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Screen grid filter capacitor ??
2/17/2013 8:08:30 AMOldetyme2
Hi: Taking apart a screen grid cathedral radio, listed as chassis 26, and under the filter condensor section, I found 2 gigantic copper cylinders, each with 1 lead. Are these the electrolytics seen in the us radio and tv schematic for the 26 listed as 8Mfd. If so, what voltage should I use to replace them, since they are obviously shot( major hum, but stations come in. I'm new to this so I appologize if this seems like too simple a question, but thanks for any help
2/17/2013 9:04:41 AMWarren
Radios with transformers use high voltage filer capacitors. No less than 350 VDC or better yet 450 VDC.


3/12/2013 9:24:36 AMJay Paul
:Radios with transformers use high voltage filer capacitors. No less than 350 VDC or better yet 450 VDC.
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Thanks much for quick answer.Computer kept me from replying any sooner(they always fritz when you need them). Thanks again jay
2/17/2013 9:43:40 AMTom McHenry
It's possible that these are the filter capacitors, but according to the parts placement diagram, these should be located on the same side of the set as the filter choke and the power transformer. Usually, parts that are under copper covers are coils, the manufacturer used copper to obtain electrostatic shielding for the coil inside without disrupting its magnetic field. Of course, there's an exception to every "rule" and your set may be it.

The best way to tell for certain is to trace the set's wiring. One wire to the first capacitor will go to the filament circuit of the rectifier tube; that same wire will also run over to the filter choke. The other wire from the filter choke will go to the other filter capacitor and then to the B+ bus in the set. (Let the schematic tell you what to look for vis a vis actual connections rather than relying on a disembodied internet being's less than encyclopedic memory).

Once you have verified the identity of the parts, you can replace them with new 8 MFD 450 volt axial-leaded electrolytics. You can get these via PayPal/online mail order from justradios.com (the seller I use and like) or several other vendors.

The new caps will be physically tiny compared with the originals, so you can either remove the OEM caps and wire the new parts in their place, or "empty out" the OEM containers and install the new parts inside them. I don't recommend the second option unless you know what you are doing, since the old caps are probably "wet electrolytics" and even after all these years may will contain a caustic fluid (the electrolyte).

The new electrolytic caps are polarized so it's important to install them in the correct "direction" (lead that's on the black insulated end of the tubular part goes to the "hot" side of the circuit; lead that's on the uninsulated (bare aluminum) end of the part goes to ground). This is important- if you reverse the parts, they will fail almost immediately.

Due to the physical size of this set, you may find the new caps' leads to be too short. It is no problem to extend them- this won't cause a problem as long as you keep the extension wires as short as possible to do the job.

Don't wire the new caps in parallel with the old ones; This may work OK for a time but it leaves the radio vulnerable to one of the old caps shorting out; its best to get it out of the circuit where it can't cause future trouble. (You can leave the old caps in place in the chassis, just make sure that you disconnect them).

That's pretty much it. Some of these screen grid tube TRF sets were excellent performers, and some weren't. Don't know where yours falls. They were a great improvement tech-wise over the neutrodyne, however- these tended to be fussy to set up, with a single RF amp tube replacement necessitating an "alignment".

3/12/2013 9:22:44 AMJay Paul
Tom:Thanks for such an exhaustive reply, looks like I have some work ahead of me to check out what is what.Sorry about delay in answering, but computer fritzed and just now found the link back to this site.Thanks again....jay
3/15/2013 8:04:14 AMEdM
:Hi: Taking apart a screen grid cathedral radio, listed as chassis 26, and under the filter condensor section, I found 2 gigantic copper cylinders, each with 1 lead. Are these the electrolytics seen in the us radio and tv schematic for the 26 listed as 8Mfd. If so, what voltage should I use to replace them, since they are obviously shot( major hum, but stations come in. I'm new to this so I appologize if this seems like too simple a question, but thanks for any help
:
You have a Gloritone Model 26. What you describe are "wet" electrolytic capacitors. These need to be replaced. And yes, Gloritone / US Radio and Television used copper cans rather than aluminum. 8 or 10 mfd at 350 volts will work for this radio. The nut is positive, the can is negative. Be sure to electrically insulate the cap from the chassis.
Ed M


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