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Old 20th Feb 2020, 5:23 pm   #1
XPModder
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Default Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Hello everyone,
I have got my hands on an old Gould 1604 Oscilloscope, that was working fine. However after a few Months it let out the magic smoke and I immediatly unplugged it. When I opened it up it took me a while to find the fault. The thing that let out the smoke was a tantalum capacitor near the input for one of the channels. I proceeded to replace all the tantalums near the input for all channels with new electrolytic capacitors. During my repair I brushed along the CRT-Driver Board. That is, when a Capacitor just completely parted with one of its legs and when I grabed it, it also became loose on the other end. This capacitor is labelled LCR FEC .01UF 10% 5KV. So I searched for a replacement capacitor, but couldn't find one. I have been searching for this capacitor for a few months now and still haven't found a suitable replacement. I found some on jotrin.com, but after requesting a quote they told me that the part is no longer available.
During this time I found a few threads on this forum discussing this very oscilloscope, so I thought maybe someone here can help me find a suitable replacement capacitor. It seems like one of the about five parts in this scope that you can't easily find a replacement for is this capacitor...
Maybe Im just using the wrong keywords to search for this capacitor. What does the FEC stand for anyways. As far as I can guess from search results it is a mettalized polyester film capacitor, however I can't really find any film capacitors, or any capacitors apart from huge industrial ones that are rated for 5kV. The best I can find are 1kV.

If it helps I do have a pdf of the service manual. The capacitor is marked C53 on the pcb and can be found on page 120 of the service manual.
Attached Files
File Type: pdf GOULD1602_1604_Oscilloscope_SERVICE_MANUAL.pdf (3.00 MB, 30 views)
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Old 20th Feb 2020, 9:54 pm   #2
WME_bill
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Goould1602-4 capacitor.
I find I have a plate ceramic, 10nf, 5kv, rescued from some equipment years ago. For the very reason you are finding, that these things are difficult to get a replacement. I will check it to be sure it is still sound.
Send me your email by Private Message.
As an encouragement, this part of the circuit is not particularly critical, as it is the CRT bright up feed for the front edge of the pulse to the CRT grid.
The voltage rating however is most important. The cathode is at -1600v, so the grid will be say -1700v and a pulse size of say 100v.
So a capacitor rated above 2 kV should be satisfactory. Yet as it is critical for the tube, for any failure would ruin the CRT, I can quite see why 5kV is specified.
But 3kV rating is much easier to find at 10nf size.
Alternatively, at 5 kv you will have to look for 4.7nf. This size would probably be satisfactory. You can tell by looking at the display of the front edge of a waveform at high speed timebase, when you will see if the trace brightens up quickly enough.
Ceramic capacitors 10nf at 3 kv are fairly easy to find. If you are nervous, put two in series.
wme_Bill
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Old 20th Feb 2020, 10:58 pm   #3
factory
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Could you use three of these 3.3nF 6kV capacitors in parallel?
https://www.ebay.co.uk/itm/3300pF-0-...4AAMXQCndRhc99

David
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Old 21st Feb 2020, 3:10 pm   #4
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Thank You for your replies!
I have just spend a bit of time to search for some ceramic capacitor and it looks like I can indeed find 3kV 10nF ceramic capacitors relatively easy. So if that will work as well, than I'm going to go with that.
@factory: I guess I could try, but there really isn't a lot of space, where the capacitor needs to go...
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Old 25th Feb 2020, 9:45 pm   #5
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Hi!

Will this help?

https://www.ebay.co.uk/itm/133196308014

If space permits there's a 22.5 mm polypropylene 11kV one:–

https://www.ebay.co.uk/itm/383295337531

Or this from Mouser UK:–

505-FKP1Y021006F00JS

Chris Williams
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Old 25th Feb 2020, 10:43 pm   #6
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

These old scopes are great, but the tants go all the time.

Daniel.
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Old 27th Feb 2020, 1:10 pm   #7
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

One post moved to a new thread: https://www.vintage-radio.net/forum/...d.php?t=164285
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Old 29th Feb 2020, 3:09 pm   #8
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Thanks for all your help everyone!

I got a new 3kV 10nF capacitor yesterday and put that in. The scope works again now and I have ordered a higher rated capacitor as well and will swap them as soon as it arrives.

I have to say, I really like the serviceability of this scope. Even though it may be a little hard to find a replacement for some components. I didn't even need to get the PCB out or remove any connections when I replaced the tants on the input channels. Just take the top and the bottom cover away and you can access the main PCB from both sides. And because it's all through-hole and no surface mount components, it's not hard to replace anything.

I don't have a modern DSO, but I guess if there would be a problem with a modern scope, it would be way more complicated to replace components, as you would have to disassemble the whole thing to get access to something. And the tiny surface-mount parts don't exactly make it easier to solder in a new one...

Florian
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Old 1st Mar 2020, 8:38 am   #9
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

"I don't have a modern DSO, but I guess if there would be a problem with a modern scope, it would be way more complicated to replace components" with a modern DSO it'd be a software de-bug/fix, board swop or chuck in the bin unless it's something simple. That is unless you have a microscope and all the kit for SMD, oh, and VERY steady hands. I recently tried to replace a SMD 100r resistor on an amp, took me an hour and I lost the bl**dy resistor three times before I got a half decent repair. Damn things stick to the tip of the iron, jump off the bench then hide.

Actually I wonder if modern DSO's are more reliable than old analogue scopes and what the succesful rate of repair is.

Andy.
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Old 1st Mar 2020, 10:30 am   #10
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Modern DSO's have proprietary chips in them or FPGA's/micro's etc that you will never be able to get the code for.

As for serviceability, unless it is something simple, repair is not a likely proposition other than a complete board replacement.
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Old 1st Mar 2020, 3:23 pm   #11
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Default Re: Need help finding a replacement capacitor for Gould 1604 Oscilloscope

Quote:
Originally Posted by Diabolical Artificer View Post

Actually I wonder if modern DSO's are more reliable than old analogue scopes and what the succesful rate of repair is.

Andy.
My three-ha’pence: modern DSOs are less reliable than older analogue ‘scopes. It may just my experience but both my Gould DSOs are much less reliable than my old Gould 3000.
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