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Old capacitor question (can type)

Discussion in 'Amp Tech Center' started by AAA71, Oct 25, 2020.

  1. AAA71

    AAA71 Tele-Meister

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    Please see attached files - good morning, question about can caps. I re-doing a very old single ended amp and it has large can capacitors.

    I have never worked with capacitors like this - I can see obviously which is the B+ cap s and which is the coupling cap but I am used to working of Fender type amps.

    If anyone can lend a thought as how one large can cap can be possibly replaced by a fender 5F1 style caps?

    Thanks everyone PS please pardon my DIY layout, first time using it. IMG_20200828_085040068.jpg IMG_20201025_094853.jpg IMG_20201025_094900.jpg IMG_20201025_095445.jpg

    IMG_20200828_085040068.jpg IMG_20201025_094853.jpg
     

    Attached Files:

  2. Peegoo

    Peegoo Poster Extraordinaire

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    Find a modern cap of identical spec and stick it in there. Look here:

    https://www.tubesandmore.com/products/capacitors

    One thing some restorers do is carefully open the original can, remove the original guts, and hide a modern cap in there since they're smaller. When it's all buttoned up it looks original.
     
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  3. AAA71

    AAA71 Tele-Meister

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    Thanks Peegoo - One of the things I wanted to learn is how one large cap can do the job of 3 phases B+1, B+2 etc.
     
  4. King Fan

    King Fan Poster Extraordinaire

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    ^^^ what @Peegoo said. You'll appreciate that there are individual cap elements inside that can -- see the cool AES video about how they make the cans on the original machines.

    For cans, look here specifically...

    https://www.tubesandmore.com/products/capacitors?filters=Type=Multi-Section / Can Type

    **But** if you can't find a 40/10/10 combo (or 20/20/10/10, and jumper the first two to get 40) it's easy enough to replace the can with individual caps inside the chassis -- mount on tag strips, or silicone to the chassis, or tie together in a log pile with a nylon tie. I used silicone here. And this has slight advantages, like you can separate the grounds if you want, and you can replace individual caps rather than the whole can in the future.

    upload_2020-10-25_8-39-3.png
     
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  5. schmee

    schmee Doctor of Teleocity Silver Supporter

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    That cap can appears to be just a single cap..... isn't it?
     
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  6. AAA71

    AAA71 Tele-Meister

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    Yes it is and you an see in the pic there have been multiple solders - I cant even get a value off it. The schematic shows 3 caps though, not sure why this one is a single.
     
  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Isn't that a second cap can I see in the pictures?

    Radial caps are usually smaller and may make for easier fitting.
     
  8. AAA71

    AAA71 Tele-Meister

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    Yup - the second one is a 20/20/450. I think i just figured it out possibly - the large can must be a 40 mfd filter cap and a supply of B+ to the output tranny. The 20/20 must be for the plates of the 6LS7 preamp and the 6V6 screen.

    Thoughts?
     
  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Seems reasonable.
     
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  10. tubegeek

    tubegeek Friend of Leo's

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    Seems reasonable.

    A little decoding advice:
    The multi-cap electrolytic cans all share a common (-) terminal and the (+) terminals are separate. If you look on the side of some of them, there are a few shapes (triangle, square, circle are typical ones.) And the specs next to each shape refer to the (+) terminals which have the hole in the middle of their terminal in the corresponding shape.

    So basically you have two or three or four caps all in one can, tied together at the (-) terminal. Usually the (-) terminal is grounded to the can itself but there are also ones with an outer insulator sleeve so that the can can be isolated from the chassis and so that there is less risk of getting shocked if the outer can is at some positive voltage.

    One thing I rarely see mentioned: the can caps are helpful in keeping the caps cooler by locating them outside the chassis, that feature can probably improve their longevity somewhat.
     
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  11. Wally

    Wally Telefied Ad Free Member

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    ....."
     
  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Many of the cap cans have a 65C temp rating. As noted, inside the chassis is a warmer location so caps with a higher temp rating should be considered if the cap cans will be replaced with individual caps. 85C and 105C temp rated caps are readily available.
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Off topic:
    Reviewing the point to point circuit.
    I like the creative use of *unused* socket pins. In particular I noticed the OT secondary connected to the rectifier pin1.

    I have been concerned with solder joints when using p-p connections. The sockets I use seem to be able wiggle to the point I worry about metal fatigue cracking the solder joint or breaking the component lead. The sockets on this example look like they have a very secure mounting reducing the possibility of metal fatigue. I may have to look for *better* sockets for p-p circuits.

    Am I overthinking the metal fatigue aspect of p-p?
     
    Last edited: Oct 26, 2020
  14. AAA71

    AAA71 Tele-Meister

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    The sockets are rigid and have ground tabs on them as well - I was going to replace them but they ar riveted in and I frankly don't want to go through the process of removing them.

    Question - what is the OT secondary to pin 1 on the rectifier doing?
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Pin1 is holding the wire from the OT secondary which gives it stability so it does not break. A wire from pin1 then continues on to the speaker solder tag.

    The rectifier does not use pin1.
     
  16. AAA71

    AAA71 Tele-Meister

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    I see...I realized pin 1 was nothing so I was confused - thanks for smacking my head :) But yes there's a lot of "sneaky" wiring on this little thing.
     
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