess, without the appropriate equipment, unless they are just hand stitched like a steering wheel,

Your idea is definitely "do-able".

When I was a little kid in the early 1950s, we had a horse, who as part of her activities, pulled a "spring cart".
When we got her, the harness that came with the (very secondhand) cart was in pretty dire condition, so my parents "reverse engineered" it in the way you suggest.

Dad bought some "Greenhide" leather, & they made a new harness.

A handle should be fairly easy, if you do enough research on the stitching method.

[Vince]

502A

OK some more.

Deoxited the XY switch.. no joy, still requires to be in-between its two stable positions in order to get dots / anything on the screen. That's strange... it must be more complex than meets the eye... but what ?! 

Then Deoxited the entire scope. No joy, nada. Zero change whatsoever to the way the scope behaves.

But that's not depressing... it's still progress ! First, now I can rule out dirty contacts... or else I would have had at least SOME kind of change, somewhere, one way or another.... but nope, not a sausage. So that means the issues I have are clearly actual electrical faults, most likely dead tubes all over the place... that purple/gassy 12AT7 was not a good start I guess... probably means there are a bunch more tubes that are cactus.

I guess I could brute force it like some would, and just pull all the tubes one by one to test them... but I don't have a tube tester anyway. Well I have my 575 transistor curve tracer, once it's restored I plan on making a little adapter to enable it to test vacuum tubes. But for now, no way to do mass tube testing...
The better, that means we actually get to use brain cells, look at schematics and probe stuff,... that's much more interesting and entertaining, to me 
But before I go probe inside this scope, it first needs a good shower ! It's too dirty / dusty inside, with cog webs to boot, brrrr....
Just a quick shower to get it to a decent state of cleanliness.

I checked the power rails. It's all fine. At first they were all a bit high, like 104V instead of 100V, 370 for 350, and -157V instead of -150V, for the reference voltage. Let it warm up for an hour, voltages decreased slightly, getting closer to spec. Like 369 instead of 371, for example. So I adjusted the -150V reference rail as good as I could (I managed -149.9V, good enough....), and all other voltages where then, logically, to spec. So that's all good.

As for ripple... I was "hoping" one rail would be tragically out of spec, given I heard that cap "vent" yesterday. That would indicate me what cap died.
But.... ripple was well within spec on all rails  ?! 

But I think I found the bad cap anyway, see pictures. It's not one of the big can caps, no. On the UNDER side of the lower deck, soldered on ceramic strips, I see 4 small axial electrolytic caps, all identical, 6.25uF.  They look similar to the bad ones in my HP 120B tube scope.... light grey/silver in colour, black text, transparent plastic wrapping...
I noticed one of them has the positive end looking bad... looks like the red seal is not in good shape eh ?!
The others are only marginally better...

I looked them up on the power supply schematic below, highlighted in yellow. They provide ADDITIONAL filtering for the vertical amplifiers... additional filtering, not primary. Since the ripple upstream is already within spec, these small caps going high ESR / drying out is not a big deal I think, ripple is still within reason.. it's not gonna cause the catastrophic failures and weird and wonderful  stuff I see all over the place in this scope...
Worst case, these caps go short-circuit, overload the rail but... in this case I would see a voltage drop, but I don't. I measured the voltage directly on the terminals of all these caps, and it's spot on. So  clearly they go high-impedance not low impedance.
So.... as much as it sucks to have these crappy caps dying in there... I highly doubt they are causing my numerous weird problems. Even more so because these caps as I said provide additional filtering for the vertical amplifiers, not for the time base or trigger, which I have problems with as well...

So looks like I have covered the basics then... visual inspection, contact cleaner, power supplies... time to start troubleshooting now ! It's converging toward bad tubes I feel, many of them....

So, I say somehow I AM making progress ?! 

3H20AM, going to bed, good night people....

[Vince]

OK so here is the 502A ! 

The less said about mine the better, last time I worked on it it keep destroying diodes in the trigger circuit, followed by the transistor.

David

Yep the cover is missing !!!   

I just noticed it earlier today while looking at my pics !
That's why one 502A is not enough, one needs at least TWO of every model !
Luckily my other 502A does have both its HV covers in place, so I am covered 

Hmm.... recurrent trigger problem ? Interesting... maybe mine suffers the same and that's why I have no sweep... maybe sweep itself is working fine, just never triggered...
I would have hoped though, that at least in "AUTO" mode, it would trigger the sweep.. but no.

I don't know, mine did have a sweep, I can't remember if that was before or after sorting the broken intensity control, it also had three white toobs, one of which was the neon voltage reference. It was rescued from a local house clearers stall at a vintage agricultural steam/yesteryear show for £20.


This diode failed twice on the Timebase mode switch (looking at the picture now probably needs the neon replacing too), then this transistor was found deceased (maybe due to open circuit neon indicator causing over-voltage), it's currently in storage.


Edit: First image below shows the top view, but correct picture of front in full size, that's a new one. Had to upload it again. 

David

Thanks for that  ! 

And also thanks for rescuing this puppy ! For 20 quid sure was worth it ! Looks a bit rough on the outside but the inside is quite clean... the contacts in the wafer switches look SO much better/shinier than mine here ! They are 100% black, horrible ! 

[med6753]

502A



But I think I found the bad cap anyway, see pictures. It's not one of the big can caps, no. On the UNDER side of the lower deck, soldered on ceramic strips, I see 4 small axial electrolytic caps, all identical, 6.25uF.  They look similar to the bad ones in my HP 120B tube scope.... light grey/silver in colour, black text, transparent plastic wrapping...
I noticed one of them has the positive end looking bad... looks like the red seal is not in good shape eh ?!
The others are only marginally better...

I looked them up on the power supply schematic below, highlighted in yellow. They provide ADDITIONAL filtering for the vertical amplifiers... additional filtering, not primary. Since the ripple upstream is already within spec, these small caps going high ESR / drying out is not a big deal I think, ripple is still within reason.. it's not gonna cause the catastrophic failures and weird and wonderful  stuff I see all over the place in this scope...
Worst case, these caps go short-circuit, overload the rail but... in this case I would see a voltage drop, but I don't. I measured the voltage directly on the terminals of all these caps, and it's spot on. So  clearly they go high-impedance not low impedance.
So.... as much as it sucks to have these crappy caps dying in there... I highly doubt they are causing my numerous weird problems. Even more so because these caps as I said provide additional filtering for the vertical amplifiers, not for the time base or trigger, which I have problems with as well...

So looks like I have covered the basics then... visual inspection, power supplies... time to start troubleshooting now ! It's converging towards bad tubes I feel, many of them....

So, I say somehow I AM making progress ?! 

3H20AM, going to bed, good night people....

That capacitor is cracked. That is probably the bang you heard. And it's probably gone open since the -150V is OK. Put it on your list to replace along with the others of the same type. You can hold off doing it now.

Since you have dots on the screen that indicates no sweep to the horizontal. I would start there. The schematic should have points indicating the sweep signal. Once you get a sweep you should have a trace. Then go after any vertical issues. If you have no trigger save that for last. Sweep first. Then vertical. Then trigger. (Make sure the trigger is set to auto, free run, while troubleshooting the sweep and vertical)

Have fun. 

[Zucca]

me: "give it to me I will try to fix it"

10 min later



upsi.....

[mnementh]

Methinks he was that way when you got there, Z.

mnem
*toddles off to ded*

[Zucca]

It's hard to design a remote control that can fail so badly....
and yes mnem I just open it up... it did not release the holy smoke on my bench.

[mansaxel]

There is a little bit of "method in their madness".

In the twilight of the tube era, there were a number of minor European brands which had a rather poor reputation.
There were also "pretend" brands which bought tubes from all over & relabelled them----"Zaerix" comes to mind!

The problem was that even "reputable" companies started doing this, notably Mullard.
In Oz, if you bought from Philips, you often got a mix of their own tubes & Mullard (or whatever) devices, so this needed watching.

Back then, we found that, during those years, in terms of reliability & meeting initial specs, the list read:-

<snip>

Now, if the valve met its specifications when put on the tester, initially, was there sound or performance issues between the brands?

Because, what is claimed by the 'phools and their brethren "some musicians" is that some brands (usually not from the top of your list!) consistently sound "more magic".  It is not about being so scientific so as to select valves by tested performance. That's too cold, and unsympathetic...

[mansaxel]

A handle should be fairly easy, if you do enough research on the stitching method.

The research start phrase is "two needle saddle stitch". It's the traditional way to make leather seams and it is both easy and strong. I use and teach it in the scout troop for our crafts sessions.

[med6753]

502A

OK some more.



But that's not depressing... it's still progress ! First, now I can rule out dirty contacts... or else I would have had at least SOME kind of change, somewhere, one way or another.... but nope, not a sausage. So that means the issues I have are clearly actual electrical faults, most likely dead tubes all over the place... that purple/gassy 12AT7 was not a good start I guess... probably means there are a bunch more tubes that are cactus.

I guess I could brute force it like some would, and just pull all the tubes one by one to test them... but I don't have a tube tester anyway. Well I have my 575 transistor curve tracer, once it's restored I plan on making a little adapter to enable it to test vacuum tubes. But for now, no way to do mass tube testing...

There's a tendency to regard vacuum tubes as unreliable when in reality they are very reliable. Yes, compared to solid state devices their total lifespan looks pretty poor. But we're talking thousands and thousands of hours. I see no need for you to pull all the tubes and test them. Your gassy 12AT7 was an outlier. I doubt you'll encounter any more bad tubes, unless some idiot pulled all tubes and installed junk. Simply start troubleshooting as I mentioned previously and fix what you find. I'll bet it turns out most likely to be a resistor, capacitor, or dirty switches, but not a tube. Want some proof? The two Type 547's that I just brought up between both of them so far one bad tube. The Type 547 I got back in March despite all it's issues had no bad tubes. Yes, two 6080 regulator tubes burned up because of shorts but not because the tubes themselves were defective. The Type 535A I restored 2 years ago has close to 60 tubes in it. Wanna know how many bad ones I found? Zero.

The only vacuum tubes that drive me nuts are nuvistors. If they have been dormant for many years they take a long time to "wake up". Seems they require many hours of burn-in to de-gas themselves and become stable. But since that Type 502A is low B/W I doubt it has any nuvistors in it.     

[Henrik_V]

...
Back then, we found that, during those years, in terms of reliability & meeting initial specs, the list read:-

AWV-----consistently exceeded specs
RCA-----consistently met specs
Siemens------consistently met specs
Sylvania------consistently met specs
GE------usually met specs
Philips------usually met specs
Mullard------usually met specs, with some "really battling"
Brimar,------usually met specs (just)

with the others making up a gaggle of "also rans">

Missed TFK (Telefunken)
and for good old TEA stuff you go for E8*CC   (12A*7WA)  

[tggzzz]

There is a little bit of "method in their madness".

In the twilight of the tube era, there were a number of minor European brands which had a rather poor reputation.
There were also "pretend" brands which bought tubes from all over & relabelled them----"Zaerix" comes to mind!

The problem was that even "reputable" companies started doing this, notably Mullard.
In Oz, if you bought from Philips, you often got a mix of their own tubes & Mullard (or whatever) devices, so this needed watching.

Back then, we found that, during those years, in terms of reliability & meeting initial specs, the list read:-

<snip>

Now, if the valve met its specifications when put on the tester, initially, was there sound or performance issues between the brands?

Because, what is claimed by the 'phools and their brethren "some musicians" is that some brands (usually not from the top of your list!) consistently sound "more magic".  It is not about being so scientific so as to select valves by tested performance. That's too cold, and unsympathetic...

I believe the magic valves do sound subjectively better. But then many people believe wellness-woo such as chemicals are bad for you. (I always pity anybody that has to work with the products in Lush shops, since even  I can smell them across the street. The amount of VOCs they inhale must be hazardous )

My understanding is that valves sound better because the 2nd harmonic distortion sounds better.

No, I do not understand audiophools' reasoning.