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On Thu, 10 Oct 2019 17:00:16 -0700 (PDT), Michael Terrell
terrell.michael.a@gmail.com> wrote:
On Thursday, October 10, 2019 at 7:40:27 PM UTC-4, John Larkin wrote:
On Thu, 10 Oct 2019 16:36:35 -0700 (PDT), whit3rd wrote:
On Thursday, October 10, 2019 at 7:50:51 AM UTC-7, John Larkin wrote:
I had a Sprague TO6 capacitor analyzer that could reform to 500VDC, and it metered the leakage current. If the oxide layer was bad, you could slowly ramp it up until it had acceptable leakage at the rated voltage. The Military had a set schedule to test and reform NOS electrolytics that were in warehouses. I used to see a lot of surplus caps with a label showing the dates.
Are modern electrolytics any better than the old ones, from the aspect
of un-forming themselves?
Or maybe the old ones are, well, just old.
On Thu, 10 Oct 2019 17:00:16 -0700 (PDT), Michael Terrell wrote:
On Thursday, October 10, 2019 at 7:40:27 PM UTC-4, John Larkin wrote:
I meant an OLD instrument.
Back in the '60 and '70s we would apply 12 to 24 volts to old equipment to warm the power transformer to drive out moisture. The tubes were pulled, first and it was left on this setup for 24 hours. It seemed like every old piece of test equipment was store in a dank basement.
I had a Sprague TO6 capacitor analyzer that could reform to 500VDC, and it metered the leakage current. If the oxide layer was bad, you could slowly ramp it up until it had acceptable leakage at the rated voltage. The Military had a set schedule to test and reform NOS electrolytics that were in warehouses. I used to see a lot of surplus caps with a label showing the dates.
Are modern electrolytics any better than the old ones, from the
aspect of un-forming themselves?
Or maybe the old ones are, well, just old.
bloggs.fre...@gmail.com wrote:
-------------------------------
Look at the ripple voltage and verify that your film can take the
ripple current.
** Absurd advice.
Then there is the turn-on time of the circuit. Does this Heath Kit have a lot of tubes in it, or what kind of electronic does it have. The old tube circuit DC supplies would overshoot at turn-on until the tube filaments warmed up and the tubes started conducting, drawing down the rail voltage.
** Funny how rectifier tubes have long warm up times too.
Until then, the applied DC voltage rail would be way high, like 150% nominal.
** Whata pile of fucking crap !!!
Even with silicon diodes in the PSU, the voltage excess is never more than 15% - something electros ARE rated for FFS.
And this could last for tens of seconds.
** No it wouldn't.
The electrolytics are designed to handle this temporary overvoltage, usually spec'd for 30 seconds, the film definitely are not.
** More complete bullshit .
Film caps have plenty of overvoltage capacity, most do not break down until double or triple DC voltage is applied.
Go away you alarmist IDIOT !!!
.... Phil
Michael Terrell wrote:
On Friday, October 11, 2019 at 9:49:58 AM UTC-4, m...@uga.edu wrote:
Perhaps one economic factor is that, as the cost of other components has
fallen, people expect the electrolytic capacitors to be very cheap also.
The capacitors now stand out as the expensive components. And that's an
incentive to lower standards.
Some of them are approaching zero value. Older equipment was expected to last
10 years or more. A lot of today's junk is lucky to last a year or two. In that
respect, the costs are going up, not down. Lower grade caps are a very high
failure item. I had one C-band receiver on the bench a few years ago. It had
about 85 electrolytics, and every one was bad Most had no brand name, and some
weren't marked for temperature. It belonged to a bar, and they needed it right
away, so they paid a large bill to have it working the next day. I generally use
Panasonic and Rubicon for repairs and my projects, these days.
Near the turn of the century a Missouri man named Chris started
badcaps.net Chris' "master list" enumerates the capacitors that he
trusts:
https://www.badcaps.net/index.php?pageid=master_list
Chris also hosts a lively forum at https://www.badcaps.net/forum/
Although its more apropos to repair.
On Thursday, October 10, 2019 at 7:50:51 AM UTC-7,
jla...@highlandsniptechnology.com wrote:
I've heard of people using a variac to slowly bring up an old
instrument.
A switchmode regulated supply, though, takes maximum current input
when voltage is low-to-borderline. So that mainly is good for
unregulated power (or power-wasting series or shunt regulated). It's
also questionable if there's a DC fan, or ferroresonant circuit...
There was debate in this thread about whether to add balancing resistors,
?and I didn't. John Larkin said "they take care of themselves."
Indeed they do, sharing the voltage to within a few percent of equal.
I wonder if Mr. Larkin could explain further. Is there some effect that makes them equalize if they have different leakages to start with?
The rest of the story...
For those who tuned in late, I'm replacing the power supply filters in a Heathkit IT-11 capacitor checker. In the original circuit they are two 40-uF 350-V in series (to handle 600 V). I ordered a 20-uF 1-kV film capacitor to replace them.
Well, there just isn't room for that film capacitor under this chassis! So I had to resort to two 47-uF 450-V in series, like Heathkit's original.
There was debate in this thread about whether to add balancing resistors, and I didn't. John Larkin said "they take care of themselves." Indeed they do, sharing the voltage to within a few percent of equal.
I wonder if Mr. Larkin could explain further. Is there some effect that makes them equalize if they have different leakages to start with? I would expect the opposite, that the leakier one would carry a lower voltage and would form less, causing the difference in leakage to increase -- but I might be wrong.
The rest of the story...
For those who tuned in late, I'm replacing the power supply filters in a Heathkit IT-11 capacitor checker. In the original circuit they are two 40-uF 350-V in series (to handle 600 V). I ordered a 20-uF 1-kV film capacitor to replace them.
Well, there just isn't room for that film capacitor under this chassis! So I had to resort to two 47-uF 450-V in series, like Heathkit's original.
There was debate in this thread about whether to add balancing resistors, and I didn't. John Larkin said "they take care of themselves." Indeed they do, sharing the voltage to within a few percent of equal.
I wonder if Mr. Larkin could explain further. Is there some effect that makes them equalize if they have different leakages to start with? I would expect the opposite, that the leakier one would carry a lower voltage and would form less, causing the difference in leakage to increase -- but I might be wrong.
I am going to look back at the bleeder network and see if there's a good way to split it in half.
Leakage currents have a tendency to increase exponentially with applied voltage, so you often don't need much voltage difference to compensate for significant differences in initial leakage current.
Some manufacturer's application note that I read back in 1970 was a full bottle on the subject.
Thanks. If the increase is exponential (more than linear), that explains why they self-regulate.
m...@uga.edu wrote:
---------------------------
There was debate in this thread about whether to add balancing resistors,
?and I didn't. John Larkin said "they take care of themselves."
Indeed they do, sharing the voltage to within a few percent of equal.
I wonder if Mr. Larkin could explain further. Is there some effect that makes them equalize if they have different leakages to start with?
** The mid point voltage will be offset such that the same leakage current flows in both caps. The total voltage of the caps should exceed the supply by 25% or more to allow this.
Adding bleeders increases the leakage through the leakier example.
Both caps will get more leaky when hot, IME more so for the leakier one.
The rest of the story...
For those who tuned in late, I'm replacing the power supply filters in a Heathkit IT-11 capacitor checker. In the original circuit they are two 40-uF 350-V in series (to handle 600 V). I ordered a 20-uF 1-kV film capacitor to replace them.
Well, there just isn't room for that film capacitor under this chassis! So I had to resort to two 47-uF 450-V in series, like Heathkit's original.
There was debate in this thread about whether to add balancing resistors, and I didn't. John Larkin said "they take care of themselves." Indeed they do, sharing the voltage to within a few percent of equal.
I wonder if Mr. Larkin could explain further. Is there some effect that makes them equalize if they have different leakages to start with?
I am going to look back at the bleeder network and see if there's a good way to split it in half.
** The mid point voltage will be offset such that the same leakage
current flows in both caps. The total voltage of the caps should
exceed the supply by 25% or more to allow this.
The leakage current must be the same in series caps, no matter what
the voltage.
Adding bleeders increases the leakage through the leakier example.
Both caps will get more leaky when hot, IME more so for the leakier one.
If they are in series, the leakier one has less voltage drop so
dissipates less power.
jla...@highlandsniptechnology.com wrote:
-----------------------------------------
** The mid point voltage will be offset such that the same leakage
current flows in both caps. The total voltage of the caps should
exceed the supply by 25% or more to allow this.
The leakage current must be the same in series caps, no matter what
the voltage.
** Really ?
Adding bleeders increases the leakage through the leakier example.
Both caps will get more leaky when hot, IME more so for the leakier one.
If they are in series, the leakier one has less voltage drop so
dissipates less power.
** The actual leakage current with HV electros is normally in the micro-amp range so dissipation causes no discernible temp rise. Ambient temp and rises in same entirely swamp it.
Where series bleeder resistors are used ( eg 100,000 Fender tube amplifiers ) they pass about 1mA which is enough to reduce and nearly eliminate mid point voltage offset.
The main benefit however is in bleeding off charge so the caps do not present a hazard if the AC supply is removed while there is no load on the PSU.
There are a couple of ways this can happen.
See typical schem:
https://schematicheaven.net/fenderamps/fender_bassman50.pdf
..... Phil
** The mid point voltage will be offset such that the same leakage
current flows in both caps. The total voltage of the caps should
exceed the supply by 25% or more to allow this.
The leakage current must be the same in series caps, no matter what
the voltage.
** Really ?
Adding bleeders increases the leakage through the leakier example.
Both caps will get more leaky when hot, IME more so for the leakier one.
If they are in series, the leakier one has less voltage drop so
dissipates less power.
** The actual leakage current with HV electros is normally in the micro-amp range so dissipation causes no discernible temp rise. Ambient temp and rises in same entirely swamp it.
Where series bleeder resistors are used ( eg 100,000 Fender tube amplifiers ) they pass about 1mA which is enough to reduce and nearly eliminate mid point voltage offset.
The main benefit however is in bleeding off charge so the caps do not present a hazard if the AC supply is removed while there is no load on the PSU.
There are a couple of ways this can happen.
See typical schem:
https://schematicheaven.net/fenderamps/fender_bassman50.pdf
Ole tube gear seldom had fans. It just cooked itself.
BLDC fans are great, small and quiet and cheap. The fans back when
were big shaded-pole motor things.
John Larkin wrote:
-------------------
** The mid point voltage will be offset such that the same leakage
current flows in both caps. The total voltage of the caps should
exceed the supply by 25% or more to allow this.
The leakage current must be the same in series caps, no matter what
the voltage.
** Really ?
Adding bleeders increases the leakage through the leakier example.
Both caps will get more leaky when hot, IME more so for the leakier one.
If they are in series, the leakier one has less voltage drop so
dissipates less power.
** The actual leakage current with HV electros is normally in the micro-amp range so dissipation causes no discernible temp rise. Ambient temp and rises in same entirely swamp it.
Where series bleeder resistors are used ( eg 100,000 Fender tube amplifiers ) they pass about 1mA which is enough to reduce and nearly eliminate mid point voltage offset.
The main benefit however is in bleeding off charge so the caps do not present a hazard if the AC supply is removed while there is no load on the PSU.
There are a couple of ways this can happen.
See typical schem:
https://schematicheaven.net/fenderamps/fender_bassman50.pdf
** For an unexplained reason JL introduces a new topic here.
Keeping the wacky guy on-topic is a battle.
Ole tube gear seldom had fans. It just cooked itself.
** Not one bit true - the cooking itself bit I mean.
BLDC fans are great, small and quiet and cheap. The fans back when
were big shaded-pole motor things.
** But could be very quiet.
Many tube scopes had fans fitted to the back panel and with a series dropping resistor could be made very quiet indeed.
Some famous tube instrument amps had AC fans as standard, but there was a big nasty waiting to catch any designer who was stupid enough.
Ampeg released a new version of their famous SVT, a 300W tube bass amp in the late 1990s. It had an AC fan that ran continuously.
The designer made two bad errors:
1. He made the air flow go under the chassis, over the main PCB with all the output tube sockets and up though holes to cool each 6550 tube's glass envelope. A similar method is used in high power RF transmitters.
2. He also fitted octal sockets that had 2 inch long pins - so the PCB could be remain deep under the chassis with the socket's flange secured to the metal deck as usual.
The result was that dust and fluff collected around all the long pins until a massive 700VDC arc-over occurred between an adjacent pair ( plate and heater ) causing extensive damage to the PCB, tubes and many other parts.
Took hours to clean up and fix.
Later production examples had plastic sleeving fitted to the long pins.
The PCB still became so badly contaminated it was no cure.
.... Phil
** The actual leakage current with HV electros is normally in the micro-amp range so dissipation causes no discernible temp rise. Ambient temp and rises in same entirely swamp it.
Where series bleeder resistors are used ( eg 100,000 Fender tube amplifiers ) they pass about 1mA which is enough to reduce and nearly eliminate mid point voltage offset.
The main benefit however is in bleeding off charge so the caps do not present a hazard if the AC supply is removed while there is no load on the PSU.
There are a couple of ways this can happen.
See typical schem:
https://schematicheaven.net/fenderamps/fender_bassman50.pdf
** For an unexplained reason JL introduces a new topic here.
Keeping the wacky guy on-topic is a battle.
This is called a "discussion group." And isn't heat related to
electrolytic cap life?
Many tube scopes had fans fitted to the back panel and with a series dropping resistor could be made very quiet indeed.
Some famous tube instrument amps had AC fans as standard, but there was a big nasty waiting to catch any designer who was stupid enough.
Ampeg released a new version of their famous SVT, a 300W tube bass amp in the late 1990s. It had an AC fan that ran continuously.
The designer made two bad errors:
1. He made the air flow go under the chassis, over the main PCB with all the output tube sockets and up though holes to cool each 6550 tube's glass envelope. A similar method is used in high power RF transmitters.
2. He also fitted octal sockets that had 2 inch long pins - so the PCB could be remain deep under the chassis with the socket's flange secured to the metal deck as usual.
The result was that dust and fluff collected around all the long pins until a massive 700VDC arc-over occurred between an adjacent pair ( plate and heater ) causing extensive damage to the PCB, tubes and many other parts.
Took hours to clean up and fix.
Later production examples had plastic sleeving fitted to the long pins.
The PCB still became so badly contaminated it was no cure.
.... Phil
It didn't help thermally that some audio gear was literally
upholstered.