Date   

Re: 7A22 improvement project

Ed Breya
 

After more experimenting with the SSR mod to the front end clamping circuits, I have concluded that this method is the best for now, but not 100 percent effective at preventing fuse-blowing. With 250VAC at low source impedance applied to the inputs, some combinations of switching the inputs and the voltage can still blow the fuse, like if contact is made near the line voltage peaks, enough times. There is some evidence of current spikes that are quite large, over 100 mA, that the 576 can't readily see, except for fleeting momentary excursions that can be observed with enough random switch cycles. In terms of meeting my original objective of handling say up to 100VDC or 120VAC, I'm confident that it will work just fine, while at higher levels, there is still some chance of blowing the input fuses.

I modified a second unit with SSRs, but in this case, the two SSRs are very different in vintage and brand. One seems to be much slower in turning off, allowing higher current spikes on one of the inputs. It is still effective, but not as nice as the first unit, which has great symmetry.

I searched and reviewed info on a number of depletion-mode MOSFETs, and conclude that none have a low enough Vt to get the right conditions for this application. I learned from the PTC version experiments that the total series resistance in the normal (non-clamping) range has to be quite low, say in the hundred ohms range or less. Otherwise, the resistance noise makes a significant and obvious increase in the overall front-end noise level. With the MOSFETs, having this kind of range - including the device Rs and degeneration R - could require well over 10 mA of current during limiting operation. This would be just fine for the fuses and input circuit clamps, but would cook the MOSFETs if they have to sustain high voltages. This is due to the trade-offs between Vt, Vds, and on-resistance of the MOSFETs - the degeneration needs to produce somewhere around 1-2V or more at the desired current, putting the resistance in the kohm region for reasonable limiting.

There are various ways to modify it to avoid some of the problems, but no simple way to make it a nice clean current limiter with smooth transitions to say 1-2 mA over the whole range.

One option is to use an incandescent lamp as the degeneration R, which could provide the desired low R in normal, but then rise after lighting up, to provide the cut-off voltage for the MOSFETs at a lower current. Another would be to use a high enough degeneration R, but bypass the noise with a cap, as I did in the PTC version. Unfortunately, either of these methods would cause current spikes during the transition into clamping, just like the SSR one does.

So anyway, I'm calling this project done for now, from a technical sense. I have to do some cleanup on the boards from all the soldering, and a few mechanical issues. I now have two units in stock condition, and two with the SSR mod, all operational. At some point I will need to buy some new fuses (I blew several during all the experimenting, so am now short) and some of those MOSFETs for experimenting and use in other applications, and probably some new SSRs to replace the marginal ones in the second unit.

Ed


Re: New member and owner of a dead 2225

phillip.lyne.barrett
 

Q923 does not appear to be shorted. However, measuring resistance pairwise across E, B and C show a very slow charging. Possible it was damaged? I believe it's a TIP31C based on a couple of internet hits on the part number.

Amazing that people are trying to sell it for $17. Mouser has it for $0.50. Bunch of crooks. Maybe not so amazing... The reasonable folks are selling it for 3 to 6 bucks.


Re: New member and owner of a Ten 465

Albert Otten
 

... I should not have doubled the percentage... so about 5 of total, or 10 % of half axis. Albert


---In TekScopes@yahoogroups.com, <aodiversen@...> wrote :

Hello Peter,

The manual (for S/N B250000-up) specifies the X-Y phase angle typically less than 3 degrees up to 50 kHz. That would be very well visible, ellipse opening (hor. or vert.) I think about 10 % of total width or height.
------
Albert


Looking for an original 2465B service manual

 

Looking for an original hard copy service manual. Not interested in copies or PDF files.


Thanks,
Manuel


Re: New member and owner of a dead 2225

 

Those are great points which I missed. Add LM358 U920 as well to the
list.

The series regulator should have protected itself and the inverter
until it failed. Was Q923 shorted also? I do not see this mentioned
in the discussion.

On Mon, 13 Nov 2017 19:16:20 -0500, you wrote:

I think U940 would have been overvoltaged. Max is 41 volts. It would have seen 67 - 15 or 52 volts. But those are very cheap and available. C972, 470/50v could have survived a 17 volt overvoltage. But they are cheap and available. I agree Q912 is probably ok as long as the stressor didn't get it before 913 shorted.

Hell, I would sure try to bring it back to life.

Tom


Re: are the 500 series scopes still usefull

Dave Seiter
 

My first scope was a 502.  It was fun to play with, but the bandwidth was so low!  I did use it to trouble shoot the Commodore PET and CBM computer I used to build from Commodore dumpster finds, but it was quite challenging.  Not the correct tool for the job.
-Dav

From: "Carl Hallberg n9ess@yahoo.com [TekScopes]" <TekScopes@yahoogroups.com>
To: TekScopes@yahoogroups.com
Sent: Tuesday, November 14, 2017 3:39 AM
Subject: Re: [TekScopes] are the 500 series scopes still usefull

  Hi Dave,
I had a 502. Bought it from work for $400 about 1967. Very sensitive input (100uV to 100KHz) and max B.W. of 1MHz on higher ranges. Limited use for me and ended up giving it away some years later. 502 had tubes for input and 502A was solid state input.
Carl
--------------------------------------------
On Sun, 11/12/17, Dave Seiter d.seiter@att.net [TekScopes] <TekScopes@yahoogroups.com> wrote:

Subject: Re: [TekScopes] are the 500 series scopes still usefull
To: "TekScopes@yahoogroups.com" <TekScopes@yahoogroups.com>
Date: Sunday, November 12, 2017, 9:30 PM

As were the 502 and 503.

-Dave



From: "Carl Hallberg n9ess@yahoo.com [TekScopes]"
<TekScopes@yahoogroups.com>

To: TekScopes@yahoogroups.com

Sent: Sunday, November 12, 2017 4:41 AM

Subject: Re: [TekScopes] are the 500 series scopes still
usefull


  Hi Bob,

The 547 is a single beam scope. It can be dual trace, 4
trace, etc, depending on plug-in. 555, 556 were dual beam.

Carl



--------------------------------------------

On Fri, 11/10/17, Bob Albert bob91343@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:

Subject: Re: [TekScopes] are the 500 series scopes still
usefull

To: TekScopes@yahoogroups.com

Date: Friday, November 10, 2017, 11:06 AM



The 530 series went to 15 MHz and the 540 series to 30 or
33

MHz.  The 580 to 80 MHz.  Plus, sampling units were

available to go a lot higher.  The high gain
differential

plug in and the calibrated offset plugin were really
nice,

and today's units don't have that.  My favorite
was

the 547 dual beam.

Bob


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[Non-text portions of this message have been removed]


Re: New member and owner of a dead 2225

 

I have run across at least 4 different files but I think they all
originate from a single scan.

On 14 Nov 2017 01:13:50 +0000, you wrote:

I have the 1982 version I think and one from a website that is no longer there called Tek-cross-ref-free. It has a sig in the pdf of www.aa4df.com http://www.aa4df.com which is available for someone to purchase but no longer online. I can't post either because they are way past the limit on upload sizes. Transistors and IC's are in both..

Mitch
N4MF


Re: New member and owner of a Ten 465

 

On 14 Nov 2017 16:25:00 +0000, you wrote:

...

I only have a problem with phasing. When I try to test the x-y mode with the same signal on both channels, I don’t have a diagonal line, but an elliptic diagonal figure.

I have to check that more out, because Now it looks like there is few degrees phase difference between the 2 channels.

When I see the both channels on my screen not in x-y mode, they seem in phase, but that is probably because the way I trigger. I don’t know, I haven’t seen this problem in a scope before. But never have had a more then 40 year olol scope that probably hasn’t had any calibration in 20 years or so.
Triggering has no meaning in X-Y mode except in that the trigger
source and trigger coupling affect the X input.

The vertical delay line and to a lesser extent low horizontal
bandwidth limits X-Y bandwidth at low phase differences. For the 465,
I think this is 50 kHz up to 3 degrees of phase difference. Some
oscilloscopes but not the 465 series or portable oscilloscopes in
general have a phase correction option which increases this to 1 MHz
or more.


Re: New member and owner of a Ten 465

Albert Otten
 

Hello Peter,

The manual (for S/N B250000-up) specifies the X-Y phase angle typically less than 3 degrees up to 50 kHz. That would be very well visible, ellipse opening (hor. or vert.) I think about 10 % of total width or height.
The signal path for the X deflection passes the horizontal amplifier. If you compare phases of CH1 and CH2 in ordinary mode then both use the same vertical amplifier. In many or most Tek 'scopes the (external) horizontal BW is very low compared to the vertical BW. For some types there is an Option for smaller X-Y phase difference.

Albert


Re: New member and owner of a dead 2225

 

On Tue, 14 Nov 2017 07:29:01 -0800, you wrote:

...

In studying the schematic of the 2225 power supply, we see that it has
at least twice as many parts as the more common 22xx family which
includes the 2235, etc. Maybe this explains why it is fairly rare to
hear about 2225 power supply problems?
tom jobe...
It is just a very different design with much less stress on the
individual parts. The price for this is having to include a large 60
Hz power transformer. The 2225 series has also not aged quite as
much.


Re: New member and owner of a dead 2225

 

On 14 Nov 2017 13:44:55 +0000, you wrote:

After a marathon session at distributor's web sites, I found a number of perfect fit replacement caps but still missing a few.

What is glaring is the absence of axial cap selection. It looks like these are disappearing fast. Not that I blame the manufacturers - I hate bending leads and would rather use SMDs any day. I was wrong about the axial caps' value - 15 uF, not 10. I wasn't able to find anything at mouser or digikey that matched except for some tant caps that were like $100. Since I need 7 of those, that ain't happening. These aren't in the power supply section so I don't HAVE to replace them. What are people doing in this situation? accepting worse tolerance? Significantly higher voltage (like 100+ for 10V caps), if that's even available?
Unless they are used for timing like in a soft start circuit, the
values are not critical. Larger values are better up to a point.

For local bulk decoupling capacitors, values are usually selected
based on ESR at high frequency so a lower value solid tantalum
capacitor can replace a larger value aluminum electrolytic capacitor
with a ratio of about 2 to 4.

There is a wonderful selection of SMD caps with tight tolerances for well less than a buck. I could imagine making a tiny little carrier board that would convert the SMD to the right pitch and size to replace an axial cap. Anything wrong with that idea?
It is much easier to use radial lead parts by insulating and bending
one lead around the capacitor body.


Re: New member and owner of a dead 2225

 

On 14 Nov 2017 10:11:05 +0000, you wrote:

On higher voltage caps, it's it the case the higher V often means higher ESR?
With higher voltage ratings up to about 100 volts, dissipation factor
and ESR drop and ripple current rating increases. Ripple current
rating depends on ESR and surface area for dissipating heat. There is
a jump at about 160 volts and higher where the dissipation factor and
ESR increase because the electrolyte is different (at least I think it
is due to a different electrolyte) to support higher voltage
operation.

I am planning on pulling all the switcher electrolytic caps out and am hoping to find what went bad to help with the general diagnosis. Right now, my bet is on either C915 or C971. Hopefully the series regulator and inverter are ok as I don't have a scope to debug my scope with...
It might just be a case of Q913 failing for whatever reason including
CR912 shorting, R920 failing open or high, base drive being
insufficient, or contamination through the package. But I would still
change the aluminum electrolytic capacitors in the power supply except
maybe for C900 if it and the bridge rectifier diodes CR901 through
CR904 test good. If diode shorted and then failed open, it might
have damaged C900 without it being apparent.

Another thing which could have caused failure of Q913 is a low input
voltage. With low input voltage, the duty cycle to maintain the
output voltage is higher so Q913 conducts longer and runs hotter.


New member and owner of a Ten 465

hendrickx.peter@...
 

Hello, my name is Peter Hendrickx. I’m a European who lives in Canada. I have worked for 22 years in cable TV for testing and repairing measurement equipment and amplifiers.
I’m licensed ham radio amateur too.
I recently bought a cheap Tek 465 on ebay with condition for parts or not working. But it was described as Trace for channel 1 and no trace for channel 2. When it arrived, the scope was like described. After take out and plugin again the transistors in vertical amp CH2, I had traces for both channels. On channel 1 , there was a problem with the level (the level displayed was 2.5 times to high). After take out and plugin the transistors for the vertical amp in Ch1, the problem was solved. Then I aligned the potters for step attenuator balance, so there is only a 0.2 Div varriation when I change Volt/Div switch from both channels between min and max.
I aligned the both voltage traces at the same voltage out on the display on a 1000 Hz frequency.
I have tested the bandwith till 20 MHz, and the output voltage seems fine. I cannot test to a higher frequency, because I don’t have a good source where I know the amplitude on a higher frequency.
I have cleaned the contacts from the attenuator with isopropyl alcohol and a small painting brush.
I calibrated the time base on 50 ns.
The power supply seems fine, gives out all the right voltages with a ripple of a few millivolts. On.y on the 110V, I have between 10 and 20 mv ripple. The high voltage, I’m not able to test.
The screen is bright and the traces are sharp focussed.
The triggering seems to work fine.
I only have a problem with phasing. When I try to test the x-y mode with the same signal on both channels, I don’t have a diagonal line, but an elliptic diagonal figure.
I have to check that more out, because Now it looks like there is few degrees phase difference between the 2 channels.
When I see the both channels on my screen not in x-y mode, they seem in phase, but that is probably because the way I trigger. I don’t know, I haven’t seen this problem in a scope before. But never have had a more then 40 year olol scope that probably hasn’t had any calibration in 20 years or so.
I will try to calibrate the complete scope as far I can with the equipment I have.


I’m looking forward to participate this group and helping as far as I can.


Greetings,

Peter


Re: New member and owner of a dead 2225

 

Just go up to 15uF, or 18uF, or maybe even 20uF. Odds are that the old part
was -10%,+100%, so an 18uF part would likely be spot on, and 20uF would not
harm any.

These are after all just decoupling caps.

Dave

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com]
Sent: 14 November 2017 13:45
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: New member and owner of a dead 2225

After a marathon session at distributor's web sites, I found a number of
perfect fit replacement caps but still missing a few.

What is glaring is the absence of axial cap selection. It looks like these
are disappearing fast. Not that I blame the manufacturers - I hate bending
leads and would rather use SMDs any day. I was wrong about the axial caps'
value - 15 uF, not 10. I wasn't able to find anything at mouser or digikey
that matched except for some tant caps that were like $100. Since I need 7
of those, that ain't happening. These aren't in the power supply section so
I don't HAVE to replace them. What are people doing in this situation?
accepting worse tolerance? Significantly higher voltage (like 100+ for 10V
caps), if that's even available?


There is a wonderful selection of SMD caps with tight tolerances for well
less than a buck. I could imagine making a tiny little carrier board that
would convert the SMD to the right pitch and size to replace an axial cap.
Anything wrong with that idea?


Phil






------------------------------------
Posted by: phillip.lyne.barrett@gmail.com
------------------------------------


------------------------------------

Yahoo Groups Links


Re: New member and owner of a dead 2225

Tom Jobe <tomjobe@...>
 

Another question. There are at least 9 10 uF axial electrolytics in
various places. I should replace them as well? I'm not wild about removing the attenuator/timebase board, though it's probably easier than it looks.

Hi Phil,
Sorry for not being clearer about my suggestion of replacing the 10 uF and up aluminum electrolytic caps, my comments are only about the repairing of the power supply, and not about any other sections of your oscilloscope.
The leads on those 'snap' caps bend easily, maybe spread them to fit and plan on not having the cap sit down on the board tightly? Maybe use two pair of pliers so the joint between the leads and the capacitor body are not disturbed?
In studying the schematic of the 2225 power supply, we see that it has at least twice as many parts as the more common 22xx family which includes the 2235, etc. Maybe this explains why it is fairly rare to hear about 2225 power supply problems?
tom jobe...


Re: Engine Analyzer Plug-In Modification

Albert Otten
 

Sure this does show on the outside. Just compare the photo in "Engine Analysis Measurements" (Measurement Concepts Series) with an ordinary 2B67.
For example, the text mentions a Rotational Function Generator position of the (modified) Time/Div switch.

Albert


---In TekScopes@yahoogroups.com, <grbosworth@...> wrote :

Does anyone know the specific modification that was done to the 2B67 horizontal sweep plug-in to make it work with the Engine Analyzer that Tektronix offered back in the 1960's and 1970's? Physically, does it show on the outside of the plug-in?


Re: New member and owner of a dead 2225

phillip.lyne.barrett
 

After a marathon session at distributor's web sites, I found a number of perfect fit replacement caps but still missing a few.

What is glaring is the absence of axial cap selection. It looks like these are disappearing fast. Not that I blame the manufacturers - I hate bending leads and would rather use SMDs any day. I was wrong about the axial caps' value - 15 uF, not 10. I wasn't able to find anything at mouser or digikey that matched except for some tant caps that were like $100. Since I need 7 of those, that ain't happening. These aren't in the power supply section so I don't HAVE to replace them. What are people doing in this situation? accepting worse tolerance? Significantly higher voltage (like 100+ for 10V caps), if that's even available?


There is a wonderful selection of SMD caps with tight tolerances for well less than a buck. I could imagine making a tiny little carrier board that would convert the SMD to the right pitch and size to replace an axial cap. Anything wrong with that idea?


Phil


Re: DIY TD Pulser

Eino Väänänen
 

I have also Tektronix 067-0513-00 with broken original tunnel diode. I have installed tunnel diode 1N3718 to GR-874 connector. Rise time is now 800 ps.


Eino


Re: are the 500 series scopes still usefull

Carl Hallberg
 

Hi Dave,
I had a 502. Bought it from work for $400 about 1967. Very sensitive input (100uV to 100KHz) and max B.W. of 1MHz on higher ranges. Limited use for me and ended up giving it away some years later. 502 had tubes for input and 502A was solid state input.
Carl
--------------------------------------------

On Sun, 11/12/17, Dave Seiter d.seiter@att.net [TekScopes] <TekScopes@yahoogroups.com> wrote:

Subject: Re: [TekScopes] are the 500 series scopes still usefull
To: "TekScopes@yahoogroups.com" <TekScopes@yahoogroups.com>
Date: Sunday, November 12, 2017, 9:30 PM

As were the 502 and 503.

-Dave



From: "Carl Hallberg n9ess@yahoo.com [TekScopes]"
<TekScopes@yahoogroups.com>

To: TekScopes@yahoogroups.com

Sent: Sunday, November 12, 2017 4:41 AM

Subject: Re: [TekScopes] are the 500 series scopes still
usefull


  Hi Bob,

The 547 is a single beam scope. It can be dual trace, 4
trace, etc, depending on plug-in. 555, 556 were dual beam.

Carl



--------------------------------------------

On Fri, 11/10/17, Bob Albert bob91343@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:

Subject: Re: [TekScopes] are the 500 series scopes still
usefull

To: TekScopes@yahoogroups.com

Date: Friday, November 10, 2017, 11:06 AM



The 530 series went to 15 MHz and the 540 series to 30 or
33

MHz.  The 580 to 80 MHz.  Plus, sampling units were

available to go a lot higher.  The high gain
differential

plug in and the calibrated offset plugin were really
nice,

and today's units don't have that.  My favorite
was

the 547 dual beam.

Bob


Re: New member and owner of a dead 2225

phillip.lyne.barrett
 

Thanks. I went through Mouser looking for the caps. 300 mil pitch doesn't seem to exist anymore. Will try Digi. On higher voltage caps, it's it the case the higher V often means higher ESR?

I am planning on pulling all the switcher electrolytic caps out and am hoping to find what went bad to help with the general diagnosis. Right now, my bet is on either C915 or C971. Hopefully the series regulator and inverter are ok as I don't have a scope to debug my scope with...


As to Dave, it's not his Aussie accent and turn of phrase, rather his high pitched voice and geeky mannerisms that bug my Wife. It sometimes gets a bit wearing to me too. Plus it can be hard to figure out if he thinks something is good or bad. I went to school with a bunch of Aussies - great group of friends.

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