Rebuild of 1930s wet electrolytics - UK Vintage Radio Repair and Restoration Discussion Forum

Oskar.B · 22nd Mar 2007, 11:03 pm

Hi everyone!

I recently aquired a Philips 940A, I am guessing that its 1934 +- a few years. I have opened up one of the wet caps as it was dead short and stubbornly refused to reform. I'm sharing some pictures in the forum as there are probably lots of these old Philips caps around and it is nice for others to be able to see at least one way to get them opened.

I think the cap I worked on is the same as described in this thread:
https://www.vintage-radio.net/forum/...ad.php?t=11743
Looks like he had more difficulties than me to get them out. I only had to cut very short ... cuts

I think after the cap is bolted back, it will not look to bad.
Next step will be to make some threads in the metal rod that previously held the anode plate. It will then be possible to fix the rod in the plastic base. I will probably solder the postitive of the new component to the metal rod, negative will go to a small wire that will be pressed between can and base.

Curiously the other cap from the old Philips was in excellent shape. I was able to reform it back into good working order. It draws about 0,7mA at 300 volts! (holds it voltage too).

Regards
Oskar

GMB · 23rd Mar 2007, 11:05 am

I have just been working on some of these, also Philips c1937, but they are not quite the same in that the central connection was just a tag and the base thickness was less. Also mine contained pure liquid (no paste).

WARNING: If you decide to keep them in original condition then be aware that it is very bad to leave them other than vertical so a notice to that effect is in order. The reason is that they are vented at the top and so any cyclic changes in temperature or pressure will act to gradually pump the liquid out (which is what had happened in my case). The fluid is boric acid and ammonium borate in a 50% water/glycol solution, and it makes a serious mess and corrodes everything if it is allowed out. By the way, the vents that you see at the top are not directly the vents, there is a little compartment at the top containing some stuff to soak up a few drops of fluid. The inner vents are just covered by a rubber band (see pic) to avoid casual leakage.

The good thing about these old capacitors is where the fluid is still OK and the central part hasn't shorted to the can and the base isn't leaking, they do seem to reform OK and unlike more recent parts I think there is rather little danger of explosion because they are freely vented and so there is little risk of pressure build up with the resulting distortion causing a spark to detonate the gases.

Sideband · 23rd Mar 2007, 1:32 pm

Quote:

Originally Posted by Oskar.B

I think the cap I worked on is the same as described in this thread:
https://www.vintage-radio.net/forum/...ad.php?t=11743
Looks like he had more difficulties than me to get them out. I only had to cut very short ... cuts

I think after the cap is bolted back, it will not look to bad.

Hi Oskar. Yes exactly the same capacitors. Really messy things to rebuild. Where you have cut around the seam, I peeled it back and the base was still solid in the can. I had to extend the saw cuts down the shoulder slightly and that freed the base. Everything else I did the same as you.

Rich.

planigan · 26th Mar 2007, 6:20 am

Hi Oskar, I would not try to solder to the rod, everything in the can is pure, or very close to pure, aluminum. Anything in the can other than aluminum will set up chemical reaction. What I did was to drill and tap into flats on rod and used terminal lug soldered to new cap and terminal screw to rod. There is a site at www.philcorepairbench.com that has information on re-stuffing electrolytics. I call it restuffing as on this side of the puddle were rather crass. PL

Oskar.B · 27th Mar 2007, 10:15 am

PL,

I don't really understand how that could be a problem. The rod is steel anyway and the capacitor can certainly didn't mind being bolted to the steel chassis for 70+ years? Has it got something to do with the fact that the electrolyte is now gone? Please explain more

Anywhay, that link was great, I remeber I used to have that site bookmarked, but I had "lost it".

/Oskar

22nd Mar 2007, 11:03 pm	#1
Oskar.B Pentode Join Date: Oct 2005 Location: Gargnäs, north of Sweden Posts: 105	Rebuild of 1930s wet electrolytics Hi everyone! I recently aquired a Philips 940A, I am guessing that its 1934 +- a few years. I have opened up one of the wet caps as it was dead short and stubbornly refused to reform. I'm sharing some pictures in the forum as there are probably lots of these old Philips caps around and it is nice for others to be able to see at least one way to get them opened. I think the cap I worked on is the same as described in this thread: https://www.vintage-radio.net/forum/...ad.php?t=11743 Looks like he had more difficulties than me to get them out. I only had to cut very short ... cuts I think after the cap is bolted back, it will not look to bad. Next step will be to make some threads in the metal rod that previously held the anode plate. It will then be possible to fix the rod in the plastic base. I will probably solder the postitive of the new component to the metal rod, negative will go to a small wire that will be pressed between can and base. Curiously the other cap from the old Philips was in excellent shape. I was able to reform it back into good working order. It draws about 0,7mA at 300 volts! (holds it voltage too). Regards Oskar Attached Thumbnails __________________ Old electronics smell better! http://gargnas.net Last edited by Oskar.B; 22nd Mar 2007 at 11:06 pm. Reason: Spelling

23rd Mar 2007, 11:05 am	#2
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,094	Re: Rebuild of 1930s wet electrolytics I have just been working on some of these, also Philips c1937, but they are not quite the same in that the central connection was just a tag and the base thickness was less. Also mine contained pure liquid (no paste). WARNING: If you decide to keep them in original condition then be aware that it is very bad to leave them other than vertical so a notice to that effect is in order. The reason is that they are vented at the top and so any cyclic changes in temperature or pressure will act to gradually pump the liquid out (which is what had happened in my case). The fluid is boric acid and ammonium borate in a 50% water/glycol solution, and it makes a serious mess and corrodes everything if it is allowed out. By the way, the vents that you see at the top are not directly the vents, there is a little compartment at the top containing some stuff to soak up a few drops of fluid. The inner vents are just covered by a rubber band (see pic) to avoid casual leakage. The good thing about these old capacitors is where the fluid is still OK and the central part hasn't shorted to the can and the base isn't leaking, they do seem to reform OK and unlike more recent parts I think there is rather little danger of explosion because they are freely vented and so there is little risk of pressure build up with the resulting distortion causing a spark to detonate the gases. Attached Thumbnails

26th Mar 2007, 6:20 am	#4
planigan Retired Dormant Member Join Date: Sep 2006 Location: Coram, New York Posts: 2	Re: Rebuild of 1930s wet electrolytics Hi Oskar, I would not try to solder to the rod, everything in the can is pure, or very close to pure, aluminum. Anything in the can other than aluminum will set up chemical reaction. What I did was to drill and tap into flats on rod and used terminal lug soldered to new cap and terminal screw to rod. There is a site at www.philcorepairbench.com that has information on re-stuffing electrolytics. I call it restuffing as on this side of the puddle were rather crass. PL

27th Mar 2007, 10:15 am	#5
Oskar.B Pentode Join Date: Oct 2005 Location: Gargnäs, north of Sweden Posts: 105	Re: Rebuild of 1930s wet electrolytics PL, I don't really understand how that could be a problem. The rod is steel anyway and the capacitor can certainly didn't mind being bolted to the steel chassis for 70+ years? Has it got something to do with the fact that the electrolyte is now gone? Please explain more Anywhay, that link was great, I remeber I used to have that site bookmarked, but I had "lost it". /Oskar __________________ Old electronics smell better! http://gargnas.net