Capacitor Can replacement

[acheld]

I'm rebuilding an old (1959) Heathkit signal generator.   The power supply uses a cap can with  50uF - 50uF in series, with a tap off the series connection.  So, there are three points of connect to the "system."  Boy this is hard to describe.   I've attached a picture of the design as printed on the cap can (1958 vintage) which better describes the part.

One of the sections is bad.  (Amazingly, the remaining cap cans measure "good").   Of course, I can not find a replacement can with this description.

Question:   I could simply take two 50uF caps and wire them up as in the picture (see attached schematic, left hand image) -- right?  Or, use a 50uF and a 25uF (right hand image on the schematic).  Should be the same, right??    I'm not clear on why the engineer chose to use this particular  cap can design.  Any ideas?

Would it be ok to use 47uF caps? 

[sluckey]

Question:   I could simply take two 50uF caps and wire them up as in the picture (see attached schematic, left hand image) -- right?  Or, use a 50uF and a 25uF (right hand image on the schematic).  Should be the same, right??    I'm not clear on why the engineer chose to use this particular  cap can design.  Any ideas?

Would it be ok to use 47uF caps? 

Yes, just use two 47µF.

Can caps were space savers when that unit was built. And HeathKit did enough business to have a custom can built. If you wanted a replacement the only place to get it was Heath (at their custom price).

[acheld]

Thank you!  Saves time and $$.

[jjasilli]

Can you post the circuit schematic.  Unless something's unique to this circuit (which does not seem likely), 2X 50uF caps in series yields 25uF @ 2X the voltage rating of ea cap.  You may get by with 1X 25uF cap at the proper voltage rating.  Higher voltage caps were more rare & expensive back then which may explain the series arrangement. Then you can maybe: dispose of the old can; fit the one new cap in the old can; or re-attach the old can for show but leave it disconnected; fit the new cap inside the chassis if there's room.

[John]

Can you post the circuit schematic.  Unless something's unique to this circuit (which does not seem likely), 2X 50uF caps in series yields 25uF @ 2X the voltage rating of ea cap.  You may get by with 1X 25uF cap at the proper voltage rating.  Higher voltage caps were more rare & expensive back then which may explain the series arrangement. Then you can maybe: dispose of the old can; fit the one new cap in the old can; or re-attach the old can for show but leave it disconnected; fit the new cap inside the chassis if there's room.

JJ, I believe that is part of the voltage doubler. I "sort of" * rebuilt an AG-10 and had to have someone explain to me the funny-looking (to me) schematic diagram of how it worked.


*I did get it working  properly, but that thing had about a hunnert bucks worth of caps in it, and I never did find the pointer indicator for the front.

[sluckey]

Can you post the circuit schematic.  Unless something's unique to this circuit (which does not seem likely), 2X 50uF caps in series yields 25uF @ 2X the voltage rating of ea cap.  You may get by with 1X 25uF cap at the proper voltage rating.  Higher voltage caps were more rare & expensive back then which may explain the series arrangement. Then you can maybe: dispose of the old can; fit the one new cap in the old can; or re-attach the old can for show but leave it disconnected; fit the new cap inside the chassis if there's room.

Look here...

     http://el34world.com/Forum/index.php?topic=24090.0

[jjasilli]

Good grief, I've never seen a voltage doubler implemented inside a cap can, and didn't see the other thread. 

[acheld]

John, amazingly all but two of the electrolytic caps in this dog tested good (at least with my trusted blue ESR meter).   I am replacing the cheaper ones just because of all the grime and the brittle wires.   You are right, there are a lot of caps. 

JJ, I'm a newbie, so I don't have a lot of experience, but this voltage doubler design was new to me.  Of course, sluckey picked up on it in a flash.

[jjasilli]

I don't get the cap can markings or the drawings in the first 2 posts.  But I do get the schematic.  I would dispense with the can and use 2X 47uF @ 250V (available, e.g., at Antique Electronics) wired per the schematic.  (I don't think Doug carries that uF @ low voltage). They're inexpensive and small - should fit in your chassis.

[sluckey]

That was a very common method of identifying which cap is connected to which lug. Triangle, half moon, square, and no symbol have been used ever since those cans came out. You will see the symbols with the value/voltage on the side of the can. Looking at the bottom of the can you will see the same symbols next to the appropriate lug. Does that clear it up?

Here's a pic of the symbols on the bottom of can...

     http://sluckeyamps.com/hammond_2/big_guts.jpg

[PRR]

> Triangle, half moon, square, and no symbol have been used ever since those cans came out.

I bet there was a stock low-price punch-set from some other industry. Maybe decorative wood trim for "gingerbread" carpentry. When they first put two different caps in one can, they needed a way to tell them apart. Cheap! Maybe one of the workers had a punch-set in his toolbox and 'womp womp' put a round and a square notch in a phenolic board. Actually the main punching of the phenolic might be set-up with "universal punch", a base which held round square notch etc bits which could be assembled "any shape or size or detail". The punch maker (Diarco??) would custom-make about any shape they thought they could sell twice; any local toolmaker could grind bits also.

[sluckey]

I bet there was a stock low-price punch-set from some other industry.

Probably so. If you look at all four cap cans in that pic you'll see the same three symbols regardless of the number of caps in the can. Two of those cans have 2 caps, one has 3 caps, and one has 4 caps.

[jjasilli]

That was a very common method of identifying which cap is connected to which lug. Triangle, half moon, square, and no symbol have been used ever since those cans came out. You will see the symbols with the value/voltage on the side of the can. Looking at the bottom of the can you will see the same symbols next to the appropriate lug. Does that clear it up?

Here's a pic of the symbols on the bottom of can...

     http://sluckeyamps.com/hammond_2/big_guts.jpg

I remember that now, thanks!