Hello,
as the title suggest, can i use 5 watt zener diodes (reverse bias) to drop 100 or 150 volts for G2 supply?
I plan using 6550 tubes, g2 cannot exceed 450 volts, my B+ will be 500 VDC.
Many thanks
as the title suggest, can i use 5 watt zener diodes (reverse bias) to drop 100 or 150 volts for G2 supply?
I plan using 6550 tubes, g2 cannot exceed 450 volts, my B+ will be 500 VDC.
Many thanks
Should work, give it a try.
Audio Research used 590VDC B+, and regulated 360VDC for the screen grid.
Audio Research used 590VDC B+, and regulated 360VDC for the screen grid.
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G2 voltage would preferably be referenced to cathode (usually signal ground) for true pentode operation, but if you're tying the G2s to primary taps ("UltraLinear") a fixed voltage drop from the tap works. You'll want to be sure that G2 current never gets lower than the Zener's minimum breakover current, often in the 0.5mA range for likely candidates, over all possible loadline conditions.
All good fortune,
Chris
All good fortune,
Chris
As someone in another thread said, you can use a resistor from the screen to ground (or to the cathode if you prefer). The resistor value can be quite high, so that if the screen current drops to 'zero', the zener still has enough current to stay in the zener region.
And, the typical Ultra Linear Tap is very low impedance, since it is a small percentage of the plate tap.
Example: The plate tap is 3k, and the UL tap is 40%.
Then the UL tap impedance is 3k (0.4 x 0.4)= 480 Ohms.
If the screen voltage is 300V, and the 'keep the zener in the zener region' takes 2mA,
then the resistor is 300V/0.002 = 150k Ohms.
Any 480 Ohm UL tap can drive 150k Ohms additional load without significant power loss to the loudspeaker.
As the tube is approaching cutoff of both the plate and screen, there will be an abundance of current to the zener from the 150k resistor.
For Pentode or Beam Power tube operation, the zener should work well, as long as the resistor from the screen to ground or cathode supplies enough current for the zener to stay in the zener region.
Just my opinions.
Your Mileage May Vary.
And, the typical Ultra Linear Tap is very low impedance, since it is a small percentage of the plate tap.
Example: The plate tap is 3k, and the UL tap is 40%.
Then the UL tap impedance is 3k (0.4 x 0.4)= 480 Ohms.
If the screen voltage is 300V, and the 'keep the zener in the zener region' takes 2mA,
then the resistor is 300V/0.002 = 150k Ohms.
Any 480 Ohm UL tap can drive 150k Ohms additional load without significant power loss to the loudspeaker.
As the tube is approaching cutoff of both the plate and screen, there will be an abundance of current to the zener from the 150k resistor.
For Pentode or Beam Power tube operation, the zener should work well, as long as the resistor from the screen to ground or cathode supplies enough current for the zener to stay in the zener region.
Just my opinions.
Your Mileage May Vary.
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This is non issue , first of all you don't need regulation just voltage drop , and second the screen idle current is in mA range ...
There was a recent topic about a factory made UL amplifier where they used suppression diodes for this role ... much more robust than a zener for peak G2 current .
There was a recent topic about a factory made UL amplifier where they used suppression diodes for this role ... much more robust than a zener for peak G2 current .
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This will usually work in UL mode. It will NOT work in triode mode as the voltage across the zener will try to approach zero as the output tube goes toward full conduction. It will never get there as the screen voltage goes to zero as the plate voltage approaches the zener voltage. Early experiments with zeners, and regulator tubes like the 0A2 and 0B2 proved this out.
This is not usually a problem with typical audio tubes since they can usually be triode wired. Some output tubes like the 6CW5, the 6W6, or 6Y6 and most TV sweep tubes can not be triode wired due to their low G2 voltage spec.
This is not usually a problem with typical audio tubes since they can usually be triode wired. Some output tubes like the 6CW5, the 6W6, or 6Y6 and most TV sweep tubes can not be triode wired due to their low G2 voltage spec.
I understand why it will not work in triode mode. But why does it work in UL mode? Is it because the voltage swing on g2 is smaller?
Something like that , AC is half if the tap is at 50% primary . So probably there is a limit on zener voltage , not for sweep tubes with 150V max G2 and 500V B+ .
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Originally tertrodes were designed to have g2 between 250 VDC and 300VDC. Schade mentions that ideally g2 should be 15 - 20V below the plate for optimum functioning. Attached document uses a string of 5.6V zeners due to the best temperature coefficient. I am using a single 30V zener in my current SE UL design resulting in a 20V difference between plate and g2. Works just as good.
What is in a Proper Name?
1. Tetrodes (with g1 snd g2, but no g3, and no Beam Formers) were originally designed for RF oscillators and RF amplifiers.
2. Then Pentodes (with g1, g2, and g3, all real wire grids) were designed.
3. Later, Beam Power tubes were designed, with Beam Formers instead of g3.
Some people mistakenly call those Tetrodes.
In some cases, g1 and g2 have the same number of grid wires, and are very carefully lined up, so that the electrons are in sheets that have a straight shot to the plates, but only between the 'opening' of the beam formers that are beyond g2.
Drawings of these, with the 'sheets' and the beam formers are in the front pages of most RCA tube manuals.
. . . Some people use the word Beam Tetrodes for Beam power tubes, But that confuses the naming term 'Tetrode' . . .
4. There are RF Radial Beam Tetrodes, with g1 and g2, but no g3, and no beam formers.
Instead, the Bird Cage construction of g1 and g2 have the same number of grid wires, spaced at the same angles as each other, and the bird cage grids are rotationally lined up, and that forms Beams (sheets) of electrons that get a straight shot on their way to the Plate.
For an example, take a look at the construction of a 4X150 Beam Power Tetrode.
The above are just my historical opinions.
Your Naming Conventions Might Vary.
Call it / Name it whatever you want, and wonder why some others are not sure what type of tube you are talking about.
1. Tetrodes (with g1 snd g2, but no g3, and no Beam Formers) were originally designed for RF oscillators and RF amplifiers.
2. Then Pentodes (with g1, g2, and g3, all real wire grids) were designed.
3. Later, Beam Power tubes were designed, with Beam Formers instead of g3.
Some people mistakenly call those Tetrodes.
In some cases, g1 and g2 have the same number of grid wires, and are very carefully lined up, so that the electrons are in sheets that have a straight shot to the plates, but only between the 'opening' of the beam formers that are beyond g2.
Drawings of these, with the 'sheets' and the beam formers are in the front pages of most RCA tube manuals.
. . . Some people use the word Beam Tetrodes for Beam power tubes, But that confuses the naming term 'Tetrode' . . .
4. There are RF Radial Beam Tetrodes, with g1 and g2, but no g3, and no beam formers.
Instead, the Bird Cage construction of g1 and g2 have the same number of grid wires, spaced at the same angles as each other, and the bird cage grids are rotationally lined up, and that forms Beams (sheets) of electrons that get a straight shot on their way to the Plate.
For an example, take a look at the construction of a 4X150 Beam Power Tetrode.
The above are just my historical opinions.
Your Naming Conventions Might Vary.
Call it / Name it whatever you want, and wonder why some others are not sure what type of tube you are talking about.
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To cinfuse things even more: one side of the Atlantic called things different from the other side. You'll have to go the to the relevant documentation to exactly know what someone is refering to.
E.G. a beam power tube is an American name for a tetrode or pentode that has beams instead of a grid for g3. (tetrode = 4 elements, pentode = 5 elements).
Hence me referring to Schade - he was mentioning a pentode with beam forming plates.
E.G. a beam power tube is an American name for a tetrode or pentode that has beams instead of a grid for g3. (tetrode = 4 elements, pentode = 5 elements).
Hence me referring to Schade - he was mentioning a pentode with beam forming plates.
Why are a '5 element' 6L6GC, a KT77, and a real 6BQ5 called Beam Power tubes, but are not called a Pentode?
(Yes, the KT77 is called a Kink-less Tetrode, but it has Beam Formers just like the 6L6GC and real 6BQ5).
Because the "5" elements are:
1. filament and cathode (electron cloud emitter)
2. g1 control grid
3. g2 screen grid
4. Beam Formers (this is the key name determinant, Beam Power)
5. Plate
Depending on whether you call the filament and cathode 'one element' or separate elements, there are 5 or 6 elements respectively.
Then there is the case of a Direct Heated Beam Power tube, with no cathode.
An old 2CY5 Tetrode has:
"4" elements:
1. filament and cathode (electron cloud emitter)
2. g1 control grid
3. g2 screen
4. Plate
Depending on whether you call the filament and cathode 'one element' or separate elements, there are 4 or 5 elements respectively. But it is not called a Pentode.
Then there is the case of a Direct Heated Tetrode such as a 4-65A or 32, with no cathode.
Why is a '5 element' EL34 and an EL84 called a Pentode, but is not called a Beam Power tube?
Because the "5" elements are:
1. filament and cathode (electron cloud emitter)
2. g1 control grid
3. g2 screen
4. g3 suppressor grid
5. Plate
Depending on whether you call the filament and cathode 'one element' or separate elements, there are 5 or 6 elements respectively.
Then there is the case of a 1LA4 Direct Heated Pentode tube, with no cathode.
A lot of this had to do with patents from the early days.
It should be noted that the original 6BQ5 was a Beam Power tube, and the EL84 was a Pentode.
The specifications were so similar, that manufacturers would put Both a 6BQ5 label and a EL84 label on the same tube (the dual labeled tube was easier to stock and sell, because whatever the customer asked for, a 6BQ5 or an EL84, the tube dealers only had to stock one kind, the "6BQ5/EL84").
Look for either the beam formers, or the g3 grid wires, in order to see what you actually have, a 6BQ5 Beam Power tube, or an EL84 Pentode.
These have exactly the same pinout connections (well, sort of: either cathode & beam formers; or cathode & g3).
I think it is fortunate, but I have never seen a 'dual labeled' EL34/KT77.
One reason is that the KT77 pin 8 is the cathode and Beam Formers;
but the EL34 pin 8 is cathode only, and pin 1 is the suppressor grid, g3.
(Yes, the KT77 is called a Kink-less Tetrode, but it has Beam Formers just like the 6L6GC and real 6BQ5).
Because the "5" elements are:
1. filament and cathode (electron cloud emitter)
2. g1 control grid
3. g2 screen grid
4. Beam Formers (this is the key name determinant, Beam Power)
5. Plate
Depending on whether you call the filament and cathode 'one element' or separate elements, there are 5 or 6 elements respectively.
Then there is the case of a Direct Heated Beam Power tube, with no cathode.
An old 2CY5 Tetrode has:
"4" elements:
1. filament and cathode (electron cloud emitter)
2. g1 control grid
3. g2 screen
4. Plate
Depending on whether you call the filament and cathode 'one element' or separate elements, there are 4 or 5 elements respectively. But it is not called a Pentode.
Then there is the case of a Direct Heated Tetrode such as a 4-65A or 32, with no cathode.
Why is a '5 element' EL34 and an EL84 called a Pentode, but is not called a Beam Power tube?
Because the "5" elements are:
1. filament and cathode (electron cloud emitter)
2. g1 control grid
3. g2 screen
4. g3 suppressor grid
5. Plate
Depending on whether you call the filament and cathode 'one element' or separate elements, there are 5 or 6 elements respectively.
Then there is the case of a 1LA4 Direct Heated Pentode tube, with no cathode.
A lot of this had to do with patents from the early days.
It should be noted that the original 6BQ5 was a Beam Power tube, and the EL84 was a Pentode.
The specifications were so similar, that manufacturers would put Both a 6BQ5 label and a EL84 label on the same tube (the dual labeled tube was easier to stock and sell, because whatever the customer asked for, a 6BQ5 or an EL84, the tube dealers only had to stock one kind, the "6BQ5/EL84").
Look for either the beam formers, or the g3 grid wires, in order to see what you actually have, a 6BQ5 Beam Power tube, or an EL84 Pentode.
These have exactly the same pinout connections (well, sort of: either cathode & beam formers; or cathode & g3).
I think it is fortunate, but I have never seen a 'dual labeled' EL34/KT77.
One reason is that the KT77 pin 8 is the cathode and Beam Formers;
but the EL34 pin 8 is cathode only, and pin 1 is the suppressor grid, g3.
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How do you know that the original 6BQ5 was a beam power tube? Did you perhaps dissect some?
According to Radiomuseum.org the EL84 was introduced in 1953 while the 6BQ5 first appeared in 1956.
According to the attached STC Application Report from 1957 the 6BQ5 is identical to the EL84.
I don't know of any datasheet which calls the 6BQ5 a beam power tube. I do notice that they are called power pentode in for instance the RCA Receiving Tube Manuals while many other power tubes in these manuals are called beam power tube. Often datasheets mention 6BQ5/EL84, which also suggests that they were identical.
I also notice that in many datasheets for the 6BQ5 the values for Ig2 are exactly the same as for the EL84. I would think that Ig2 in a beam power tube often is a bit lower than in a power pentode (compared at the same voltages).
In many "CV-number - Civilian Tube designation" lists the CV2975 is said to be 6BQ5/EL84. However, CV8069 is said to be EL84 and CV10321 is said to be 6BQ5. But note that these CV numbers are higher than CV2975. So this could be an indication that later on there were differences between the EL84 and the 6BQ5.
The above is not solid evidence of the original 6BQ5 being identical to the EL84 but for me it does cast some doubt on the original 6BQ5 being a beam power tube.
According to Radiomuseum.org the EL84 was introduced in 1953 while the 6BQ5 first appeared in 1956.
According to the attached STC Application Report from 1957 the 6BQ5 is identical to the EL84.
I don't know of any datasheet which calls the 6BQ5 a beam power tube. I do notice that they are called power pentode in for instance the RCA Receiving Tube Manuals while many other power tubes in these manuals are called beam power tube. Often datasheets mention 6BQ5/EL84, which also suggests that they were identical.
I also notice that in many datasheets for the 6BQ5 the values for Ig2 are exactly the same as for the EL84. I would think that Ig2 in a beam power tube often is a bit lower than in a power pentode (compared at the same voltages).
In many "CV-number - Civilian Tube designation" lists the CV2975 is said to be 6BQ5/EL84. However, CV8069 is said to be EL84 and CV10321 is said to be 6BQ5. But note that these CV numbers are higher than CV2975. So this could be an indication that later on there were differences between the EL84 and the 6BQ5.
The above is not solid evidence of the original 6BQ5 being identical to the EL84 but for me it does cast some doubt on the original 6BQ5 being a beam power tube.
The 6CA7 is often labelled as EL34 but there are 6CA7 that were beam power tubes whereas the E34 was a pentode. IIRC the 6CA7 was developped to circumvent the Philips patent (but may be mistaken, memory no longer being what it once was).
Some 7189 were relabeled as EL84 and the confusion goes on. Just check how many different ECC83 (12AX7) there are and then start checking for the different recommended operating points. IIRC the ECC83 from Mazda has a totally different recommended operating point than most other manufacturers'. In other words they may work but they are not identical and some sensitive circuits can/will give problems.
As the ECC83 documentation shows not all datasheets are the same, you cannot assume that a datasheet from e.g. Mazda is representative for e.g. a Philips tube.
To give another example: Brimar's ECC81 has a Vhk of 250V whereas all the other ECC81 (12AT7) have a Vhk of 90V.
Just look at the well documented differences of the 7868 / 7591. The current manufactured ones will quickly fail if you use the original values for Rg1.
It is always best to stick with the valves recommended by the manufacturer of the equipment.
Some 7189 were relabeled as EL84 and the confusion goes on. Just check how many different ECC83 (12AX7) there are and then start checking for the different recommended operating points. IIRC the ECC83 from Mazda has a totally different recommended operating point than most other manufacturers'. In other words they may work but they are not identical and some sensitive circuits can/will give problems.
As the ECC83 documentation shows not all datasheets are the same, you cannot assume that a datasheet from e.g. Mazda is representative for e.g. a Philips tube.
To give another example: Brimar's ECC81 has a Vhk of 250V whereas all the other ECC81 (12AT7) have a Vhk of 90V.
Just look at the well documented differences of the 7868 / 7591. The current manufactured ones will quickly fail if you use the original values for Rg1.
It is always best to stick with the valves recommended by the manufacturer of the equipment.
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The original document by Schade - Beam Power Tubes, publication ST-59, March 1938, RCA.
page 155 mentions screen 10 to 20 volt below plate
page 160 in the document it mentions 10 to 15 Volts below plate to prevent secondary emission effects
page 169 mentions designed for screen to be between 250 and 300 V
page 155 mentions screen 10 to 20 volt below plate
page 160 in the document it mentions 10 to 15 Volts below plate to prevent secondary emission effects
page 169 mentions designed for screen to be between 250 and 300 V
EL506,
Thanks for mentioning the 6CA7 and EL34.
I think a simple fact, and a bit of logic can shed some light on the subject.
The fact: look at any, and all diagrams of the 6CA7 pinout.
Data sheets for the 6CA7 show pin 1 as the Suppressor grid, g3, and only g3.
And it shows the 6CA7 pin 8 is the cathode, and only the cathode.
I am not aware of any Beam Power tube that has Beam Formers that are connected to a pin that does not also connect to the cathode. (But someone will find one).
"ALL generalizations have exceptions" - Mr. Spock, find the logic in that quote.
Therefore, I say that all real 6CA7 tubes are Pentodes, with a suppressor grid that has real grid wires. They do not have beam formers connected to pin 1.
If you can find a 6CA7 that has the beam formers connected to pin 8, then I think that tube should be dual labeled 6CA7/KT77. (Try and find a 6CA7 such as that, with beam formers, and that are only connected to pin 8, along with the cathode; and with pin1 not connected to anything). That pinout looks like a KT77.
And so much for the patent wars, patent work-arounds, and the lawsuits, part of the cause of all this confusion.
Most of the original players have passed away by now, or their brain's memory is now suspect.
Note: Whenever I say Beam Formers, I am talking about some metal plates (but not 'The Plate'), that shape the paths of the electrons to the Plate.
The kind of Beam Formation that makes beams (sheets) by lining up g1 and g2 grid wires is a different thing.
Some tubes do that g1 and g2 wire lineup, and also employ Beam Formers too.
Thanks for mentioning the 6CA7 and EL34.
I think a simple fact, and a bit of logic can shed some light on the subject.
The fact: look at any, and all diagrams of the 6CA7 pinout.
Data sheets for the 6CA7 show pin 1 as the Suppressor grid, g3, and only g3.
And it shows the 6CA7 pin 8 is the cathode, and only the cathode.
I am not aware of any Beam Power tube that has Beam Formers that are connected to a pin that does not also connect to the cathode. (But someone will find one).
"ALL generalizations have exceptions" - Mr. Spock, find the logic in that quote.
Therefore, I say that all real 6CA7 tubes are Pentodes, with a suppressor grid that has real grid wires. They do not have beam formers connected to pin 1.
If you can find a 6CA7 that has the beam formers connected to pin 8, then I think that tube should be dual labeled 6CA7/KT77. (Try and find a 6CA7 such as that, with beam formers, and that are only connected to pin 8, along with the cathode; and with pin1 not connected to anything). That pinout looks like a KT77.
And so much for the patent wars, patent work-arounds, and the lawsuits, part of the cause of all this confusion.
Most of the original players have passed away by now, or their brain's memory is now suspect.
Note: Whenever I say Beam Formers, I am talking about some metal plates (but not 'The Plate'), that shape the paths of the electrons to the Plate.
The kind of Beam Formation that makes beams (sheets) by lining up g1 and g2 grid wires is a different thing.
Some tubes do that g1 and g2 wire lineup, and also employ Beam Formers too.
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Most horizontal output tubes had a separate pin for beam former; slight positive bias killed VHF/UHF oscillation in the knee region. (Which showed up as vertical bands on the right side of the picture - were called "snivets")