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Re: Need help choosing a scope and some other RF capable equipment.

 

On Fri, Jan 4, 2013 at 8:12 PM, sknaugler <steven1955@...> wrote:
"Bound water and ice have critical frequencies at about 10 MHz"

"That is not resonance."

Sorry for using the wrong terminology. I am not an RF engineer. I don't even play one on TV, but not through lack of auditioning.

So of it is not resonance, what is the correct terminology?
What's wrong with calling it a critical frequency? The article says
it's the frequency of maximum dielectric loss, which is kind of the
opposite of resonance.

Anyway, how does it help you? If you want to heat the water, you
could do it just as well with a heating element.
Re: New old scope owner

[email protected]
 

Steve, I am SO glad you have acquired a Tek scope! I have a rather 'large' collection of different scopes. While I LOVE my 2465A and others, the new digital (color) models makes it real obvious how far the 'state of the art' has advanced!
I have a very expensive LeCroix (Swiss) digital (mono) scope that is cool, but the new Chinese (color) tool makes it look silly. Especially when comparing the function/weight ratio!! ha ha
There is a FANTASTIC resource here and don't be afraid to take advantage of it!!!
I LOVE all my Teks!!!

ron
N4UE



-----Original Message-----
From: Steve Purcell
To: TekScopes
Sent: Fri, Jan 4, 2013 5:37 pm
Subject: [TekScopes] New old scope owner

?
Hi to everyone,
?
I've been reading the posts and researching the old analog Tek scopes. It's very exciting to see the interest shown even after all these years.
?
My 453 has arrived. I haven't been able to test it yet but it supposedly was working according to the ebay seller.
?
I'm sure I will have many questions and as an engineer who came into the field after all the basics were hidden inside IC's it's going to be exciting to see the textbooks come to life.
?
The Tek analog scopes are the perfect vehicle to learn analog design.
?
I'm not familiar with this type of format. There must be a lot of really interesting stuff that's been posted over the years. Is there a way to search archives?
?
Thanks
Steve
?
?
?
?
Re: High Voltage Probe to work on Scopes.

Don Black
 

开云体育

Thanks Alex, I've done similar in the past. In my case, I made a small plastic box up with a mic connector one end to take the probe and a pair of banana plugs on the other to fit into the meter. I then wired a shunt resistor (it was about 1.2 Meg from distant memory to give 1000:1 division) on the 10 Meg DMM input. Since the DMMs read much lower voltages than a VTVM it still measured down to 100 mV (0.1 Volt).
The input resistance is still 1 Gohm it's just reduced the bottom divider value. Before I get pulled up, the input resistance will have dropped by about 10 Meg but that's insignificant in a Gohm. It's useful for measuring small voltages with minimum loading.
From you description it sounded like you reduced the series 1 Gohm resistor slightly to get it to read correctly on a 10 Meg meter, I think it's a good idea to leave that alone.
I suspect it would be possible to get a cheap DMM with 10 Meg input just for the HV probe and recalibrate it to read correctly while still dividing by 100.

Don Black.

On 05-Jan-13 1:50 PM, Alex wrote:

?



Well it is a RCA WG-289 and I didn't replace the shunt resistor so much as add one. I think the probe originally came with shunt resistors in the box but it turns out it was for another probe and that's why I thought I "replaced" them.

I simply unscrewed (carefully) the red body from the black handle. The 1G resistor in the body is just held in place by pressure and you don't want it to fall out. Just touching it to put it back in changes the resistance, and might even make it arc over...

Inside the black handle is a spring contact and a metal ground ring. I added my shunt resistor there. I must have selected from a whole bunch to get the right value. I also made a slot in the plastic sleeve to make space for the resistor. It's a simple carbon film 1/4W 10% part.

Then I put a sticker that says 1000:1 with 10M input.

I also replace the microphone connector with a BNC connector so I can plug it to a banana adapter. This makes the least damage to the original part and I can even put back the old connector if I want.

--- In TekScopes@..., Don Black wrote:
>
> Hi Alex, could you explain more on your modifications to the RCA probe
> for use with a DMM please. I guess you must have reduced the resistance
> because it originally was designed for use with VTVM with 11 meg input
> resistance while modern meters are usually 10 Meg (beware the cheap
> meters are usually only 1 Meg). I imagine any mods to the resistor would
> be best at the meter end away from high voltage.
>
> Don Black.
>
> On 05-Jan-13 5:33 AM, Alex wrote:
> >
> > Aren't these voltages mostly DC? Wouldn't a good old DC HV probe do
> > the trick as well? No CFCs.
> >
> > I got an old RCA HV probe, and once I replaced the shunt resistor with
> > a home-made (filed down) "calibrated" resistor so it reads correctly
> > on modern DMMs, it works fine.
> >
> > --- In TekScopes@... ,
> > "fiftythreebuick" wrote:
> > >
> > > I would recommend a P6015 or P6015A. That's what I've used for
> > decades. A P6013A would do it as well in most cases where the voltage
> > is not above it's max rating.
> > >
> > >
> > > --- In TekScopes@...
> > , "lazystrings" wrote:
> > > >
> > > > What High voltage probe/s do you recommend to work on Oscilloscopes?
> > > > The older scopes seem to have much higher voltages. The 7603 has
> > 12KV and -2975V. Newer scopes have only 2KV :(
> > > > Thank you
> > > > Daniel
> > > >
> > >
> >
> >
>
Differences between 465 and 465B

 

The nomenclature I will be using is what is on the face of the front panel. For instance, the label on the front panel is in capital letters and continued in lower case to point out the function.

The most significant change between the 465 and the 465B is the way the delayed sweep is handled. On the 465, when you are in the MIX HORIZONTAL DISPLAY mode, the trace starts at the A TIME/DIV rate and continues until the trace reaches the point set on the DELAY TIME POSITION control. At that time the trace is swept the remainder of the 10 DIV trace width at the B TIME/DIV setting. This means that if you have the DELAY TIME POSITION control set at 8.0 then you will only see the B portion of the trace for 2.0 DIVisions.

On the 465B the trace also starts at the A TIME/DIV setting and when it reaches the point set on the DELAY TIME POSITION the intensified portion of the A trace is swept out over the entire 10 DIV on a separate trace at the speed set on the B TIME/DIV setting. This second trace can be moved above, on top of, or below the original A trace by rotating the TRACE SEParation control when the HORIZontal DISPLAY is in the ALT mode. The TRACE SEParation control is new on the 465B, it is not present on the 465. This is a very significant improvement as you can now view the intensified portion of the A trace over the entire 10 DIV on the CRT.

Other upgrades are the use of LED in place of the incandescent or neon bulbs on the VOLTS/DIV (4 LED's), UNCAL (3 LED's), X10 MAG, READY, TRIGgered and POWER.

The 465 uses pushbutton knobs with the legends on the surface. These legends have a tendency to wear off after prolonged use and you are left with a nameless control. The 465B uses smaller pushbutton knobs that are labeled on the front panel, not on the pushbutton surface. You are never left with a nameless control.

The 465 used a coarse and fine HORIZontal POSition control. This dual concentric control stuck out in front of the front panel and was in such a position that it could be damaged rather easily. The 465B also uses a fine and coarse HORIZontal control but it is in one potentiometer with one control shaft and is a definite improvement.

The 465 used a rather complicated arrangement of fixed attenuators in the input vertical circuit for the X1 and X2 attenuators. The X10 and X100 used the plug in hybrid circuits. The 465B uses the plug in hybrid attenuator circuits in all four attenuator positions, a definite improvement.

The circuit boards have been redesigned on the 465B and numerous small changes have been incorporated into the design to improve reliability, flexibility and ease of repair. Boards from a 465 will not fit the 465B and visa-versa although much of the circuitry is the same. The service manuals are significantly different as new component labels are used on the 465B which makes troubleshooting a bit easier.

Everything considered, if you are looking for a superior 100 MHz, delayed trace oscilloscope you should choose the 465B over the 465 if you have the option.

Reed Dickinson
Re: Which would you pick? 454 or 475?

fiftythreebuick
 

454 or 454A. Sharper trace. Unless, of course, you need every last bit of bandwidth.

--- In TekScopes@..., Matt Jodz wrote:

Looking at getting either a 454 or a 475 and would appreciate any opinions as to reliability and ease of maintenance and repair for these two scopes.? The 454 is working fine and the 475 needs some (hopefully) minor repair.? I will be using them for hobby repair of older radio and test equipment.? Which would you prefer?? Thanks.
Re: High Voltage Probe to work on Scopes.

fiftythreebuick
 

That's true, as long as you're checking/adjusting. I used my P6015 for both checking/adjusting the power supplies as well as looking at the HV to see what's there if I'm troubleshooting. Plus, it's nice to be able to use that P6015 with a 7A13 and dial in an offset in order to get a really close look at ripple, noise, etc if you're looking for problems.

But, I do admit to using a scope in a lot of occasions when most folks use a meter. :-)

--- In TekScopes@..., "Alex" wrote:

Aren't these voltages mostly DC? Wouldn't a good old DC HV probe do the trick as well? No CFCs.

I got an old RCA HV probe, and once I replaced the shunt resistor with a home-made (filed down) "calibrated" resistor so it reads correctly on modern DMMs, it works fine.

--- In TekScopes@..., "fiftythreebuick" wrote:

I would recommend a P6015 or P6015A. That's what I've used for decades. A P6013A would do it as well in most cases where the voltage is not above it's max rating.


--- In TekScopes@..., "lazystrings" wrote:

What High voltage probe/s do you recommend to work on Oscilloscopes?
The older scopes seem to have much higher voltages. The 7603 has 12KV and -2975V. Newer scopes have only 2KV :(
Thank you
Daniel
Re: Which would you pick? 454 or 475?

 

David DiGiacomo <daviddigiacomo@...> wrote:
(And BTW, I
think there are some late model 454s with JFET front ends.)
I don't have any references handy, but memory says that was the case
for both 453's and 454's. I think the A version of both were FET's.
-ls-
Re: Need help choosing a scope and some other RF capable equipment.

sknaugler
 



"Bound water and ice have critical frequencies at about 10 MHz"

"That is not resonance."

Sorry for using the wrong terminology.? I am not an RF engineer.? I don't even play one on TV, but not through lack of auditioning.

So of it is not resonance, what is the correct terminology?
Re: Which would you pick? 454 or 475?

 

The 454A also drifts a lot, compared to later scopes. (And BTW, I
think there are some late model 454s with JFET front ends.)

On Fri, Jan 4, 2013 at 5:26 PM, David <davidwhess@...> wrote:
It is funny you should mention that. I told someone on the
funwithtubes list that the warm up drift he complained about in the
454 was expected because its Nuvistor based vertical amplifiers are
not temperature compensated unlike the later 454A dual FET vertical
amplifiers.

My CA amplifier is pretty drifty as well but it is not temperature
compensated either.

On Fri, 4 Jan 2013 17:04:56 -0700, David DiGiacomo
<daviddigiacomo@...> wrote:

The 475 is definitely a better scope, but... I really enjoy using the
454. The sharp trace is very, very nice. The thing I like least
about it is the DC drift/unstable attenuator balance. You end up
tweaking the vertical position quite a bit.

I wouldn't say either model is particularly reliable or fun to fix.
Re: High Voltage Probe to work on Scopes.

Alex
 

Well it is a RCA WG-289 and I didn't replace the shunt resistor so much as add one. I think the probe originally came with shunt resistors in the box but it turns out it was for another probe and that's why I thought I "replaced" them.

I simply unscrewed (carefully) the red body from the black handle. The 1G resistor in the body is just held in place by pressure and you don't want it to fall out. Just touching it to put it back in changes the resistance, and might even make it arc over...

Inside the black handle is a spring contact and a metal ground ring. I added my shunt resistor there. I must have selected from a whole bunch to get the right value. I also made a slot in the plastic sleeve to make space for the resistor. It's a simple carbon film 1/4W 10% part.

Then I put a sticker that says 1000:1 with 10M input.

I also replace the microphone connector with a BNC connector so I can plug it to a banana adapter. This makes the least damage to the original part and I can even put back the old connector if I want.

--- In TekScopes@..., Don Black wrote:

Hi Alex, could you explain more on your modifications to the RCA probe
for use with a DMM please. I guess you must have reduced the resistance
because it originally was designed for use with VTVM with 11 meg input
resistance while modern meters are usually 10 Meg (beware the cheap
meters are usually only 1 Meg). I imagine any mods to the resistor would
be best at the meter end away from high voltage.

Don Black.

On 05-Jan-13 5:33 AM, Alex wrote:

Aren't these voltages mostly DC? Wouldn't a good old DC HV probe do
the trick as well? No CFCs.

I got an old RCA HV probe, and once I replaced the shunt resistor with
a home-made (filed down) "calibrated" resistor so it reads correctly
on modern DMMs, it works fine.

--- In TekScopes@... ,
"fiftythreebuick" wrote:

I would recommend a P6015 or P6015A. That's what I've used for
decades. A P6013A would do it as well in most cases where the voltage
is not above it's max rating.


--- In TekScopes@...
, "lazystrings" wrote:

What High voltage probe/s do you recommend to work on Oscilloscopes?
The older scopes seem to have much higher voltages. The 7603 has
12KV and -2975V. Newer scopes have only 2KV :(
Thank you
Daniel
Re: Dynamic Characteristics

jerryszesf
 

In case anyone is interested, Radiotron Designer's Handbook as usual has all the answers already.

Jaz
Re: Need help choosing a scope and some other RF capable equipment.

 

Hi Don,

I really enjoy the group. Thanks.

Jerry Massengale



-----Original Message-----
From: Don Black
To: TekScopes
Sent: Fri, Jan 4, 2013 5:33 pm
Subject: Re: [TekScopes] Need help choosing a scope and some other RF capable equipment.
?
Hi jerry,
??? ??? ????? I'm in Australia, shipping costs here would be much more than the scope. It looks like a nice package, I'm sure it will sell.
I always enjoy your posts to the group, usually learn something from them.

Don Black.

On 05-Jan-13 10:24 AM, jerry massengale wrote:
?
Thanks Don,

Yes it is 200MHZ. I will see if I can fix the listing. Where are you?


Jerry Massengale
-----Original Message-----
From: Don Black
To: TekScopes
Sent: Fri, Jan 4, 2013 4:08 pm
Subject: Re: [TekScopes] Need help choosing a scope and some other RF capable equipment.
?
Hi Jerry,
??? ??? ??? ??? Nice looking scope, too far away for me. However, you've listed it as a 200 MHz scope in the title but only 100 MHz in the description. I guess I could look it up but which is correct? I suspect 200 MHz.

Don Black.

On 05-Jan-13 5:03 AM, jerry massengale wrote:
?
Hi,

Sounds like Hybrid battery work. There are several nice 475s on ebay. Just search for tektronix 475. If you like, I have a 3 channel 7704A on ebay. See item 290839243077. It should serve well and other options can be added.


Jerry Massengale



-----Original Message-----
From: sknaugler
To: TekScopes
Sent: Fri, Jan 4, 2013 10:34 am
Subject: [TekScopes] Need help choosing a scope and some other RF capable equipment.

?
Sorry, this is long. Maybe you folks can help with our project, point us to sources of RF help, or at least help me find a scope. But because this is a scope forum I'll start with the scope part. I should add that a DSO would be nice, but an old fashioned CRT analog scope may be perfectly fine.

We need a scope to examine a waveform that we want to apply to a pair of electro-chemical cells wired in series. Currently we power the cells with 1.0 VDC, and they normally they draw between 3 and 5 A. It is thought that cell performance would improve if we can cause the chemicals in the cells to resonate, hence the desire to superimpose an AC signal on top of the DC. We have been able to explore frequencies up to 100 kHz for square waves and pulses and 300 kHz for sine waves, but not surprisingly those lowish frequencies did not help.

We now want to explore frequencies from about 1 MHz to as much as we can afford on a shoestring budget, but no less than 30 MHz for square waves and pulses and 50 MHz for sine waves. 100 MHz would be nice, but there's that budget issue.

The waveforms, at least initially, would be limited to 1 V maximum, and never going negative. We are thinking that the maximum AC amplitude would be 0.5 V peak, or 1.0 V peak to peak, and that would be superimposed on a 0.5 V DC bias voltage. A minimum AC amplitude would be 0.05 V peak, or 0.10 V peak to peak, and that would be superimposed on a 0.95 DC bias voltage.

We'd also like to monitor current if we can find a shunt that does not distort the waveform.

An issue is that I can't guarantee that the final wiring will give us a common ground point so we may need a scope and lead set up where can can measure two differential voltages. (Our Tek 222 with it's isolated inputs is nice in that regard, but at 10 MHz bandwidth won't work for these higher frequencies.)

So if you guys can point us in the right direction for what models of new or used scopes might work for us. Or even sell us one of your surplus working scopes.

Local Craiglist scopes available that appear to work from pics and description: (I know, buyer beware.)

Tek 2465 (not A or B) $350 firm. (Seems a little high)
Tek 2215A, $100 firm (Not quite enough bandwidth)
Tek TDS 3052B (No price given, and I don't know much about this other than labeled 500 MHz)
Anritsu MS2711D (I know nothing about this brand or model)

We're also going to need an arbitrary waveform generator, and the "superimposed RF on top of DC" power supply. These could be the subject of another posting if there's any interest, or we could keep those non scope subjects off forum.

If it makes any difference, our 3 person start up is in Seaford, Delaware.


Re: 2246 Mod A main board overloading the SMPS

 

Tom,

I was only able to get enough time to assemble the SMPS into the chassis with just the main board and it runs fine - without the 40W series bulb:). The voltages are a bit off (5.28V, 7.46V etc) but I won't adjust anything till the proc board and the pot boards are in and providing normal operating load.

That's for the weekend. More to come.

Thanks for taking the time to make resistance measurements - very similar to mine.

Priya.

--- In TekScopes@..., "Tom Jobe" wrote:

Hi Priya,
Resistances were taken on a nice working 2246 with a Fluke 110 which does not have enough voltage to forward bias the diodes.
I tried this Fluke meter on some standard diodes and some Schottky diodes and there was not much of a connection either way, just a little leakage depending on the polarity
There is not much difference from your readings, and no obvious indication of a problem on any of the voltages.
I will add my readings on to the end of your list.

+5:100 ?? - mine is 99 ohm - 106 ohm
-5:50 ?? - mine is 41 ohm - 53 ohm
-15:500 ?? - mine is 750 ohm - 590 ohm
+15:400 ?? - mine is 583 ohm - 483 ohm
+7.5:150 ?? - mine is 134 ohm - 152 ohm
-7.5:180 ?? - mine is 143 ohm - 150 ohm
+58: 7500 ?? - mine is almost open ( 8M ohm) - 2.5 M ohm? impossible to get a good reading
+130: 9000 ?? - mine is 10,000 - 9000 ohm
I guess the next step is to see what happens when you put the scope back together tonight.
tom jobe...



----- Original Message -----
From: Mover
To: TekScopes@...
Sent: Friday, January 04, 2013 12:20 PM
Subject: [TekScopes] Re: 2246 Mod A main board overloading the SMPS



Tom & Francis,

I discovered what it is - the ultra cautious in me had left a 40W light bulb in series with the isolation transformer secondary providing AC line power to the scope. It was there originally to prevent further collateral damage to the scope through my repair and testing. With any load exceeding the load provided by the fan, the SMPS pulls enough current through the light bulb that the AC line power to the scope drops below the 80V required to keep the SMPS running. This shuts down the SMPS and the 40W bulb comes on as the SMPS restarts - absolutely normal behavior. I had completely forgotten about the light bulb till this afternoon when I chanced to glance at it cycling with the SMPS and then I had an AHA moment!

Regardless, I did measure resistances (with a Fluke 116 - don't own a meter recommended by TEK) and here they are:
> +5:100 ?? - mine is 99 ohm
> -5:50 ?? - mine is 41 ohm
> -15:500 ?? - mine is 750 ohm
> +15:400 ?? - mine is 583 ohm
> +7.5:150 ?? - mine is 134 ohm
> -7.5:180 ?? - mine is 143 ohm
> +58: 7500 ?? - mine is almost open ( 8M ohm)
> +130: 9000 ?? - mine is 10,000

Other than the 58V resistance probably becuase my meter can't drive the diodes, my measurements looks fine.

I ran it without the series light bulb and it happily drives a 10 ohm resistor from the 5V and regulation is excellent at 5.05 VDC. With the light bulb in series, it won't run anything more than the fan. Indeed, the fan is not sufficient load to test the SMPS.

Believe I am ready to put the SMPS back into the scope tonight. I apologize to everyone who I misled with my earlier post on this and thanks as always for quick and thoughtful responses. You guys are great!

Priya.

--- In TekScopes@..., "Francis" wrote:
>
> Hi,
>
> several things:
>
> as Tom Jobe suggested, you can do the following:
> with the scope disconnected from the mains, check the resistances
> between ground and each supply. As Tek says, use an ohmeter that is able to forward bias diodes, usually a low range.
>
> Values are
> +5:100 ??
> -5:50 ??
> -15:500 ??
> +15:400 ??
> +7.5:150 ??
> -7.5:180 ??
> +58: 7500 ??
> +130: 9000 ??
>
> these values are taken from a 2245A manual, but should not be
> very different on your scope. If one is significantly lower,
> check the related circuitry.
>
> The fan is not a sufficient load for the SMPS. When I make
> my trials, I use 2 4.7 ?? paralleled on the +5v.
> If the supply still ticks, try to disconnect the crowbar protection,
> or tie together the gate and the cathode of the SCR. Maybe some
> overvoltage due to a dying cap can fire it. Same recommendation
> about Q2208 (base tied to ground).
>
> --- In TekScopes@..., "Mover" wrote:
> >
> > Alas - if only it were that simple ...
> >
> > I finally fixed my SMPS and put it back into the chassis with only the main board. It runs in chirp mode - about every 1 sec there is a clicking sound - the secondary voltages rise and then something gets overloaded and the SMPS shuts down and then cycles again.
> >
> > I quickly disconnected power, isolated the SMPS and again verified that the SMPS is fine on its own with just the cooling fan load with a steady internal 44 VDC. No new or collateral damage thankfully.
> >
> > There are no obvious shorts on any of the supply lines on the main board. The issue may still very well be with the SMPS being unable to handle load even though the fan runs fine and the other voltages are fine.
> >
> > I assume that chirp mode is a common issue with these SMPS supplies. What have others done to (1) find whether the issue is with the SMPS or with the main board and if the latter, (2) which supply line or lines is drawing too much current and how to isolate the problem further?
> >
> > Thanks in advance.
> >
> > Priya.
> >
>
Re: Need help choosing a scope and some other RF capable equipment.

Jim
 

David,

A bias tee isn't a big deal at all, but injecting the properly biased RF voltage with the DC and RF currents at workable voltages/currents might be.

I think it's an interesting project, from a standpoint of "how do we do this" -- based on their three-person, self-funded, bootstrapped startup paradigm.

Even if the project fails, helping develop the technology might be fun for many of us.

From my computer? ?This looks like as interesting a challenge as helping the neighbor across the backyard fence rebuild his fence to keep his daughter's pit bulldog confined -- neighbor knew less than nothing about fence-building, but we shared a common vision.

We succeeded, and we accomplished our shared vision of fixing the fence to keep that G%^&D*(%%$(&^)* mutt confined.

I would hope that all of us would see this particular project from the same standpoint -- achieve success, or at least experience failure at the peak of our shared technical abilities. ?

I hesitate to list my projects that I've started but that failed on the first endeavor. ? Most of you should have a similar record of failure -- if you don't, then you're not looking high enough nor reaching far enough.

73
Jim N6OTQ


From: David DiGiacomo
To: TekScopes@...
Sent: Friday, January 4, 2013 5:49 PM
Subject: Re: [TekScopes] Re: Need help choosing a scope and some other RF capable equipment.

A bias tee is not a big deal.
Re: Cleaning Tek475A Attenuator Switches

 

Great job.

I did the same thing on my 465 after several months of erratic behavior and several cleanups of contacts. In the end I decided to try the chance, took off modules attenuators, took off their caps and remade with the utmost care all the solderings on the pins.
I'm short-sighted so I can see very well close.
The procedure was finally decisive. Never again I had problems with the attenuators.

Max
Re: what is the differences between 465 and 465B?

 

开云体育

On 01/04/2013 06:48 PM, Matt Jodz wrote:
?
Another newbie question and let me say thanks for the groups patience beforehand!!? I have been trying to research the differences between the Tek 465 and 465B scopes.? Can I use the 465 Service Manual on the 465B or must I get the 465B service manual?? I have only been able to find an internet comment that the B was an improved 465 and that it is preferred.? Is that because it is a newer design/model or is there some better capability in the B over the plain jane 465?? Can anybody enlighten me?? Thanks.
There is a nice article in one of the Tekscopes flyers which covers the updates.
If nobody else gets it in the next few hours, I'll see if I can find it and attach it to a new message.
I have a high-mileage 465B ( among many others )... it just seems to go on forever.
Never had a 465 but have used them in at least ten different countries.
They were very much the goto scope for the early computer industry.
There is a free PDF for the 'B' on the web.

Re: Which would you pick? 454 or 475?

 

It is funny you should mention that. I told someone on the
funwithtubes list that the warm up drift he complained about in the
454 was expected because its Nuvistor based vertical amplifiers are
not temperature compensated unlike the later 454A dual FET vertical
amplifiers.

My CA amplifier is pretty drifty as well but it is not temperature
compensated either.

On Fri, 4 Jan 2013 17:04:56 -0700, David DiGiacomo
<daviddigiacomo@...> wrote:

The 475 is definitely a better scope, but... I really enjoy using the
454. The sharp trace is very, very nice. The thing I like least
about it is the DC drift/unstable attenuator balance. You end up
tweaking the vertical position quite a bit.

I wouldn't say either model is particularly reliable or fun to fix.
Re: 2246 Mod A main board overloading the SMPS

Tom Jobe
 

开云体育

Hi Priya,
Resistances were taken on a nice working 2246 with a Fluke 110 which does not have enough voltage to forward bias the diodes.
I tried this Fluke meter on some standard diodes and some Schottky diodes and there was not much of a connection either way,?just?a little?leakage?depending on the?polarity
There is not much difference from your readings, and no?obvious indication of a problem on any of the voltages.
I will add my readings on to the end of your list.
?
> +5:100 ?? - mine is 99 ohm????-??? 106 ohm
> -5:50 ?? - mine is 41 ohm??? -??? 53 ohm
> -15:500 ?? - mine is 750 ohm??? -??? 590 ohm
> +15:400 ?? - mine is 583 ohm??? -??? 483 ohm
> +7.5:150 ?? - mine is 134 ohm??? -??? 152 ohm
> -7.5:180 ?? - mine is 143 ohm??? -??? 150 ohm
> +58: 7500 ?? - mine is almost open ( 8M ohm)??? -??? 2.5 M ohm??impossible to get a good reading
> +130: 9000 ?? - mine is 10,000??? -??? 9000 ohm
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I guess the next step is to see what happens when you put the scope back together tonight.
tom jobe...

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----- Original Message -----
From: Mover
Sent: Friday, January 04, 2013 12:20 PM
Subject: [TekScopes] Re: 2246 Mod A main board overloading the SMPS

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Tom & Francis,

I discovered what it is - the ultra cautious in me had left a 40W light bulb in series with the isolation transformer secondary providing AC line power to the scope. It was there originally to prevent further collateral damage to the scope through my repair and testing. With any load exceeding the load provided by the fan, the SMPS pulls enough current through the light bulb that the AC line power to the scope drops below the 80V required to keep the SMPS running. This shuts down the SMPS and the 40W bulb comes on as the SMPS restarts - absolutely normal behavior. I had completely forgotten about the light bulb till this afternoon when I chanced to glance at it cycling with the SMPS and then I had an AHA moment!

Regardless, I did measure resistances (with a Fluke 116 - don't own a meter recommended by TEK) and here they are:
> +5:100 ?? - mine is 99 ohm
> -5:50 ?? - mine is 41 ohm
> -15:500 ?? - mine is 750 ohm
> +15:400 ?? - mine is 583 ohm
> +7.5:150 ?? - mine is 134 ohm
> -7.5:180 ?? - mine is 143 ohm
> +58: 7500 ?? - mine is almost open ( 8M ohm)
> +130: 9000 ?? - mine is 10,000

Other than the 58V resistance probably becuase my meter can't drive the diodes, my measurements looks fine.

I ran it without the series light bulb and it happily drives a 10 ohm resistor from the 5V and regulation is excellent at 5.05 VDC. With the light bulb in series, it won't run anything more than the fan. Indeed, the fan is not sufficient load to test the SMPS.

Believe I am ready to put the SMPS back into the scope tonight. I apologize to everyone who I misled with my earlier post on this and thanks as always for quick and thoughtful responses. You guys are great!

Priya.

--- In TekScopes@..., "Francis" wrote:
>
> Hi,
>
> several things:
>
> as Tom Jobe suggested, you can do the following:
> with the scope disconnected from the mains, check the resistances
> between ground and each supply. As Tek says, use an ohmeter that is able to forward bias diodes, usually a low range.
>
> Values are
> +5:100 ??
> -5:50 ??
> -15:500 ??
> +15:400 ??
> +7.5:150 ??
> -7.5:180 ??
> +58: 7500 ??
> +130: 9000 ??
>
> these values are taken from a 2245A manual, but should not be
> very different on your scope. If one is significantly lower,
> check the related circuitry.
>
> The fan is not a sufficient load for the SMPS. When I make
> my trials, I use 2 4.7 ?? paralleled on the +5v.
> If the supply still ticks, try to disconnect the crowbar protection,
> or tie together the gate and the cathode of the SCR. Maybe some
> overvoltage due to a dying cap can fire it. Same recommendation
> about Q2208 (base tied to ground).
>
> --- In TekScopes@..., "Mover" wrote:
> >
> > Alas - if only it were that simple ...
> >
> > I finally fixed my SMPS and put it back into the chassis with only the main board. It runs in chirp mode - about every 1 sec there is a clicking sound - the secondary voltages rise and then something gets overloaded and the SMPS shuts down and then cycles again.
> >
> > I quickly disconnected power, isolated the SMPS and again verified that the SMPS is fine on its own with just the cooling fan load with a steady internal 44 VDC. No new or collateral damage thankfully.
> >
> > There are no obvious shorts on any of the supply lines on the main board. The issue may still very well be with the SMPS being unable to handle load even though the fan runs fine and the other voltages are fine.
> >
> > I assume that chirp mode is a common issue with these SMPS supplies. What have others done to (1) find whether the issue is with the SMPS or with the main board and if the latter, (2) which supply line or lines is drawing too much current and how to isolate the problem further?
> >
> > Thanks in advance.
> >
> > Priya.
> >
>
Re: Need help choosing a scope and some other RF capable equipment.

Jim
 

Only Kansas and my high-school girlfriends are flat.

:)

73
Jim N6OTQ

From: Don Black
To: TekScopes@...
Sent: Friday, January 4, 2013 4:58 PM
Subject: Re: [TekScopes] Need help choosing a scope and some other RF capable equipment.

You mean it really isn't flat???

Don Black.

On 05-Jan-13 9:24 AM, Jim wrote:
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History teaches us the unfortunate lessons and fates of people who believed that a flat Earth was the center of the Universe.

73
Jim N6OTQ
Re: Rear feet for 475

Rob
 

开云体育

Could be. Admittedly all the functionality I have observed is at room temperature here in southern Louisiana. I can but assume they would/may turn quite a bit more brittle at subzero temperatures.(which I hopefully never have to experience * smile *)

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From: TekScopes@... [mailto:TekScopes@...] On Behalf Of John Griessen
Sent: Friday, January 04, 2013 8:30 AM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Rear feet for 475

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Sounds like ABS -- it has some flex and does not shatter easily, (maybe if in Alaska winter).
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