Add group to favorites
Back to post list
Send new message to group Search:
Post Subject:
Does heater voltage affect grid current?
Does heater voltage affect grid current?
Refering to tube data, several have the following statement
pertaining to the grid bias voltage:
"With cathode bias, the grid circuit may have a resistance
not to exceed 0.5 megohm, provided the heater voltage is not
allowed to rise more than 10% above the rated value uinder
any condition of operation."
It's obvious that the idea is to keep grid current from
affecting bias, but how does the heater voltage come into play?
How would a 10%+ rise in heater voltage affect the grid circuit?
As an example, check out:
http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
Also found the same or similar statement for the older 6K6G,
6F6 and 6L6 metal.
--
If it's not broken, fix it till it is.
Refering to tube data, several have the following statement
pertaining to the grid bias voltage:
"With cathode bias, the grid circuit may have a resistance
not to exceed 0.5 megohm, provided the heater voltage is not
allowed to rise more than 10% above the rated value uinder
any condition of operation."
It's obvious that the idea is to keep grid current from
affecting bias, but how does the heater voltage come into play?
How would a 10%+ rise in heater voltage affect the grid circuit?
As an example, check out:
http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
Also found the same or similar statement for the older 6K6G,
6F6 and 6L6 metal.
--
If it's not broken, fix it till it is.
Re: Does heater voltage affect grid current?
"Doggone" <Running@parked.cars> wrote in message
news:Xns9A8ECE5F9E13DRunningparkedcars@216.221.81.119...
> Refering to tube data, several have the following statement
> pertaining to the grid bias voltage:
>
> "With cathode bias, the grid circuit may have a resistance
> not to exceed 0.5 megohm, provided the heater voltage is not
> allowed to rise more than 10% above the rated value uinder
> any condition of operation."
>
> It's obvious that the idea is to keep grid current from
> affecting bias, but how does the heater voltage come into play?
> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> Also found the same or similar statement for the older 6K6G,
> 6F6 and 6L6 metal.
>
>
> --
> If it's not broken, fix it till it is.
The heaters are there to excite the electrons. It serves to reason that
excessive voltage on the heaters will increase excitement. Also the tubes
will burn out quicker, as it's going to be hotter inside the bottle.
"Doggone" <Running@parked.cars> wrote in message
news:Xns9A8ECE5F9E13DRunningparkedcars@216.221.81.119...
> Refering to tube data, several have the following statement
> pertaining to the grid bias voltage:
>
> "With cathode bias, the grid circuit may have a resistance
> not to exceed 0.5 megohm, provided the heater voltage is not
> allowed to rise more than 10% above the rated value uinder
> any condition of operation."
>
> It's obvious that the idea is to keep grid current from
> affecting bias, but how does the heater voltage come into play?
> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> Also found the same or similar statement for the older 6K6G,
> 6F6 and 6L6 metal.
>
>
> --
> If it's not broken, fix it till it is.
The heaters are there to excite the electrons. It serves to reason that
excessive voltage on the heaters will increase excitement. Also the tubes
will burn out quicker, as it's going to be hotter inside the bottle.
Re: Does heater voltage affect grid current?
On Tue, 29 Apr 2008 00:17:13 GMT, Doggone <Running@parked.cars> wrote:
>Refering to tube data, several have the following statement
>pertaining to the grid bias voltage:
>
>"With cathode bias, the grid circuit may have a resistance
>not to exceed 0.5 megohm, provided the heater voltage is not
>allowed to rise more than 10% above the rated value uinder
>any condition of operation."
>
>It's obvious that the idea is to keep grid current from
>affecting bias, but how does the heater voltage come into play?
>How would a 10%+ rise in heater voltage affect the grid circuit?
>
>As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
>Also found the same or similar statement for the older 6K6G,
>6F6 and 6L6 metal.
You'll find some restriction on the "DC path to ground" parameter on
any power pentode. Maybe not published but the principles hold.
The parameter (a resistance in ohms), will be lower for fixed bias--
usually a fraction of the spec for cathode bias.
The reason for this is not just short-term affect on bias voltage.
That could be trimmed. It is long-term ionization and slow destruction
of the tube. Also an obscure lockup condition can arise (covered in
Radiotron, if you're interested).
Of course the rate of emission is affected by the filament, and that
in turn will affect the above. But that is the tie to the grid
resistance spec that you mentioned.
On Tue, 29 Apr 2008 00:17:13 GMT, Doggone <Running@parked.cars> wrote:
>Refering to tube data, several have the following statement
>pertaining to the grid bias voltage:
>
>"With cathode bias, the grid circuit may have a resistance
>not to exceed 0.5 megohm, provided the heater voltage is not
>allowed to rise more than 10% above the rated value uinder
>any condition of operation."
>
>It's obvious that the idea is to keep grid current from
>affecting bias, but how does the heater voltage come into play?
>How would a 10%+ rise in heater voltage affect the grid circuit?
>
>As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
>Also found the same or similar statement for the older 6K6G,
>6F6 and 6L6 metal.
You'll find some restriction on the "DC path to ground" parameter on
any power pentode. Maybe not published but the principles hold.
The parameter (a resistance in ohms), will be lower for fixed bias--
usually a fraction of the spec for cathode bias.
The reason for this is not just short-term affect on bias voltage.
That could be trimmed. It is long-term ionization and slow destruction
of the tube. Also an obscure lockup condition can arise (covered in
Radiotron, if you're interested).
Of course the rate of emission is affected by the filament, and that
in turn will affect the above. But that is the tie to the grid
resistance spec that you mentioned.
Re: RS spammer running scared!
On Apr 29, 4:06=EF=BF=BDam, RS <R...@sorrynospam,com > wrote:
>I'm a fucking moron. I stalk people. I hate myself! Baaa waaaaa
>
LOL at this idiot!
No wonder no one talks to his stupid ass!
Even Mulay killfiled his sorry ass. LOL
On Apr 29, 4:06=EF=BF=BDam, RS <R...@sorrynospam,com > wrote:
>I'm a fucking moron. I stalk people. I hate myself! Baaa waaaaa
>
LOL at this idiot!
No wonder no one talks to his stupid ass!
Even Mulay killfiled his sorry ass. LOL
Re: Does heater voltage affect grid current?
RS <RS@sorrynospam,com > wrote in
news:ievd14pifojub4g0g17qfo25nj8eq7ic4n@4ax,com :
> On Tue, 29 Apr 2008 00:17:13 GMT, Doggone <Running@parked.cars> wrote:
>
>>Refering to tube data, several have the following statement
>>pertaining to the grid bias voltage:
>>
>>"With cathode bias, the grid circuit may have a resistance
>>not to exceed 0.5 megohm, provided the heater voltage is not
>>allowed to rise more than 10% above the rated value uinder
>>any condition of operation."
>>
>>It's obvious that the idea is to keep grid current from
>>affecting bias, but how does the heater voltage come into play?
>>How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>>As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>>Also found the same or similar statement for the older 6K6G,
>>6F6 and 6L6 metal.
>
> You'll find some restriction on the "DC path to ground" parameter on
> any power pentode. Maybe not published but the principles hold.
> The parameter (a resistance in ohms), will be lower for fixed bias--
> usually a fraction of the spec for cathode bias.
>
Although most guitar amp designs use grid leak resistors well
in excess of the tube manuf. recomended values.
>
> The reason for this is not just short-term affect on bias voltage.
> That could be trimmed. It is long-term ionization and slow destruction
> of the tube. Also an obscure lockup condition can arise (covered in
> Radiotron, if you're interested).
>
Would like to read about that if you can post a link. TIA.
>
> Of course the rate of emission is affected by the filament, and that
> in turn will affect the above. But that is the tie to the grid
> resistance spec that you mentioned.
>
I'll have to setup a test bed and experiment with varying fil. voltages.
I have a few metal/microphonic/sacrificial 6L6's and 6F6's in my junk
box.
>
--
If it's not broken, fix it till it is.
RS <RS@sorrynospam,com > wrote in
news:ievd14pifojub4g0g17qfo25nj8eq7ic4n@4ax,com :
> On Tue, 29 Apr 2008 00:17:13 GMT, Doggone <Running@parked.cars> wrote:
>
>>Refering to tube data, several have the following statement
>>pertaining to the grid bias voltage:
>>
>>"With cathode bias, the grid circuit may have a resistance
>>not to exceed 0.5 megohm, provided the heater voltage is not
>>allowed to rise more than 10% above the rated value uinder
>>any condition of operation."
>>
>>It's obvious that the idea is to keep grid current from
>>affecting bias, but how does the heater voltage come into play?
>>How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>>As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>>Also found the same or similar statement for the older 6K6G,
>>6F6 and 6L6 metal.
>
> You'll find some restriction on the "DC path to ground" parameter on
> any power pentode. Maybe not published but the principles hold.
> The parameter (a resistance in ohms), will be lower for fixed bias--
> usually a fraction of the spec for cathode bias.
>
Although most guitar amp designs use grid leak resistors well
in excess of the tube manuf. recomended values.
>
> The reason for this is not just short-term affect on bias voltage.
> That could be trimmed. It is long-term ionization and slow destruction
> of the tube. Also an obscure lockup condition can arise (covered in
> Radiotron, if you're interested).
>
Would like to read about that if you can post a link. TIA.
>
> Of course the rate of emission is affected by the filament, and that
> in turn will affect the above. But that is the tie to the grid
> resistance spec that you mentioned.
>
I'll have to setup a test bed and experiment with varying fil. voltages.
I have a few metal/microphonic/sacrificial 6L6's and 6F6's in my junk
box.
>
--
If it's not broken, fix it till it is.
Re: Does heater voltage affect grid current?
On Wed, 30 Apr 2008 23:44:35 GMT, Doggone <Running@parked.cars> wrote:
>RS <RS@sorrynospam,com > wrote in
>> You'll find some restriction on the "DC path to ground" parameter on
>> any power pentode. Maybe not published but the principles hold.
>> The parameter (a resistance in ohms), will be lower for fixed bias--
>> usually a fraction of the spec for cathode bias.
>>
>Although most guitar amp designs use grid leak resistors well
>in excess of the tube manuf. recomended values.
You noticed that. Yeah, it's one of those places where liberties are
taken. Generally won't lead to hard failure. But you gotta wonder
about the changes to the '68 vintage Fenders. Maybe they were getting
some field failures as a result of their 220ks.
>> The reason for this is not just short-term affect on bias voltage.
>> That could be trimmed. It is long-term ionization and slow destruction
>> of the tube. Also an obscure lockup condition can arise (covered in
>> Radiotron, if you're interested).
>>
>Would like to read about that if you can post a link. TIA.
Sorry, I don't think Radiotron is online. I've never tried to simulate
the condition, so all I know is what is written in the Good Book. If
you're an experimenter, maybe you should get that? The 3rd edition is
much smaller, but you can often find them cheap.
>> Of course the rate of emission is affected by the filament, and that
>> in turn will affect the above. But that is the tie to the grid
>> resistance spec that you mentioned.
>>
>I'll have to setup a test bed and experiment with varying fil. voltages.
>I have a few metal/microphonic/sacrificial 6L6's and 6F6's in my junk
>box.
Sounds like fun. I suppose a variac will allow you to jack the
filament voltage. Those tubes may be starting off with contaminants,
so I'm not sure if you'll be able to gauge changes in ionization.
On Wed, 30 Apr 2008 23:44:35 GMT, Doggone <Running@parked.cars> wrote:
>RS <RS@sorrynospam,com > wrote in
>> You'll find some restriction on the "DC path to ground" parameter on
>> any power pentode. Maybe not published but the principles hold.
>> The parameter (a resistance in ohms), will be lower for fixed bias--
>> usually a fraction of the spec for cathode bias.
>>
>Although most guitar amp designs use grid leak resistors well
>in excess of the tube manuf. recomended values.
You noticed that. Yeah, it's one of those places where liberties are
taken. Generally won't lead to hard failure. But you gotta wonder
about the changes to the '68 vintage Fenders. Maybe they were getting
some field failures as a result of their 220ks.
>> The reason for this is not just short-term affect on bias voltage.
>> That could be trimmed. It is long-term ionization and slow destruction
>> of the tube. Also an obscure lockup condition can arise (covered in
>> Radiotron, if you're interested).
>>
>Would like to read about that if you can post a link. TIA.
Sorry, I don't think Radiotron is online. I've never tried to simulate
the condition, so all I know is what is written in the Good Book. If
you're an experimenter, maybe you should get that? The 3rd edition is
much smaller, but you can often find them cheap.
>> Of course the rate of emission is affected by the filament, and that
>> in turn will affect the above. But that is the tie to the grid
>> resistance spec that you mentioned.
>>
>I'll have to setup a test bed and experiment with varying fil. voltages.
>I have a few metal/microphonic/sacrificial 6L6's and 6F6's in my junk
>box.
Sounds like fun. I suppose a variac will allow you to jack the
filament voltage. Those tubes may be starting off with contaminants,
so I'm not sure if you'll be able to gauge changes in ionization.
Re: Does heater voltage affect grid current?
On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
> Refering to tube data, several have the following statement
> pertaining to the grid bias voltage:
>
> "With cathode bias, the grid circuit may have a resistance
> not to exceed 0.5 megohm, provided the heater voltage is not
> allowed to rise more than 10% above the rated value uinder
> any condition of operation."
>
> It's obvious that the idea is to keep grid current from
> affecting bias, but how does the heater voltage come into play?
> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> Also found the same or similar statement for the older 6K6G,
> 6F6 and 6L6 metal.
>
> --
> If it's not broken, fix it till it is.
The answer to your question (in the header) is "no". That spec. you
referred to, and what the spec. mentions on the data sheet link is
based upon operational stability of the valve. Series control grid
resistance (composed of the bias feed R + the snubber R (if present)
has a lower spec on a fixed / grid bias circuit when compared to a
cathode bias circuit because the grid biased circuit has it's cathode
at ground potential and increased isolation in the form of resistance
in the grid circuit limits the ability of the negative grid potential
to control the valve - especially when the grid is excited with
varying potentials like that found in an audio amp. A cathode bias
circuit is more immune to isolation of the control grid to ground path
because changes in plate current have a direct correlation to changes
in cathode potential thus making it self correcting (self biasing).
The "heater voltage spec" "not to exceed" 10% rated spec is tied to
the 500K g1 R upper limit (throw the control out of the experiment and
everything goes out the window) is simply a "runaway" point where bias
control between cathode voltage and grid ground reference will no
longer be stable at the elevated limits. It's not a grid "current"
issue.
On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
> Refering to tube data, several have the following statement
> pertaining to the grid bias voltage:
>
> "With cathode bias, the grid circuit may have a resistance
> not to exceed 0.5 megohm, provided the heater voltage is not
> allowed to rise more than 10% above the rated value uinder
> any condition of operation."
>
> It's obvious that the idea is to keep grid current from
> affecting bias, but how does the heater voltage come into play?
> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> Also found the same or similar statement for the older 6K6G,
> 6F6 and 6L6 metal.
>
> --
> If it's not broken, fix it till it is.
The answer to your question (in the header) is "no". That spec. you
referred to, and what the spec. mentions on the data sheet link is
based upon operational stability of the valve. Series control grid
resistance (composed of the bias feed R + the snubber R (if present)
has a lower spec on a fixed / grid bias circuit when compared to a
cathode bias circuit because the grid biased circuit has it's cathode
at ground potential and increased isolation in the form of resistance
in the grid circuit limits the ability of the negative grid potential
to control the valve - especially when the grid is excited with
varying potentials like that found in an audio amp. A cathode bias
circuit is more immune to isolation of the control grid to ground path
because changes in plate current have a direct correlation to changes
in cathode potential thus making it self correcting (self biasing).
The "heater voltage spec" "not to exceed" 10% rated spec is tied to
the 500K g1 R upper limit (throw the control out of the experiment and
everything goes out the window) is simply a "runaway" point where bias
control between cathode voltage and grid ground reference will no
longer be stable at the elevated limits. It's not a grid "current"
issue.
Re: Does heater voltage affect grid current?
Premier Spigot <bighorseshoebob@yahoo,com > wrote in news:a5e4d47b-8f39-
4c3b-99f4-198270e73f0d@r66g2000hsg.googlegroups,com :
> On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
>> Refering to tube data, several have the following statement
>> pertaining to the grid bias voltage:
>>
>> "With cathode bias, the grid circuit may have a resistance
>> not to exceed 0.5 megohm, provided the heater voltage is not
>> allowed to rise more than 10% above the rated value uinder
>> any condition of operation."
>>
>> It's obvious that the idea is to keep grid current from
>> affecting bias, but how does the heater voltage come into play?
>> How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>> As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>> Also found the same or similar statement for the older 6K6G,
>> 6F6 and 6L6 metal.
>>
>> --
>> If it's not broken, fix it till it is.
>
> The answer to your question (in the header) is "no". That spec. you
> referred to, and what the spec. mentions on the data sheet link is
> based upon operational stability of the valve. Series control grid
> resistance (composed of the bias feed R + the snubber R (if present)
> has a lower spec on a fixed / grid bias circuit when compared to a
> cathode bias circuit because the grid biased circuit has it's cathode
> at ground potential and increased isolation in the form of resistance
> in the grid circuit limits the ability of the negative grid potential
> to control the valve - especially when the grid is excited with
> varying potentials like that found in an audio amp. A cathode bias
> circuit is more immune to isolation of the control grid to ground path
> because changes in plate current have a direct correlation to changes
> in cathode potential thus making it self correcting (self biasing).
>
Thanks for the biasing review.
>
> The "heater voltage spec" "not to exceed" 10% rated spec is tied to
> the 500K g1 R upper limit (throw the control out of the experiment and
> everything goes out the window) is simply a "runaway" point where bias
> control between cathode voltage and grid ground reference will no
> longer be stable at the elevated limits.
>
What is the cause of this "runaway" situation you describe? And don't
be shy with the techo jargon.
>
> It's not a grid "current"
> issue.
I'm not convinced of that. Grid current and high grid leak resistor is,
as I understand it, the only thing that would cause a cathode biased
tube to become unstable.(other than polished turd catastrophic failure)
If there's something else, this inquisitive mind wants to know.
--
If it's not broken, fix it till it is.
Premier Spigot <bighorseshoebob@yahoo,com > wrote in news:a5e4d47b-8f39-
4c3b-99f4-198270e73f0d@r66g2000hsg.googlegroups,com :
> On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
>> Refering to tube data, several have the following statement
>> pertaining to the grid bias voltage:
>>
>> "With cathode bias, the grid circuit may have a resistance
>> not to exceed 0.5 megohm, provided the heater voltage is not
>> allowed to rise more than 10% above the rated value uinder
>> any condition of operation."
>>
>> It's obvious that the idea is to keep grid current from
>> affecting bias, but how does the heater voltage come into play?
>> How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>> As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>> Also found the same or similar statement for the older 6K6G,
>> 6F6 and 6L6 metal.
>>
>> --
>> If it's not broken, fix it till it is.
>
> The answer to your question (in the header) is "no". That spec. you
> referred to, and what the spec. mentions on the data sheet link is
> based upon operational stability of the valve. Series control grid
> resistance (composed of the bias feed R + the snubber R (if present)
> has a lower spec on a fixed / grid bias circuit when compared to a
> cathode bias circuit because the grid biased circuit has it's cathode
> at ground potential and increased isolation in the form of resistance
> in the grid circuit limits the ability of the negative grid potential
> to control the valve - especially when the grid is excited with
> varying potentials like that found in an audio amp. A cathode bias
> circuit is more immune to isolation of the control grid to ground path
> because changes in plate current have a direct correlation to changes
> in cathode potential thus making it self correcting (self biasing).
>
Thanks for the biasing review.
>
> The "heater voltage spec" "not to exceed" 10% rated spec is tied to
> the 500K g1 R upper limit (throw the control out of the experiment and
> everything goes out the window) is simply a "runaway" point where bias
> control between cathode voltage and grid ground reference will no
> longer be stable at the elevated limits.
>
What is the cause of this "runaway" situation you describe? And don't
be shy with the techo jargon.
>
> It's not a grid "current"
> issue.
I'm not convinced of that. Grid current and high grid leak resistor is,
as I understand it, the only thing that would cause a cathode biased
tube to become unstable.(other than polished turd catastrophic failure)
If there's something else, this inquisitive mind wants to know.
--
If it's not broken, fix it till it is.
Re: Does heater voltage affect grid current?
"Doggone" <Running@parked.cars> wrote in message
news:Xns9A91CDA22F976Runningparkedcars@216.221.81.119...
> Premier Spigot <bighorseshoebob@yahoo,com > wrote
...
>> The "heater voltage spec" "not to exceed" 10% rated spec is tied to
>> the 500K g1 R upper limit (throw the control out of the experiment and
>> everything goes out the window) is simply a "runaway" point where bias
>> control between cathode voltage and grid ground reference will no
>> longer be stable at the elevated limits.
>>
> What is the cause of this "runaway" situation you describe? And don't
> be shy with the techo jargon.
Think of it as the throttle return spring... heating up the cathode
even more may take the grid out of it's control capability range.
Weak throttle return spring equals no or sluggish return to idle.
__
Steve
.
"Doggone" <Running@parked.cars> wrote in message
news:Xns9A91CDA22F976Runningparkedcars@216.221.81.119...
> Premier Spigot <bighorseshoebob@yahoo,com > wrote
...
>> The "heater voltage spec" "not to exceed" 10% rated spec is tied to
>> the 500K g1 R upper limit (throw the control out of the experiment and
>> everything goes out the window) is simply a "runaway" point where bias
>> control between cathode voltage and grid ground reference will no
>> longer be stable at the elevated limits.
>>
> What is the cause of this "runaway" situation you describe? And don't
> be shy with the techo jargon.
Think of it as the throttle return spring... heating up the cathode
even more may take the grid out of it's control capability range.
Weak throttle return spring equals no or sluggish return to idle.
__
Steve
.
Re: Does heater voltage affect grid current?
"Stephen Cowell" <scowell@sbcglobal,net > wrote in news:kNtSj.6980$LQ4.6624
@newssvr11.news.prodigy,net :
>
> "Doggone" <Running@parked.cars> wrote in message
> news:Xns9A91CDA22F976Runningparkedcars@216.221.81.119...
>> Premier Spigot <bighorseshoebob@yahoo,com > wrote
> ...
>
>>> The "heater voltage spec" "not to exceed" 10% rated spec is tied to
>>> the 500K g1 R upper limit (throw the control out of the experiment and
>>> everything goes out the window) is simply a "runaway" point where bias
>>> control between cathode voltage and grid ground reference will no
>>> longer be stable at the elevated limits.
>>>
>> What is the cause of this "runaway" situation you describe? And don't
>> be shy with the techo jargon.
>
> Think of it as the throttle return spring... heating up the cathode
> even more may take the grid out of it's control capability range.
> Weak throttle return spring equals no or sluggish return to idle.
> __
> Steve
> .
>
>
>
Interresting analogy, thanks.
--
If it's not broken, fix it till it is.
"Stephen Cowell" <scowell@sbcglobal,net > wrote in news:kNtSj.6980$LQ4.6624
@newssvr11.news.prodigy,net :
>
> "Doggone" <Running@parked.cars> wrote in message
> news:Xns9A91CDA22F976Runningparkedcars@216.221.81.119...
>> Premier Spigot <bighorseshoebob@yahoo,com > wrote
> ...
>
>>> The "heater voltage spec" "not to exceed" 10% rated spec is tied to
>>> the 500K g1 R upper limit (throw the control out of the experiment and
>>> everything goes out the window) is simply a "runaway" point where bias
>>> control between cathode voltage and grid ground reference will no
>>> longer be stable at the elevated limits.
>>>
>> What is the cause of this "runaway" situation you describe? And don't
>> be shy with the techo jargon.
>
> Think of it as the throttle return spring... heating up the cathode
> even more may take the grid out of it's control capability range.
> Weak throttle return spring equals no or sluggish return to idle.
> __
> Steve
> .
>
>
>
Interresting analogy, thanks.
--
If it's not broken, fix it till it is.
Re: Does heater voltage affect grid current?
On May 1, 8:12 pm, Doggone <Runn...@parked.cars> wrote:
> Premier Spigot <bighorseshoe...@yahoo,com > wrote in news:a5e4d47b-8f39-
> 4c3b-99f4-198270e73...@r66g2000hsg.googlegroups,com :
>
>
>
>
>
> > On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
> >> Refering to tube data, several have the following statement
> >> pertaining to the grid bias voltage:
>
> >> "With cathode bias, the grid circuit may have a resistance
> >> not to exceed 0.5 megohm, provided the heater voltage is not
> >> allowed to rise more than 10% above the rated value uinder
> >> any condition of operation."
>
> >> It's obvious that the idea is to keep grid current from
> >> affecting bias, but how does the heater voltage come into play?
> >> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> >> As an example, check out:
>
> >> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> >> Also found the same or similar statement for the older 6K6G,
> >> 6F6 and 6L6 metal.
>
> >> --
> >> If it's not broken, fix it till it is.
>
> > The answer to your question (in the header) is "no". That spec. you
> > referred to, and what the spec. mentions on the data sheet link is
> > based upon operational stability of the valve. Series control grid
> > resistance (composed of the bias feed R + the snubber R (if present)
> > has a lower spec on a fixed / grid bias circuit when compared to a
> > cathode bias circuit because the grid biased circuit has it's cathode
> > at ground potential and increased isolation in the form of resistance
> > in the grid circuit limits the ability of the negative grid potential
> > to control the valve - especially when the grid is excited with
> > varying potentials like that found in an audio amp. A cathode bias
> > circuit is more immune to isolation of the control grid to ground path
> > because changes in plate current have a direct correlation to changes
> > in cathode potential thus making it self correcting (self biasing).
>
> Thanks for the biasing review.
>
> > The "heater voltage spec" "not to exceed" 10% rated spec is tied to
> > the 500K g1 R upper limit (throw the control out of the experiment and
> > everything goes out the window) is simply a "runaway" point where bias
> > control between cathode voltage and grid ground reference will no
> > longer be stable at the elevated limits.
>
> What is the cause of this "runaway" situation you describe? And don't
> be shy with the techo jargon.
>
>
>
> > It's not a grid "current"
> > issue.
>
> I'm not convinced of that. Grid current and high grid leak resistor is,
> as I understand it, the only thing that would cause a cathode biased
> tube to become unstable.(other than polished turd catastrophic failure)
> If there's something else, this inquisitive mind wants to know.
>
> --
> If it's not broken, fix it till it is.- Hide quoted text -
>
> - Show quoted text -
"Thanks for the biasing review." ? Why the smart ass stance? If you
don't want "techo" jargon, what did you want for an explanation? You,
of limited thought on the subject, are scolding me? Show me a tube
power amp with "grid leak" biasing alone (a "zero bias", grounded
cathode arrangement?). Then, we can hammer it out. Yes, the throttle
return spring was a good analogy; maybe I should have used something
about a dam, water, recent precipitation, the dam's openings, fish
swimming near the opening, the fish calories required to avoid the
opening based on the proximity of the fish to the opening and the
velocity of the water flowing through the opening? Better yet, here's
the fish. Enjoy.
On May 1, 8:12 pm, Doggone <Runn...@parked.cars> wrote:
> Premier Spigot <bighorseshoe...@yahoo,com > wrote in news:a5e4d47b-8f39-
> 4c3b-99f4-198270e73...@r66g2000hsg.googlegroups,com :
>
>
>
>
>
> > On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
> >> Refering to tube data, several have the following statement
> >> pertaining to the grid bias voltage:
>
> >> "With cathode bias, the grid circuit may have a resistance
> >> not to exceed 0.5 megohm, provided the heater voltage is not
> >> allowed to rise more than 10% above the rated value uinder
> >> any condition of operation."
>
> >> It's obvious that the idea is to keep grid current from
> >> affecting bias, but how does the heater voltage come into play?
> >> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> >> As an example, check out:
>
> >> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> >> Also found the same or similar statement for the older 6K6G,
> >> 6F6 and 6L6 metal.
>
> >> --
> >> If it's not broken, fix it till it is.
>
> > The answer to your question (in the header) is "no". That spec. you
> > referred to, and what the spec. mentions on the data sheet link is
> > based upon operational stability of the valve. Series control grid
> > resistance (composed of the bias feed R + the snubber R (if present)
> > has a lower spec on a fixed / grid bias circuit when compared to a
> > cathode bias circuit because the grid biased circuit has it's cathode
> > at ground potential and increased isolation in the form of resistance
> > in the grid circuit limits the ability of the negative grid potential
> > to control the valve - especially when the grid is excited with
> > varying potentials like that found in an audio amp. A cathode bias
> > circuit is more immune to isolation of the control grid to ground path
> > because changes in plate current have a direct correlation to changes
> > in cathode potential thus making it self correcting (self biasing).
>
> Thanks for the biasing review.
>
> > The "heater voltage spec" "not to exceed" 10% rated spec is tied to
> > the 500K g1 R upper limit (throw the control out of the experiment and
> > everything goes out the window) is simply a "runaway" point where bias
> > control between cathode voltage and grid ground reference will no
> > longer be stable at the elevated limits.
>
> What is the cause of this "runaway" situation you describe? And don't
> be shy with the techo jargon.
>
>
>
> > It's not a grid "current"
> > issue.
>
> I'm not convinced of that. Grid current and high grid leak resistor is,
> as I understand it, the only thing that would cause a cathode biased
> tube to become unstable.(other than polished turd catastrophic failure)
> If there's something else, this inquisitive mind wants to know.
>
> --
> If it's not broken, fix it till it is.- Hide quoted text -
>
> - Show quoted text -
"Thanks for the biasing review." ? Why the smart ass stance? If you
don't want "techo" jargon, what did you want for an explanation? You,
of limited thought on the subject, are scolding me? Show me a tube
power amp with "grid leak" biasing alone (a "zero bias", grounded
cathode arrangement?). Then, we can hammer it out. Yes, the throttle
return spring was a good analogy; maybe I should have used something
about a dam, water, recent precipitation, the dam's openings, fish
swimming near the opening, the fish calories required to avoid the
opening based on the proximity of the fish to the opening and the
velocity of the water flowing through the opening? Better yet, here's
the fish. Enjoy.
Re: Does heater voltage affect grid current?
On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
> Refering to tube data, several have the following statement
> pertaining to the grid bias voltage:
>
> "With cathode bias, the grid circuit may have a resistance
> not to exceed 0.5 megohm, provided the heater voltage is not
> allowed to rise more than 10% above the rated value uinder
> any condition of operation."
>
> It's obvious that the idea is to keep grid current from
> affecting bias, but how does the heater voltage come into play?
> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> Also found the same or similar statement for the older 6K6G,
> 6F6 and 6L6 metal.
I just ran across this group looking for vacuum tube groups, so here's
an answer from an outsider. What I've read is that the danger of
excessive heater voltage is that you can actually boil off cathode
material, some of which can end up on the grid. Once the grid has
cathode material on it, if it gets too hot it will start emitting
electrons and thus drive the grid voltage more positive, which is a
recipe for runaway.
Mike
On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
> Refering to tube data, several have the following statement
> pertaining to the grid bias voltage:
>
> "With cathode bias, the grid circuit may have a resistance
> not to exceed 0.5 megohm, provided the heater voltage is not
> allowed to rise more than 10% above the rated value uinder
> any condition of operation."
>
> It's obvious that the idea is to keep grid current from
> affecting bias, but how does the heater voltage come into play?
> How would a 10%+ rise in heater voltage affect the grid circuit?
>
> As an example, check out:
>
> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>
> Also found the same or similar statement for the older 6K6G,
> 6F6 and 6L6 metal.
I just ran across this group looking for vacuum tube groups, so here's
an answer from an outsider. What I've read is that the danger of
excessive heater voltage is that you can actually boil off cathode
material, some of which can end up on the grid. Once the grid has
cathode material on it, if it gets too hot it will start emitting
electrons and thus drive the grid voltage more positive, which is a
recipe for runaway.
Mike
Re: Does heater voltage affect grid current?
Mike Silva wrote:
> On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
>> Refering to tube data, several have the following statement
>> pertaining to the grid bias voltage:
>>
>> "With cathode bias, the grid circuit may have a resistance
>> not to exceed 0.5 megohm, provided the heater voltage is not
>> allowed to rise more than 10% above the rated value uinder
>> any condition of operation."
>>
>> It's obvious that the idea is to keep grid current from
>> affecting bias, but how does the heater voltage come into play?
>> How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>> As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>> Also found the same or similar statement for the older 6K6G,
>> 6F6 and 6L6 metal.
>
> I just ran across this group looking for vacuum tube groups, so here's
> an answer from an outsider. What I've read is that the danger of
> excessive heater voltage is that you can actually boil off cathode
> material, some of which can end up on the grid. Once the grid has
> cathode material on it, if it gets too hot it will start emitting
> electrons and thus drive the grid voltage more positive, which is a
> recipe for runaway.
>
> Mike
Thanks for your info. Mike and welcome. I'm not a tech, but if you're
correct here, the a.holes will be totally silent. Oddly, that's how
this newsgroup tends to work.
mvm
http :// tinyurl,com /32j32m
Mike Silva wrote:
> On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
>> Refering to tube data, several have the following statement
>> pertaining to the grid bias voltage:
>>
>> "With cathode bias, the grid circuit may have a resistance
>> not to exceed 0.5 megohm, provided the heater voltage is not
>> allowed to rise more than 10% above the rated value uinder
>> any condition of operation."
>>
>> It's obvious that the idea is to keep grid current from
>> affecting bias, but how does the heater voltage come into play?
>> How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>> As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>> Also found the same or similar statement for the older 6K6G,
>> 6F6 and 6L6 metal.
>
> I just ran across this group looking for vacuum tube groups, so here's
> an answer from an outsider. What I've read is that the danger of
> excessive heater voltage is that you can actually boil off cathode
> material, some of which can end up on the grid. Once the grid has
> cathode material on it, if it gets too hot it will start emitting
> electrons and thus drive the grid voltage more positive, which is a
> recipe for runaway.
>
> Mike
Thanks for your info. Mike and welcome. I'm not a tech, but if you're
correct here, the a.holes will be totally silent. Oddly, that's how
this newsgroup tends to work.
mvm
http :// tinyurl,com /32j32m
Re: Does heater voltage affect grid current?
Mike Silva <snarflemike@yahoo,com > wrote in news:6b642f66-8d36-4557-a4a2-
5a8fbb464e8d@i76g2000hsf.googlegroups,com :
> On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
>> Refering to tube data, several have the following statement
>> pertaining to the grid bias voltage:
>>
>> "With cathode bias, the grid circuit may have a resistance
>> not to exceed 0.5 megohm, provided the heater voltage is not
>> allowed to rise more than 10% above the rated value uinder
>> any condition of operation."
>>
>> It's obvious that the idea is to keep grid current from
>> affecting bias, but how does the heater voltage come into play?
>> How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>> As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>> Also found the same or similar statement for the older 6K6G,
>> 6F6 and 6L6 metal.
>
> I just ran across this group looking for vacuum tube groups, so here's
> an answer from an outsider. What I've read is that the danger of
> excessive heater voltage is that you can actually boil off cathode
> material, some of which can end up on the grid. Once the grid has
> cathode material on it, if it gets too hot it will start emitting
> electrons and thus drive the grid voltage more positive, which is a
> recipe for runaway.
>
> Mike
Thank you Mike and all others for clarifying the issue for me.
(I understand quickly, you just have to explain it a long time)
--
If it's not broken, fix it till it is.
Mike Silva <snarflemike@yahoo,com > wrote in news:6b642f66-8d36-4557-a4a2-
5a8fbb464e8d@i76g2000hsf.googlegroups,com :
> On Apr 28, 8:17 pm, Doggone <Runn...@parked.cars> wrote:
>> Refering to tube data, several have the following statement
>> pertaining to the grid bias voltage:
>>
>> "With cathode bias, the grid circuit may have a resistance
>> not to exceed 0.5 megohm, provided the heater voltage is not
>> allowed to rise more than 10% above the rated value uinder
>> any condition of operation."
>>
>> It's obvious that the idea is to keep grid current from
>> affecting bias, but how does the heater voltage come into play?
>> How would a 10%+ rise in heater voltage affect the grid circuit?
>>
>> As an example, check out:
>>
>> http :// www .mif.pg.gda.pl/homepages/frank/sheets/084/6/6V6GT.pdf
>>
>> Also found the same or similar statement for the older 6K6G,
>> 6F6 and 6L6 metal.
>
> I just ran across this group looking for vacuum tube groups, so here's
> an answer from an outsider. What I've read is that the danger of
> excessive heater voltage is that you can actually boil off cathode
> material, some of which can end up on the grid. Once the grid has
> cathode material on it, if it gets too hot it will start emitting
> electrons and thus drive the grid voltage more positive, which is a
> recipe for runaway.
>
> Mike
Thank you Mike and all others for clarifying the issue for me.
(I understand quickly, you just have to explain it a long time)
--
If it's not broken, fix it till it is.
