AR88 block paper capacitor connections - UK Vintage Radio Repair and Restoration Discussion Forum

AndyWright · 26th Dec 2012, 4:50 pm

Hi
I need to replace the block paper capacitor on one of my AR88's as it dumped all of its oil over the bench.

There are 5 terminals on the underside. How do these correspond to the 3 capacitors within the block?

Thanks

Andy G4OJY

Station X · 26th Dec 2012, 4:54 pm

Can you be more specific please. Component designations for example?

The bath tub capacitors generally have one terminal for each capacitor and a common return via the casing.

Perhaps you're talking about the smoothing capacitors?

AndyWright · 26th Dec 2012, 4:57 pm

Hi

yes I'm referring to the power supply smoothing capacitor. It has 4 terminals at each corner of a rectangle and one in the centre.

Andy

Station X · 26th Dec 2012, 6:21 pm

That's C96, C97 and C98. You should be able to work it out by checking the wiring against the circuit diagram.

turretslug · 26th Dec 2012, 6:25 pm

Hi Andy,

Wisely and cunningly, RCA arranged that the rotationally symmetrical connections could be turned through 180 degrees when replacing this non-polarised multi-capacitor. Thus:

Centre terminal = Junction of C96, 97.

Diagonally opposite terminals= Other (seperate) ends of C96, C97.

Remaining terminals= C98 terminals. (One of these has a short wire link to chassis).

I (and no doubt others) have posted replacement options for substituting this multi-block on the forum- I opted for fitting modern components (630V polyester) in the original tin. Whatever you opt for, bear in mind that the HT floats scarily high (approaching 500V) in the "TRANS" position of the mode switch,

Colin.

AndyWright · 26th Dec 2012, 6:48 pm

Thanks Colin that's exactly the info I needed. I intend to replace with some high voltage polyester capacitors I've got, I'm not sure yet if they will go in the original can, or on a PCB board, it depends how difficult it is to get the can apart.

Cheers,

Andy

RobinBirch · 27th Dec 2012, 11:16 am

The can comes apart relatively easily so long as you've got a small blowlamp or a tinman's soldering iron, say 150 Watt.

There are three cells IIRC in the capacitor which are in separate metal chambers. Drill a number of holes in the bottom and leave it stand in a bucket or on a tray for a long time to let as much of the oil drain out as you can.

Do it outside and keep well clear of the fumes from the oil. Use gloves.

Clean the whole thing up (remember the gloves, especially if you are sensitive to oils). Put back together with new components and solder back together.

Clean up and paint slate grey.

Robin

G6Tanuki · 27th Dec 2012, 9:34 pm

Be careful: unless you have solid evidence to the contrary you should assume that the "oil" is one based on Polychlorinated Biphenyls (PCBs).

Known to be carcinogenic and likely to trigger a number of skin-complaints (e.g. "Chloracne") if I came across an oil-leaking capacitor in my professional capacity I'd be calling in the professionals to dispose of it and provide me with the relevant certificates saying they'd done so in accordance with the relevant regulations.

Whether you choose to take such precautions in a 'domestic' situation, well, it's up to you - but I intend to live to over-100 and grow old disgracefully, so choose to minimise my exposure to known risk-materials.

26th Dec 2012, 4:50 pm	#1
AndyWright Tetrode Join Date: Feb 2012 Location: Bishop Auckland, County Durham, UK. Posts: 92	AR88 block paper capacitor connections Hi I need to replace the block paper capacitor on one of my AR88's as it dumped all of its oil over the bench. There are 5 terminals on the underside. How do these correspond to the 3 capacitors within the block? Thanks Andy G4OJY

26th Dec 2012, 4:54 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: AR88 block paper capacitor connections Can you be more specific please. Component designations for example? The bath tub capacitors generally have one terminal for each capacitor and a common return via the casing. Perhaps you're talking about the smoothing capacitors? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

26th Dec 2012, 4:57 pm	#3
AndyWright Tetrode Join Date: Feb 2012 Location: Bishop Auckland, County Durham, UK. Posts: 92	Re: AR88 block paper capacitor connections Hi yes I'm referring to the power supply smoothing capacitor. It has 4 terminals at each corner of a rectangle and one in the centre. Andy

26th Dec 2012, 6:21 pm	#4
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: AR88 block paper capacitor connections That's C96, C97 and C98. You should be able to work it out by checking the wiring against the circuit diagram. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

26th Dec 2012, 6:25 pm	#5
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: AR88 block paper capacitor connections Hi Andy, Wisely and cunningly, RCA arranged that the rotationally symmetrical connections could be turned through 180 degrees when replacing this non-polarised multi-capacitor. Thus: Centre terminal = Junction of C96, 97. Diagonally opposite terminals= Other (seperate) ends of C96, C97. Remaining terminals= C98 terminals. (One of these has a short wire link to chassis). I (and no doubt others) have posted replacement options for substituting this multi-block on the forum- I opted for fitting modern components (630V polyester) in the original tin. Whatever you opt for, bear in mind that the HT floats scarily high (approaching 500V) in the "TRANS" position of the mode switch, Colin.

26th Dec 2012, 6:48 pm	#6
AndyWright Tetrode Join Date: Feb 2012 Location: Bishop Auckland, County Durham, UK. Posts: 92	Re: AR88 block paper capacitor connections Thanks Colin that's exactly the info I needed. I intend to replace with some high voltage polyester capacitors I've got, I'm not sure yet if they will go in the original can, or on a PCB board, it depends how difficult it is to get the can apart. Cheers, Andy

27th Dec 2012, 11:16 am	#7
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: AR88 block paper capacitor connections The can comes apart relatively easily so long as you've got a small blowlamp or a tinman's soldering iron, say 150 Watt. There are three cells IIRC in the capacitor which are in separate metal chambers. Drill a number of holes in the bottom and leave it stand in a bucket or on a tray for a long time to let as much of the oil drain out as you can. Do it outside and keep well clear of the fumes from the oil. Use gloves. Clean the whole thing up (remember the gloves, especially if you are sensitive to oils). Put back together with new components and solder back together. Clean up and paint slate grey. Robin

27th Dec 2012, 9:34 pm	#8
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: AR88 block paper capacitor connections Be careful: unless you have solid evidence to the contrary you should assume that the "oil" is one based on Polychlorinated Biphenyls (PCBs). Known to be carcinogenic and likely to trigger a number of skin-complaints (e.g. "Chloracne") if I came across an oil-leaking capacitor in my professional capacity I'd be calling in the professionals to dispose of it and provide me with the relevant certificates saying they'd done so in accordance with the relevant regulations. Whether you choose to take such precautions in a 'domestic' situation, well, it's up to you - but I intend to live to over-100 and grow old disgracefully, so choose to minimise my exposure to known risk-materials.