Thanks for the bump, this thread is quite old that I almost forgot that I created it.
Btw, this gadget since it was bought, its frequently borrowed among friends used it as comb generator to check their analog spectrum analyzers.
Why used two different wires type instead of just using the copper enameled for both ?
Because the silver or nickel one solders in instantly and the enamelled one needs to have it's ends cleaned, so it's only used where insulation is required.
Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.
Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.
I was wondering about that. While admiring the photos I noticed that tiny little thing positively glowing with essence of gold-plated unobtainium.
What is it, a tunnel diode as the active element in that stripline oscillator?
Now I'm all envious and want to buy one of these things. Too bad the current ebay crop is quite high priced.
Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.
I was wondering about that. While admiring the photos I noticed that tiny little thing positively glowing with essence of gold-plated unobtainium.
What is it, a tunnel diode as the active element in that stripline oscillator?
Now I'm all envious and want to buy one of these things. Too bad the current ebay crop is quite high priced.
It's a varactor used in the frequency multiplier. I don't know how it works so I don't know what modern part you could shove in there.
The OCXO in my 2901 is not great, you can see the frequency shift up and down as the oven turns on and off. It's quite crude.
Awesome!
IC's with datecodes starting with 69
You don't see that very often
Great pictures. I wonder why the sockets for small signal transistors. Was this a holdover from the tube days which would have to replaced regularly? I remember that some manuals mention that it's not recommended to periodically remove and check semiconductors, suggesting that it is recommended for some equipment. It may also be because they considered semiconductors expensive, just like how people often used sockets for expensive DIP parts. Not much choice now most expensive parts are BGA, however.
I think the sockets cause more issues due to bad connections than they solve by making part replacement easier.
In the past transistors were less reliable and relatively more expensive so the extra cost of using sockets was small. Eventually reliability become high enough that the sockets themselves caused more failures than bad transistors so they stopped using them.
This also happened with ICs and IC sockets although in this case it may have been helped along by those cheap edge wipe sockets Texas Instruments made which were unusually unreliable.
Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.
I was wondering about that. While admiring the photos I noticed that tiny little thing positively glowing with essence of gold-plated unobtainium.
What is it, a tunnel diode as the active element in that stripline oscillator?
Now I'm all envious and want to buy one of these things. Too bad the current ebay crop is quite high priced.
It's a varactor used in the frequency multiplier. I don't know how it works so I don't know what modern part you could shove in there.
Varactor multipliers rely on non-linear change in reactance whereas normal diode multipliers rely on non-linear change in resistance. Varactor multipliers are higher efficiency but have much narrower bandwidths and are more difficult to tune. In the schematic you can see where they used a pair of tuned circuits (idlers) to short out two of the harmonics; probably the 2nd and 3rd. (I just now looked in the theory section and it was indeed the 2nd and 3rd.)
The specifications for the diode Tektronix used are available and it would not be difficult to find a suitable surface mount varactor diode to replace it. They are not expensive so a bunch of different diodes could be evaluated to find the best one.
The OCXO in my 2901 is not great, you can see the frequency shift up and down as the oven turns on and off. It's quite crude.
The earlier type 184 time mark generator uses the same OCXO with the on-off oven. I never understood what application Tektronix had in mind for these which would require an OCXO. Analog sweep calibration does not require this kind of accuracy.
Yay! Got one! Ebay 151502733003. Seems in nice condition, and cheap enough.
Will be a while before it gets here, and fingers crossed it works. From seller's description that's not guaranteed.
Just so long as that tiny gold plated unobtainium varactor is OK.
This also happened with ICs and IC sockets although in this case it may have been helped along by those cheap edge wipe sockets Texas Instruments made which were unusually unreliable.
Arrgh! Those damned TI sockets... how I hated them. How did TI manage to make anything so flakey? I never could decide if it was mainly due to the very weak and stretchy spring contacts, or the plating which seemed to become non-conductive.
Before learning about those, I once made the mistake of constructing a fairly complex prototype board with them, and point to point soldered kynar wire. Urrrgh...
After that I always used Augat machined pin sockets. Expensive, but they never failed.
Yay! Got one! Ebay 151502733003. Seems in nice condition, and cheap enough.
Will be a while before it gets here, and fingers crossed it works. From seller's description that's not guaranteed.
Just so long as that tiny gold plated unobtainium varactor is OK.
With some diagnostic work, the varactor can be replaced with a modern surface mount one.
This also happened with ICs and IC sockets although in this case it may have been helped along by those cheap edge wipe sockets Texas Instruments made which were unusually unreliable.
Arrgh! Those damned TI sockets... how I hated them. How did TI manage to make anything so flakey?
TI has a history of making mistakes like this and then ignoring or covering them up. I try to avoid their products.
Before learning about those, I once made the mistake of constructing a fairly complex prototype board with them, and point to point soldered kynar wire. Urrrgh...
After that I always used Augat machined pin sockets. Expensive, but they never failed.
I like the machined pin sockets for repair work because if I am expending that much effort, then I only want to do it once. I like cutting the pins out of the socket and mounting them individually as shown in the attached photo.
Yes, looks nice and you can see the tracks. I did the same thing a few times, I recall.
Needs something plugged into them to hold them in line for soldering.
Those other sockets are the offending items, aren't they? Are you replacing them all?
Ha ha, and the same people that chose those sockets for that board thought it was OK to alternate the orientation of ICs.
I spy tantalums. Together with *those* sockets I bet that board was soooo reliable.
Edit: PS I should have the 2901 in about 3 days.
Edit: PS I should have the 2901 in about 3 days.
Please, it its not too troublesome, do a detail macro shots as well, especially if you spotted there are differences vs mine, thanks in advance.
Please, it its not too troublesome, do a detail macro shots as well, especially if you spotted there are differences vs mine, thanks in advance.
Sure, I was intending to. Though, just yesterday my camera lens (Canon) developed a problem. So now I have two Canon bodies (EOS 20D & EOS 40D) but no fully functional lens. Not sure how long that will take to fix.
The
http://w140.com/tekwiki/wiki/2901 page could do with a lot better info.
Yes, looks nice and you can see the tracks. I did the same thing a few times, I recall.
Needs something plugged into them to hold them in line for soldering.
No, I just friction fit them and solder from the top if necessary. You have to be very careful about plugging something in to hold them because if it is tin plated, the tin will melt during soldering and fuse it into the socket.
Those other sockets are the offending items, aren't they? Are you replacing them all?
They are but the ones I replaced were used for ceramic packaged 723 regulators which ran hot and the heat caused the sockets to become loose. There was not an actual failure but I did not like it.
Ha ha, and the same people that chose those sockets for that board thought it was OK to alternate the orientation of ICs.
That does not bother me. I am sure they did that to make the layout easier.
I spy tantalums. Together with *those* sockets I bet that board was soooo reliable.
It is a Tektronix DC505 universal counter. It had some bad transistors and a design flaw but none of the solid tantalum capacitors failed.
Can someone point out what pic this rare diode is in and where it is located? I am trying to find what you guys are talking about...
http://everist.org/NobLog/pics/20141220/05_9163_top_close.jpgSee the little clip between the 3 open core inductors at the bottom. That is the clip and the tiny gold button under it is the varactor in question.
At least is is possible to replace that, try getting a tunnel diode or even worse a backwards diode. Noone dopes a zener diode that heavily any more, you would have to use pieces of zone refining ends to get silicon that heavily doped.
Ah, ok, I had seen that but didn't think it was it, heh. Thanks!
Ah, ok, I had seen that but didn't think it was it, heh. Thanks!
This one has better view as in one of my photoshoot.
It's so small you'd hardly miss it if you put it in an envelope and mail it to me.
It would probably fall out of the envelope though, unless you tape it to a card.
I was fortunate to come across one today. But there are two issues, one is the power switch and then the power indicator which I guess is incandesent? Anyway is it possible to replace both by just removing bottom cover?
Thanks,
Nicholas
I am a new owner of a 2901, hope it correspond to specs.There are some people are having problems with
A heater and a crystal inside it,do you see any problem in your unit around this?
, thanks, looking forward to see you fix the other problems as well.