Hello!
When a tube radio is first turned on, what is the tube filament resistance, high or low? Then what happens to this resistance as the radio is played for awhile?
Thank you!!
Daniel

:Hello!
: When a tube radio is first turned on, what is the tube filament resistance, high or low? Then what happens to this resistance as the radio is played for awhile?
:Thank you!!
:Daniel

The resistance is low at first, and increases with temperature.
Lewis
:

::Hello!
:: When a tube radio is first turned on, what is the tube filament resistance, high or low? Then what happens to this resistance as the radio is played for awhile?
::Thank you!!
::Daniel
:
:
:The resistance is low at first, and increases with temperature.
:Lewis
::
:
:
Yes, at set turn-on with stone cold tubes the filament resistance will be low, and you can pull a tubes and ohm it to see what the actual value is. After power on, the filament temperature rises very quickly (in mere milliseconds) and so does its resistance. The reason sleeved-cathode tubes (such as a 6J5, as a random example) take 20-30 seconds to start to operate is that the filament has to heat up the cathode sleeve until it is hot enough to start emitting electrons. A directly-emitting tube (such as the rectifier type 80) will start to operate seemingly immediately, because there is no cathode sleeve to heat up.(Actually it still takes several milliseconds to come up to operating temperature, but the short time lag is imperceptible to humans.)

This turn-on phase is deleterious to tube life because it stresses the filament. Some manufacturers recognized this in the 1960s and began to produce sets that never really shut off filament power- it just reduced it, leaving the tubes ready for a warm start. That way, the set could have an "instant on" feature like solid-state units but with greatly enhanced tube life for most installations.

:::Hello!
::: When a tube radio is first turned on, what is the tube filament resistance, high or low? Then what happens to this resistance as the radio is played for awhile?
:::Thank you!!
:::Daniel
::
::
::The resistance is low at first, and increases with temperature.
::Lewis
:::
::
::
:Yes, at set turn-on with stone cold tubes the filament resistance will be low, and you can pull a tubes and ohm it to see what the actual value is. After power on, the filament temperature rises very quickly (in mere milliseconds) and so does its resistance. The reason sleeved-cathode tubes (such as a 6J5, as a random example) take 20-30 seconds to start to operate is that the filament has to heat up the cathode sleeve until it is hot enough to start emitting electrons. A directly-emitting tube (such as the rectifier type 80) will start to operate seemingly immediately, because there is no cathode sleeve to heat up.(Actually it still takes several milliseconds to come up to operating temperature, but the short time lag is imperceptible to humans.)
:
:This turn-on phase is deleterious to tube life because it stresses the filament. Some manufacturers recognized this in the 1960s and began to produce sets that never really shut off filament power- it just reduced it, leaving the tubes ready for a warm start. That way, the set could have an "instant on" feature like solid-state units but with greatly enhanced tube life for most installations.
:
Thank you very much for the information.

:::Hello!
::: When a tube radio is first turned on, what is the tube filament resistance, high or low? Then what happens to this resistance as the radio is played for awhile?
:::Thank you!!
:::Daniel
::
::
::The resistance is low at first, and increases with temperature.
::Lewis
:::
::
::
:Yes, at set turn-on with stone cold tubes the filament resistance will be low, and you can pull a tubes and ohm it to see what the actual value is. After power on, the filament temperature rises very quickly (in mere milliseconds) and so does its resistance. The reason sleeved-cathode tubes (such as a 6J5, as a random example) take 20-30 seconds to start to operate is that the filament has to heat up the cathode sleeve until it is hot enough to start emitting electrons. A directly-emitting tube (such as the rectifier type 80) will start to operate seemingly immediately, because there is no cathode sleeve to heat up.(Actually it still takes several milliseconds to come up to operating temperature, but the short time lag is imperceptible to humans.)
:
:This turn-on phase is deleterious to tube life because it stresses the filament. Some manufacturers recognized this in the 1960s and began to produce sets that never really shut off filament power- it just reduced it, leaving the tubes ready for a warm start. That way, the set could have an "instant on" feature like solid-state units but with greatly enhanced tube life for most installations.
: Here's a good one. On sets with a pilot lamp, the lamp gets real bright when first turned on for a second, then goes real dim as the filaments get warmed up. THEN when the set is up & ready to work, why does the pilot lamp get brighter. It goes from bright to dim then bright. Does the filament resistance get less as it gets warmer?

:::Hello!
::: When a tube radio is first turned on, what is the tube filament resistance, high or low? Then what happens to this resistance as the radio is played for awhile?
:::Thank you!!
:::Daniel
::
::
::The resistance is low at first, and increases with temperature.
::Lewis
:::
::
::
:Yes, at set turn-on with stone cold tubes the filament resistance will be low, and you can pull a tubes and ohm it to see what the actual value is. After power on, the filament temperature rises very quickly (in mere milliseconds) and so does its resistance. The reason sleeved-cathode tubes (such as a 6J5, as a random example) take 20-30 seconds to start to operate is that the filament has to heat up the cathode sleeve until it is hot enough to start emitting electrons. A directly-emitting tube (such as the rectifier type 80) will start to operate seemingly immediately, because there is no cathode sleeve to heat up.(Actually it still takes several milliseconds to come up to operating temperature, but the short time lag is imperceptible to humans.)
:
:This turn-on phase is deleterious to tube life because it stresses the filament. Some manufacturers recognized this in the 1960s and began to produce sets that never really shut off filament power- it just reduced it, leaving the tubes ready for a warm start. That way, the set could have an "instant on" feature like solid-state units but with greatly enhanced tube life for most installations.
: Here's a good one. On sets with a pilot lamp, the lamp gets real bright when first turned on for a second, then goes real dim as the filaments get warmed up. THEN when the set is up & ready to work, why does the pilot lamp get brighter. It goes from bright to dim then bright. Does the filament resistance get less as it gets warmer?

:: Here's a good one. On sets with a pilot lamp, the lamp gets real bright when first turned on for a second, then goes real dim as the filaments get warmed up. THEN when the set is up & ready to work, why does the pilot lamp get brighter. It goes from bright to dim then bright. Does the filament resistance get less as it gets warmer?
:
:
Resistance for an incandescent lamp, or a tube heater, never decreases as the filament warms up. What you are seeing is the effect of unequal parallel resistances (the lamp filament and the rectifier tube filament) warming up at different rates and therefore conducting different amounts of current until a steady state is reached.

I think I have seen that effect mainly where the rectifier tube has a filament tap for the dial lamp.

Mainly for AC/DC radios without a power xfmr.

:Mainly for AC/DC radios without a power xfmr.
: Thanks so much for responding on the pilot lamp-- brightness & dimming & brightness

:Mainly for AC/DC radios without a power xfmr.
: Thanks so much for responding on the pilot lamp-- brightness & dimming & brightness

::Mainly for AC/DC radios without a power xfmr.
:: Thanks so much for responding on the pilot lamp-- brightness & dimming & brightness
:

If you will go to a site called "Fun With Tubes", this guy knows all about the AA5 and will tell you what each part does and anything else you want to know.
Lewis
:

::Mainly for AC/DC radios without a power xfmr.
:: Thanks so much for responding on the pilot lamp-- brightness & dimming & brightness
:

If you will go to a site called "Fun With Tubes", this guy knows all about the AA5 and will tell you what each part does and anything else you want to know.
Lewis
:

:
::: Here's a good one. On sets with a pilot lamp, the lamp gets real bright when first turned on for a second, then goes real dim as the filaments get warmed up. THEN when the set is up & ready to work, why does the pilot lamp get brighter. It goes from bright to dim then bright. Does the filament resistance get less as it gets warmer?
::
::
:Resistance for an incandescent lamp, or a tube heater, never decreases as the filament warms up. What you are seeing is the effect of unequal parallel resistances (the lamp filament and the rectifier tube filament) warming up at different rates and therefore conducting different amounts of current until a steady state is reached.
:
The resistance is low on the filaments when the radio is turned on causing the lamp to be bright, as the filaments warm and their resistance increases the lamp will dim. As the radio starts drawing B+ the lamp will again get brighter as B+ is fed through the lamp.

Dave