"Squashed" capacitors - UK Vintage Radio Repair and Restoration Discussion Forum

bluepilot · 25th Jul 2011, 9:09 pm

I am restoring an old German Mende radio from ca. 1938. Some of the capacitors are in difficult to get at places and I was wondering whether I should replace them whilst I have everything dismantled rather than waiting until I get everything back together and then finding they don't work. At present they appear to be OK but I have no idea what will happen when they get a lot of voltage applied.

The ones in question are generally tubular in shape but have an oval rather than circular cross-section. Does anyone know what type of capacitor they are likely to be? They all have values in the range of hundreds of pF. The cases have the brand name Mende on them so they are possible something peculiar to that company. As they are a bit unusual, I would like to keep them if possible.

Thanks

Station X · 25th Jul 2011, 9:18 pm

Capacitors with values in 100s of pFs don't generally need replacing.

Can you post a picture of one please.

MikeyPP · 25th Jul 2011, 10:05 pm

like this sort of thing (metallised polyprop) > http://upload.ecvv.com/upload/Produc..._Capacitor.jpg ?

jjl · 25th Jul 2011, 11:32 pm

Low value caps from the '30s are most likely to be silvered mica types, certainly not polypropylene nor any other plastic dielectric.
This type of capacitor is often wax encapsulated, but as Station X stated, they rarely fail. Any waxy, paper dielectric capacitor should, of course, be assumed to be faulty.

John

bluepilot · 26th Jul 2011, 9:35 am

Quote:

Originally Posted by Station X

Capacitors with values in 100s of pFs don't generally need replacing.

Can you post a picture of one please.

I'll post one tonight when I get home.

bluepilot · 26th Jul 2011, 4:16 pm

I've now taken a couple of pictures. The radio is a Mende radio which makes me think they may be some sort of manufacturers own make. I've not seen any like this anywhere else. There is no voltage rating given but this one came out of the power supply so it must be several hundred volts. Whatever the cap is, it is stuffed into a white plastic tube and sealed at the ends.

Station X · 26th Jul 2011, 4:25 pm

I don't know what sort of reputation these capacitors had. You could try testing them for leakage at the HT voltage.

bluepilot · 26th Jul 2011, 5:31 pm

Normally I'd just wait for something to go bang and then replace it. However in this case, the radio is assembled using bent metal tabs - not a screw in sight. I don't like to bend them too often or they might break off. So I'd rather make sure the caps are OK now.

300pf is an unusual size and so far I've not found a replacement that would fit in the tube. If no-one knows what they are, maybe I'll dismantle one from a concealed place to see what's inside. The I'll know whether I can leave the others or not.

Thanks

Diabolical Artificer · 26th Jul 2011, 6:14 pm

Silva mica caps of 300pf can be had at Audio cap last time I looked (happy customer etc) . 330pf I found harder to source,Andy.

Hermit6345 · 26th Jul 2011, 11:46 pm

330pF from here:

http://www.justradios.com/mica.html

No connection etc etc.

regards

Ian

25th Jul 2011, 9:09 pm	#1
bluepilot Heptode Join Date: Feb 2010 Location: Duffort, Gers, France Posts: 714	"Squashed" capacitors I am restoring an old German Mende radio from ca. 1938. Some of the capacitors are in difficult to get at places and I was wondering whether I should replace them whilst I have everything dismantled rather than waiting until I get everything back together and then finding they don't work. At present they appear to be OK but I have no idea what will happen when they get a lot of voltage applied. The ones in question are generally tubular in shape but have an oval rather than circular cross-section. Does anyone know what type of capacitor they are likely to be? They all have values in the range of hundreds of pF. The cases have the brand name Mende on them so they are possible something peculiar to that company. As they are a bit unusual, I would like to keep them if possible. Thanks __________________ Stuart The golden age is always yesterday - Asa Briggs

25th Jul 2011, 9:18 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: "Squashed" capacitors Capacitors with values in 100s of pFs don't generally need replacing. Can you post a picture of one please. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

25th Jul 2011, 10:05 pm	#3
MikeyPP Retired Dormant Member Join Date: Jun 2011 Location: Berkshire Posts: 389	Re: "Squashed" capacitors like this sort of thing (metallised polyprop) > http://upload.ecvv.com/upload/Produc..._Capacitor.jpg ?

25th Jul 2011, 11:32 pm	#4
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: "Squashed" capacitors Low value caps from the '30s are most likely to be silvered mica types, certainly not polypropylene nor any other plastic dielectric. This type of capacitor is often wax encapsulated, but as Station X stated, they rarely fail. Any waxy, paper dielectric capacitor should, of course, be assumed to be faulty. John

26th Jul 2011, 4:16 pm	#6
bluepilot Heptode Join Date: Feb 2010 Location: Duffort, Gers, France Posts: 714	Re: "Squashed" capacitors I've now taken a couple of pictures. The radio is a Mende radio which makes me think they may be some sort of manufacturers own make. I've not seen any like this anywhere else. There is no voltage rating given but this one came out of the power supply so it must be several hundred volts. Whatever the cap is, it is stuffed into a white plastic tube and sealed at the ends. Attached Thumbnails __________________ Stuart The golden age is always yesterday - Asa Briggs

26th Jul 2011, 4:25 pm	#7
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: "Squashed" capacitors I don't know what sort of reputation these capacitors had. You could try testing them for leakage at the HT voltage. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

26th Jul 2011, 5:31 pm	#8
bluepilot Heptode Join Date: Feb 2010 Location: Duffort, Gers, France Posts: 714	Re: "Squashed" capacitors Normally I'd just wait for something to go bang and then replace it. However in this case, the radio is assembled using bent metal tabs - not a screw in sight. I don't like to bend them too often or they might break off. So I'd rather make sure the caps are OK now. 300pf is an unusual size and so far I've not found a replacement that would fit in the tube. If no-one knows what they are, maybe I'll dismantle one from a concealed place to see what's inside. The I'll know whether I can leave the others or not. Thanks __________________ Stuart The golden age is always yesterday - Asa Briggs

26th Jul 2011, 6:14 pm	#9
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: "Squashed" capacitors Silva mica caps of 300pf can be had at Audio cap last time I looked (happy customer etc) . 330pf I found harder to source,Andy. __________________ Curiosity hasn't killed this cat...so far.

26th Jul 2011, 11:46 pm	#10
Hermit6345 Rest in Peace Join Date: Oct 2006 Location: North Wiltshire, UK. Posts: 638	Re: "Squashed" capacitors 330pF from here: http://www.justradios.com/mica.html No connection etc etc. regards Ian