Discussion:
6,3V for heaters...but?
(too old to reply)
Tommy Dale
2003-11-25 16:35:23 UTC
Permalink
When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?

I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?

Tommy
Phil Symonds
2003-11-25 19:42:05 UTC
Permalink
Post by Tommy Dale
When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?
I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?
Tommy
It's gotta be 6.3 + 6.3 or you couldn't supply a 12AX7 and the like.
Unless, of course, you've got some oddball tranny.
Phil
nuke
2003-11-25 20:16:35 UTC
Permalink
<< It's gotta be 6.3 + 6.3 or you couldn't supply a 12AX7 and the like.
Unless, of course, you've got some oddball tranny.
Phil
Post by nuke
<BR><BR>
No, Phil, a 12AX7 is designed to operate with either a 12v or a 6v filament
supply. Most guitar amps run all the filaments at 6.3vac.

In the 12A_7 series of tubes, the filaments in the two sections can be wired as
series for 12v operation, or in parallel for 6.3v operation.


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Phil Symonds
2003-11-25 22:11:21 UTC
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Post by nuke
<< It's gotta be 6.3 + 6.3 or you couldn't supply a 12AX7 and the like.
Unless, of course, you've got some oddball tranny.
Phil
Post by nuke
<BR><BR>
No, Phil, a 12AX7 is designed to operate with either a 12v or a 6v filament
supply. Most guitar amps run all the filaments at 6.3vac.
In the 12A_7 series of tubes, the filaments in the two sections can be wired as
series for 12v operation, or in parallel for 6.3v operation.
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Oops! I oughta know better, Nuke. Thanks for clarifying. Sorry Tommy for
bad info.
Phil
JTM50
2003-11-25 22:40:28 UTC
Permalink
Post by nuke
<< It's gotta be 6.3 + 6.3 or you couldn't supply a 12AX7 and the like.
Unless, of course, you've got some oddball tranny.
Phil
Post by nuke
<BR><BR>
No, Phil, a 12AX7 is designed to operate with either a 12v or a 6v filament
supply. Most guitar amps run all the filaments at 6.3vac.
In the 12A_7 series of tubes, the filaments in the two sections can be wired as
series for 12v operation, or in parallel for 6.3v operation.
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While were discussing the topic: What about DC heater supplies?
What is the correct DC voltage for 12a_7 tubes?

Lloyd
RonSonic
2003-11-26 01:08:43 UTC
Permalink
Post by JTM50
c: What about DC heater supplies?
What is the correct DC voltage
The reason we so often measure AC voltage in RMS is that it is equivalent to the
same DC voltage value with no conversion required.

IOW 6.3Vrms is just as capable of driving a heater as is 6.3VDC.

If we're designing an amp and want to describe the AC voltage of the signal at
some point, then peak to peak or Peak is more convenient, but for purposes of
heaters and lamps RMS is simplest and equates to the same DC value.

Ron
nuke
2003-11-26 12:04:06 UTC
Permalink
<< While were discussing the topic: What about DC heater supplies?
What is the correct DC voltage for 12a_7 tubes?

Lloyd >><BR><BR>


It's the same, DC or AC. The AC value is RMS which means it has the same
heating value as DC of the same voltage.

For a 12AX7, depending on how it is wired for operation, 6.3v or 12.6v, DC or
AC RMS at 300ma or 150ma respectively.




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stringbend
2003-11-25 22:27:07 UTC
Permalink
Post by Phil Symonds
Post by Tommy Dale
When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?
I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?
Tommy
It's gotta be 6.3 + 6.3 or you couldn't supply a 12AX7 and the like.
Unless, of course, you've got some oddball tranny.
Phil
Damn. I thought 6.3VCT meant 3.15 from each leg to the center-tap and
the expected 6.3 *across* the leads, just like you'd want. In other
words, I think 'the guy' is right, depending I suppose on how you
interpret what he said.

Chances are, if he knows what he's doing at all, he'll build you a
6.3VCT as you need. (He's built tube power trannys before, right?).

stringbend
nuke
2003-11-25 20:14:42 UTC
Permalink
<< When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?

I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?

Tommy >><BR><BR>

This is the classic Fender design. You ground the CT and connect each 3.15v tap
to your filaments. The ground at the CT helps to reduce hum and references the
6.3vac to the chassis ground without favoring one side.

I'd consider grounding the CT through a 50ohm resistor, in case something
shorts to protect the transormer.

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Tommy Dale
2003-11-25 20:42:33 UTC
Permalink
Post by nuke
This is the classic Fender design. You ground the CT and connect each 3.15v tap
to your filaments. The ground at the CT helps to reduce hum and references the
6.3vac to the chassis ground without favoring one side.
But usually, in most designs, it's 6,3 + 6,3, right?
Post by nuke
I'd consider grounding the CT through a 50ohm resistor, in case something
shorts to protect the transormer.
I'm a bit new at this. What exactely will prevent the tranny from blowing,
if you put a 50 ohm resistor between the center tap and ground?

Tommy.
Recruiterman
2003-11-26 00:38:46 UTC
Permalink
Post by Tommy Dale
Post by nuke
I'd consider grounding the CT through a 50ohm resistor, in case something
shorts to protect the transormer.
I'm a bit new at this. What exactely will prevent the tranny from blowing,
if you put a 50 ohm resistor between the center tap and ground?
Tommy.
I always use 2 - 100 ohm resistors to make an artificial "center tap". Even
if the tranny has a center tap, I'll just tape it out of the way, and use
the resistors as the tap, not both. The resistors act as a "fuse" to prevent
damage to the tranny in the case of a short. To give you an example of how
these resistors can save your tranny, I was checking some voltages on the
power tubes of my rebuilt DRRI with my meter. I accidentally touched two
pins of one of the power tubes with my meter probe. I should have used
insulated alligator clips but I was just doing some quick measurements, so I
used the straight probe. When the probe touched both of the pins, there was
a pretty spectacular electrical arc (fire) between the pins, and the 2 - 100
ohm carbon comp resistors that I used to create the artificial center tap
started to smoke and burnt up in a flash, both actually burned in half. If
those resistors weren't there, that surge would have went straight into my
tranny and it probably would have been toast. I'll sacrifice $.50 worth of
resistors to protect a $50.00 tranny any day.

Mikey
Tommy Dale
2003-11-26 22:33:34 UTC
Permalink
Post by Recruiterman
I always use 2 - 100 ohm resistors to make an artificial "center tap". Even
if the tranny has a center tap, I'll just tape it out of the way, and use
the resistors as the tap, not both. The resistors act as a "fuse" to prevent
damage to the tranny in the case of a short. To give you an example of how
these resistors can save your tranny, I was checking some voltages on the
power tubes of my rebuilt DRRI with my meter. I accidentally touched two
pins of one of the power tubes with my meter probe. I should have used
insulated alligator clips but I was just doing some quick measurements, so I
used the straight probe. When the probe touched both of the pins, there was
a pretty spectacular electrical arc (fire) between the pins, and the 2 - 100
ohm carbon comp resistors that I used to create the artificial center tap
started to smoke and burnt up in a flash, both actually burned in half. If
those resistors weren't there, that surge would have went straight into my
tranny and it probably would have been toast. I'll sacrifice $.50 worth of
resistors to protect a $50.00 tranny any day.
I see.

What I have a problem with understanding, is how you can connect both the
wires for heaters to ground, through a 100 Ohm resistor, and still have
current for the heaters. I would imagine that the current would go to
ground... Or even...why do I have to ground the heaters at all? Will the
heaters heat if I don't ground anything at all, just connect the heaters in
paralell, without any ground?

Tommy
Recruiterman
2003-11-27 05:09:37 UTC
Permalink
Post by Tommy Dale
I see.
What I have a problem with understanding, is how you can connect both the
wires for heaters to ground, through a 100 Ohm resistor, and still have
current for the heaters. I would imagine that the current would go to
ground... Or even...why do I have to ground the heaters at all? Will the
heaters heat if I don't ground anything at all, just connect the heaters in
paralell, without any ground?
Tommy
Tommy, what you do, is to run your heater wires (green) from the PT to the
pilot light. On the Fenders, there's 2 separate metal (arms) that the wires
will attach to, one wire for each arm. This is what powers the pilot light,
so that it lights when you turn the power on. From both of those metal arms
on the pilot light fixture, you going to run a twisted pair of wires to your
first power tube, then from that tube to the next power tube, then on down
to the preamp tubes, one after another until you reach the last tube. From
those 2 metal arms on the pilot light fixture, you'll solder a 100 ohm
resistor to each of those arms, where the heater wires from the tranny
connect, and where you added the additional twisted pair to run to the first
power tube.

Once you solder both of those resistors to the pilot light, you can then
solder the other ends of the resistors to a ring terminal, which you can
then attach to one of the PT mounting bolts. I have my 100 ohm resistors
mounted on my board, so I just run the twist pair from the pilot light to
the turrets where I have my 100 ohm resistors (connected to ground), then I
run another twisted pair from those turrets to my first power tube, and then
on down the line from there. The heater wires from the PT will heat the
tubes, even if you don't ground the heater wires, either by using the 2 -
100 ohm resistors, or by using the center tap if the PT has one. BUT, if you
don't either ground the center tap, or, ground the heater wires through the
100 ohm resistors, you're gonna get hummmmmm, not good. I like grounding
the heater wires through the 100 ohm resistors personally, I like the extra
protection that the resistors provide. Those 2 carbon comp 1/2 watt
resistors have already saved my PT once already.

Mikey
RonSonic
2003-11-26 01:04:20 UTC
Permalink
Post by Tommy Dale
When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?
I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?
6.3VAC center tapped is 3.15-0-3.15. Yeah, the tranny winder knows what he's
talking about.

Ron
Tommy Dale
2003-11-26 22:31:33 UTC
Permalink
Post by RonSonic
Post by Tommy Dale
When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?
I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?
6.3VAC center tapped is 3.15-0-3.15. Yeah, the tranny winder knows what he's
talking about.
So this is how most power transformers are made. Why does it say 6,3V for
heaters, when it's actually 3,15?

To make my question simple: Most tube amps have 6,3V listed for their
heaters. Does the trannies ever have 6,3 - 6,3 ? or is it always 3,15 -
3,15...or is the difference here wether the trannyhas a center tap or not?

Does a tranny with no center tap need to have 6,3 - 6,3, and with a center
tap 3,15 - 0 - 3,15 ?
RonSonic
2003-11-26 23:20:38 UTC
Permalink
Post by Tommy Dale
Post by RonSonic
Post by Tommy Dale
When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?
I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?
6.3VAC center tapped is 3.15-0-3.15. Yeah, the tranny winder knows what
he's
Post by RonSonic
talking about.
So this is how most power transformers are made. Why does it say 6,3V for
heaters, when it's actually 3,15?
Because it IS actually 6.3V you can look at it as 6.3 with a CT or as two 3.15
windings in series.
Post by Tommy Dale
To make my question simple: Most tube amps have 6,3V listed for their
heaters. Does the trannies ever have 6,3 - 6,3 ? or is it always 3,15 -
3,15...or is the difference here wether the trannyhas a center tap or not?
The former would be 12.6 center-tapped, yeah that exists but isn't what we're
talking about.
Post by Tommy Dale
Does a tranny with no center tap need to have 6,3 - 6,3, and with a center
tap 3,15 - 0 - 3,15 ?
If it has no CT it's just plain 6.3. You might look at the two leads as 0-6.3
to keep the same nomenclature but nobody bothers.

On your question from the other post, the two 100 Ohm resistors add up to 200
Ohms from tap to tap and in the world of heaters, that's a big resistor. You'll
only lose about 30 mA's that way which is trivial. My experience is that a CT to
ground is quieter and I'm not convinced of any safety or ruggedness advantage in
case of misadventure.

Ron
Tommy Dale
2003-11-27 15:23:22 UTC
Permalink
Post by RonSonic
The former would be 12.6 center-tapped, yeah that exists but isn't what we're
talking about.
A good thing I asked about this. I would have ordered a 6,3 - 0 - 6,3 and
believed it would have given me 6,3V for the heaters.

So even if I don't use the center tap, but two 100 Ohm in stead of, I still
want 3,15 - 0 - 3,15

Tommy
Miles O'Neal
2003-11-27 16:25:00 UTC
Permalink
Post by Tommy Dale
A good thing I asked about this. I would have ordered a 6,3 - 0 - 6,3 and
believed it would have given me 6,3V for the heaters.
Well, you can use it that way, just putting
some of the heaters across one half, and some
across the other half.
Post by Tommy Dale
So even if I don't use the center tap, but two 100 Ohm in stead of, I
still want 3,15 - 0 - 3,15
Well, you want a 6.3V heater secondary. If
you get one with a center tap, the standard
way of referring to this is 6.3V center-tapped,
or 6.3V CT. But whether you get a CT doesn't
really matter if you don't plan to use it.

-Miles


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RonSonic
2003-11-28 01:47:06 UTC
Permalink
Post by Tommy Dale
Post by RonSonic
The former would be 12.6 center-tapped, yeah that exists but isn't what
we're
Post by RonSonic
talking about.
A good thing I asked about this. I would have ordered a 6,3 - 0 - 6,3 and
believed it would have given me 6,3V for the heaters.
So even if I don't use the center tap, but two 100 Ohm in stead of, I still
want 3,15 - 0 - 3,15
Get a tranny with a 6.3V winding, center tapped or not. That's all you gotta ask
for. If you say "6.3 without a tap," that's whacha get. If you say "6.3V CT"
you'll get the 3-0-3.

Yes, it IS a little confusing. I just pray there's no confusion about the HT
winding and what sort of rectifier you'll be using. :-)

Ron
Jimmy
2003-11-28 10:03:20 UTC
Permalink
IF your 6.3 volt fil xformer has a centertap it is probably there for hum
reduction. Grounding either side of the filament string will often reduce
hum but better yet is grounding the centertap if the xformer has one. If no
centertap you can make one by connecting each side of the filament string to
ground through a resistor.
Post by Tommy Dale
When the spec's for a transformer is 6,3V for heaters, with a center tap,
does each heater wire measure 6,3V, or do they measure 3,15 each?
I'm about to order a custom made transformer, and the guy suggested 3,15V
for each lead, with a center tap...but that won't work, will it?...or?
Tommy
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