Forming filter caps

[budubum]

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

Larry

you are a genius:)

[novosibir]

you are a genius:)

I know, I know - I'm the greatest

I've already been the greatest, as Muhammed Ali still has been Cassius Clay

*haha*

Larry

[5150loveeddie]

LOLL!

Larry in your opinion if we would do that forming cap procedure every couple of years to keep our caps healty, do you think old DALY, HUNT even RADIO SPARE could last indefinitly or almost..?

I ask because I've just done this to an original jtm45 form 1965 with all the original filter (RS) and I was able to reform then below the 5Volts accross the 100w, and I'm almost certain thatr no one did this before once even so I suppose if we do this on a regular basis we would prolonge them even more but till when?... Jesus those RS are 40 some years old and still working, we are far away from the 10-15 or even 20 years life spand here!!

[novosibir]

Larry in your opinion if we would do that forming cap procedure every couple of years to keep our caps healty, do you think old DALY, HUNT even RADIO SPARE could last indefinitly or almost..?

This only helps when the amp often is unused for longer than a half year. The best what you can do for the lifespan of your filter caps is, to have the amp in use regularly. But in amps, which are often used at high or full power over a longer time, the filter caps have to work hard to smooth this amount of ripple, always become very hot, and therefore also will wear out earlier. The best for the lifespan of filter caps actually would be, to play the amp every 3 months for about 30 minutes at moderate power... then they maybe last 100 years. But is this the sense of having an amp

Jesus those RS are 40 some years old and still working, we are far away from the 10-15 or even 20 years life spand here!!

The 15 years is the manufacturer's claim - not the reality

Larry

[5150loveeddie]

Thx Larry, good info as ususal..

I'm doing a 1979 super lead now, it is gonna be 48hrs at 20H tonight, I'm at 10v now, it was at 12v then back up at 14v last night, was a little concern of that, now it is back at 10v.

I will let it continue wishing it will still continue to drops to 5v!! Let me know what you think with that little rise (last night 12v up to 14V) or is this normal... 48hrs now, it is getting longggggg...

[guilds100]

I just finished my jtm45 (man this amp cranks!) that i formed the caps on and I must say its the quietest amp ive built. I thought the amp wasnt working 2 times with the volume on the normal channel on 5 as i heard nothing and tried to debug. It wasnt till i turned up the bright side before i heard any noise. Once the guitar was plugged in i finally realized the dream I had when I was building my first amp, nearly noise silent when dimed. I'm hooked on forming and will never start a new amp again without doing it. Now if only I knew of this 4 weeks ago when i fired up my Valve jr 18w circuit board conversion. That thing makes almost as much noise as sound. I thinking about recapping it to see if I can tame it down.

[eddie25]

- 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

This is obvious for most, but for those who try this method, don't flip the standby switch like I did. I was wondering why I got no drop for a second, then it dawned on me how stupid I was. Caps are forming good now, I just thought I would mention this for new guys like myself.

[Structo]

I don't have a variac.

I was wondering instead of using different resistors on the B+, how would a light bulb current limiter work for forming caps?

For instance, I built an 18 watt amp for a guy.

When I first powered it up I started with a 25 watt bulb which severely limits the current.
Somewhere around 250ma.

I left it like that for about an hour, then switched to a 40 watt bulb and so on until I was at a 75 watt bulb.

Was that a waste of time or do you think it helped to form the caps more slowly than just plugging that sucker into the wall?

I didn't have any tubes in it when I did this, I just powered it up and also flipped the standby to play.

[guilds100]

I'm no expert, but I think the inline resistor is the way to go. The current limiter works great for testing your amp without giving it access to full power, but I dont think you'll get the same results. I use a current limiter to check for shorts. If none are found, I then switch it out of the circuit to check actual voltages. If you changed lamps during the forming that means the power to the amp was cut temperarily, not recommended when cap forming. It was probably better than nothing, but I don't think you achieved what you set out to do. I'm cap forming for the second time now and plan on doing this to every amp as I'm pleased with the rusults (back a couple of posts).

[eddie25]

Another question:

How much are the dropping resistors before the current limiting resistor gonna drop the voltage? Since the voltage is gonna be full B+ even at the preamps without tubes I'm worried about my 400V coupling caps.... Or do you think they can handle it with no signal going through 'em? Thanks.

[novosibir]

... I'm worried about my 400V coupling caps.... Or do you think they can handle it with no signal going through 'em? Thanks.

Don't worry, they can and will - up to about 480VDC!
Only insure, that your preamp filter isn't a 350V type!
A 450V type withstands about 470V, as long as it hasn't to filter out ripple.

Larry

[5150loveeddie]

Larry, Was wondering about a 1972 SL with original Daly filter caps.

My question is that after an hour of forming the caps via your procedure I still get around 300v accross the 100k, was just wondering if this is still safe and ok to continue the process, those caps looks good, no visual leaks, no bulges, no ac above a volts or so on top of each. Normaly we should get a drop accross the 100k to 40-60v within a few minutes but not in this case!

Thx Larry!

[novosibir]

... after an hour of forming the caps via your procedure I still get around 300v accross the 100k, was just wondering if this is still safe and ok to continue the process.

Have you removed the cap discharging lead on V1's plate?
Have you removed the two 56K bleeder resistors across the screen filter caps?
(or at least disconnected one lead of each)
Have you unsoldered the yellow cable from the PT between the 1-st filter caps?
Have you pulled all the tubes?

If one is NO, then read my signature once again!
If all's YES, then you have a short in the circuit, what you have to fix before continuing forming!

Larry

[5150loveeddie]

YES I did...

Now it's at 275v after 4hrs

Short? Humm I got to figured that one out

THx LArry

[5150loveeddie]

LArry, that amp PT seems not wired right or it has an issue!!

HEre it goes: When I check the high voltages secondaries directly at the stby switch I get 265vac on one side and 85vac on the other of the stby switch's terminals. The amp is in stby mode (not in play mode while checking, only power is ON, stby is OFF). Heaters, bias supply seems normal...

I left the yellow wire disconnected from the power tranny while checking the voltages (the one that goes to the first caps)

That is how the PT was wired form the factory it seems...by the look of the red die untouched!!