Date   
Re: 2246 no display/odd behavior

chipbee40
 

For transistors and 2 leg components etc definitely work from the component side. way too much trouble otherwise. Cutting leads may be a good idea before pulling or maybe tacking to existing leads.

Re: Weird(?) behaviour in tek 492BP power distribution - Please help

radioconnection@...
 

Can the supply be run while removed and disconnected from the analyzer? A cap could have failed after being installed and used for a few minutes. I'd wonder what the voltages are without the instrument being involved.

Re: DC voltage on a DC coupled spectrum analyzer

DW
 

Great answer, thanks

Re: Looking for replacement case for TDS303X

 

On Tue, May 28, 2019 at 11:30 AM, Raymond Domp Frank wrote:


I guess all non-suffix TDS303X'es but any others?
Most obvious when compared to letter scopes:

B has:
Parallel port
DC OUT on different location
Cal switch and GND terminal are the same
Ethernet port
EXT Trig connector on 4 CH scopes

C has:
No Parallel port
No DC OUT
Cal switch and GND terminal are the same
Ethernet port
EXT Trig connector on 4 CH scopes

There may be some internal changes too so the safest option is to look for a no letter donor.

/Håkan

Re: DC voltage on a DC coupled spectrum analyzer

radioconnection@...
 

Unless you have a need to go into the LF region, a DC blocking accessory is cheap insurance.

Re: DC voltage on a DC coupled spectrum analyzer

Chuck Harris
 

Often, a DC block isn't insurance at all.

Every DC block I have met is simply a series capacitor, usually
about 0.1uf... those for lower frequency SA's, can be several uf,
so as to not degrade the low frequency performance too much.

If you suddenly apply a high DC voltage, from a low impedance
source to the DC block, it will apply all of the charging current
impulse directly to the SA's front end. This impulse can quite
easily destroy the mixer, if it is directly exposed without an
attenuator.

Best is to be cognizant of what you are doing, and discharge long
coax runs, and antennas, before connecting, and simply don't connect
any DC charged source to the SA without using using a high
impedance probe... preferably with a series capacitor.... 10M scope
probes are often a very good choice for probing in dodgy situations.

-Chuck Harris

radioconnection@... wrote:

Unless you have a need to go into the LF region, a DC blocking accessory is cheap insurance.



Re: Tektronix 4205 Display Terminal

Dave Wise
 

I worked on the 420x firmware. I don't remember the mechanical details except that the connector for the Option CX board (which I did) is not on the bottom at all; Option CX is vertically mounted in back, with a right-angle connector to another vertical board that's on the left or right side when viewed from the front. So that board might be the processor board; at least it contains address and data buses. I think the board on the bottom is actually the monitor. I could be wrong, it's been 30 years since I gave it a thought.

Tek was OEM-ing some monitor hardware around that time; they may not have had the info themselves.

HTH,
Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Gary Robert Bosworth <@grbosworth>
Sent: Monday, May 27, 2019 11:10 PM
To: TekScopes@groups.io
Subject: [TekScopes] Tektronix 4205 Display Terminal

Does anyone know if the processor board located in the bottom of the 4205 CRT Display easily slides out through the rear? Also, are the ROMs located on this processor circuit board? Unfortunately, the 4205 is radically different from the 4105 in its physical layout. I am unable to locate service manuals for the 4205 Display monitor.

Re: DC voltage on a DC coupled spectrum analyzer

DW
 

Here is a thought, for example a HP 8566 which can go down to 100 Hz. I assume they choose that number as that is the lowest it can go for certified performance, but I wonder if they choose that number could also be the minimum safe frequency range. For example if you go below the 100 Hz minimum to say 60 or 30 Hz, or maybe even 10 Hz, I wonder if that presents a hazard to the mixer as there is a longer but brief duration of positive and negative DC without a DC blocking capacitor that could cause eventual damage.

2215 problem

Bob Albert
 

My 2215 stopped working. At first I thought it was the power switch but that isn't the case.

The manual shows an inductor off the power circuit board but mine doesn't have that. It has an FET instead. There is a pair of wires going from one board to the other. I apparently don't have the correct diagram for my unit. Would it be safe to short the two leads to get the unit working? Would that provide a path for the power?

This is a sophisticated power supply. No voltage is reaching the switching circuit. The FET I mentioned is on a sort of heat sink in a little plastic box. I lifted the part to read its designation (IRF820) and one lead promtly broke. I have in my stock an IRF740 that appears to be close enough.

Anyway I am uncertain how to proceed. All help appreciated.

Bob

Re: DC voltage on a DC coupled spectrum analyzer

Ed Breya
 

You also have to worry about plain old component failure. RF amplifiers are typically capacitor-coupled, and relatively safe DC-wise - unless the output cap shorts out, for instance. Then the DC from inside can be applied to the SA. For higher frequencies, the cap is usually small and reliable, but for very broad band and low frequency coverage, it may need to be quite large, including getting into tantalum territory, with its reliability risks.

One particularly scary situation I have is in one of my broadband noise generator projects (I think I discussed it somewhat here or in the HP-agilent group a while back). The noise generator uses a breakdown diode as the source, which is amplified through about ten stages - all coupled with rather large solid Ta caps, in order to have a very low cutoff frequency. These are off-shelf modules, but I can open them up to modify them, and I can add external protection features. A large part of the project effort is in making it "safe" for SAs and such, without compromising the RF and high crest factor capability. It is still unfinished, partly because of this issue. Not only is there risk of a Ta cap shorting anywhere in the chain, but also just powering it up and down can cause a large surge at the output while the caps all get charged or discharged to their new quiescent levels.

Ed

Re: DC voltage on a DC coupled spectrum analyzer

Jim Ford
 

Good points, Chuck.It's a good habit to discharge coax cables that have been lying or hanging around for a while before connecting them to ESD sensitive equipment.  Obviously if you have just been using a cable there's no point in discharging it, but cables are capacitors and will charge up.  Easy enough to forget that.Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chuck Harris <cfharris@...> Date: 5/28/19 9:54 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] DC voltage on a DC coupled spectrum analyzer Often, a DC block isn't insurance at all.Every DC block I have met is simply a series capacitor, usuallyabout 0.1uf... those for lower frequency SA's, can be several uf,so as to not degrade the low frequency performance too much.If you suddenly apply a high DC voltage, from a low impedancesource to the DC block, it will apply all of the charging currentimpulse directly to the SA's front end.  This impulse can quiteeasily destroy the mixer, if it is directly exposed without anattenuator.Best is to be cognizant of what you are doing, and discharge longcoax runs, and antennas, before connecting, and simply don't connectany DC charged source to the SA without using using a highimpedance probe... preferably with a series capacitor.... 10M scopeprobes are often a very good choice for probing in dodgy situations.-Chuck Harrisradioconnection@... wrote:> Unless you have a need to go into the LF region, a DC blocking accessory is cheap insurance.> > > >

Re: DC voltage on a DC coupled spectrum analyzer

Jim Ford
 

Not sure why the 100 Hz low end, but I  did take my 8566A down that low a couple months ago just to see what it would do.   Lots of 1/f noise!  I would use my Stanford Research Systems SR780 FFT analyzer if I were looking at signals in the audio range.Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: DW <wilson2115@...> Date: 5/28/19 10:14 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] DC voltage on a DC coupled spectrum analyzer Here is a thought, for example a HP 8566 which can go down to 100 Hz. I assume they choose that number as that is the lowest it can go for certified performance, but I wonder if they choose that number could also be the minimum safe frequency range. For example if you go below the 100 Hz minimum to say 60 or 30 Hz, or maybe even 10 Hz, I wonder if that presents a hazard to the mixer as there is a longer but brief duration of positive and negative DC without a DC blocking capacitor that could cause eventual damage.

Re: DC voltage on a DC coupled spectrum analyzer

Rajesh VS
 

Thanks Chuck and Jim,
These are very valuable points, specially around DC block and co-ax
cables.
Any comments /suggestion about using fast acting lowest current pico fuses
(sub miniature ) as an added protection along the probe? about their
impact on input loading/parasitic ?

//** I almost burned the front end of my hp 8568B by accidentally plugging
it in to DC rail instead of RF out in a tracking generator board.
I was saved by the built in pico fuse **//

On Tue, May 28, 2019 at 11:07 AM Jim Ford <james.ford@...> wrote:

Good points, Chuck.It's a good habit to discharge coax cables that have
been lying or hanging around for a while before connecting them to ESD
sensitive equipment. Obviously if you have just been using a cable there's
no point in discharging it, but cables are capacitors and will charge up.
Easy enough to forget that.Jim Ford Sent from my Verizon, Samsung Galaxy
smartphone
-------- Original message --------From: Chuck Harris <cfharris@...>
Date: 5/28/19 9:54 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re:
[TekScopes] DC voltage on a DC coupled spectrum analyzer Often, a DC block
isn't insurance at all.Every DC block I have met is simply a series
capacitor, usuallyabout 0.1uf... those for lower frequency SA's, can be
several uf,so as to not degrade the low frequency performance too much.If
you suddenly apply a high DC voltage, from a low impedancesource to the DC
block, it will apply all of the charging currentimpulse directly to the
SA's front end. This impulse can quiteeasily destroy the mixer, if it is
directly exposed without anattenuator.Best is to be cognizant of what you
are doing, and discharge longcoax runs, and antennas, before connecting,
and simply don't connectany DC charged source to the SA without using using
a highimpedance probe... preferably with a series capacitor.... 10M
scopeprobes are often a very good choice for probing in dodgy
situations.-Chuck Harrisradioconnection@... wrote:> Unless you have a
need to go into the LF region, a DC blocking accessory is cheap insurance.>

--
/Rajesh

Re: DC voltage on a DC coupled spectrum analyzer

DW
 

Disregard my post above as it has become obvious to me from Ed's post about exceeding the lower limits of the spectrum analyzer that source impedance is important when running low frequencies especially DC which I want to avoid anyways

I must add at one time I used the output of an iPhone and an iPad turned down low generating a sine wave before, it worked but now it has me thinking was that a bad idea?

Thanks for the excellent replies

Re: DC voltage on a DC coupled spectrum analyzer

Ed Breya
 

Jim wrote:

"Not sure why the 100 Hz low end, but I did take my 8566A down that low a couple months ago just to see what it would do. Lots of 1/f noise! "

That's not 1/f noise - it's just the DC impulse or zero frequency (or IF) response, viewed through the narrowest resolution BW filter (10 Hz). The 100 Hz bottom spec is just where it's still usable, since you can view a 100 Hz signal close to the noise floor, just past where the RBW filter response falls reasonably far down. Below 100 Hz, the signal becomes swamped and hidden under the filter skirt. You can see that it's a very narrow bandpass filter by viewing the negative frequency range. Set CF=0, SPAN=1 kHz, RBW=10 Hz, for example.

Ed

Re: REVISED, UPDATED, EXPANDED, and IMPROVED Evaluation of the Tektronix 012-0482-00 cable for the SG503

 

Hi John,
The ideal shape for a 50 ohm terminator is exactly like what you described at the bottom of the N connector that you found as a child: a disk with the same diameter as the connector's outer shell with a metallized hole in the middle for the center conductor to be soldered to and metallization around the edge so that can be soldered all around to the shell of the connector. The disk should only be thick enough to be able to dissipate the power that will be applied.
Dennis Tillman W7PF

-----Original Message-----
From: hpxref, Sent: Sunday, May 26, 2019 9:46 PM
Subject: Re: [TekScopes] REVISED, UPDATED, EXPANDED, and IMPROVED Evaluation of the Tektronix 012-0482-00 cable for the SG503

Craig said
<<Quite a long time ago I bought some disc 50-ohm resistors that have a hole that takes a centre pin of a BNC. Bought them from https://www.surplussales.com/ ages ago.>>

As a teenager (15) I bought a very nice piece of WW11 surplus, contained within an olive green metal case with hinged lid, a variable coaxial wave guide to 750MHz with a point contact microwave crystal detector , two short lengths of N connector coaxial cables clipped into the hinged cover, the usual round micro ammeter calibrated in mW and a circular plastic calculator attached the lid, and a spare crystal detector diode Probably a piece of radar test gear The unit was lost many years ago on a move so have forgotten its military (APN?) number. It was beautifully made , I think by Westinghouse, and had a battery compartment.
Whats relevant to Craig's post was that one of the short coax cables measured 50 Ohms . On dissembling as I at first thought, child like, it was faulty,
(the cable sheath was extra secured to its N connector by three tiny screws to an internal silvered ring through the barrel ) I found a circular
carbon button press fitted to the bottom of the N connector with a silvered pin pushed through the hole in its centre.
This was the 50 Ohm terminator resistance, so this form of termination was known during WW11.
I first used it to measure the output of an RF UHF signal generator I had made at the time and it worked well enough to tell me that I needed a piston attenuator to replace the hopeless shielded rotary switch one I had innocently implemented.
So there nothing new under the sun, even N connectors had them then and the microwave engineers of the time really knew there stuff.
Seems to me this form of termination would be superior to a radially spoked terminator.

John




--
Dennis Tillman W7PF
TekScopes Moderator

Re: REVISED, UPDATED, EXPANDED, and IMPROVED Evaluation of the Tektronix 012-0482-00 cable for the SG503

Adrian
 

We had an old box full of those in the Cavendish Radio Astronomy stores back in the 70's, they had "Erie Great Yarmouth, England" on the box IIRC. Had them in both 50 and 75 ohms, color coded red for 75 and green for 50 if memory serves. I tried them as 1.4GHz cold loads dunked in LN2 - they didn't like it one bit!

On 5/28/2019 9:29 PM, Dennis Tillman W7PF wrote:
Hi John,
The ideal shape for a 50 ohm terminator is exactly like what you described at the bottom of the N connector that you found as a child: a disk with the same diameter as the connector's outer shell with a metallized hole in the middle for the center conductor to be soldered to and metallization around the edge so that can be soldered all around to the shell of the connector.

Re: DC voltage on a DC coupled spectrum analyzer

Jim Ford
 

Thanks, Ed.I'll have to try that sometime.  Maybe this coming weekend.Learn something new every day!JimSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: "Ed Breya via Groups.Io" <edbreya=yahoo.com@groups.io> Date: 5/28/19 1:08 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] DC voltage on a DC coupled spectrum analyzer Jim wrote:"Not sure why the 100 Hz low end, but I  did take my 8566A down that low a couple months ago just to see what it would do.   Lots of 1/f noise! "That's not 1/f noise - it's just the DC impulse or zero frequency (or IF) response, viewed through the narrowest resolution BW filter (10 Hz). The 100 Hz bottom spec is just where it's still usable, since you can view a 100 Hz signal close to the noise floor, just past where the RBW filter response falls reasonably far down. Below 100 Hz, the signal becomes swamped and hidden under the filter skirt. You can see that it's a very narrow bandpass filter by viewing the negative frequency range. Set CF=0, SPAN=1 kHz, RBW=10 Hz, for example.Ed

2N2207 replacement in 547.

rbmerckx@...
 

Hi folks, first time posting here. I am a clinical biologist, not an electronics nor scope expert. My hobbies are mainly soccer and Arduino , and on the software side of the latter. I recently got my hands on a package deal of 4 scopes..2 x 547 , 1 scope mobile, a 475 and a TDS 320 with cart ..all for 200..I couldn't resist. Was told all were working...turned out only the TDS 320 was. Managed to get one working 547 out of the 2 by swapping a few broken tubes and failed transistors and repairing knobs/dials, cleaning....( and hours of reading thru articles in this group and online in general). Now I would like to get the second one working. For qualitative measurements, not quantitative. I do not plan on going thru the whole calibration etc.. The working one already has a place into my 60's modern look living room interior because I find the combo scope + 202 model c cart a marvel of industrial design and engineering. I guess we could argue about the scope shape design itself as not being as elegant as the cart :)
The "working" 547 : serial 13996 works great.. but only for 20 minutes...waveform starts to fade ( not really "blooming" , trace remains very sharp..just looses intensity) and disappears all together. I can make it work for 10 minutes longer if from start up I keep trace intensity low. When measuring the voltage as per manual at pin 8 of V800 it starts off at 90 V...it slowly creeps up to 109.5 V and remains there. Pin 2 at V814 measures 161.3 volt. Is this for sure an HV transformer issue ? I am asking because according to a video from Lazyelectrons, that rising voltage symptom on pin 8 can also be due to other parts going bad in the CRT circuitry ( his words..not mine..lol)
The non- working one: serial 10602: What's a modern substitute for the 2N2207 for both Q554 and Q564 on horizontal amplifier. Mr Wise recommended replacing with BC556 or KSA992, but that was in the sweep circuitry. I had to use the good ones of this one to replace the shorted ones of the serial 13996 who came to life after that substitution ( and 5 tubes that had lost vacuum).

Anecdote : Well..i think it's nifty...the working serial 13996 had the CRT replaced on the 6th of January 1975 and was tested and re-calibrated by " R Clark".....2 small decals with the Tektronix Logo on top of the CRT enclosure tell us that part of it's history. And yes..it still contains the little roll of silver solder. I guess Mr Clark had his own supply :).

Re: REVISED, UPDATED, EXPANDED, and IMPROVED Evaluation of the Tektronix 012-0482-00 cable for the SG503

 

Hi Craig,
I looked at the Surplus Sales link you included. Right now all he has is
non-inductive thick disc shaped resistors with contacts on either side.
There is a very big hole in the middle so these are not something that could
be used. They are meant to be wired up from each side.

The disk we need must have a connection in the middle and all along the
perimeter. What we would be looking for was a disc about the diameter of the
BNC shell with silver or metal deposited all around the outer edge that
could be soldered to. There would need to be a small hole in the middle with
silver or metal deposited to form a contact that could be soldered to. The
resistive material would preferably be ceramic rather than carbon composite.
Ceramic would be stronger.

If the disks you bought fit that description send me two and I will mount
them up and test them.
Contact me off list for my address.

Dennis

-----Original Message-----
From: Craig Sawyers, Sent: Sunday, May 26, 2019 11:08 AM

Next try four 200 ohm resistors in parallel. Spread them around the
center pin to the outer ground
to
lower the capacitance between them. But there is now a little more
capacitance and a little less inductance.
On and on. Eventually you end up with a circular cylinder of resistive
material.
Dennis Tillman W7PF
Quite a long time ago I bought some disc 50-ohm resistors that have a hole
that takes a centre pin of a BNC. Bought them from
https://www.surplussales.com/ ages ago.

It would be interesting to see what the HF performance was as compared with
four discrete surface mount.

Craig




--
Dennis Tillman W7PF
TekScopes Moderator