Date   

Re: Idle Question About the 485

Mark Vincent
 

Jeff,

You want the scope, not need it. That is enough to hold onto the money. I have done this and was glad I did. I soon needed the money for something that was a necessity/emergency. Had I spent the money initially, I would have been screwed when I needed it. There is a huge difference between want and need, although many do not believe this.

Mark


TDS3012 and up

durechenew@...
 

Gentlemen,
I while back I informed here that I'm trying to revive a TDS3012; essentially that was done with good results.
That scope came to me with Rack Mount RM3000 (includes all the hardware to install the scope) that doesn't have room (or usage) in my 'lab' (let's call it that); it's in fairly good shape and if someone has a need for it, can have it for postage (that might mean something, I'm in Toronto, Ontario, Canada).

The main subject is different: assuming there would be available another TDS3012, what would be the challenges (from electronic point of view - disregard mechanical stuff), to convert to a TDS3014? I believe Håkan is one of the people with a lot of info and knowledge about these scopes and I'd love to hear his opinion. Anyone else interested or with knowledge is invited to share opinion; I believe is doable.
All the best to all
TT


Re: Idle Question About the 485

Dave Daniel
 

My first two ‘scopes in my home lab (many years ago) were a 7904A and a 485. I chose these because those were the two ‘scopes that I had in my lab at StorageTek (back in the 80s).

The 485 served my purposes well back then. Remember that, when considering what BW one wants in a ‘scope, it is not the highest expected signal repetition rate that one should consider but rather the highest edge rate one expects to need to measure and the smallest-width “glitch” that one may encounter when troubleshooting a circuit.

The 465 and 475 are more easily repaired than a 485, which is one of the main criteria that I consider when purchasing test equipment.

As it turns out, my go-to bench ‘scope these days is a 2465B (I own 9 Tektronix ‘scopes, down from 11 before I moved a couple of years ago). While I’d like to own another 485, I’d probably never use it.

DaveD

On Oct 21, 2021, at 16:51, Jeff Dutky <jeff.dutky@gmail.com> wrote:

Bob,

I appreciate the perspective. I know that people love their 485s, and I presume there are good reasons. It really was the best of the line for at least a decade. I'm not sure that I need it for the things I'm doing (retro-micro-computing with 8-bit CPUs and a very occasional 16 mini-computer, or fixing assorted test equipment), but its industrial design is pleasing (but I've scratched that itch with my 7k-series scopes).

I did mention that I'm looking for reasons NOT to bid on this scope, though, right? ;-)

-- Jeff Dutky





Re: Idle Question About the 485

 

On Thu, Oct 21, 2021 at 08:42 PM, Jeff Dutky wrote:


I don't see the fusible element in the 485 schematics, maybe you're thinking
of the 7A19, or the 7A24?
You're right, Jeff. The 485 has an extremely nice and clever arrangement to protect the 50 Ohm input, without fuses.

Raymond


Re: Idle Question About the 485

 

Gary,

Had you tried cleaning the leaf contacts in the attenuators?

I've had that same problem on every 475 I've ever worked on, as well as on a number of 7k plug-ins, and cleaning the leaf contacts with IPA and slips of bond paper has been very effective at clearing up those malfunctions, even when I've done a half-assed job of the cleaning (cleaning only the upper set of contacts, which are easy to get at). Are the 485's attenuator contacts built differently than the 465/475 or 7A18/7A26? Are they significantly harder to clean?

I would have expected Tek to have used the same technology in the 485 as they used in the lower bandwidth models released in the early 70s, but Tek engineering of that period often surprises me.

-- Jeff Dutky


Re: Idle Question About the 485

 

Bob,

I appreciate the perspective. I know that people love their 485s, and I presume there are good reasons. It really was the best of the line for at least a decade. I'm not sure that I need it for the things I'm doing (retro-micro-computing with 8-bit CPUs and a very occasional 16 mini-computer, or fixing assorted test equipment), but its industrial design is pleasing (but I've scratched that itch with my 7k-series scopes).

I did mention that I'm looking for reasons NOT to bid on this scope, though, right? ;-)

-- Jeff Dutky


Re: TEK 475: Dead on Start Up.

Tom Lee
 

I don’t fully agree with that recommendation, although it is fine in many circumstances. The impedance of tants stays low at high freqs, while aluminums generally don’t. Tripling the capacitance doesn’t necessarily reduce the impedance. Above self-resonance the impedance is dominated by parasitics, not the capacitive reactance.

Sent from my iThing, so please forgive brevity and typos


If Changing to electrolytic, triple the value… 22 uF/20Volt tant -> 100uF/25, 35, or 50Volt electrolytic

Steven


Re: TEK 475: Dead on Start Up.

Steven Bender
 

1) I understand that I should start with checking the +50V (UNREG) and then 50V (REG)\, next the+ 110V, +15V, and then +5V, -8V and finally -15V.

Is this correct?.

4) I understand that TEK used a way too low margin in Voltage rating for the Tantum capacitors on power rails.
- Are there any which particularly have a bad reputation and should ALWAYS be replaced?.

or

5) Should I eventually replace ALL those tantalum caps on the various power rails with 105 deg. C electrolytic capacitors?
- or are there "solid aluminum" alternatives to the tantalums used in that era (mid 1970's - mid 1980 's ?



I’m not an expert on the 475, but I believe you are correct, starting in the 50 Volt lines.

Tant caps from the 1970’s & 1980’s had failures over time, due to impurities that crept in during manufacturing.

I tend to replace old 20V tants with 35V tants.

If Changing to electrolytic, triple the value… 22 uF/20Volt tant -> 100uF/25, 35, or 50Volt electrolytic



Steven


Re: Idle Question About the 485

Gary Appel
 

My own thoughts - for what they are worth.

I have owned two 485's, and they both displayed issues with intermittent attenuators. I would wiggle the knob and try to get a stable trace, but often the attenuation would not settle down, so I was often not able to trust the display.

I have given them both away.

Gary Appel


Re: Tek VAR Pot Repair Rings

Jim Adney
 

On Wed, Oct 20, 2021 at 07:30 PM, Dave Casey wrote:

For anyone needing more than just a repair ring, I have a handful of NOS
Tek Made pots in this style. Send your part number requests and I'll see
what I have.
That's a very generous offer and one that we should all keep in mind. I will add, however, that even a new pot may fail in this same way. My guess, and it's only a guess, is that the Tek assembly techs knew exactly how tight they could tighten these, but many of us, or previous owners, may have tightened them just a bit too hard. And then there's shrinkage and embrittlement over time, which may be the cause of failure.

If I ever have cause to touch one of these pots, I'd be tempted to add one of the rings, just to avoid future disappointment.


Re: Idle Question About the 485

redarlington
 

Jeff,

The 485 is the finest portable Tek made in its day. I paid $350 for mine
about 15 years ago and I'd gladly do it again if I had to, but obviously
would rather pay less. That 350MHz BW rating is highly conservative. I
prefer it over other scopes for some things (many of us have favorites for
certain tasks). If ya need one, it's probably the right one. If not,
it's still probably the right one unless you need 4 channels. Two
channels is just right for the work I used to do when I bought it
(amplifier design and prototyping). And the size is just right to plop
right up on the bench. Mine lives on a scope cart these days but it
really is right at home ON the bench -unlike a lot of our other boat
anchors.

-Bob N3XKB

On Thu, Oct 21, 2021 at 12:43 PM Jeff Dutky <jeff.dutky@gmail.com> wrote:

Walter,

I don't see the fusible element in the 485 schematics, maybe you're
thinking of the 7A19, or the 7A24?

My wife might not kill me if I got a 485, but I'm in the middle of a reorg
of my bench and lab (making storage and organization for a bunch of
plug-ins, and finding a reasonable way to arrange portable and bench-top
scopes along side other instruments for use) and I'm already thinking that
some of my scopes are surplus to requirements. A 485 would not make the
project any easier.

The 7903 is clearly superior to the 485, unless you have to travel with
it. My whole reorg is being done because I've become quite fond of a couple
of 7600s (two 7603s and a 7633) in recent months. My bench was organized
around a couple of portable scopes originally, which could be easily
arrayed around my desk sitting upright on the floor, but the 7600s demand
bench or shelf space. Having one 7600 on the bench as a tool doesn't leave
much space for a second one as a patient.

I have not technical need for a 485. My only emotional connection is that
I let a nice one slip through my fingers this past spring at a similar
price. It had a blue phosphor CRT! I suspect that another member of this
group might have bought it while I was napping.

-- Jeff Dutky






Re: 7704A - Delayed Sweep Intensity Too Bright

SCMenasian
 

Barry,
If it's that way with several plugins, it might be in hte receiving side of that interface in the 7704A.

Stephen


Re: rare lot

leonard scheepsma
 

What a fantastic translation. Ramp generator into "catastrophe" generator into "disaster". Google translate without context.
I love it!


Re: USPS shipments comments

Steven Bender
 

Hi All,

A few years back, (not Tek equipment) I won a beautiful, museum quality cosmetics, Bang & Olufson linear tracking turntable, 1980’s Made in Europe, heavy, IIRC around $225. and the weight was about 40 lbs. It was coming from nearby, less than 50 miles away (next state over). The mailman carried it up the steps, walked over, (I was at the door watching) as he got near to me, he tossed it forward three feet onto the cement. He managed to break almost everything possible to break in the unit. I had taken out full replacement insurance, while I was eventually paid (minus $50. - no reason given). What can you do?

I’ve seen UPS do worse… a Sony TC-650 RTR arrived with a side of the box ripped open, trailing packing material, dropped so the metal frame warped so bad, unable to be repaired, the nice wood sides were a thousand tiny toothpicks, picked up again to go to the UPS Evaluation Center (likely it was dumped in some green recycle bin) and I got a massive $100. back, which was like a third of the cost before shipping.


Steven


Re: rare lot

Tim Phillips
 

'Disastergenerator' ? I have some of those lying around here !! <grin>

Wasn't this setup a replacement for the 160 generators when Tek were
getting into Biophysical market.?
I understood they rather took a hit on the product.

Tim


Re: Idle Question About the 485

 

Walter,

I don't see the fusible element in the 485 schematics, maybe you're thinking of the 7A19, or the 7A24?

My wife might not kill me if I got a 485, but I'm in the middle of a reorg of my bench and lab (making storage and organization for a bunch of plug-ins, and finding a reasonable way to arrange portable and bench-top scopes along side other instruments for use) and I'm already thinking that some of my scopes are surplus to requirements. A 485 would not make the project any easier.

The 7903 is clearly superior to the 485, unless you have to travel with it. My whole reorg is being done because I've become quite fond of a couple of 7600s (two 7603s and a 7633) in recent months. My bench was organized around a couple of portable scopes originally, which could be easily arrayed around my desk sitting upright on the floor, but the 7600s demand bench or shelf space. Having one 7600 on the bench as a tool doesn't leave much space for a second one as a patient.

I have not technical need for a 485. My only emotional connection is that I let a nice one slip through my fingers this past spring at a similar price. It had a blue phosphor CRT! I suspect that another member of this group might have bought it while I was napping.

-- Jeff Dutky


rare lot

Miguel Work
 


Re: 7704A - Delayed Sweep Intensity Too Bright

n4buq
 

Mark,

Yes, I believe the intent is to "highlight" part of the trace; however, mine is highlighting much to bright. I'll have to check those voltage levels in the Z-Axis circuit and see if the plugins are somehow providing the wrong voltages.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Thursday, October 21, 2021 10:17:14 AM
Subject: Re: [TekScopes] 7704A - Delayed Sweep Intensity Too Bright
Barry,

See if having the A/B intensity turned up and the crt bias up (more negative at
the grid) helps. If your S/N is <210000, check Q320, Q322, Q420 and Q422. These
are in the two heatsinks on the right side top. If these are leaky, use
KSP10BU. I do not see any internal intensity control in this model. It may be
that the delayed signal is to be brighter to give contrast.

Mark



Re: 7704A - Delayed Sweep Intensity Too Bright

n4buq
 

Stephen,

I'll have to check that. I think the problem is seen for other time-bases so not sure if it's a problem with the plugin but it could be.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "SCMenasian" <scm@menasians.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Thursday, October 21, 2021 11:04:37 AM
Subject: Re: [TekScopes] 7704A - Delayed Sweep Intensity Too Bright
Barry,

Maybe the discussion of Aux Z axis Control and Aux Z Axis Out on pages 3-16 and
3-17 of the 7B53A manual will give a clue. It describes the Z-Axis interface to
the mainframe. Since the 7B92A has a front panel contrast adjustment, the
interface probably has the ability to control intensity via a voltage level.
Perhaps a bad component in those sections of your 7B53A has that level pegged.

Stephen Menasian



Re: Idle Question About the 485

Ozan
 

Hi Walter,

On Thu, Oct 21, 2021 at 09:14 AM, walter shawlee wrote:
50 ohm protection on the 485 is a fusible ceramic element in the attenuator
chain, a rare and hard to find object.
---
485 has an active protection circuit that flips input relay to 1M-ohm setting to protect the 50-ohm attenuator. There could be a fusible element as well although I can't see it in the schematic or the pictures I took on my unit. Perhaps it was on certain serial number range.

Ozan

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