Al wrote:
In article ,
kenneth scharf wrote:


Paul Keinanen wrote:

On Wed, 29 Oct 2003 23:28:28 +0200, "Deos"
wrote:



the 6.3 VAC is ok ,no need to go into the fuss for dc.
dont take my word for it, after making the nice rig put some diodes on the
ac line and you will not see anythig special..


Using a single floating 6.3V secondary winding with a potentiometer
connected across it and the wiper connected to the ground and adjusted
for minimum hum should be enough.

This kind of system works quite well when you have a single high
sensitivity input (such as in a radio receiver), but if you have
multiple sensitive inputs (as in audio mixing consoles) you would need
a separate filament winding for each input tube, in order to be able
to adjust the filament balance without compromises. In such situations
a DC filament system would be simpler to implement.

Paul OH3LWR


Except for high gain AF stages, a center tapped filament winding with the
center tap grounded should be ok. Otherwise a resistor of a few hundred to
a few thousand ohms from each side to ground (resistors of identical value).
Use of a pot is probably overkill, but if you have one in the junk box and
room to mount it ok.



Maybe he's thinking about the antique radio sets which just ran off
batteries. Weren't the filaments run off 6 Vdc?

Al


Old radios used 5v tubes off 6v batteries and a rheostat to control filament
voltage. I was talking about using resistors to create a center tap for
a transformer
without one. While this was used to power directly heated tubes off ac,
it could be
used as a hum balance for heater cathode types.

Al wrote:
In article ,
kenneth scharf wrote:


Paul Keinanen wrote:

On Wed, 29 Oct 2003 23:28:28 +0200, "Deos"
wrote:



the 6.3 VAC is ok ,no need to go into the fuss for dc.
dont take my word for it, after making the nice rig put some diodes on the
ac line and you will not see anythig special..


Using a single floating 6.3V secondary winding with a potentiometer
connected across it and the wiper connected to the ground and adjusted
for minimum hum should be enough.

This kind of system works quite well when you have a single high
sensitivity input (such as in a radio receiver), but if you have
multiple sensitive inputs (as in audio mixing consoles) you would need
a separate filament winding for each input tube, in order to be able
to adjust the filament balance without compromises. In such situations
a DC filament system would be simpler to implement.

Paul OH3LWR


Except for high gain AF stages, a center tapped filament winding with the
center tap grounded should be ok. Otherwise a resistor of a few hundred to
a few thousand ohms from each side to ground (resistors of identical value).
Use of a pot is probably overkill, but if you have one in the junk box and
room to mount it ok.



Maybe he's thinking about the antique radio sets which just ran off
batteries. Weren't the filaments run off 6 Vdc?

Al


Old radios used 5v tubes off 6v batteries and a rheostat to control filament
voltage. I was talking about using resistors to create a center tap for
a transformer
without one. While this was used to power directly heated tubes off ac,
it could be
used as a hum balance for heater cathode types.

HAVE YOU EVER HEARD OF
DRILLING LOTS OF SMALLER HOLES AROUND
THE DIAMATER , UNTILL THE CENTER DROPS OUT
AND THEN FILLING THE EDGES SMOOTH


THE GOOD OLD FLE WORKS WONDERS ...HMMMM


DE PAUL

HAVE YOU EVER HEARD OF
DRILLING LOTS OF SMALLER HOLES AROUND
THE DIAMATER , UNTILL THE CENTER DROPS OUT
AND THEN FILLING THE EDGES SMOOTH


THE GOOD OLD FLE WORKS WONDERS ...HMMMM


DE PAUL

In article , W7TI
writes:

On Sat, 8 Nov 2003 13:27:07 -0000, "uk-hamman"
wrote:

HAVE YOU EVER HEARD OF
DRILLING LOTS OF SMALLER HOLES AROUND
THE DIAMATER , UNTILL THE CENTER DROPS OUT
AND THEN FILLING THE EDGES SMOOTH

THE GOOD OLD FLE WORKS WONDERS ...HMMMM
_________________________________________________ ________

This is how our Neanderthal ancestors did it, and if it was good enough
for them....
--
Bill, W7TI

Practically speaking (as one neanderthal to another...):

That method does work if there's no drill press available. But, be
sure to buy an extra drill bit for the size desired going around the
rim. Had to do that with a 4 1/4" diameter speaker hole in an 1/8"
aluminum rack panel (alloy tougher than 2024 but not as stiff as
6061). That included light oil lubrication. The "center" didn't
"drop right out" but centerpunching the many holes right allowed
using old wire cutters to snip the narrow left-overs between holes.

A Hand File to complete?!?!? Good grief, no. A Dremel Moto-Tool
with several "mill type" cutter bits is much preferred to smooth out
the rough edges. Note: Home Depot, Lowe's, Do-It-Centers, OSH,
all carry extra bits for Dremel Moto-Tools, many which aren't
included in the Dremel kits. Use a biggie mill cutter to hog out the
worst, go to a small bit to smooth those edges. One of several
grind wheels can be used to finish it off. Takes a steady hand
(usually both hands if panel is in a vise).

Absolutely needed: A scribe marked circle on the panel as a guide!
Maybe two concentric circles, the inner one slightly smaller than
desired as a "target." If one gets sloppy, it's possible to cut farther
out than the inner, smaller "target" circle. To get the scribed circle,
use a grade-school compass in REVERSE, the "pencil" part in a
small drill hole at center, the "center" part (pointy end) doing the
scribing.

Dremel also makes a dandy mini-drill-press stand for the Moto-Tool
which is just lovely for through-hole PCB drilling. I use one for that
plus the AC line voltage adjusted with a Powerstat (Superior Electric)
variable autotransformer to control the "drill press" speed. BTW,
liquid hand soap, slightly diluted, works out as a PCB drilling
lubricant and washes out with hot water...and can be used with a
rough-surface sponge to buff out surface oxidation on the copper
foil or removing tiny burrs in the drill holes.

Len Anderson
retired (from regular hours) electronic engineer person

In article , W7TI
writes:

On Sat, 8 Nov 2003 13:27:07 -0000, "uk-hamman"
wrote:

HAVE YOU EVER HEARD OF
DRILLING LOTS OF SMALLER HOLES AROUND
THE DIAMATER , UNTILL THE CENTER DROPS OUT
AND THEN FILLING THE EDGES SMOOTH

THE GOOD OLD FLE WORKS WONDERS ...HMMMM
_________________________________________________ ________

This is how our Neanderthal ancestors did it, and if it was good enough
for them....
--
Bill, W7TI

Practically speaking (as one neanderthal to another...):

That method does work if there's no drill press available. But, be
sure to buy an extra drill bit for the size desired going around the
rim. Had to do that with a 4 1/4" diameter speaker hole in an 1/8"
aluminum rack panel (alloy tougher than 2024 but not as stiff as
6061). That included light oil lubrication. The "center" didn't
"drop right out" but centerpunching the many holes right allowed
using old wire cutters to snip the narrow left-overs between holes.

A Hand File to complete?!?!? Good grief, no. A Dremel Moto-Tool
with several "mill type" cutter bits is much preferred to smooth out
the rough edges. Note: Home Depot, Lowe's, Do-It-Centers, OSH,
all carry extra bits for Dremel Moto-Tools, many which aren't
included in the Dremel kits. Use a biggie mill cutter to hog out the
worst, go to a small bit to smooth those edges. One of several
grind wheels can be used to finish it off. Takes a steady hand
(usually both hands if panel is in a vise).

Absolutely needed: A scribe marked circle on the panel as a guide!
Maybe two concentric circles, the inner one slightly smaller than
desired as a "target." If one gets sloppy, it's possible to cut farther
out than the inner, smaller "target" circle. To get the scribed circle,
use a grade-school compass in REVERSE, the "pencil" part in a
small drill hole at center, the "center" part (pointy end) doing the
scribing.

Dremel also makes a dandy mini-drill-press stand for the Moto-Tool
which is just lovely for through-hole PCB drilling. I use one for that
plus the AC line voltage adjusted with a Powerstat (Superior Electric)
variable autotransformer to control the "drill press" speed. BTW,
liquid hand soap, slightly diluted, works out as a PCB drilling
lubricant and washes out with hot water...and can be used with a
rough-surface sponge to buff out surface oxidation on the copper
foil or removing tiny burrs in the drill holes.

Len Anderson
retired (from regular hours) electronic engineer person