Forming filter caps

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axeman
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Re: Forming filter caps

Post by axeman » Mon Aug 03, 2015 2:41 pm

neikeel wrote:
marblues2 wrote:So only one end of the resistor is attached to the standby switch via croc clip?
No, not sure you have entirely understood the princple of what we are doing.

The resistor is clipped to bypass the standby switch (which if it is a Metro 50 will be a Carling switch with only two terminals. In the off position the switch is open circuit, when in the on position the terminals are made and current flows.

If you clip the resistor across the two terminals you have made a circuit so all the HT from your rectifier diodes flows through the resistor and on to the filter caps and the rest of the circuit, do not switch the standby on or the current will flow through the switch not your resistor.

The resistor acts as a limiter to keep the current down whilst the capcitors reform, when they are fully reformed there is minimal voltage drop across the resistor and you know you are done.
Ok so add a 100k resistors across the 2 terminals/soldering lugs.
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Re: Forming filter caps

Post by neikeel » Mon Aug 03, 2015 2:50 pm

Yes that is it!
Neil

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Re: Forming filter caps

Post by axeman » Mon Aug 03, 2015 11:47 pm

Thanks Neikeel, I built my last 1987 and did not form the filter caps. Getting ready to help a friend with his build, so this would really make the deference, plus it will make me look smart. :lol:

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Re: Forming filter caps

Post by JayBe » Thu Oct 01, 2015 3:18 pm

neikeel wrote:...unplug from mains, drain the filter caps with your other croc lead (where the V of v1 plate resistors with one end and the other to the chassis) and then remove the clip on 100k.

You are now good to go.
I've thought that the amp needed to be plugged in when draining to ground. Am I mistaken?
David Bray wrote me it could be done by just flicking the standby switch on for 2-3 minutes.

Thanks for the reforming for dummies explanation! ;)

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Re: Forming filter caps

Post by neikeel » Fri Oct 02, 2015 3:52 am

JayBe wrote:
neikeel wrote:...unplug from mains, drain the filter caps with your other croc lead (where the V of v1 plate resistors with one end and the other to the chassis) and then remove the clip on 100k.

You are now good to go.
I've thought that the amp needed to be plugged in when draining to ground. Am I mistaken?
David Bray wrote me it could be done by just flicking the standby switch on for 2-3 minutes.

Thanks for the reforming for dummies explanation! ;)
Countries vary

In the UK you can have the amp plugged into wall - ie earthed, but with live switched off at the wall socket, many countries the socket does not have a switch
Neil

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Re: Forming filter caps

Post by JayBe » Tue Oct 06, 2015 12:07 pm

neikeel wrote:
JayBe wrote:
neikeel wrote:...unplug from mains, drain the filter caps with your other croc lead (where the V of v1 plate resistors with one end and the other to the chassis) and then remove the clip on 100k.

You are now good to go.
I've thought that the amp needed to be plugged in when draining to ground. Am I mistaken?
David Bray wrote me it could be done by just flicking the standby switch on for 2-3 minutes.

Thanks for the reforming for dummies explanation! ;)
Countries vary

In the UK you can have the amp plugged into wall - ie earthed, but with live switched off at the wall socket, many countries the socket does not have a switch
So if there is no switch and the plug is live, the caps won't drain? But they will drain into the 'air' unplugged? Sorry, I'm no electrician.

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Re: Forming filter caps

Post by neikeel » Tue Oct 06, 2015 12:43 pm

The point is in the UK we have 3 pronged plugs and sockets, one earth which is always connected when you plug in.

The live and neutral are marked and differentiated and when the wall switch is off you are not live, so the amp chassis can drain to ground via the earth without the amp being live.

In most of Europe and US I believe, correct me if I am wrong, the outlets have 3 terminals including ground but you cannot switch the live off at an individual socket?
Neil

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Re: Forming filter caps

Post by JayBe » Fri Oct 09, 2015 1:14 pm

All right, switching off live but keeping ground attached will let it drain to ground.
How about when no cord is attached, where do the caps drain?

I used an extension cord with an on/off switch today, connected v1 to chassis and swithced on standby. Seemed to work.

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Re: Forming filter caps

Post by neikeel » Sat Oct 10, 2015 2:56 am

JayBe wrote:All right, switching off live but keeping ground attached will let it drain to ground.
How about when no cord is attached, where do the caps drain?

I used an extension cord with an on/off switch today, connected v1 to chassis and swithced on standby. Seemed to work.
Sounds like the best solution for where you are!
Neil

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Re: Forming filter caps

Post by JayBe » Fri Oct 16, 2015 1:43 am

quick related question:

Do I need to remove the board the change a top mounted preamp filter can? Seems it's grounded directly to a lug on the chassis. thanks.

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Re: Forming filter caps

Post by neikeel » Sat Oct 17, 2015 3:45 am

JayBe wrote:quick related question:

Do I need to remove the board the change a top mounted preamp filter can? Seems it's grounded directly to a lug on the chassis. thanks.
The preamp can can often be removed from above as there is JUST enough slack in the wires to do it but you ideally need a clip to stop the wires falling back inside.

What I ofter do is extend the wires by a couple of cms if the board is out to make it easier next time.

You do not need to remove the board totally either, you undo the input jacks and control pots and flip the board up and prop it out of the way whilst you work.
Neil

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Re: Forming filter caps

Post by JayBe » Tue Oct 20, 2015 9:37 am

Thanks, the cap is grounded with a stiff wire, doesn't move at all. I've changed the plate and PI caps. Yet to do the preamp. Maybe I'll stick with the 50+50 for now :/

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Re: Forming filter caps

Post by bahady30 » Tue Nov 10, 2015 11:49 am

Hello, today I received my 3 new filter capacitors from F&T , 50uf + 50uf 500V each. I have send F&T an email if it is necessary to form their new cans. The answer was after 2 years you need to form them...Because I don't know how long the have been lying on the shelf I have decided to form the new cans. I have a JMP 2104 50W amp and this is my situation: After the rectifier diodes a red wire goes to the fuse (500mA) .From that SAME point of the fuse , a yellow wire goes to the "+" of the first filter can. The other side of the fuse goes to the center tab of the output transformer AND to the choke .Where do I have to put my resistor? Thanks !

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Re: Forming filter caps

Post by danman » Tue Nov 10, 2015 1:17 pm

With the 50 watt circuit, you can solder the resistor across the standby switch terminals. Just make sure that the standby switch is in the open position so that the current has to flow through the resistor and not through the switch itself. As soon as you plug in the amp, and turn on the power switch, the forming process will begin.

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Re: Forming filter caps

Post by bahady30 » Tue Nov 10, 2015 1:49 pm

Oke, thanks but I think I don't get it sorry. I thought the resistor has to be inserted after de rectifier diodes and not before if I read Larry's instructions correctly....my situation is that 2 red wires from the PT go to one site of standby switch . From the other side of the standby switch I see 2 blue wires go to the rectifier diodes. After the rectifier is the situation that I mentioned before. There is also one white wire that goes to the bias section. Where do I have to put my 100 K resistor now? Across which terminals of the standby switch should I solder my resistor? Thanks

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