In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?
Thanks,
Ross NS7F

On Jun 12, 5:00 pm, "Ross, NS7F" wrote:
In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?
Thanks,
Ross NS7F

Depends on the tubes . If the two are same type ,you can series
them ,no problem.. If the two tubes draw different current,then you
can use a parallel resistor to equal the current in each tube...Old
radio amateurs handbook is a good source fr this inf... GL W4PQW

Ross, NS7F wrote:
In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?
Thanks,
Ross NS7F

I'm an almost tube newbie, but here's what I know of this, in order of
importance:

* the tubes have to draw the same current, else one tube will get too
hot and the other will run cold.

* some tubes take longer to warm up than others. When they started
putting color TV's together with long strings of filaments that added up
to 110V, they also instituted "controlled warm-up" filaments so they'd
all warm up in about the same amount of time. I don't know if this is
such a big deal at 12V.

* If you're doing really low-level audio (or a VFO for that matter), the
filament can "talk" to the cathode a little bit. Running your 6V tubes
from a winding with a center tap will minimize this. Running the
filament slightly positive (I think) to the cathode will suppress issues
of the filament emitting electrons that bias the cathode. Building your
circuits so the cathode goes to a hard ground will significantly
minimize these effects, at the cost of quite a bit of circuit
convenience, although you see it done.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Jun 13, 8:11 am, " wrote:
On Jun 12, 5:00 pm, "Ross, NS7F" wrote:

In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?
Thanks,
Ross NS7F

Depends on the tubes . If the two are same type ,you can series
them ,no problem.. If the two tubes draw different current,then you
can use a parallel resistor to equal the current in each tube...Old
radio amateurs handbook is a good source fr this inf... GL W4PQW

hi yes i agree with w4pqw........

bob vk4la

"Tim Wescott" wrote in message
news
Ross, NS7F wrote:
In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?
Thanks,
Ross NS7F


* some tubes take longer to warm up than others. When they started
putting color TV's together with long strings of filaments that added up
to 110V, they also instituted "controlled warm-up" filaments so they'd all
warm up in about the same amount of time. I don't know if this is such a
big deal at 12V.

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


A suffix tubes I believe will work in series string (providing the
filament currents are the same that is..).

Pete

Ross, NS7F wrote:
In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?

You can, but the tube filaments won't last as long because of the turn-on
surge. If it's a circuit where the tubes fail with poor emission long before
the filament fails, that's fine.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In message , Scott Dorsey
writes
Ross, NS7F wrote:
In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?

You can, but the tube filaments won't last as long because of the turn-on
surge. If it's a circuit where the tubes fail with poor emission long before
the filament fails, that's fine.
--scott

I don't get it. Maybe I'm a bit thick, but why would the turn-on surge
higher? Provided the filament current is the same for both tubes, I
wouldn't have thought that it would have made any difference. In the
good old days, I'm sure that I have connected up 12AX7/12AU7/12AT7
heaters (12.6V centre-tap) to run off 12.6V (pinout =
anode-grid-cathode-heater-heater-anode-grid cathode-heater CT). Would
the switch-on surge be less if they were run connected for 6.3V?
Ian.
--

Ian Jackson wrote:
I don't get it. Maybe I'm a bit thick, but why would the turn-on surge
higher?

When you turn it on, the filament resistance is very low, BUT even worse,
the tube is in series with another tube whose resistance is ALSO very low.

Watch a series string device like an AA5 radio or a TV set turn on... the
filaments get VERY bright, then they drop down to normal brightness after
a second or so. There are tubes designed to deal with that, but not all
of them are.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In message , Scott Dorsey
writes
Ian Jackson wrote:
I don't get it. Maybe I'm a bit thick, but why would the turn-on surge
higher?

When you turn it on, the filament resistance is very low, BUT even worse,
the tube is in series with another tube whose resistance is ALSO very low.

Watch a series string device like an AA5 radio or a TV set turn on... the
filaments get VERY bright, then they drop down to normal brightness after
a second or so. There are tubes designed to deal with that, but not all
of them are.
--scott

Nope. I still don't see the difference between a single 6.3V filament
fed from a 6.3V source, and 2 x 6.3 V filaments in series fed from a
12.6V source.

What you say is true. When you turn it on, the (cold) filament
resistance will be low, and there will be a current surge. What you see
is a heart-stopping bright-up of the filament, before it dims to normal
brightness.

However, you could argue that, with a single filament, it is in series
with nothing, other than the resistance of the transformer. As this will
probably be lower than that of a 12.6V transformer, the surge could be
higher. But this doesn't really hold water either, as you only have 6.3V
driving it.

Ian.
--

Ian Jackson wrote:
In message , Scott Dorsey
writes
Ian Jackson wrote:
I don't get it. Maybe I'm a bit thick, but why would the turn-on surge
higher?

When you turn it on, the filament resistance is very low, BUT even worse,
the tube is in series with another tube whose resistance is ALSO very
low.

Watch a series string device like an AA5 radio or a TV set turn on... the
filaments get VERY bright, then they drop down to normal brightness after
a second or so. There are tubes designed to deal with that, but not all
of them are.
--scott

Nope. I still don't see the difference between a single 6.3V filament
fed from a 6.3V source, and 2 x 6.3 V filaments in series fed from a
12.6V source.

What you say is true. When you turn it on, the (cold) filament
resistance will be low, and there will be a current surge. What you see
is a heart-stopping bright-up of the filament, before it dims to normal
brightness.

However, you could argue that, with a single filament, it is in series
with nothing, other than the resistance of the transformer. As this will
probably be lower than that of a 12.6V transformer, the surge could be
higher. But this doesn't really hold water either, as you only have 6.3V
driving it.

Ian.

The only case where series is a problem is if one of the filaments heats
up more quickly than the rest. Because filament resistance is very
nonlinear, and changes about 30-to-1 in value from cold to hot, the
filament that heats up first will be drastically overloaded for a brief
period.

Most modern (if I can use that term) filaments are of the controlled heating
variety and should be ok in a series configuration.

-Chuck