Idle Question About the 485


 

I'm trying to convince myself not to bid on this 485 (https://www.ebay.com/itm/393631311648) which has no bids, mostly because I don't have the cash, but also because I already have a 2465 that I am quite happy with, and that I perceive as an upgraded version of the 485 (it has almost the same bandwidth, 50 ohm input mode, and ALT horizontal mode, along with on-screen readout, cursors, and in my case, a multimeter and counter/timer).

While perusing the TekWiki page for the 485, however, I noticed that the 485, unlike the 465 and 475, does not appear to have a TRIG VIEW feature (or, at least, it doesn't have an obviously labeled button). Is this true? Does the 485 have no way to display, even momentarily, the external trigger signals?

-- Jeff Dutky


Tom Gardner
 

The 485 has two separate inputs: 50ohm and 1Mohm//20pF.

The 24x5 have 1Mohm//15pF inputs, and you can add a 50ohm resistor to make that 50ohm//15pF.

By and large, my preference is for two "proper" inputs, or for >4 inputs - as found in a logic analyser or protocol decoder.

On 21/10/21 12:14, Jeff Dutky wrote:
I'm trying to convince myself not to bid on this 485 (https://www.ebay.com/itm/393631311648) which has no bids, mostly because I don't have the cash, but also because I already have a 2465 that I am quite happy with, and that I perceive as an upgraded version of the 485 (it has almost the same bandwidth, 50 ohm input mode, and ALT horizontal mode, along with on-screen readout, cursors, and in my case, a multimeter and counter/timer).

While perusing the TekWiki page for the 485, however, I noticed that the 485, unlike the 465 and 475, does not appear to have a TRIG VIEW feature (or, at least, it doesn't have an obviously labeled button). Is this true? Does the 485 have no way to display, even momentarily, the external trigger signals?


teamlarryohio
 

On 485, A Ext trig view is the little button at left end of vert mode switches.


Jean-Paul
 

Dear Jeff the trigger difference is the least of the considerations

Beware the 485 are very old, notice the small gray knobs are deteriorated.

The ebay lot has total with shipping $225 minimum, and the seller is a surplus dealer, so I would advise to pass on this, especially if shipping will be international eg to UK or Japan.

With patience a nice 246xB can be found for perhaps $100..200 more.

Bon Chance


 

Tom,

no disrespect intended, but I'm looking directly at my 2465, and it has five input coupling positions for channels 1 and 2, labeled in order: 1MΩ AC, 1MΩ Gnd, 1MΩ DC, 1MΩ Gnd, and 50Ω DC (with a red border around the 50Ω DC label). It also has, according to the manual, overload protection in 50Ω DC mode, and will revert to 1MΩ Gnd position in such a case. The precise mechanism of the overload protection seems to be more direct in the case of the 2465, which appears to have a thermal sensor that triggers the switch back to 1MΩ input, but the effect is the same.

-- Jeff Dutky


 

Jean-Paul,

I have already lucked out on a 2465 in January of this year, which cost slightly less than this 485 ($120 before shipping). I'm not really interested in the 2465A or 2465B, both because the controls move further and further away from direct control of the instrument on the A and B models, and because of a certain fellow in California who sells disfigured 2465As as 2465Bs, so I'm unsure if I can trust any second-hand 2465Bs I would find in the wild.

I did notice the deterioration of the upper trigger slope knob, but the rest of the unit looks to be in fairly good condition, considering its age. Also, this is a scope from exactly the period that I most like (which includes the 475 and the 7000-series). I also noticed that the hinge covers on the handle seem to be quite faded, which makes me worry that they are about to go brittle, and there is some damage to one of the rear feet. The serial number is B010156, which I think means that it is a very early production unit indeed.

For being so old, most of the knobs appear to be in excellent shape, and the CRT looks quite strong (the intensity is set at less than the half way mark and the traces look nice and bright). Still, your warning is heard and heeded.

Actually, on a second examination of the images, it appears that the CH 1 and CH 2 VOLTS/DIV knobs don't match, which means that one (probably CH 2) had to be replaced, and all they could find was a knob from a much later instrument (a knob without the black insert at the top).

teamlarryohio,

That is a very small button for trigger view. Even in the close-up of the CRT section (second picture) I can barely tell that's actually a button.

-- Jeff Dutky


Tom Gardner
 

No disrespect taken :)

Looking at the circuit diagrams, the 485 has two separate attenuators, one 1Mohm and one 50ohm. A relay connects the BNC input to the relevant attenuator. Overload causes the relay to switch to the 1Mohm attenuator.

OTOH, the 24x5 has a single 1Mohm attenuator, and a relay simply puts a 50ohm resistor in parallel with that.

Using a NanoVNA to (imperfectly) measure the VSWR of my 485 shows it is between 1.00 and 1.03, rising to 1.04 at 350MHz.

OTOH, my 2465 varies between 1.01 and 1.15, and is 1.12 at 350MHz.

On 21/10/21 15:06, Jeff Dutky wrote:
Tom,

no disrespect intended, but I'm looking directly at my 2465, and it has five input coupling positions for channels 1 and 2, labeled in order: 1MΩ AC, 1MΩ Gnd, 1MΩ DC, 1MΩ Gnd, and 50Ω DC (with a red border around the 50Ω DC label). It also has, according to the manual, overload protection in 50Ω DC mode, and will revert to 1MΩ Gnd position in such a case. The precise mechanism of the overload protection seems to be more direct in the case of the 2465, which appears to have a thermal sensor that triggers the switch back to 1MΩ input, but the effect is the same.

-- Jeff Dutky




 

Jeff,

50 ohm protection on the 485 is a fusible ceramic element in the attenuator chain, a rare and hard to find object.
having said that, the 485 scope is very nice, but quite complex (especially in the vertical section) AND old, not a great combination today.

I was surprised at the relatively good condition of that 485 unit on ebay, it looks like a worthy overhaul candidate to me, especially considering the brightness of the unobtainable CRT. I was tempted myself, but aside from the fact susan would almost certainly kill me on its arrival, I have two (R)7903's which I far prefer for fast analog work. THAT is a great scope, and not adequately appreciated.

all the best,
walter
sphere research corp.


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


 

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


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






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


 

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


 

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


 

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


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





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


Dave Daniel
 

Mark, that is excellent advice. Unfortunately, it doesn’t work when it comes to Tektronix oscilloscopes.

DaveD

On Oct 21, 2021, at 17:56, Mark Vincent <orangeglowaudio@gmail.com> wrote:

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





Dave Peterson
 

DaveD, that is so true!

I'm entertaining myself watching another item by the same seller that is about to expire. It pushes a lot of "want" buttons, but for the cost I can easily buy several items that I could really use. I'm fascinated by my own irrational urge to bid. This auction thing is diabolical.

Speaking of need: anyone have a line on a 067-0525-01 or 02?

I have a current work around with fairly well matched 3' cables. But I'd really rather have the right thing.

Sorry for the thread crashing.
Dave

On Thursday, October 21, 2021, 03:04:27 PM PDT, Dave Daniel <kc0wjn@gmail.com> wrote:

Mark, that is excellent advice. Unfortunately, it doesn’t work when it comes to Tektronix oscilloscopes.

DaveD

On Oct 21, 2021, at 17:56, Mark Vincent <orangeglowaudio@gmail.com> wrote:

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





 

Dave Peterson wrote:

sorry this thread is crashing
As the OP I don’t think that the thread is crashing at all, the question about the 485 trigger view feature was only half of the original question. Avoiding bidding on auctions was at least as important.

I feel bad when I see a nice item with a low starting bid and nobody bidding. I always imagine that it’s an individual just trying to sell the item, may it had sentimental value, or maybe they need the money so badly that they’re parting with it, and I just feel bad. Of course sometimes I bid because the starting bid is ridiculously low, and I’d be a fool to pass it up for that price. Other times it’s because the item is something that imagine might go to the dump and be picked over by tube thieves if it doesn’t sell.

None of that obtains here. I’ve got so empathy for surplus businesses, and the price is not low enough to be impossible to refuse. I’m still willing to have a bull session over the particulars of our shared addiction.

— Jeff Dutky