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Re: Way off topic: Radio antennas
John Miles
Might be a symptom of front-end overloading. What does the "static" sound
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like -- AM-style random static, or distortion of a tonal (pager transmitter?) signal? -- jm ----- Original Message -----
From: "james89es" <james89es@...> To: <TekScopes@...> Sent: Tuesday, January 01, 2002 8:20 PM Subject: [TekScopes] Way off topic: Radio antennas I know this has nothing to do with Tek-scopes (I do own a RM547, so I |
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Way off topic: Radio antennas
james89es
I know this has nothing to do with Tek-scopes (I do own a RM547, so I
do belong "in the club") but I know many of you are also into HAM radio. Here's the story: I bought my mother a new police scanner (from Rasio Shack) for x- mas. She has had scanners for 25+ years. Her old Uniden was 15 years old. The outside antenna is about 20 years old. Problem: When we plug the outside antenna into the new scanner, it CAUSES static and reduces signal strength!! I ruled out the plug on the radio itself by connecting a short piece of cable, and touching the bare wire with my finger. In this scenario the signal is stronger and there's less static when I touch the wire, as I would expect. Once I plug in the outside antenna, however, more static and less strength ... even if I leave the little inside antenna on. They replaced the coax just in case, they used the recommended 50ohm cable - a run of about 30 feet. What would explain this?? Keep in mind that the old Uniden still works fine with the outside antenna. |
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Re: Broken YIG oscillator wanted
DEANE KIDD
¿ªÔÆÌåÓýHi Jim:
?? I can provide a set of board extenders.? They are
available from Norway Labs, Inc. matt@... for a fair price of
about $90.00.? Your set is available at no charge as a friend to friend
deal.? You can pick them up on Sat in the early afternoon.? Please
call first to make sure that I am awake and available.? I if I don't
answer, try again in a few minutes.
Deane
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Re: TDS Schematics
DEANE KIDD
¿ªÔÆÌåÓýTo all users of Tek scopes:
?? I would like to suggest that it might help if all scope users
would use the correct numbers for their scopes.? There is a 544 scope and
there is a TDS544 scope and they are two different products with two different
manuals.? It makes no sense to omit any of the alpha numeric symbols and it
does not make it very easy to know what you really need.?
Deane
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Re: Broken YIG oscillator wanted
DEANE KIDD
¿ªÔÆÌåÓý
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Re: unsoldering tricks
A de-soldering trick from an old gas passer.
Cutting the leads off the IC works well, you use a pair of dikes with narrow jaws and cut the legs right at the body of the IC. What I do next is turn the board over and heat the pad with a low temperature iron then push the cut-off leg out using a dental explorer. Push the explorer all the way through the hole cleaning the hole out. Then turn the board back over and clip the solder mounds off, insert the new IC and, again using a low temperature iron, carefully solder the new IC back in. Fast, reliable and with minimal board damage! Reed Dickinson |
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Re: Did Tek mod all older scopes from UHF to BNC connectors?
DEANE KIDD
¿ªÔÆÌåÓýHi Steve:
?? As Stan just reported about UHF connectors, not all Tek scopes
had a mod for UHF connectors but these connectors were stock items and could be
ordered from the factory.? I have BNC connectors with the large flange and
they can be mounted in the same holes as the UHF connectors or they were
available in single hole mounts.? I can supply ten of each for ten dollars
plus postage but I will need your mailing address and I guess that postage will
be about ten dollars.? Please advise,
Deane
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Re: electrical safety box for 576
DEANE KIDD
¿ªÔÆÌåÓýHi Anand:
?? I know of no source for the safety box as used on the 576 cure
tracer.? For many years I had this box as spare parts but they have all
been used until there are none left.?I have never used the box with my 576
and have never needed to have one.? I use the 576 with only the low
voltages but when I need the higher voltages I use test leads and caution
knowing that these voltages can cause shocks and death.
Deane
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465 Problem
oggelbe2001
I just picked up a beautiful 465 scope for my workbench.
It appears to have a low voltage power supply problem and I have no prints for this scope. Would anybody have a scan of just the power supply section for this model? I intend to get a full service manual but I was hoping to pick this problem off and get it back operational over the next few days. Thanks, Dave |
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Sampling bridges
Craig Sawyers
Hi folks
Trawling around the web I came across a company that sells GaAs diode bridges, and Schottky diode bridges "for sampling applications". The url's are and . I haven't contacted them, and I have no idea of prices. But if anyone has a sampler with a dead front end, this may be one possibility for fixing it. Craig |
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Re: Fun with the 1A1
morriso2002
Hi Miroslav,
Thanks for the message --- In TekScopes@y..., Miroslav Pokorni <mpokorni2000@y...> wrote: of. resistors. graduates from complex to a kluge. Please, let me know what was voltage drop. It was no kludge, just a faulty batch of 130 ohm resistors I suspect. They are in series from the 11 volt supply to ground so each had 5.5 volts across them. That's less than 0.25 watts. Morris |
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Re: Odd item on eBay
Stan or Patricia Griffiths
Hi Gang,
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The 282 is an adapter that allows use of conventional X1 and X10 probes on a sampling unit such as the 1S1, 3S1, 4S1, 4S2A and others. There is a good picture and explanation of it on page 319 of the 1969 Tek Catalog. This item requires power which is obtained from a connector on the front of the above sampling units. The risetime (and bandwidth) of the a system using the 282 will be limited primarily by the probe you use with it. For example, a P6008 (X10, 10 meg Ohm input R) will have a risetime of 4 ns and P6011 (X1, 1 meg Ohm input R) will have a risetime of 12 ns. New cost of a 282 in 1969 was $95. Stan w7ni@... Craig Sawyers wrote: Hi gang |
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Re: Odd item on eBay
Craig Sawyers
Hello Craig,Thanks, Leo! A scan would be very welcome - thanks. Cheers Craig |
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Re: Odd item on eBay
Leo Schleider
Hello Craig,
this thing is to connect a conventional high impedance probe to a 50 Ohm input. Sampling plug ins usually have 50 Ohm input impedance to match the RF. The 282 has a high impedance input to connect a normal probe and a 50 Ohm GR output to match to 50 Ohm inputs of e.g sampling plug ins. It's an amplifier inside and it needs a DC power supply. I mail you a scan out ot the 1968 Tek catalog to your e-mail adress Leo -----Urspr¨¹ngliche Nachricht----- Von: Craig Sawyers [mailto:c.sawyers@...] Gesendet: Freitag, 28. Dezember 2001 13:19 An: TekScopes@... Betreff: [TekScopes] Odd item on eBay Hi gang Just seen a "Tektronix model 282 probe adaptor" on eBay. Anyone any suggestion what this thing is? It is item number 1683252239. Thanks Craig To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. |
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Re: Fun with the 1A1
Hello Morris,
That was quite a thing that you found, really something to be proud of. I am curious what was voltage drop across each of these two 130 Ohm resistors. I have seen a number of resistors in Tek instruments that were discolored from overheating, because they were undersized. In an 1A1, the resistors would be probably carbon composition, a tough beast to kill, but they do not show discoloration either, so you would not have a visual indication that there is something wrong. If those two resistors were really overloaded, then circuitry graduates from complex to a kluge. Please, let me know what was voltage drop. Regards Miroslav Pokorni morriso2002 <morriso2002@...> wrote: Hi all, Here's a tale of a diabolical fault I recently encountered in a piece of classic Tek equipment. The experienced Tek people here might say "I knew about that" but it was a great achievement for me! The patient was my youngest 1A1 plugin, with FET inputs and lever input switches. The symptoms - low gain on both channels on switching on, with further gradual drop in gain as the unit warmed up over 5-10 minutes. DC balance was preserved. For those of you not familiar with the 1A1 (what are you doing here?) it's a standard 2 channel vertical amplifier for the 530 to 550 series. Early models had nuvistor inputs and later models have FET inputs. Each channel has an amplifier board with the transistor amplifiers following the input stage and there is a common output card with the chop/alt/add circuitry and a hybrid cascode output using nuvistors for the final grounded grid stages. Amplification is differential throughout. Since the fault was common to both channels I initially thought it was in the output card and spent a lot of time swapping my small stock of nuvistors and probing around, all to no avail. The clue to the solution came when I substituted boards from a known good 1A1. I found that swapping the channel 2 board cured the problem. Further measurements with the original card showed that the 11 volt supply was high at 12.25 volts. Because the fault seemed temperature sensitive I tried using freeze spray and found that cooling transistors Q253A&B (a pair of 2N3563s) temporarily restored performance on channel 2. The base bias for these 2 was derived from the +11 volt rail and was too high, causing excess collector current. Where does the +11 volts come from? Tek designs of this era were notorious for clever and tricky use of the power supplies. Plugins are provided with the standard scope supplies at the connector and one pin has to sink 150 mA at 75 volts. This is derived from the +100 volt supply in the scope dropped through a couple of 12.6 volt tube heaters. In different plugins it is used for a series heater string and miscellaneous DC supplies. My 1A1 has 2 tubes and this accounts for 12.6 volts of the 75. The rest is dropped through a string of resistors and provides +39, +11 and +5 volt rails. The 11 volt rail supplies grid bias for the output tubes and is also the collector supply for the transistors feeding Q253A&B from where it affects the bias on all the following amplifiers. Tracing through the divider, I found R496 and R497, both 130 ohms 5% half watt and in series, had drifted high. Not by much, they were 140 and 147 ohms when cold but this was enough to increase the bias which caused thermal runaway of Q253A&B. I checked this by temporarily shunting them with 2.7K which I calculated would reduce the total resistance to the proper value - this fixed the problem instantly! I replaced them permanently with 1% half watt metal film resistors, the 11 volt supply is now at 11.4 volts and the plugin works perfectly. Why did swapping the Ch 2 card cure the problem? The two resistors are each on one of the input cards. Swapping one card reduced the total resistance just enough to stop the problem and point me to what was going on. Why was DC balance preserved? Because the fault was common mode, and fortunately didn't upset the operating conditions of the output tubes. What a sneaky fault! Who would have imagined a problem in the output tube heater supply would cause thermal runaway of a couple of pairs of transistors a few stages back which would in turn upset differential gain but not DC balance? It shows how carefully you have to understand how this complex circuitry works. It also shows how interlinked all the various parts of the circuit are - there's no such thing as an isolated stage for troubleshooting purposes. Since I was using a 556 (850 watts consumption) for simultaneously supplying the 1A1 and troubleshooting it, it was a hot experience so a cold beer was very welcome afterwards!! Cheers, Morris Yahoo! Groups Sponsor To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. --------------------------------- Do You Yahoo!? Send your FREE holiday greetings online at Yahoo! Greetings. |
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Re: Fun with the 1A1
Leo Schleider
Hi,
that story reminds me a bit about onother story were 2 identical parts in separate circuits failed at the same time in the same way. In my collection I have also a Philips PM3230, a real dual beam scope with tubes. After the scope hasn't been used for a while, I wasn't able to turn the brighness down. And that was the case for both beams. I spent hours in measuring in the HV supply circuits common for both electron guns, but everything was OK. Then I started looking at the voltages of one individual gun. What I found: The Z-Axis modulation is done via the grid. A capacitor is connected between the grid and the Z-Axis input on the back. On the Z-Axis connector side of the capacitor a 1 MOhm resistor is shunted to GND. That's a common construction used in many scopes. When I removed the cap, the brightness control worked for that particular channel. I measured across the cap and found it had a resistance of several 100 Kohms. And that was exactly also the case in the 2nd channel. Both parts failed at the same time in the same way. The leaking cap in series with the 1MOhm resisitor was pulling up the grid voltage towards GND and was overriding the intensity control Leo -----Urspr¨¹ngliche Nachricht----- Von: morriso2002 [mailto:morriso2002@...] Gesendet: Donnerstag, 27. Dezember 2001 23:56 An: TekScopes@... Betreff: [TekScopes] Fun with the 1A1 Hi all, Here's a tale of a diabolical fault I recently encountered in a piece of classic Tek equipment. The experienced Tek people here might say "I knew about that" but it was a great achievement for me! The patient was my youngest 1A1 plugin, with FET inputs and lever input switches. The symptoms - low gain on both channels on switching on, with further gradual drop in gain as the unit warmed up over 5-10 minutes. DC balance was preserved. For those of you not familiar with the 1A1 (what are you doing here?) it's a standard 2 channel vertical amplifier for the 530 to 550 series. Early models had nuvistor inputs and later models have FET inputs. Each channel has an amplifier board with the transistor amplifiers following the input stage and there is a common output card with the chop/alt/add circuitry and a hybrid cascode output using nuvistors for the final grounded grid stages. Amplification is differential throughout. Since the fault was common to both channels I initially thought it was in the output card and spent a lot of time swapping my small stock of nuvistors and probing around, all to no avail. The clue to the solution came when I substituted boards from a known good 1A1. I found that swapping the channel 2 board cured the problem. Further measurements with the original card showed that the 11 volt supply was high at 12.25 volts. Because the fault seemed temperature sensitive I tried using freeze spray and found that cooling transistors Q253A&B (a pair of 2N3563s) temporarily restored performance on channel 2. The base bias for these 2 was derived from the +11 volt rail and was too high, causing excess collector current. Where does the +11 volts come from? Tek designs of this era were notorious for clever and tricky use of the power supplies. Plugins are provided with the standard scope supplies at the connector and one pin has to sink 150 mA at 75 volts. This is derived from the +100 volt supply in the scope dropped through a couple of 12.6 volt tube heaters. In different plugins it is used for a series heater string and miscellaneous DC supplies. My 1A1 has 2 tubes and this accounts for 12.6 volts of the 75. The rest is dropped through a string of resistors and provides +39, +11 and +5 volt rails. The 11 volt rail supplies grid bias for the output tubes and is also the collector supply for the transistors feeding Q253A&B from where it affects the bias on all the following amplifiers. Tracing through the divider, I found R496 and R497, both 130 ohms 5% half watt and in series, had drifted high. Not by much, they were 140 and 147 ohms when cold but this was enough to increase the bias which caused thermal runaway of Q253A&B. I checked this by temporarily shunting them with 2.7K which I calculated would reduce the total resistance to the proper value - this fixed the problem instantly! I replaced them permanently with 1% half watt metal film resistors, the 11 volt supply is now at 11.4 volts and the plugin works perfectly. Why did swapping the Ch 2 card cure the problem? The two resistors are each on one of the input cards. Swapping one card reduced the total resistance just enough to stop the problem and point me to what was going on. Why was DC balance preserved? Because the fault was common mode, and fortunately didn't upset the operating conditions of the output tubes. What a sneaky fault! Who would have imagined a problem in the output tube heater supply would cause thermal runaway of a couple of pairs of transistors a few stages back which would in turn upset differential gain but not DC balance? It shows how carefully you have to understand how this complex circuitry works. It also shows how interlinked all the various parts of the circuit are - there's no such thing as an isolated stage for troubleshooting purposes. Since I was using a 556 (850 watts consumption) for simultaneously supplying the 1A1 and troubleshooting it, it was a hot experience so a cold beer was very welcome afterwards!! Cheers, Morris Yahoo! Groups Sponsor ADVERTISEMENT To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. |
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Re: Fun with the 1A1
Stan or Patricia Griffiths
That's a new one on me, Morris. Congratulations and thanks for sharing that
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info. Stan w7ni@... morriso2002 wrote: Hi all, |
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Re: Fun with the 1A1
Phil (VA3UX)
I'll "second" that Jim. That one is worth printing (already done).
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Nice work Morris and thanks for the details and explanation. I learned a lot from that post. Phil At 08:17 PM 12/27/2001 -0800, you wrote:
Morris |
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