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Old 16th November 2012, 02:01 PM   #21
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to find the value of the inductors, remove the inductor, put a resistor in series with the inductor, put a sine wave across the inductor and resistor, measure the AC voltage across the inductor and resistor. When the voltages are equal, try different frequencies and resistor values, you can calculate the inductor. XL = 2*pi*f*L or XL=6.28*f*L or L=XL/6.28 *f, where Xl is the resistance you measured and f is the frequency you used.
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Old 16th November 2012, 02:17 PM   #22
Trileru is offline Trileru  Romania
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Heh lots of info
So, I might replace the connectors. I cleaned the face plate and I will proceed at cleaning the connectors tonight. It's the last thing to clean on the faceplate. It seems to me that the connectors are made out of aluminium. If I were to replace them I'd replace them with this: BNC Chassis Panel Mounting Socket Pack 2 | eBay
Much more convenient and seem to keep the mounting points. Anyway, those SO-259 sockets were added later to the scope and one of the previous owners made the 4 holes in the faceplate so he could mount the socket. I can't go to the original sockets as I'd have 4 holes next to them.
Yes, the scope is all tube (only germanium rectifier). I think it is circa 1950-1955.
I am amazed at the level of quality in wiring inside. They sure did know how to make it pretty on the inside as well as on the outside! It uses 4xE88CC tubes, 2 EF184 and 1 ECF80. All of them are Valvo. I tried to make a total to replace them with same make but it seems that those Valvo E88CC are something of a luxury nowadays... I wonder if it would be ok to replace them with brand new E88CC JJ tubes or anything that's acceptable. Right now the finals (EF184) are out of spec, especially to each other. I'm suspecting those for the problems, plus I found 3 electrolytics on the underside. They are fluorescent green and axial so at first glance I thought they were NP. After a close inspection I saw the + an - symbols. So I'll replace those as well (one seems to be leaking), the resistors that were hot and I'll just short the inductors for now. After I receive the new EF184 tubes I'll resume testing. The problems appeared on the sine weave when testing a EL84 push-pull amp starting at half volume. I don't remember exactly the measurements. Also I remembered just now that the issue had a thermic character as well. I took the cover off and the problem manifested itself again when probing higher voltage. Also I probed the temperatures of the EF184 and one of them was crazy hot.
I will resume testing with the schematic in front of me when I have the tubes. I might be able to get another digital scope from a friend. I am really curious as to what the problem is. I have to say that I very much enjoy repairing old tube gear Parts are large enough to handle with ease and every time I open a device like this I feel like I'm traveling back in time

Ah, I must stress about this. Is it ok to put any brand tube inside as long as they are new and closely matched? I really don't want to spend a lot on it, at least not now. At some point I might restore the original Valvo tubes inside but right now I cannot afford those tubes.
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Old 16th November 2012, 02:21 PM   #23
Trileru is offline Trileru  Romania
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Quote:
Originally Posted by multisync View Post
to find the value of the inductors, remove the inductor, put a resistor in series with the inductor, put a sine wave across the inductor and resistor, measure the AC voltage across the inductor and resistor. When the voltages are equal, try different frequencies and resistor values, you can calculate the inductor. XL = 2*pi*f*L or XL=6.28*f*L or L=XL/6.28 *f, where Xl is the resistance you measured and f is the frequency you used.
Great info! Could I use the soundcard as a signal generator? I have a M-Audio Fast Track pro. Would line level suffice?
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Old 16th November 2012, 02:22 PM   #24
freax is offline freax  Australia
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Those bnc connectors that you linked to have a mounting point which is phyiscally smaller than the holes that are cut for the SO-259's and won't fit!

You sure its not a Selenium rectifier?

Btw if its Selenium they can and do explode on occasion and in doing so generate highly toxic fumes.

Quote:
Originally Posted by Trileru View Post
I wonder if it would be ok to replace them with brand new E88CC JJ tubes or anything that's acceptable.
A question best left answered to the tube section of diyaudio.com

Quote:
Ah, I must stress about this. Is it ok to put any brand tube inside as long as they are new and closely matched? I really don't want to spend a lot on it, at least not now. At some point I might restore the original Valvo tubes inside but right now I cannot afford those tubes.
NOPE! Stop!!!!!!!!!! Keep the original tubes!!!!

It puzzles me that you are replacing them willy nilly anyway, they're not like incandescent lights where simply replacing one will solve all of your problems, thats a lamens persons myth. Take this thread to the experts! take it to the tube section!

RCA, Sylvania, Telefunken, Valvo, G.E, they are ALL different! especially when it comes to an oscilloscope!!!!!!
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Last edited by freax; 16th November 2012 at 02:34 PM.
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Old 16th November 2012, 02:58 PM   #25
Trileru is offline Trileru  Romania
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Ok. The thing is that I had a friend test all tubes in the scope. He said that one of the two EF184 was rated 165% and the other one 90%. That was the current measured compared to the original sheet. So...I am sure that a pair of new ones and closely matched would work better than the Valvo ones that are in. The other E88CC are all in the same ballpark with minor variations. 65-70%...

Looking at some pictures it might be selenium Don't know why that stuck in my head...

Last edited by Trileru; 16th November 2012 at 03:00 PM.
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Old 16th November 2012, 03:04 PM   #26
Trileru is offline Trileru  Romania
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How would I move this thread to the Tube section? It makes more sense as the schematic is similar to an audio amp.
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Old 17th November 2012, 01:36 AM   #27
freax is offline freax  Australia
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you simply click on the little /!\ button to the far left on any post, then when that page loads you simply type into the box "Hi, can you please move this thread over to the tubes section as it involves a piece of equipment that contains tubes, thank you very much"

And no sooner than a few minutes a moderator will have moved the entire thread over.
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Old 17th November 2012, 01:51 AM   #28
Trileru is offline Trileru  Romania
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great, thank you.
I attached some photos of the scope. Seems like the connectors are SO-239. After some cleaning they came out great! I will clean up the inside as well, maybe even redo the boards if I find the time. They don't have copper traces.
Sadly the manual is in german. I will try to use an OCR software on the pdf. If I'm lucky I will try an online translator and maybe make something out of it. I'd love to know how to calibrate it.
Attached Images
File Type: jpg IMG_8267.jpg (129.8 KB, 69 views)
File Type: jpg IMG_8289.jpg (123.8 KB, 66 views)
File Type: jpg IMG_8285.jpg (110.1 KB, 65 views)
File Type: jpg so239.jpg (192.3 KB, 68 views)
File Type: jpg IMG_8275.jpg (180.7 KB, 62 views)
File Type: jpg IMG_8276.jpg (137.8 KB, 37 views)

Last edited by Trileru; 17th November 2012 at 01:53 AM.
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Old 17th November 2012, 04:12 AM   #29
freax is offline freax  Australia
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Quote:
Originally Posted by Trileru View Post
great, thank you.
I attached some photos of the scope. Seems like the connectors are SO-239. After some cleaning they came out great! I will clean up the inside as well, maybe even redo the boards if I find the time. They don't have copper traces.
Sadly the manual is in german. I will try to use an OCR software on the pdf. If I'm lucky I will try an online translator and maybe make something out of it. I'd love to know how to calibrate it.
Hell yes! one of those, the middle one, are amphenol connectors don't replace them! Not unless they are making a bad connection!

What a beautiful looking piece of kit!

Could've sworn I had one of those CRO tubes a long time ago too! Its long gone now though...

Just put one word at a time into translate.google.com and re-write it back onto the schematic (make a copy of the original first!) and do your scribbling on the copy.

Shouldnt thake you much longer than a day, I done the same thing with a kit of russian (cryllic) radiation dosimeters and the windows on screen keyboard.
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Last edited by freax; 17th November 2012 at 04:21 AM.
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Old 17th November 2012, 12:37 PM   #30
Trileru is offline Trileru  Romania
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It would take forever to translate word by word... I will scan the document with OCR software, it's easier.
Can one still find those CRO tubes? I'd love to get a spare one just to make sure.

I've extracted all the electrolytic capacitors from the schematic. I'm used to them looking the way they look these days and I missed a few. I've searched for them and I found these solutions. Please mention if you know any other ones. I've also added the film caps that I want to replace on the trouble board. There have been elevated temperatures and I decided that it's best to replace them with new caps even thou they were not leaking and tested ok on the capacitance meter:

For 0.15uF/125V, 0.22uF/125V coupling caps
Vishay:
V-730P154X9250 x 3
V-730P224X9250 x 3

For: 4uF/500V/550V, 8uF/500V/550V PSU CRC

Vishay Sprague:

TVA1702 x 2
TVA1704 x 1

For 100uF/15V:

Panasonic FM:

EEUFM1E101 x 2

For 250uF/15V:
paralleled 2x EEUFM1C121=240uF (4 caps total)
(couldn't find 250uF value, only 220uF and it seemed low)

For 1uF/25V:
Panasonic NHG 1uF/50V ECA1HHG010 or
Panasonic M 1uF/50V ECA1HM010

There's also the 3 large can type capacitors that are 50uF+50uF each (on the 200V line). The voltage rating is 350V. One of the three cans is paralleled (into one 100uF cap). These cans tested out ok each of them. I might hold back on replacing them at the moment. They are Siemens and have a threaded base and they hold in the chasis with a large nut.
There are those 3 other electrolytic caps with inconvenient values,2x 4uF and 1x 8uF and have a voltage rating of 500/550V (500 normal, 550V on spikes?). They are in the PSU on the 300VAC line. The 8uF one is connected between 300VAC and 0V across the secondary right after the first diode. The two 4uF ones form a CRC filter with a 33k resistor right after the second diode. Theres a voltage noted between the second diode and first cap from crc. It is 375V. The voltage rating on the Vishay ones is 450VDC. Do you know a larger voltage cap at 4uF and 8uF? Is this Vishay cap good for coupling? http://www.vishay.com/docs/42092/v730p.pdf
I like this because it is an axial cap and will fit good on the board.
Any word on the tube types for this scope? Will it work the same with other brands of tubes for E88CC and EF184? I really cannot afford Valvo tubes. Will any brand work as long as the tubes are new and matched?
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