tektronix 2235

[Radio Tech]

Well I am taking a chance here.
One of the guys I do a lot of work for called me this morning while he was at a sale.  He found a pallet with a tektronix 2235 and other junk that he wanted. I told him to bid on it. he called me back and won the bid. $20 USD.
So he is bringing me the scope this week.

I do not know at this time if the scope works, or if there are any probes or power cord with it.  But for 20 bucks I cant go wrong lol. I spent the past 20 minutes reading a bit about the scope and downloaded the user manual.  For what little I read looks like a nice little scope.

Anyone using this scope that can comment on it?

[KJDS]

I've got one with a power supply fault that I really should get round to fixing.

Most Tek scopes of that era are good to use, though well known for flaky electrolytic caps.

[Radio Tech]

Yep, I may have to check caps in this one.

[valentinc]

      I have a Tektronix 2235 (AN/USM-488 version) for about 2 years or so... I don't know exactly what are the differences between the standard version and the AN/USM... But in my unit, I measured all the electrolytic capacitors in the power supply and found values better than some new ones bought at a local electronics parts shop... 

      I also bought a couple of moths ago a Tektronix 2465A from ebay, with a faulty power supply, and the main problem was an 100uF capacitor in the start circuitry for the TL594... And the X capacitors in the mains filter...

      I'm inclined to belive that the military version used higher quality caps... In my opinion, the best thing to do is to check them... It they are ok... Don't change them... And the only ones that could have a problem are the ones in the output filters of the power supply (which carry high ripple currents) and the ones around the TL494/594...

      It's a bargain at $20 USD, if it's working... I paid almost $250 (including shipping) on mine when bought it...

      I also put a fan on mine, the power supply does get hot after a few hours...

      Please put some pictures when you have the scope...

[Radio Tech]

      I have a Tektronix 2235 (AN/USM-488 version) for about 2 years or so... I don't know exactly what are the differences between the standard version and the AN/USM... But in my unit, I measured all the electrolytic capacitors in the power supply and found values better than some new ones bought at a local electronics parts shop... 

      I also bought a couple of moths ago a Tektronix 2465A from ebay, with a faulty power supply, and the main problem was an 100uF capacitor in the start circuitry for the TL594... And the X capacitors in the mains filter...

      I'm inclined to belive that the military version used higher quality caps... In my opinion, the best thing to do is to check them... It they are ok... Don't change them... And the only ones that could have a problem are the ones in the output filters of the power supply (which carry high ripple currents) and the ones around the TL494/594...

      It's a bargain at $20 USD, if it's working... I paid almost $250 (including shipping) on mine when bought it...

      I also put a fan on mine, the power supply does get hot after a few hours...

      Please put some pictures when you have the scope...

Will do. I hope to have it Friday, maybe saturday.  I post pics and check it out and see what it does. If all is well with it I will be tearing down my Sencore Cs-61. It is starting to give a few errors, BNC jacks have worked loose and the horizontal control acts a bit flakey.

[Radio Tech]

Scope came in today.
Had power cord but no probes 
Oh well.
Now for the moment of truth. Plug inserted, power on. Nice beautifull trace on the CRT     
Grabbed my Phillips ECG PR 200 probe and connected it up. Cannot remember but think this is a 200MHz probe. Had it a long time.

Thing works a treat 
20 bucks well spent. Now waiting for my second one to arrive.  It costed me 25 bucks 

[valentinc]

   Great looking unit... If you can, I'm curios to see some pictures with the inside of it, to see the differences between yours and mine... (military version) ...

[Radio Tech]

   Great looking unit... If you can, I'm curios to see some pictures with the inside of it, to see the differences between yours and mine... (military version) ...

Sure, I will try my best to do that this week end.

[markce]

      I have a Tektronix 2235 (AN/USM-488 version) for about 2 years or so... I don't know exactly what are the differences between the standard version and the AN/USM... But in my unit, I measured all the electrolytic capacitors in the power supply and found values better than some new ones bought at a local electronics parts shop... 

Same here, I've a 2236 model, regular production. All the electrolytic capacitors are fine when measured (cap and esr). Some are better than available replacements. However, modern cap are smaller, so you could increase value's when needed. Only really needed to replace some tantalum cap's (high esr). Other where just to reset live expectation in smps: witch Nichicon PJ, PM and PW, Panasonic FM.

[Radio Tech]

Today I got my second 2235.
Noticed it did not come with probes like I was told it did. 
So what the heck lets fire it up. Plug it in and turn it on, see a flash on the screen and nothing.
No trace at all. Hit the beam find and there is a dot on the screen.  Cant be much then.
So I took it apart. Found a vertical bord leaning towards the front. Straighten it out and turned on.

We now have trace. So took the iron to the pins for good measure.
Here is a few inside pics.
please excuse the quality of my phone. Damn got to buy a new digital cam. And a video cam!!

[valentinc]

    Very nice ....  At a first look, seems exactly as mine... Did you take the cover of the power supply of  ? 

[Radio Tech]

    Very nice ....  At a first look, seems exactly as mine... Did you take the cover of the power supply of  ?

Cool thanks,
Not yet. But I plan too.  Thinking about the age of these scopes I am looking through the service manual at caps in the HV circuit.  Will probably order the ones that are most likely to fail. Will try and find some high quality caps to replace with.  I know the saying if it isn’t broke don’t fix it. But want to do a little preventative maintenance.  Don’t want them to break down during a very busy time in the shop.

On another note I do mostly RF related repairs. Ham radio and some Citizen band stuff.  I have fell in love with these 2 2235 scopes. The X Y function is great for looking at a trapezoid wave form from a AM transmitter using w2aew’s RF sampler / Demod circuit.  Never could figure out how to get my old Sencore CS 61 to do that.  And the DSO I have is not as sharp as the analogs are.

I am having a blast with these at the moment

[valentinc]

    Most DSOs, show only dots in X-Y mode... And don't use the full sample rate they're capable of...

    And I agree with you, some preventive maintenance is always good, I didn't change any capacitors in mine, because it worked well... Only failed one IRF720 (didn't turn on completely so the power supply won't turn on) in the power supply, which I replaced at that time and works well since then...

    Please take some pictures of the power supply when you do this cap replacement job... And also the shield of the frontend amplifiers... I'm just curios if there is any diffrence between yours and mine... 

[alm]

Most DSOs, show only dots in X-Y mode... And don't use the full sample rate they're capable of...

Most analog scopes (I think there were a few exceptions) are limited to a few MHz horizontal bandwidth in XY mode.

[valentinc]

Most analog scopes (I think there were a few exceptions) are limited to a few MHz horizontal bandwidth in XY mode.

    True, but what you're saying is valid only for the X input, the Y input has the full bandwidth as if used in Y-T mode...

[Maturola]

There is a Tektronix 2235 AN/USM-488 in a local shop for $90, it is fully working with some minors signs of usage. It may need calibration since it was in storage for a bit. don't think it have any probes.

Does that sound like a good deal? I was saving up for a DSO but I think the 2235 would cover me for a while and $90 won't breaks he bank.

[valentinc]

     It sounds like a very good deal to me... A readjustment procedure would be needed anyway on this kind of equipment because most of the adjustment are done with pots, that can change their position slightly due to mechanical vibrations for example... And the readjustment is a straight-forward process... And of course, not to mention that I would be a pain in the ass to buy a calibrated one for example and due to mechanical vibrations in the transport have to readjust it again... It happened to me more than once...

[Radio Tech]

There is a Tektronix 2235 AN/USM-488 in a local shop for $90, it is fully working with some minors signs of usage. It may need calibration since it was in storage for a bit. don't think it have any probes.

Does that sound like a good deal? I was saving up for a DSO but I think the 2235 would cover me for a while and $90 won't breaks he bank.

I seen reconditioned one go for 600 USD from companies..
So yes, if it works it is a good deal. I own 2 of these and love them. And would not sell either

[plexar]

Hi Everyone,

I'm new to the forum so please let me know if this is a bad place to post. 

I just won my first scope at ebay.  A Tektronix AN/USM-488 2235.  Waiting for it to arrive.  It does not come with probes.  I don't have too much experience with scopes so I am looking for some advice on what type of probes to buy and where is a good place to purchase them online.  I have read that the 2235 has more bandwidth headroom than 100Mhz so it should be paired with 150Mhz probes to get the most out of it.  Thanks in advance for any advice.

Thanks!

[valentinc]

       Any probes that have an interval of compensation, so that the input capacitance of the scope (which is 20pF) fits somewhere within the interval of adjustment are ok... You can buy them on ebay... The original Tektronix probes are too expensive in my opinion and there are many alternatives to that...

       About the bandwidth, the quoted bandwidth is given at -3dB (http://www.ens-lyon.fr/DSM/AGREG-Physique/oral/Notices/N036-003.pdf) to be (at least) 100 Mhz from 5mV to 5V/div and 90 Mhz at 2 mV/div... And it also deacreses by 10 Mhz when the ambient temperature rises above 35 degrees celsius...
        The bandwidth of the probes is also given at -3dB... So, in my opinion, you don't earn anything by buying an 150 Mhz probe...

        It is very rellevant what you intend to do with the scope... If you want to just check the presence or absence of a signal (and the wave shape does not matter much at all), of course you can use this scope well above 100 Mhz... But the signals (any other than sinewaves) will be distorted... And there will come a point where the harmonics are attenuated so much, that you only see the fundamental... And you would see a 150 Mhz sinewave, which in reality might be a squarewave... And it will be confusing...
        If you only want to measure sinusoidal signals (which I doubt), you would only see an attenuation at frequencies above 70 Mhz or so (where there is no attenuation at all - 0 dB)...

[David Hess]

Most Tek scopes of that era are good to use, though well known for flaky electrolytic caps.

I would not consider the aluminum electrolytic capacitors on these oscilloscopes to be flaky if they lasted 20+ years.

       About the bandwidth, the quoted bandwidth is given at -3dB (http://www.ens-lyon.fr/DSM/AGREG-Physique/oral/Notices/N036-003.pdf) to be (at least) 100 Mhz from 5mV to 5V/div and 90 Mhz at 2 mV/div... And it also deacreses by 10 Mhz when the ambient temperature rises above 35 degrees celsius...
        The bandwidth of the probes is also given at -3dB... So, in my opinion, you don't earn anything by buying an 150 Mhz probe...

With oscilloscopes like these, Tektronix specifies the bandwidth at the probe tip when the proper probe is used.  My 22xx oscilloscopes have no problem meeting their 100 MHz bandwidth specifications with the cheap 100 MHz probes that I use.

Linear Technology included an article from Tektronix which discusses this on PDF page 72 of application note 47.  I never found the original Tektronix article although I am pretty sure I have seen the same discussion in some of their much older publications but Probe Fundamentals is close.

http://www.linear.com/docs/4138
http://circuitslab.case.edu/manuals/Probe_Fundamentals-_Tektronix.pdf

* I tried to include these attachments but the forum choked on them. *