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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.
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Sent from my iThing, so please forgive brevity and typos
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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
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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
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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 NOSThat'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.
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Re: Idle Question About the 485
Jeff,
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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@...> wrote:
Walter,
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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
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Re: rare lot
leonard scheepsma
What a fantastic translation. Ramp generator into "catastrophe" generator into "disaster". Google translate without context.
I love it!
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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
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Re: rare lot
Tim Phillips
'Disastergenerator' ? I have some of those lying around here !! <grin>
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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
On Thu, 21 Oct 2021 at 19:42, Miguel Work <harrimansat@...> wrote:
I have seen a rare lot in ebay:
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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
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rare lot
Miguel Work
I have seen a rare lot in ebay:
https://www.ebay.com/itm/284496059395?_trkparms=amclksrc%3DITM%26aid%3D777008%26algo%3DPERSONAL.TOPIC%26ao%3D1%26asc%3D234498%26meid%3Db62e4b819f45423c8b63ab2690dc0a35%26pid%3D101251%26rk%3D1%26rkt%3D1%26itm%3D284496059395%26pmt%3D0%26noa%3D1%26pg%3D2380057%26algv%3DPersonalizedTopicsV2WithMLR%26brand%3DTektronix&_trksid=p2380057.c101251.m47269&_trkparms=pageci%3A4643e9ed-329e-11ec-97fd-fe1dc856a4c8%7Cparentrq%3Aa426fb4117c0ab9ca4bd873afff5e3e8%7Ciid%3A1 I don´t have any aflitiation
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Re: 7704A - Delayed Sweep Intensity Too Bright
n4buq
Mark,
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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@...> Barry,
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Re: 7704A - Delayed Sweep Intensity Too Bright
n4buq
Stephen,
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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@...> Barry,
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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--- 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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Re: Debugging begins: Tek 606
toby@...
On 2021-10-17 11:12 p.m., toby@... wrote:
Hi,The next step seems to be to power the board to investigate further. The HV section is basically this (but my unit shows some updates as mentioned previously): https://imgur.com/gtO35ue Can anyone comment on whether it will be safe to operate this topology onnected to the LV supplies but with the CRT disconnected completely (grids, filament, cathode)? Or should I test with the CRT connected? Either way I think I will probably be able to do this with the HV safety shield in place until I reach a point where I need to measure the HV itself. --Toby --Toby
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Re: Idle Question About the 485
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.
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Re: 7704A - Delayed Sweep Intensity Too Bright
SCMenasian
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
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Re: USPS shipments comments
Dave Seiter
My brother-in-law worked for a law firm that specialized in maritime law. He tells a story that happened at the port of Oakland- someone was importing two old MIGs, and they had survived the trip thus far without a scratch. A team was supposed to move the planes (I would assume the fuselages at this point) onto flatbed(s) with forklifts. They dropped the first one almost right away, thought they had figured out what they had done wrong (I guess, or didn't care), and then proceeded to drop the second one. The customer was NOT happy, to say the least!
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-Dave
On Thursday, October 21, 2021, 06:01:31 AM PDT, stevenhorii <sonodocsch@...> wrote:
I’ve been to quite a few warehouses to pick up stuff I had delivered by freight. It’s a lot cheaper to pick it up compared with home delivery since they need to dispatch a truck with a lift gate for most home deliveries (unless you have a truck dock!) I have had to uncrate stuff in the customer parking area when the crate was too large for my SUV. I know why they generally do not allow customers to walk around the warehouse. It’s dangerous. The forklift drivers zoom around and are not expecting inexperienced folks to be on the floor. I have been allowed on the floor when they were having trouble finding the crate I was expecting. They did find it with my help - it turned out that it got moved to a staging area for a later pickup day than I had told them. I got talking with one of the foremen about the hazards of the fork lifts. He told me that they are usually very good and that accidents with shipments are few (but he would say that). He did tell me about a couple of incidents with the driver running the forks through a crate. One of them was a large screen flat-panel TV (in those days it meant a large insurance payout). Things falling off the forks is another problem, but the drivers usually know when they start to lift a pallet or crate if it is not far enough back on the forks. I worried a little when they used a lift to get my crate into my SUV. I could imagine the forks going through the rear bumper or something. But the guy got it in and then raised the forks so the ends of them were at the wood frame around the rear of the crate. He then very slowly pushed it all the way into the back of the SUV managing to avoid pushing into the backs of the front seats (I had folded the rear seats down). These guys can be careful when they need to be. On Thu, Oct 21, 2021 at 07:03 Michael A. Terrell < terrell.michael.a@...> wrote: That sounds like a Drew Carey show episode where Oswald smashed the scanner
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Re: USPS shipments comments
I have driven forklifts and worked in a workbasket from one. That time, the
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idiot driver who was assigned to the job kept disappearing. It ran out of propane while I was working near the roof, running cables. He replaced the tank, and opened the valve. It was leaking badly. I yelled to close the valve. He just shrugged and said, "It'll stop", and walked off. My yelling got the attention of the plant manager. They stopped the leaking propane, and went to find him. The jackass could have destroyed the building and killed over 100 production workers with a single spark. It took hours to get the odor out of the building. They could only open all the doors to let out the gas, because the contactors on the motors would have set off an explosion if the machines were shut down.
On Thu, Oct 21, 2021 at 9:01 AM stevenhorii <sonodocsch@...> wrote:
I’ve been to quite a few warehouses to pick up stuff I had delivered by
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485 input attenuation circuit protection modification
Mark Vincent
For those that have a 485, look at the S/N to see if it is in the lower range. At one point it was changed to protect the round IC from pluses from the relay coil when switching from 50 ohm to 1meg input. You can modify the circuit by adding the parts of the higher S/N to the lower to protect the IC. I did this in mine. The schematic will show both versions. The NPN transistor that is added is a 2N3904. A 2N2222/A or other will work.
There is also a 12V axial tantalum that is for the 9V filtering on each input. I removed the tantalums and put in a ULD 16V to prevent those tantalums from shorting. There is a 13V circuit that has 15V tantalums that will short. I used 47mfd 25V ULD types in this circuit. Mark
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