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Elmo GS1200 recording capacitor repair

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  • Elmo GS1200 recording capacitor repair

    Dear GS1200 enthousiasts, I performed the capacitor replacement, in order to make the recording bias oscillator work properly again and enable my Elmo GS1200 to record high quality stereo again.
    turned out that the capacitor I replaced indeed had an increased value of around 7200 pF instead of the required 3300pF.
    I think this causes the bias frequency to drop dramatically and that caused my recording results to be so poor. Only high frequency scratchy sound with no mod or low tones. And also fading etc I thought it was the magnetic tracks at first. But it was the GS not being able to get the molecules to get really spinning and ready to be magnetized properly.
    see this video I made. The replacement is pretty straightforward if you know how to open up the GS1200 and know how to solder.
    I bought my capacitor (3300pF, 600V) at ToneFactory in Belgium, online of course. Really only a few euros.
    watch this: https://youtu.be/ezS5yf2tRdE


  • #2
    Nice work! But in the future you do not have to remove the board. You can remove the capacitor and replace it while still connected.

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    • #3
      Yes Patrick, Excellently done! Having a reference video is a bonus to all GS-1200 owners who haven't made the swap yet. Rik, you are right in that the Cap can be swapped without removing the board. After removing the front cover I put the rear cover back on to lay the projector on its back. Easy to de-solder and install the new Cap I found.
      Click image for larger version

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      • #4
        Will any kind of 3300pf capacitor do? Disc, electrolytic............?

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        • #5
          It has to be a polystyrene or polyester or polypropylene film capacitor. Voltage tolerance can be higher such as 630V or so. So it is NOT an electrolytic or disc. Has to also be able to carry 600V peaks minimum

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          • #6
            Google 3300pF 600V capacitor and you probably find some. I got mine on ToneFactory in Belgium

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            • #7
              Thanks for that info Patrick, glad I asked before installing the wrong type. Clearly I need an education on capacitors because I would have thought that one 3300pf capacitor is interchangeable with any other 330opf capacitor provided it can handle the voltage.
              Maybe Steve can jump in here and enlighten us?

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              • #8
                Thanks for the compliment, Paul!

                A ceramic or mica or film capacitor would be much better than an electrolytic. Electrolytics have quite a bit of stray resistance and inductance and wouldn't do very well throughout the entire audio range. Years ago in my youth, I saw a small ceramic in parallel with a couple of big electrolytics and I asked what difference that tiny additional bit of capacitance could possibly make. The answer was the electrolytics basically disappeared at high frequency and the ceramic dealt with those much more effectively.

                Besides that, most electrolytics are polarized and become...interesting when the voltage gets backward.

                -and an electrolytic that small is nothing I have ever seen.
                Last edited by Steve Klare; April 10, 2021, 04:19 PM.

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                • #9
                  I ordered mine from eBay. I just searched 3300pf polystyrene and it came up. it is 630v.

                  Click image for larger version

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                  • #10
                    Great job Patrick and a nice ref to other GS1200 owners, many never use the recording on them so when they do the capacitors give up, Mark

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                    • #11
                      Does this capacitor have any effect at all on playback quality, or is it totally non-functional during playback?

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                      • #12
                        I'm sure its non functional Paul as you can have non functioning capacitors and playback is perfect, Mark

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                        • #13
                          Nice little video Pat. First time I changed the cap some years ago now I dropped it in the amp works as was trying to change it without removing the boards. Done a few since and take much more care.

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                          • #14
                            Originally posted by Burton Sundquist View Post
                            I ordered mine from eBay. I just searched 3300pf polystyrene and it came up. it is 630v.

                            Click image for larger version

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                            That one should do.

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                            • #15
                              Hi Patrick,

                              I love this video , very informative.

                              Concerning capacitor for this spécific use : Try to find capacitor with a very low ESR (Equivalent Serie Resistance); If ESR value is a bit too High , a capacitor operating under high frequencies could onverheat. You can measure ESR with a small device called ESR Meter for few money.
                              You can also find a capacitor ESR value in its Datasheet. ESR is given for a typical Frequency. Only compare an ESR for a same Frequency.
                              Also measure ESR on capacitor(s) you have bought , because you never know if what you bought is an old stock or not.
                              For information , you can find easily Electrolitic Capacitor too with low ESR technologie : There are systematicaly used on "switching Power Supply" that you find everywhere now.
                              Electrolitic caps are often polarized (showing a plus and -). If you need one "not polarized", you assemble them together in opposite serial....



                              This one (picture) is Polystyrene 3300pF or 3.3nF , however, letter "J" is the tolerance (+/- 5%) . (For exemple Letter "K" means +/- 10% of full value) .

                              So I suggest you to keep original capacitor value : Increasing a bit this value will not improve its overheating resistance.


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