Help! Light bulb current limiter
Phil S.
comfortable with it. Please tell me if you think something is wrong.
I carefully checked to be sure of which is the hot wire and which is the
neutral. I am sure those are correct. I know this because I'm using an old
orange extension cord that long ago got cut, leaving me with four feet of
wire to the molded 3-prong and it uses the USA standard black-white-green.
I ran the black into the light bulb socket and then another black to the hot
side of a "service outlet", making the light bulb in series on the hot leg
of the wall supply. [wall supply -- light socket -- service receptacle]
The white and green are appropriately connected to the other respective
terminals on the service receptacle.
I plugged an IEC cord into the outlet and again checked to see if the hot
leg is in the right place, and it is.
The end of the IEC cord plugged into the service outlet (in series with the
light bulb socket, no bulb) puts out 32VAC. Measuring at the light bulb
socket (where the bulb screws in), I see about 24VAC (bulb removed). I
expected the same reading. Actually, I expected 0VAC without the bulb at
the service receptable. I understand that putting the meter across the bulb
socket closes that connection.
I expect that bulb acts like a fuse, so when removed, there is no power at
the receptacle. This isn't happening.
With the bulb screwed in, I see 124VAC at the end of IEC cord (assume it is
the same at the service outlet), but the bulb doesn't glow.
What's going on here? Is this OK? Defective socket (when removed from
service it was working but stuck in the ON position and the chain broke --
I'm sure because I wrote this on the socket with a sharpie)? Does the
socket itself have so much resistance that it drops the voltage?
I expect the bulb to light whether in series or parallel, as long as it gets
adequate voltage. Is this not the case?
Yes, the bulb is fine. After checked everything (above), I put it in a
regular lamp and it lights up. So, it was in working order throughout.
Needless to say, I didn't attempt to plug the amp into it.
I'd appreciate some help, even if you just need to tell me to buy a new
socket.
Thanks.
Phil
mykeym...@yahoo.com
the SHIT out of himself?
Elvis Kabong
"Phil S." <psymonds...@comcast.net> wrote in message
news:KvudnfC7-Y67ojHY...@comcast.com...
And the bulb has how many watts?
I use a 100watt bulb and that's all that is needed unless one is testing
a SS high watt power amp. Then you need more bulbs parallel with the
first one while the entire bulb rig is still in series between the AC wall outlet
and the amp's AC cord.
Hope I'm not having to explain the obvious, but this is such a simple rig,
either you did something wrong or you don't understand how it's supposed
to work. I can't tell based on your post. But in your post, you *seemed* to
have wired it correctly, but the way you tested it is questionable.
If you plug your rig into a wall outlet and no amp to the other end,
of course the bulb won't light up.
Some amps don't draw that much current at idle so the bulb barely lights up.
Or perhaps the fuse was already blown on the amp you plugged in to the
light bulb rig.
I used to use a variac, but now I like this method better for checking for
excessive current flow. On the variac, a short might just kick in, blow the
amp's fuse, the variac's fuse and the shop's breaker before I get a chance
to back it off before it does blow everything. Instead the bulb just glows brighter
if there is excessive current and implodes if there is too much current for the
bulb to handle.
Good luck,
Ed
mainm...@choiceonemail.com
>From the AC cord ==> black wire ==> one side of socket
white wire ==> neutral side of the
"service outlet"
Then just add a wire from the other side of the socket to the hot side
of the service outlet.
What I have at my shop is a standard 2 outlet wall box installed below
my bench with both outlets in series. An extension cord is routed
through a hole in the back to a normal wall outlet. I have a nice
orange plastic 1960's lamp that gets plugged into one recepticle, and
the device under testing plugs into the other.
Here's a picture of another version someone's made- might help to
visualize it:
http://pontoppidan.info/lars/index.php?proj=repairstories&page=5
Phil S. wrote:
> I built the gizmo with the light bulb to power up the TMB18W. but am not
> comfortable with it. Please tell me if you think something is wrong.
>
> I carefully checked to be sure of which is the hot wire and which is the
> neutral. I am sure those are correct. I know this because I'm using an old
> orange extension cord that long ago got cut, leaving me with four feet of
> wire to the molded 3-prong and it uses the USA standard black-white-green.
> I ran the black into the light bulb socket and then another black to the hot
> side of a "service outlet", making the light bulb in series on the hot leg
> of the wall supply. [wall supply -- light socket -- service receptacle]
> The white and green are appropriately connected to the other respective
> terminals on the service receptacle.
When you say "another black" it's not clear- are you running a wire
between the side of the socket with the black AC lead, or the other
side? It should be the other side
Just double check your wiring- you'll figure it out.
Ya, know, this is probably the best case for buying a copy of Gerald
Weber's hip-vintage-guru amp book- It's got an excellent drawing of
this DIY current limiter! Most of it is mis-informed BS with a healthy
dose of conjecture, though.
-dave M.
RonSonic
wrote:
>I built the gizmo with the light bulb to power up the TMB18W. but am not
>comfortable with it. Please tell me if you think something is wrong.
>
>I carefully checked to be sure of which is the hot wire and which is the
>neutral. I am sure those are correct. I know this because I'm using an old
>orange extension cord that long ago got cut, leaving me with four feet of
>wire to the molded 3-prong and it uses the USA standard black-white-green.
>I ran the black into the light bulb socket and then another black to the hot
>side of a "service outlet", making the light bulb in series on the hot leg
>of the wall supply. [wall supply -- light socket -- service receptacle]
>The white and green are appropriately connected to the other respective
>terminals on the service receptacle.
>
>I plugged an IEC cord into the outlet and again checked to see if the hot
>leg is in the right place, and it is.
>
>The end of the IEC cord plugged into the service outlet (in series with the
>light bulb socket, no bulb) puts out 32VAC. Measuring at the light bulb
>socket (where the bulb screws in), I see about 24VAC (bulb removed). I
>expected the same reading. Actually, I expected 0VAC without the bulb at
>the service receptable. I understand that putting the meter across the bulb
>socket closes that connection.
Your meter is going to read all sorts of trash with an open circuit in proximity
to AC.
>I expect that bulb acts like a fuse, so when removed, there is no power at
>the receptacle. This isn't happening.
>
>With the bulb screwed in, I see 124VAC at the end of IEC cord (assume it is
>the same at the service outlet), but the bulb doesn't glow.
That's because it will only glow when current is flowing. Short the outlet and
it'll glow.
>What's going on here? Is this OK? Defective socket (when removed from
>service it was working but stuck in the ON position and the chain broke --
>I'm sure because I wrote this on the socket with a sharpie)? Does the
>socket itself have so much resistance that it drops the voltage?
>
>I expect the bulb to light whether in series or parallel, as long as it gets
>adequate voltage. Is this not the case?
There's no connection from one end of the lamp to the power is there? How could
it light.
>Yes, the bulb is fine. After checked everything (above), I put it in a
>regular lamp and it lights up. So, it was in working order throughout.
>
>Needless to say, I didn't attempt to plug the amp into it.
>
>I'd appreciate some help, even if you just need to tell me to buy a new
>socket.
Plug it in.
Ron
Xtrchessreal
On Jan 15, 10:12 pm, RonSonic <ronso...@tampabay.rr.com> wrote:
> On Mon, 15 Jan 2007 21:57:33 -0500, "Phil S." <psymonds_no_s...@comcast.net>
> wrote:
>
>
>
>
>
> >I built the gizmo with the light bulb to power up the TMB18W. but am not
> >comfortable with it. Please tell me if you think something is wrong.
>
> >I carefully checked to be sure of which is the hot wire and which is the
> >neutral. I am sure those are correct. I know this because I'm using an old
> >orange extension cord that long ago got cut, leaving me with four feet of
> >wire to the molded 3-prong and it uses the USA standard black-white-green.
> >I ran the black into the light bulb socket and then another black to the hot
> >side of a "service outlet", making the light bulb in series on the hot leg
> >of the wall supply. [wall supply -- light socket -- service receptacle]
> >The white and green are appropriately connected to the other respective
> >terminals on the service receptacle.
>
> >I plugged an IEC cord into the outlet and again checked to see if the hot
> >leg is in the right place, and it is.
>
> >The end of the IEC cord plugged into the service outlet (in series with the
> >light bulb socket, no bulb) puts out 32VAC. Measuring at the light bulb
> >socket (where the bulb screws in), I see about 24VAC (bulb removed). I
> >expected the same reading. Actually, I expected 0VAC without the bulb at
> >the service receptable. I understand that putting the meter across the bulb
> >socket closes that connection.Your meter is going to read all sorts of trash with an open circuit in proximity
> to AC.
>
> >I expect that bulb acts like a fuse, so when removed, there is no power at
> >the receptacle. This isn't happening.
>
> >With the bulb screwed in, I see 124VAC at the end of IEC cord (assume it is
> >the same at the service outlet), but the bulb doesn't glow.That's because it will only glow when current is flowing. Short the outlet and
> it'll glow.
>
> >What's going on here? Is this OK? Defective socket (when removed from
> >service it was working but stuck in the ON position and the chain broke --
> >I'm sure because I wrote this on the socket with a sharpie)? Does the
> >socket itself have so much resistance that it drops the voltage?
>
> >I expect the bulb to light whether in series or parallel, as long as it gets
> >adequate voltage. Is this not the case?There's no connection from one end of the lamp to the power is there? How could
> it light.
>
> >Yes, the bulb is fine. After checked everything (above), I put it in a
> >regular lamp and it lights up. So, it was in working order throughout.
>
> >Needless to say, I didn't attempt to plug the amp into it.
>
> >I'd appreciate some help, even if you just need to tell me to buy a new
> >socket.Plug it in.
>
> Ron- Hide quoted text -- Show quoted text -
I am not sure how this device is being used. I understand what current
limiting does but if you are worried about too much current then why
not use a fuse? If you want to control the current directly then get a
current limiting voltage source and set the limit to the desired
current. Or build one.
This method will only show you a current is present - So? If you are
using it for protection it makes no sense to me. And, some current is
expected for any device to work. If you want to know what the current
actually is then use a resistor and measure the Voltage drop across it.
A light bulb is not a resistor and though it is rated for some wattage
value it can still take more or less than that before it burns open -
depending on manufacture, materials, age. And the resistance will
change as the current is increased and decreased.
There may be some old school reason for this device but I dont know
what that is. Explain it to me please.
mainm...@choiceonemail.com
Xtrchessreal wrote:
> I am not sure how this device is being used. I understand what current
> limiting does but if you are worried about too much current then why
> not use a fuse? If you want to control the current directly then get a
> current limiting voltage source and set the limit to the desired
> current. Or build one.
>
> This method will only show you a current is present - So? If you are
> using it for protection it makes no sense to me. And, some current is
> expected for any device to work. If you want to know what the current
> actually is then use a resistor and measure the Voltage drop across it.
> A light bulb is not a resistor and though it is rated for some wattage
> value it can still take more or less than that before it burns open -
> depending on manufacture, materials, age. And the resistance will
> change as the current is increased and decreased.
>
> There may be some old school reason for this device but I dont know
> what that is. Explain it to me please.
Very simply, you can see if an amp will blow a fuse, without blowing
the fuse. I use mine all the time. It's also a cheap way to re-form old
electrolytics. I used this technique on an old silvertone turntable-
got it working well enough. The benefits are it's cost and it's
simplicity.
-dave M.
Dave Curtis
http://antiqueradio.org/dimbulb.htm
HTH,
-Dave
Phil S.
help. (We've got one person just sucking bandwidth with nothing to
contribute and he can go fuck himself as far as I'm concerned.) It's funny
how things go sometimes and the many comments helped to cure my
misunderstandings about this circuit.
Indeed, this thing is as simple as it gets. When I bridged the secondary
service outlet with my voltage tester, I expected it you light the 40W bulb
because I closed the circuit. When it didn't light, I got nervous and did a
bunch of silly stuff. The voltage tester is a special kind of light bulb
really and wasn't the right thing to use. I assume that a simple shorted
plug will indeed light the bulb, but not the voltage tester or the DMM.
This morning, after coffee and with a clear head, I plugged a work lamp into
the service outlet. The test bulb burns bright and the work lamp is dim.
The amp is more of a piggy than the work light, so it will make the test
bulb glow dim. I think I get it now.
Gotta go to the day job now. Maybe I'll get back to this tonight.
Regards,
Phil
Brian
glow brighter, the more current you draw the brighter the test light.
RonSonic
>
>
>On Jan 15, 10:12 pm, RonSonic <ronso...@tampabay.rr.com> wrote:
>> On Mon, 15 Jan 2007 21:57:33 -0500, "Phil S." <psymonds_no_s...@comcast.net>
>> wrote:
>
>I am not sure how this device is being used. I understand what current
>limiting does but if you are worried about too much current then why
>not use a fuse? If you want to control the current directly then get a
>current limiting voltage source and set the limit to the desired
>current. Or build one.
A fuse takes a very long time to react, it is self destructive and requires
annoying replacement when it does its job. Fuses will allow a solid state amp to
melt itself to the ground long before it does any good. A lamp will allow you to
test and work on a malfunctioning piece of gear at length without doing further
damage.
>This method will only show you a current is present - So? If you are
>using it for protection it makes no sense to me. And, some current is
>expected for any device to work. If you want to know what the current
>actually is then use a resistor and measure the Voltage drop across it.
> A light bulb is not a resistor and though it is rated for some wattage
>value it can still take more or less than that before it burns open -
>depending on manufacture, materials, age.
It doesn't normally burn open in our application. Why would it with only 120V
applied.
> And the resistance will
>change as the current is increased and decreased.
This is exactly what makes it so useful.
>There may be some old school reason for this device but I dont know
>what that is. Explain it to me please.
The inline light bulb does a near perfect job of current limiting and they are
available in handy values suitable for a wide range of repairs. They cost a hell
of a lot less than whatever current limiting device you might propose, they're
extremely rugged electrically and once you've worked with one for a while you'll
learn how to read it for more troubleshooting information. Strap an analog meter
across the outlet and watch the needle. You can often tell what sort of problem
you're looking for, e.g. an amp with a bad diode in the bridge looks different
on that meter from one that has faulty bias when both of those problems would
only blow a fuse and make some more burnt smell.
The lamp does not protect by burning out. Here's what a bulb does: It has an
extremely low resistance at low current levels. Only a couple of ohms when cold.
If you draw more current through one it will heat up very rapidly and the
resistance of the filament will also go way up. What this does is allow a normal
device under test to operate at nearly full voltage, but restricts current into
a malfunctioning gadget that's pulling excess current.
I rarely feel the need for one on most tube amp repairs but wouldn't want to
deal with a solid state output stage without one.
Ron
RonSonic
>Hi,
>One thing when filament of lamp heats up, the resistance drops.
>So at initial power on, lamp will do good job as current surge limiter.
Where do we get these NTC lamps?
Ron
John King
Right-O Brian... That is the one of the main reasons for the
device in the first place. (1) It will only allow a certain amount
of current to flow through the circuit depending on the wattage
rating of the bulb (2) The more current the tested device draws, the
brighter the bulb will glow, until it is at full intensity, then
the current is limited to no more than that
The Librarian
series with the AC mains. You get a bright flash when the caps charge,
and then it goes (almost) out as the idling supply current reaches its
nominal low value. The amplifier will then work normally at low
volumes. If the amp draws too much current for whatever reason, the
lightbulb will glow brightly, increase resistance, and limit the power
to the circuit. Usually, there will either be a mis-wire (use your DMM)
or oscillation (will show up on a scope or RF power measuring device).
If the bulb goes dim-bright-dim-bright... then the amp is marginally
stable and the grounding layout should be checked. Compensation
capacitor values may need to be adjusted if any significant changes
were made. Mine is stable the way it is.
http://www.ee.washington.edu/circuit_archive/circuits/km241.html
The sto - you get light bulbs at the sto.
What you want to do is limit current to the critical parts - usually
the
horizontal output transistor (HOT). Most of the time you will get away
with
putting it in series with the AC line. However, sometimes, putting a
light
bulb directly in the B+ circuit will provide better protection as it
will
limit the current out of the main filter capacitors to the HOT.
Actually,
an actual power resistor is probably better as its resistance is
constant
as opposed to a light bulb which will vary by 1:10 from cold to hot.
The
light bulb, however, provides a nice visual indication of the current
drawn
by the circuit under test. For example:
* Full brightness: short circuit or extremely heavy load - a fault
probably
is still present.
* Initially bright but then settles at reduced brightness: filter
capacitors
charge, then lower current to rest of circuit. This is what is
expected
when the equipment is operating normally. There could still be a
problem
with the power circuits but it will probably not result in an
immediate
catastrophic failure.
* Pulsating: power supply is trying to come up but shutting down due to
overcurrent or overvoltage condition. This could be due to a
continuing
fault or the light bulb may be too small for the equipment.
Note: for a TV or monitor, it may be necessary (and desirable) to
unplug the
degauss coil as this represents a heavy initial load which may prevent
the unit
from starting up with the light bulb in the circuit.
The following are suggested starting wattages:
* 40 W bulb for VCR or laptop computer switching power supplies.
* 100 W bulb for small (i.e., B/W or 13 inch color) monitors or TVs.
* 150-200 W bulb for large color monitors or projection TVs.
A 50/100/150 W (or similar) 3-way bulb in an appropriate socket comes
in
handy for this but mark the switch so that you know which setting is
which!
http://www.repairfaq.org/REPAIR/F_monfaq3.html#MONFAQ_005
and last but not least Webger's book - here's the link
http://books.google.com/books?id=lG8361HKf6kC&pg=RA2-PA328&lpg=RA2-PA328&dq=light+bulb+current+limiter&source=web&ots=2fTtDVsTfa&sig=j0FLDja1YmQhMVTl6oKBcE5DaUw
you're welcome :)
John King
Whut? You never been shocked? Must not work on or test live
circuits much...
J.P.
See schematic on alt.binaries.schematics.electronic ... oh yeah, the
green wire goes to the grnd terminal on plug... J.P.
Phil S.
"J.P." <jpa...@hotmail.com> wrote in message
news:t0fqq2d17pmg0dd6b...@4ax.com...
> See schematic on alt.binaries.schematics.electronic ... oh yeah, the
> green wire goes to the grnd terminal on plug... J.P.
LOL! I think I managed that one OK
Phil S.
"John King" <kin...@swbell.net> wrote in message
news:gE7rh.60431$qO4....@newssvr13.news.prodigy.net...
>
>> If the amp is more of a piggy than the work lamp the test light will glow
>> brighter, the more current you draw the brighter the test light.
>
>
> Right-O Brian... That is the one of the main reasons for the
> device in the first place. (1) It will only allow a certain amount
> of current to flow through the circuit depending on the wattage
> rating of the bulb (2) The more current the tested device draws, the
> brighter the bulb will glow, until it is at full intensity, then
> the current is limited to no more than that
Uhhuh...this is what I didn't get at first. I'm reasonably certain the
limter is built correctly. I just didn't have the courage to plug in
something I didn't understand.
John, how've you been. Haven't heard from you in a while. Glad to know you
are still around.
Regards,
Phil
John King
> "John King" <kin...@swbell.net> wrote in message
> news:gE7rh.60431$qO4....@newssvr13.news.prodigy.net...
>>> If the amp is more of a piggy than the work lamp the test light will glow
>>> brighter, the more current you draw the brighter the test light.
>>
>> Right-O Brian... That is the one of the main reasons for the
>> device in the first place. (1) It will only allow a certain amount
>> of current to flow through the circuit depending on the wattage
>> rating of the bulb (2) The more current the tested device draws, the
>> brighter the bulb will glow, until it is at full intensity, then
>> the current is limited to no more than that
>
> Uhhuh...this is what I didn't get at first. I'm reasonably certain the
> limter is built correctly. I just didn't have the courage to plug in
> something I didn't understand.
>
From your first description, it sounded like it should be wired OK.
The understanding of how it works as a limiter is all in Ohm's law.
> John, how've you been. Haven't heard from you in a while. Glad to know you
> are still around.
> Regards,
> Phil
I've been doing well and I trust the same is true for you(rs).
Yeah, I still pass through and read a bit now and then, but
I've bought an old motorcycle I'm fixing up, and post a lot on
a group involved with them.
Kind of peaked out on how many guitars and amps I can have around
here at one time, IOW I'm neck deep in them ;-) haven't been turning
them over as quickly as in the past. Need to sell off a bunch to
get the money to finish some projects that I've left laying around
for too long.
CYA,
John
>
Phil S.
> Phil S. wrote:
>> "John King" <kin...@swbell.net> wrote in message
>> news:gE7rh.60431$qO4....@newssvr13.news.prodigy.net...
>>>> If the amp is more of a piggy than the work lamp the test light will
>>>> glow brighter, the more current you draw the brighter the test light.
>>>
>>> Right-O Brian... That is the one of the main reasons for the
>>> device in the first place. (1) It will only allow a certain amount
>>> of current to flow through the circuit depending on the wattage
>>> rating of the bulb (2) The more current the tested device draws, the
>>> brighter the bulb will glow, until it is at full intensity, then
>>> the current is limited to no more than that
>>
>> Uhhuh...this is what I didn't get at first. I'm reasonably certain the
>> limter is built correctly. I just didn't have the courage to plug in
>> something I didn't understand.
>>
>
> From your first description, it sounded like it should be wired OK.
> The understanding of how it works as a limiter is all in Ohm's law.
>
>> John, how've you been. Haven't heard from you in a while. Glad to know
>> you are still around.
>> Regards,
>> Phil
>
> I've been doing well and I trust the same is true for you(rs).
> Yeah, I still pass through and read a bit now and then, but
> I've bought an old motorcycle I'm fixing up, and post a lot on
> a group involved with them.
Very nice. I suppose a change in venue is a good thing from time to time.
>
> Kind of peaked out on how many guitars and amps I can have around
> here at one time, IOW I'm neck deep in them ;-) haven't been turning
> them over as quickly as in the past. Need to sell off a bunch to
> get the money to finish some projects that I've left laying around
> for too long.
>
Maybe the 'cycle has temporarily relieved the GAS?
> CYA,
> John
>
Phil
David Axt
ground off the plug directly to the outlet.
For added testing capabilities I use a GFCI outlet instead of a normal 3
grounded outlet. The GFCI helped me find a very slight leak in a power
transformer that I would have otherwise not found.
-David
Phil S.
"David Axt" <daxtATpacifierDOTcom> wrote in message
news:12qqnem...@corp.supernews.com...
grounded and a proper faceplate on it. I didn't think about GFCI. It's an
interesting point. I bet that PT I've got with the CT in the frame would
blow a GFCI! That's not the one on the amp I'm about to blow...uh...power
up. Thanks.
Phil
Doggone
news:%n7rh.661970$1T2.55572@pd7urf2no:
> Hi,
> One thing when filament of lamp heats up, the resistance drops.
> So at initial power on, lamp will do good job as current surge
> limiter. Tony
You're having a senior moment Tony?
--
If it's not broken, fix it till it is.
Doggone
Why didn't I think of that. I'm installing one on my bench today.
Does anyone know if they'll still work on a variac at low voltage.
Dave Curtis
I haven't (and wouldn't) use a GFCI on the load side of the variac (I
doubt they'll work), but I have 2 GFCI circuits at the bench, and the
variac invariably gets plugged into one of them. I have the variac
(Powerstat, actually) and my series-bulb circuit mounted on a board
ready to plug in. One of the bulbs I have kickin around is a very old
250w blacklight bulb I got in a batch of old tubes.
FWIW, the GFCI has "found" 3 bad death caps to date, just by plugging
the amps in.
-Dave
mainm...@choiceonemail.com
Dave Curtis wrote:
> ready to plug in. One of the bulbs I have kickin around is a very old
> 250w blacklight bulb I got in a batch of old tubes.
Man, that's funny! I use a low power (25W?- i forget) "blacklight" bulb
for initial testing.
Is that a typo- 250W?
I thought most colored "party" bulbs were lower wattage?
-dave M.
Dave Curtis
<mainm...@choiceonemail.com> wrote:
>
>Dave Curtis wrote:
>> ready to plug in. One of the bulbs I have kickin around is a very old
>> 250w blacklight bulb I got in a batch of old tubes.
>
>Man, that's funny! I use a low power (25W?- i forget) "blacklight" bulb
>for initial testing.
>Is that a typo- 250W?
No. "250W 105-125V" It's a GE Purple-X "Burn intermittently only" and
"80 hours at 115V". Burn is the keyword; that sucker can get hot!
>I thought most colored "party" bulbs were lower wattage?
I guess they really knew how to party when this was made.
;o)
-Dave
Rich Koerner
Hi guys.
I've been really busy as hell knocking myself out on stuff that just has to get done around here.
However, I really miss some of you guys who are really trying to learn what free electrons are all
about, and thought I'd look in, and see if anything had improved in here.
But, this thread caught my attention, as being the most important thread I've seen in here in a long
freaking time. Not because of the use of a light bulb for current limiting. That's been here many
times before.
But, because of the comments and questions along the way from the experts, and those wanting to KNOW
and understand the control of the AC power source for units under test on the bench. This flashed me
back to a talk on this very subject I had here in the shop with one of the new fellows just starting
out a few months ago.
http://www.timeelect.com/internprg.htm
If it weren't for you guys wanting to learn, I wouldn't be here now. Not to mention, a few past
topics from here have found their way into an FAQ I decided to start on my site. Which is 400-PS
specific in nature.
But relates to this LINE CURRENT THING that is going on here. Likewise, the Class A and AB
questions thread prompted #24 to address the class of operation in the future. I've really never
seen so many ways to say the same thing in other words, and not really improve the clarity in a
thread. The difference in the technical and musical views, when mixed together, creates the fog.
You can't do that, and have clarity.
Ed Jahns made me aware of the importance of LINE CURRENT, and its many useful applications on the
test bench way back in the early 1970's.
For background:
http://www.timeelect.com/400-histy.htm
http://www.timeelect.com/6550a-ex.htm
http://www.timeelect.com/400-faq.htm
http://www.timeelect.com/400-PS-IDX.htm
Now, I'll get to the heart of the matter for the benefit of those who opened the door to what I've
long ago tried to promote here. That, is the usefulness of monitoring line current, to the point of
even setting the bias of a vacuum tube amplifier's the output stage using it.
To do this, you have to add to that AC power source on the test bench a few more things than the
hardware required to throw a light bulb in series with the AC power line to the unit under test.
Here, look again at this picture taken way back when Ed Jahns got me smart.
http://www.timeelect.com/6550a-ex.jpg
Look carefully at the shelf in front of me to my right. See that gray panel with those two big
panel meters, and one big ass knob. That is exactly what Ed Jahns REQUIRED for final setup and test
on the Fender 400-PS assembly line back then.
You are looking at... from the 400 FAQ....
TEST EQUIPMENT REQUIRED:
1- 0 to 150 volt 60 Hz A.C. voltmeter 2% accuracy
1- G.R. Variac type W10M, 13A 0-140v.
1- Weston 0-10 Amperes Iron Vane R.M.S. meter model 1944-2%
mounted into a rack panel. Yes, it's a basic metered variac. But, it has been modified for add
on's, or plug in's too.
Using a switch or two, some binding posts, etc.... without any disconnect of the two main analog
meters on the panel, make previsions to switch in or out a digital current meter, and/or a light
bulb socket.
You may want to provide an ADDITIONAL safety device on the digital meter's low current range setup
too. We all make mistakes and unexpected current spikes can happen. An additional fuse holder in
line with the right fast acting fuse saves time playing with the digital meter replacing fuses.
BTW, those two big analog meters do things digital meter can't. Like show the different startup
bump patterns in line current. Learn what those different patterns look like, and what they mean.
With the accuracy of the low current range of the digital current meters available, you can set bias
on amplifiers with prior line current AND voltage specs, that you develop and record by *tubes used*
for each *model* of unit under test. You learn to keep records.
Talk about a time saver. Accuracy? Dead nuts!!!!!!!!!!!!!!!!!
What? You think a few ma. difference in plate current will get LOST, and won't be detected as an
accurate change in line current by that digital current meter?
You can set bias by line current.
You can identify Polished Turds in a heartbeat!!!!!!!!!!!!!!!!!!!!
You can find otherwise un-noticed trapped energy in a test unit not getting to the loads too.
You'll find *where* in minutes, when normally it can take hours, if not days.
Is it the power transformer, filter cap, output transformer, out of spec output tubes, etc.. that
is the cause of the problem?
If you want to know what's going on every second the unit is under test in BOTH static and dynamic
conditions.... then you have to learn the details in line current monitoring of your test subjects.
You have to KNOW, how much energy is pulled from the wall at all times, for output comparison.
For Ohm's Law to be useful, you have to have two components to find the third.
Here,.... in AGA, as well as other like forums, the focus is always placed on the DIRECT voltage
measurement. Never the DIRECT current measurement.
The best it gets is a voltage drop across a resistor, for indirect current measurement. You can't
live by THAT alone, in the world of free electrons.
What resistor are you going to put in series with the AC line cord to find the current pulled from
the wall?
A light bulb only indicates only so much. Learn the rest of the story. Add the METER!!!!!!!!!!!!!
<thinking>
THANKS Miles for providing the code which I swiped for my FAQ page!!!!!!!!!!!!!!!!
How's it going.
Regards,
Rich Koerner,
Time Electronics.
http://www.timeelect.com
Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
PMG
Just passing through?
You didn't even get the explanation gun warmed up!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!<||||||||||||||||>!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
On Wed, 17 Jan 2007 10:28:44 -0500, Rich Koerner <ri...@timeelect.com>
wrote:
--
We figured out how to travel through time
at the speed of regular time... with plastic bags.
--Nathan Explosion
John King
Hey Rich,
Been meaning to call you with some Fender Bass-VI questions...
You are THE MAN for those questions I'm sure.
Here I thought I was doing all good by documenting this old
thing put together ages ago:
http://www.catoosatrading.com/light_bulb_current_limiter.html
Then along come the other guys making me want it to incorporate
a GFCI, and now you make me want amp and volt meters in it too!!!
Oh well, it (my simple DIY bulb limiter) does help a lot, but
I agree completely, it only tells the tip of the iceberg about
what is really going on down the electron stream.
Curses! Nothings ever good enough around here without someone
coming along and making you want something better!
J.P.
Did you ever get yourself a Dremel? J.P.
Phil S.
Not yet. I'll be on the lookout for one. It's not an immediate priority.