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Old 14th Aug 2019, 3:08 pm   #41
ColinTheAmpMan1
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Default Re: Tektronix 453 poorly.

Quote:
Originally Posted by rambo1152 View Post
Quote:
Originally Posted by M3VUV51 View Post
i was looking to have something i have to try.
It's silicon NPN, so try the BC108.

I know we have established beyond doubt that yours is the later FET model, I must say, given the serial numbers of yours and mine, I am very surprised.

Does your scope say "Type 453A Oscilloscope" on the front or just 453?
My 453 doesn't mention the "A" and is S/N 102671, made in Guernsey. The "IBM" screening has been erased by a previous owner. It doesn't have any nuvistors in it.

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Old 14th Aug 2019, 4:05 pm   #42
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Default Re: Tektronix 453 poorly.

Q524 etc were originally 2n4275. Tek semi look-up subsequently quotes 2n5769. These are 15V Vceo. I'd recommend good old 2N3904 as a general sub to get things going. I believe Bill is of the same mind.

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Old 14th Aug 2019, 4:09 pm   #43
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Default Re: Tektronix 453 poorly.

Here's a re-statement of the position regarding Guernsey made scopes:
S/n below 100200 - Nuvistor = equivalent to Beaverton s/n below 20,000
S/n above 100200 - FET = equivalent to Beaverton s/n above 20,000



The 453A was a much later (and major) update.



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Old 14th Aug 2019, 4:27 pm   #44
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Default Re: Tektronix 453 poorly.

Tek 453.
We seem to have now established that it is a Guernsey made, not 453A, with the smaller tube face with graticule 10 x 6 of 0.8cm/division, without nuvistors, circa 1967. The 453A, of circa 1973 has the larger screen10 x 8 of 0.8.
Transistors were in short supply in early 1970's, so often makers specifying by their own house type number, which would be attached to any suitable commercial version. HP, Tek and Solartron did this a lot.

I suggest don't waste time and money searching for replacement 2N4275. It is an outdated case, the TO106. The modern plastic T092 or metal cased TO72 will do just as well. The chip inside is likely to be the same, similar to 2N2369 / BSX20. The standard npn gold doped switching transistor, 400Mhz or so.
And for the pnp 2N4122, try the BFX48. PNP substitutes are more difficult to find, so check the voltage rating.
There is always the 2N3904 npn and 2N3906 pnp. Good standbys. I use these as replacements for MPS6520/6518 in Telequipment 67 and 67A, which seem to fail from old age.
When you have a dead scope, substitute any comparable transistor you have. Once the scope is working, then you can see if a higher performance part is required. (Which happens only very rarely indeed).
Only things to watch are the voltage rating and the actual base connections. (TO92 plastic transistors are do vary. Texas are particularly bad: the K variant is different from L.)

Looking at your Q524. That is acting as an emitter follower for the gate ouput and alternate Y switching, so is quite uncritical. Your BC108 or any small npn will do.
But that will not have stopped the timebase working anyway. So I fear you will have to do a bit more searching.
I see that you have established that the X Amplifier is working.
JohnBS seeems to be taking good commonsense. Particularly as we seem to agree!
wme_bill

Last edited by WME_bill; 14th Aug 2019 at 4:38 pm.
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Old 14th Aug 2019, 4:51 pm   #45
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Default Re: Tektronix 453 poorly.

What I was having difficulty getting my head around was the small production volumes.

These scopes didn't roll off the production line quite like TV sets, in fact, there couldn't have been more than 200 instruments like mine made in the Guernsey plant.
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Old 14th Aug 2019, 5:19 pm   #46
M3VUV51
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Default Re: Tektronix 453 poorly.

Any ideas what to check next? Would looking at the A trigger side of things be viable?

Regards, Paul M3VUV.
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Old 14th Aug 2019, 5:31 pm   #47
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Default Re: Tektronix 453 poorly.

Before we start on more circuit measurements, could you post the actual voltages you measure for +12,-12 +75 and +150V unreg? The latter will be significantly higher than 150V



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Old 14th Aug 2019, 6:03 pm   #48
M3VUV51
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Default Re: Tektronix 453 poorly.

I measured -12v, +12v, +75v and 164v, that was on the low voltage PCB.
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Old 14th Aug 2019, 6:32 pm   #49
John_BS
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Default Re: Tektronix 453 poorly.

The -12V should be set between -11.98 and -12.02V. Are you using a dvm?



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Old 14th Aug 2019, 8:51 pm   #50
M3VUV51
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Default Re: Tektronix 453 poorly.

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The -12V should be set between -11.98 and -12.02V. Are you using a dvm?



John
Yup Fluke 85V
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Old 15th Aug 2019, 5:52 am   #51
M3VUV51
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Default Re: Tektronix 453 poorly.

These seem to be within spec.
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Old 15th Aug 2019, 7:40 am   #52
6AL5W-Martin
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Default Re: Tektronix 453 poorly.

That looks fine.

Greetings Martin
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Old 15th Aug 2019, 9:23 am   #53
M3VUV51
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Default Re: Tektronix 453 poorly.

So now what to check?
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Old 15th Aug 2019, 9:47 am   #54
M3VUV51
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Default Re: Tektronix 453 poorly.

Has anyone a pic of the tunnel diodes used in these so I know what im looking for?

I've never had anything to do with them.
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Old 15th Aug 2019, 10:58 am   #55
MrBungle
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Default Re: Tektronix 453 poorly.

Tiny, gold ones.

https://upload.wikimedia.org/wikiped...nnel_diode.jpg
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Old 15th Aug 2019, 10:58 am   #56
John_BS
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Default Re: Tektronix 453 poorly.

They're delicate, hard to replace, and not prone to failure. So I'd leave them alone until all other components are eliminated.


Perhaps the next step is to post your voltage readings for the ebc's of all the 500 series transistors, to one decimal place.

John
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Old 15th Aug 2019, 11:00 am   #57
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Default Re: Tektronix 453 poorly.

Tek tunnel diodes usually look like the one in the attached photo and should also be identifiable via the location diagrams in the manual. However, what leads you to think that the tunnel diodes are at fault? I'm not familiar with the 453 but I would think that there are four TDs, two for each sweep mode (A & B). Has only one of the sweep circuits failed? Whatever you do don't try to test the diodes with a DMM. Chances are you will destroy them instantly.

Alan
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Old 15th Aug 2019, 11:17 am   #58
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Default Re: Tektronix 453 poorly.

Might also be worth checking continuity between R536 and R805 (and both R's while you're there).

You know everything is mostly working AFTER R805 (as H-Pos control moves the spot) so its good to check the timebase output is actually connected. There is a 50R line, plugs / sockets and a switch ...

Then Vbe's as John suggests.
So much easier with another scope

dc
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Old 16th Aug 2019, 3:54 am   #59
M3VUV51
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Default Re: Tektronix 453 poorly.

Hi. I can see R536, but not R805, any idea where to look?

Cheers.
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Old 16th Aug 2019, 9:36 am   #60
dave cox
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Default Re: Tektronix 453 poorly.

R805 is on the horizontal amp, you'll see the H-Pos control on that sheet too.

dc
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