Bandwidth Finally

[Tubetec]

At long last I have my sights set on a couple of good late 80's analog TEC scopes , made contact with the seller today and its all but deal done , not only that but he's offering to drop them the 3hrs 15 minutes on the motorway to me rather than take the risk of transportation via any other means .

I've had a series of bad ends with scopes over the years , not so much due to techincal misshaps but simply the age of the gear
fingers crossed I can sort out any gremlins , 2215 in working order 2235 in need of attention , from what I've seen so far the fixes are very well documented as well as any components that didnt make it over the last 30 years . Another plus or minus is its the AM spec version of the 2235 , it has a fissile material warning on the back ,probably tested/hardened under attack from sub atomic particles before being released as worthy .

 

[Tubetec]

I'll keep that unit in shed-17 until I can run a gieger over it ;-)

 

[Brian Roth]

I spent what was a small fortune for me and bought a new 2215 in the early 1980's. It's still running fairly well 40 years later. Main problem is the trace width has shrunken a bit. Nevertheless, it's been a real workhorse that traveled thousands of miles with me when I was regularly doing onsite service work. Attached a pic from 12 years ago while I was servicing an Amek 9098 desk.

Bri

 

[Tubetec]

I think the Aussie with the hand signal sign( Dave the Wave EEV blog ) has a series of videos about the TEK 22xx series , many others too dedicated to renovating maybe the last of the great analog scopes , I been waiting my whole life to get my hands on one of these .


Cheers Brian

 

[Tubetec]

Tek Scopes are getting delivered this afternoon ,
I need to get the basic test gear together to have a look ,
I'll grab the Arbgen and Fluke 187 ,
I got a big yellow Fluke tool carry case for 10 euros + 10 delivery , Its a bit grubby and greasy but nothing a good wash wont fix .

 

[Tubetec]

After a quick dust down of the front panel with a small paintbrush then a wipe of the housing with a cloth moistened with surgical spirit to help remove any label residue the 2215A looks brand new ,
Two 100mhz Tek probes were part of the deal , they came complete in their original plastic envelope with all accesories .
I only did a basic check on the unit so far but it looks good even with minimal warm up time ,the trace is bright and crisp
It correctly displayed the reference voltage , it also displayed 1khz sine with no issues ,
The only thing I can find wrong with this scope is a small blob of what seems to be super glue on the top panel , I went at it with thumbnail and bamboo scraper and managed to make it almost dissappear without touching the original finish , I might just leave it at that in terms of cosmetic treatments.
Next I might check the inside for dust , any of the silicone boots or wiring in the EHT thats accumulated carbon need to be cleaned . I'll do the best I can not no allow this crud get anywhere near the PCB's/switches etc , I'll most likely use the vacuum cleaner to evacuate the air nearby as I clean with the unit on its side so nothing falls down into the works .
I'll get a service manual for it and check the rail voltages for any potential problems .

What are a good battery of basic tests to throw at a scope to check performance ?

 

[cyrano]

Seems like you got a good deal! Have fun!

 

[Tubetec]

I found the service manual , has everything I need , theres a great chapter on preventative maintenance ,its full of great hints and tips . I might as well pop off the lid for closer visual examination before doing anything else . The manual explains any signs of overheating ie cold solder joints ,scorch marks or over heated components signals a potential problem and need thourough investigation .
One major issue in these scopes is the use of Rifa 'death caps' , these components are encapsulated in a kind of acrylic plastic which tends to crack , that allows moisture in causing these to blow violently and take out other stuff up and down stream as well as other damage due to flying shrapnel .

I have to head out now so I couldnt preceed with bed bathing my new baby ,
I took off the plastic panel from the back and it had a very light coat of dust inside ,
next step is to lift the cover , I'll need to refer to the manual for that .
This thing is as close to immaculate condition as it gets for a 30 or more year old unit .

 

[Tubetec]

The manual for the 2215A is a work of literary art ,
its concise ,to the point and written in plane mans language ,
I had already found the screws to release the housing , but I didnt want to force anything and do damage so I refered back to the manual . It details 3 screws that need to be removed before the cover comes away from the chassis but there is in fact a fourth underneath the unit , it was obvious anyway the cover wouldnt come away without it removed .

I got in under the hood and had a good look around for signs of trouble , this thing is pristine , I didnt even need to dust it out , I just cleaned the EHT leads , I can see from marks inside the case it obviously had its regular trip back to the cal lab , but not one single component has been replaced , the solder joints are bright and shiny still . Appart from some small instabillity in terms of the vertical position of the trace its rock solid , I suspect this unit hasnt been powered up for any extended period of time for many years ,so some settling of the lytic caps in the psu is to be expected.
The other thing is the probes are 10:1 so measuring the 500mv pk of the reference voltage at high gain does allow some noise in and slightly upsets the shape of the square wave , Im pretty sure this is just down to the laws of physics and not any underlying problem with the scope itself . I might leave the unit powered up over night with the intensity all the way down then tomorrow check the rails are within spec . No bad smells or smoke so far which is always a plus .

The only real issue I can identify so far is some dryness of the lube in the pot shafts which makes them a little awkward to adjust accurately ,this issue is dealt with in the service manual and they spec what product to use and where to remedy it . 2215A seems to have gotten rid of the dodgey Rifa caps and instead uses polypropylene yellow jackets , I might pop the lid on the psu tomorrow just to ensure all is well inside .
Im happy now as a pig in shit , I have the first decent scope Ive ever owned after taking on a long series of hard luck cases that needed to be stripped and binned, not time wasted upon then they blow up on you .

 

[Tubetec]

The two probes that came with the unit are the same model
P6120
10:1 Atten
10MΩ
14pF

I have another Tek 1:1 probe floating around somewhere that needs fixing up a bit and a couple of replacement parts , I think it came from a model 465 scope .
I was wondering about high voltage differential probes , is this the safe way to connect across the anodes of push pull tube amps ?

Obviously I'd rather avoid damaging my new machine due to user error , Im a bit unsure how to interpret the 400v rating . Whats safe in terms of tube gear to hook directly to the front end of the scope ? lets assume a HT of 400v my scope is technically capable of withstanding the DC voltage to ground , but if I have it connected across the anodes of a guitar amp ,driven with a chirp , what AC voltage might I see.
Is there a buffered output from the scope after the attenuator that I can connect to an ADC to allow REW handle the FFT end on the PC ?
Im re-learning to appreciate the immediacy of the way an analog scope locks to source , makes digital look like its off someplace else with its thumb up its ass, never the less doing the FFT number crunching via pc makes tons of sense.

 

[fazer]

allow some noise in and slightly upsets the shape of the square wave

Congrats on your find.
Did you adjust the probe compensation for the squarewave display? My 2245 varies squarewave cal output frequency with sweep speed. It will show up problems with the probes quality and shows the problems with cheap Chinese bargain probes. Your lucky getting the 6120 probes with your purchase/ find.

 

[Tubetec]

I was able to do the probe compensation ,adjust trace rotation and focus , Im getting a crystal clear trace now .
I did try measuring the RMS of the scope reference voltage with the Fluke 187 , then using an online RMS to PK-PK calculator ,work it out , I was getting the wrong answer , then I remembered its a square wave , so the crest factor needs accounting for , I did find one of the online calculator that allowed you choose the input waveform , but I lost it and couldnt find it again , everything is well up to spec in any case .

There is a slight whine from the PSU for about an hour after power up ,that gradually fades out .
Theres a person over on EEV who's given a very good account about the repair/renovation of his 2215 and no stone remains uncovered .
I got an AN/USM-488 version of the TEK 2235 thrown in also , once Ive familiarised myself with the 2215 repairing that shouldnt be too difficult , everything about these scopes is so well documented , not only the manual ,but also owners documenting faults 30 or more years down the line .

I had a look at the Cathode follower probes from Tektronix , they were designed to be powered from some sort of ancient 8 bit data aquisition scopes , its just a simple 100v ht and 12 v heater which uses a resistor to get 6.3v for the EC1000 tube , Im getting my hands on a couple of these asap , looks like a perfect tool for capsule measurement or other tube mic experimentations . It comes with a selection of attenuators and a DC blocking attachment .
A modification of the circuit might allow very much larger input impedences and still have more than enough bandwidth for audio . Interesting how they've included inductances to iron out the frequency response of the triode upto hundreds of mhz .
The clipping line is mentioned in the manual ,thats the one thing they dont really explain about very well , I'll post a copy of the service in technical documents , as usual theres a great circuit description from TEK .
If anyone has one of these lying around and wants rid of it , PM me .

Hmmm,
a battery powered tube magic wand add on to the scope would be nice wouldnt it ?

 

[user 37518]

I spent what was a small fortune for me and bought a new 2215 in the early 1980's. It's still running fairly well 40 years later. Main problem is the trace width has shrunken a bit. Nevertheless, it's been a real workhorse that traveled thousands of miles with me when I was regularly doing onsite service work. Attached a pic from 12 years ago while I was servicing an Amek 9098 desk.

Bri

Is that the Amek in Mexico, Bri?

 

[Brian Roth]

The pic was taken here in Kansas as we were restoring it, and yes, it was ultimately installed in Mexico City.

Bri

 

[AnalogPackrat]

We used Tek 2215 and 2235 scopes in our EE labs in college, so c.1996 when I was setting up a home lab I bought one from a now defunct silicon valley test equipment rental/dealer for $900 freshly calibrated. It's a 2235 and is my main bench scope--never given me any trouble. I've since acquired a 7834 frame with plug-ins and a 2440, but the 2235 gets 90% of the work. Delayed timebase, flexible triggering, X-Y mode, Z input, etc. make for a very useful tool with an intuitive user interface (no menus, no soft buttons).

I do need to check to see if it has the RIFA smoke bombs in it and replace them. Enjoy your new toys. They were among the last of the software-free scopes made.

 

[Tubetec]

Thanks AP ,
I got the two scopes for 250 euros and the guy drove 4 hours each way to deliver them safe and sound , he also has a collection of tubes he's selling off at a good price , so I will do business with him again .

I found a few 7000 series Tek scopes here ,
https://www.adverts.ie/other-electronics/oscilloscopes/27899302
looks like they went for 65 euros in the end .
This metrology thing's got me hooked .

 

[Tubetec]

I noticed a noise issue on the TEK 2215A ,
theres both an audible acoustic tone from one of the inductive components in the PSU and visible spurs on the screen in the vicinity of the invertor switching frequency , when I power the scope off theres a weird Bloop-squeal sound as the voltage collapses .
Its a fairly well known issue with these scopes and theres at least one well documented fix .
It appears as the caps age the ESR rises ,this allows noise appear in places where it would normally have been more effectively shunted to ground . From what Ive read about the PSU it uses feedback to help cancel some of the noise inherent to its opperation , this isnt as effective as the electrolytic capacitors age .
The guy who sucessfully repaired the problem used higher spec low ESR modern caps .
In any case new old stock parts even from Tektronix are going to be well past their sell by date by now and crazy money if you can find them .
Im just worried about upsetting some kind of synergistic balance if I swap out for all modern high spec capacitors.

 

[fazer]

Ya. One at a time, check performance and repeat with next cap. IMO