Forming Caps?

[kefestvog]

I'm starting to put together a JTM45. I've heard some people talking about forming caps. As I undestand this it has to do with bringing amp up to voltage with a Variac. How is this done? What do you gain from doing it? What's the minimum size Variac (500w or 1kw) that you need to do it? Any anything else I need to know about it. Thanks.

[NY Chief]

go here....

http://www.sozoamplification.com/audio/break_in.html

[mightymike]

That link has more to do with the "break in" period with the Sozo caps.

I think what this guy was referring to was, on first fire up of an old amp that had been sitting, or even a new amp's first fire up; The process of using a Variac (with the tubes pulled out and connected to a dummy load) to slowly bring up the wall voltage up to 120, to form or reform the caps.

A few people here do that, or somerhing similiar to that, and it's one of the many benifits of owning a Variac

The reason you do it with the tubes pulled because at real low heater voltage, you can mess up your tubes with cathode stripping.

I think Larry (Novisbir) does this, or something similiar.

[novosibir]

The reason you do it with the tubes pulled because at real low heater voltage, you can mess up your tubes with cathode stripping.

I think Larry (Novisbir) does this, or something similiar.

Yep, the low heater voltage wouldt badly hurt the tube's cathodes.

But I'm not using a variac, I pull out all tubes and put a 100K resistor between the rectifier diodes and the entire power supply rail, so that all the caps will be charged through the 100K resistor with a very very low current and also with a pretty low voltage of about 200...230V at the beginning.

The voltage drop across the resistor becomes les and less - and first when the voltage drop is less than 10V across the resistor, the caps are formed.

With new caps this process will take about 3...4 hours - with long stored caps or NOS LCR's (which I'm using in my amps) it usually takes 8...12 hours.

Larry

[Tubes]

wheres the link...

[novosibir]

@ Tubes

All your requested infos you should get here:

http://forum.metroamp.com/viewtopic.php ... ht=forming

Larry

[white room]

The reason you do it with the tubes pulled because at real low heater voltage, you can mess up your tubes with cathode stripping.

I think Larry (Novisbir) does this, or something similiar.

Yep, the low heater voltage wouldt badly hurt the tube's cathodes.

But I'm not using a variac, I pull out all tubes and put a 100K resistor between the rectifier diodes and the entire power supply rail, so that all the caps will be charged through the 100K resistor with a very very low current and also with a pretty low voltage of about 200...230V at the beginning.

The voltage drop across the resistor becomes les and less - and first when the voltage drop is less than 10V across the resistor, the caps are formed.

With new caps this process will take about 3...4 hours - with long stored caps or NOS LCR's (which I'm using in my amps) it usually takes 8...12 hours.

Larry

Larry, I read your post on this subject, in another thread, last week and I want to make sure I have it straight before I do it.

On my 67 build, I would put the 100k between the diodes and the first mains filter cap, correct?

[novosibir]

Correct!

Larry

[mightymike]

..

[Tubes]

@ Tubes

All your requested infos you should get here:

http://forum.metroamp.com/viewtopic.php ... ht=forming

Larry

Thanks a bunch! I missed that thread when searching the other day and today.

[ritasamson]

@ Tubes



All your requested infos you should get here:



http://forum.metroamp.com/viewtopic.php" onclick="window.open(this.href);return false; ... ht=forming



Larry

thanks for the info.