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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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31st Jan 2009, 11:37 pm | #1 |
Pentode
Join Date: Dec 2008
Location: Nottinghamshire, UK.
Posts: 239
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Quad II Main Smoothing Capacitor
I repaired one of my Quad II’s main smoothing caps today by cutting open the top very carefully with a dremel cutting disc. I was able to use a hot air gun to gently melt the wax potting compound and remove the leaky caps inside. I replaced them using caps in series with a couple of balancing resistors. Finally, I used some JB Weld to neatly glue the top back on and it all turned out fine.
Eddie |
1st Feb 2009, 12:43 am | #2 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
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Re: Quad II Main Smoothing Capacitor
Or alternatively you can cut a 1.5" diameter hole in the dead centre of the base and, once you're through the paper inside, you'll see the bottom of the old capacitor. Apparently this can be extracted with a corkscrew (it takes a bit of wiggling) provided you've remembered to desolder the wires from the top connectors of course. F&T make a 16+16uF 500V cap which fits back into the same hole, or you can increase to 32+32uF if you want a bit more ooomph and don't mind compromising Peter Walker's original design. (Actually I think the F&T caps are shorter, so they might need a bit of packing underneath.) Resolder the wires, check it works, glue the disc back into the base, make good and Robert's your mother's brother
Cheers, GJ |
3rd Feb 2009, 5:37 pm | #3 |
Pentode
Join Date: Feb 2006
Location: East London, UK.
Posts: 231
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Re: Quad II Main Smoothing Capacitor
Hi All,
Just to let you know. If you do decide to increase the caps to 32+32uf, you will probably need to change the rectifiers to GZ34's as GZ32's do not like the extra capacity and will quickly wear and die (from personal experience !). Cheers, Alan. |
3rd Feb 2009, 11:48 pm | #4 | |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
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Re: Quad II Main Smoothing Capacitor
Quote:
The Mullard data sheet for the GZ32 says it needs a minimum of 100 ohms if it's going to be loaded with 32uF. It only needs 50 ohms if the first cap is 16uF (the one after the choke is much less of a problem). One solution would be to insert a couple of 22 ohm resistors, one in each anode. However this would drop the HT voltage a little. Changing to a GZ34 is a much better solution. Not only can it handle more capacitance (even 60uF only needs a series resistance of about 55 ohms) but it also draws less heater current than the GZ32 so will be slightly more gentle on the mains transformer. Cheers, GJ |
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