Forming filter caps

[rip]

or the other side of the 100K?

[budubum]

something like this right?

i think larry said to put the pull down resistor BEFORE the main resistor for the cap forming. meaning to put that 220k 2watt on teh rectifier side and not the cap side

[novosibir]

something like this right?

No, still before the 100K at the side facing to the fuse, so that the 100K hasn't to draw the bleeder current of the 220K

Larry

[novosibir]

i think larry said to put the pull down resistor BEFORE the main resistor for the cap forming. meaning to put that 220k 2watt on teh rectifier side and not the cap side

Yep! Exactly!

Larry

[rip]

cool thank you guys for the clarification. So in case anyone else gets confused here is the good schematic

[budubum]

cool thank you guys for the clarification. So in case anyone else gets confused here is the good schematic

yes this is correct

[Twistingcrow]

Hi!
I've read through most of the topics about caps forming and I'm really interested in doing so with my JTM45. I have just received the SoZo Vintage caps so I may give that technique a try (if it's useful for those caps).
Larry (or someone else), tell me if this is right:
- On the JTM45 I just need to solder a 100K resistor across the standby switch, and that's it? And then measure the voltage dropping?
Thanks!

[novosibir]

- On the JTM45 I just need to solder a 100K resistor across the standby switch, and that's it? And then measure the voltage dropping?

You even haven't to solder it, you just can clamp it across the standby switch with two crocodile cables - and you have to pull all tubes except the rectifier tube. But the described method is for forming filter caps, not signal caps

Larry

[Twistingcrow]

But the described method is for forming filter caps, not signal caps

Larry

Of course, silly me... Cool, then I'm gonna do it, if it's that easy! I have to go get some crocodile cables now...

[Twistingcrow]

Hey!
Just thought I'd keep you posted. I'm done with my new JTM45, filter caps formed, tests and bias done. Can't wait to fire it up!
Larry's technique is really easy and I'm surprised by my results. I formed them in two steps: 2 hours yesterday night and 2 more hours this morning and voltage has gone down to 0.95V, unbelievable! The stock F&T Metro kit caps are relly good!
So, all in all, DO IT!

[axeman]

What do you mean " 2 hours yesterday night and 2 more hours this morning" your not to shut the amp off until the caps are formed.

[Twistingcrow]

Well I mean that I formed them for 2 hours yesterday night and had 1.35V jst before I turned it OFF. Then I repeated the operation this morning for another 2 hours and before I turned it OFF I had 0.95V. So it seems that doing it in two separate steps didn't have any negative impact on the forming, did it?

[axeman]

You should read this entire section of forming "electrolytic" capacitors, you'll find a section were Larry explains not to shut the amp off.

[guilds100]

Larry

I enjoyed your explanation on cap forming so much I was wondering if I could make a cap forming jig. My plan is to rectify 120v, sending it through a 100k 2w resistor, then adding caps with 1k 2watt resistor between each cap, kinda simulating an amp setup. Would this work? Do the cap have to be charged up to operating voltage of the amp? I do have a couple of small transformers that could be used to generate ~400v dc.

[novosibir]

I enjoyed your explanation on cap forming so much I was wondering if I could make a cap forming jig. My plan is to rectify 120v, sending it through a 100k 2w resistor, then adding caps with 1k 2watt resistor between each cap, kinda simulating an amp setup. Would this work?

Shure, no prob!

I'm doing it this way, before I put my NOS LCR's into a new build. A small PT - rectified - then a 220K/3W to ground, to give the PT a pre load - and from there I go through each a 220K/1W to each 50+50/500 double can - always four at a time in parallel. They're sitting about 16-24h for forming, while I continue building the amp. Then the formed and discharged caps go in the amp

And moreover every 2-3 years I'm forming my complete stack of NOS LCR's, to keep it 'healthy' - they are from 1992

Before forming I put the caps (solder lugs upside) into hot water for about 20-30 minutes, to decristallize the electrolytic inside. It's similar as what you have to do with hard, old honey, to make it fluid again - and this pre procedure helps much to reduce the forming time.

Ouch - so many of my 'secrets' in only one post.....

Larry