Hi at all.
It is possible to use a pentode like a 6l6 or any
Beam Tetrode, with a single-ended OPT transformer without 40% UL Tap ?
It is possible to use a pentode like a 6l6 or any
Beam Tetrode, with a single-ended OPT transformer without 40% UL Tap ?
Loop NFB of some kind is essential, when full pentode mode is employed. Even if open loop distortion was sufficiently low (it isn't), the NFB is needed to obtain a satisfactory damping factor.
Open loop distortion performance in full pentode mode is obtained by regulating g2 B+ at a fraction of anode B+. In particular, highly irritating intermodulation distortion (IMD) is held down.
Open loop distortion performance in full pentode mode is obtained by regulating g2 B+ at a fraction of anode B+. In particular, highly irritating intermodulation distortion (IMD) is held down.
santitrucco,
This thread is already going several directions.
First, let us know what kind of amplifier you want to build.
(If that is what you originally started this thread to do).
You want a single ended amp with a Beam Power tube, right?
Do you want to use:
A Beam Power Tube, sometimes called Beam Power Tetrode, such as a 6L6, KT66, KT77, 7591, 6BQ5, or 6V6, 807, 813, or other?
Or, a Pentode, such as an EL84 or EL34, or other?
(There is a difference)
What operating mode do you want the output tube to be in?
Beam Power mode, Pentode mode?
Triode wired mode?
Ultra Linear Mode? #
# Yes, it is possible to build an Ultra Linear output stage with an output transformer that does not have a UL tap, but that is quite a lot of work and complex circuitry *.
Unless this is a fantasy you have, to do a UL stage without having the UL tap, then I would not recommend it.
Instead, get an output transformer that has the UL tap.
(And yes, I have thought of doing it an even different way than the complex circuitry I mentioned above *, but have not had the time to find how well or poorly that might work).
So are we back to the Beam Power mode (or Pentode mode)?
Or, are we back to the Triode wired Beam Power tube (or Triode wired Pentode tube)?
Other questions to ask are: how much power do you need, what model speakers, room size, kinds of music;
and somewhat important: for a Hi Fi amp, or a Guitar amp?
I hope that gets us going in the right direction.
This thread is already going several directions.
First, let us know what kind of amplifier you want to build.
(If that is what you originally started this thread to do).
You want a single ended amp with a Beam Power tube, right?
Do you want to use:
A Beam Power Tube, sometimes called Beam Power Tetrode, such as a 6L6, KT66, KT77, 7591, 6BQ5, or 6V6, 807, 813, or other?
Or, a Pentode, such as an EL84 or EL34, or other?
(There is a difference)
What operating mode do you want the output tube to be in?
Beam Power mode, Pentode mode?
Triode wired mode?
Ultra Linear Mode? #
# Yes, it is possible to build an Ultra Linear output stage with an output transformer that does not have a UL tap, but that is quite a lot of work and complex circuitry *.
Unless this is a fantasy you have, to do a UL stage without having the UL tap, then I would not recommend it.
Instead, get an output transformer that has the UL tap.
(And yes, I have thought of doing it an even different way than the complex circuitry I mentioned above *, but have not had the time to find how well or poorly that might work).
So are we back to the Beam Power mode (or Pentode mode)?
Or, are we back to the Triode wired Beam Power tube (or Triode wired Pentode tube)?
Other questions to ask are: how much power do you need, what model speakers, room size, kinds of music;
and somewhat important: for a Hi Fi amp, or a Guitar amp?
I hope that gets us going in the right direction.
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Hi 6a3sUMMER. The tube is a Western Electric 350B Beam Tetrode.
The OPT that i have is a Lundahl 3K 8ohms , not have a UL tap.
I used this OPT with a 300B tube.
Triode wired only can i have 2 watts.
In Ultralineal mode, could have about 15 watts.
I want HIFI amp.
And about 8 or 10 watts.
Most Lundahl transformers have multiple primary windings. You might be able to use those models to do UL (maybe not a very good transformer for UL, but it might work).
Most Lundahl transformers I have used have multiple windings; but some of the windings are over one air gap, and the other windings are over the other air gap. That means those 2 sets of windings may not be coupled very well (higher than normal leakage reactance.
That is why I say it may not work well for UL operation (phase problems at high frequency). Do a Bass amp that way, perhaps.
If your Lundahl does not have multiple windings, then it will not be able to do UL without the assistance of extra circuitry.
And this probably is the best way to do it, even if the lundahl does have multiple primary windings.
There are some UL amplifiers on this forum that use a resistive divider and a MOSFET Source follower to drive the Beam Tetrode's Screen Grid. That is the UL method I am talking about which allows UL operation even if you have a transformer primary that has only 2 wires.
You will need to search the forum for amplifiers that use that UL method.
One of my amplifiers uses a KT66 Beam Power Tetrode in Ultra Linear mode, the UL tap is the 1/2 winding, 50%. But all the windings are wound over each other (a traditional single ended transformer with all E's on one side and all I's on the other side of the air gap).
Most Lundahl transformers I have used have multiple windings; but some of the windings are over one air gap, and the other windings are over the other air gap. That means those 2 sets of windings may not be coupled very well (higher than normal leakage reactance.
That is why I say it may not work well for UL operation (phase problems at high frequency). Do a Bass amp that way, perhaps.
If your Lundahl does not have multiple windings, then it will not be able to do UL without the assistance of extra circuitry.
And this probably is the best way to do it, even if the lundahl does have multiple primary windings.
There are some UL amplifiers on this forum that use a resistive divider and a MOSFET Source follower to drive the Beam Tetrode's Screen Grid. That is the UL method I am talking about which allows UL operation even if you have a transformer primary that has only 2 wires.
You will need to search the forum for amplifiers that use that UL method.
One of my amplifiers uses a KT66 Beam Power Tetrode in Ultra Linear mode, the UL tap is the 1/2 winding, 50%. But all the windings are wound over each other (a traditional single ended transformer with all E's on one side and all I's on the other side of the air gap).
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When you are going to use a type as rare and expensive as a Western electric 350B, I would advice against experimenting with them.
Either go for the datasheet: anode voltage between 250 & 350V, g2 regulated at 250V. Pentode mode requires some NFB to reduce the high output impedance. Cathode feedback can help as well. You can use the speaker winding for that.
Best option I think, is to go for a proven design for a full pentode mode amp. Alex Kitic's RH universal looks like a candidate (no personal experience).
Whatever you do: make it work with cheap 6L6's before putting in the expensive exotics.
Either go for the datasheet: anode voltage between 250 & 350V, g2 regulated at 250V. Pentode mode requires some NFB to reduce the high output impedance. Cathode feedback can help as well. You can use the speaker winding for that.
Best option I think, is to go for a proven design for a full pentode mode amp. Alex Kitic's RH universal looks like a candidate (no personal experience).
Whatever you do: make it work with cheap 6L6's before putting in the expensive exotics.
This is a possible solution
Tube Output (25 - 75 Watts) Single Ended - HI-FI (1627-1642 Series) - Hammond Mfg.
You can use three different solutions
Walter
Tube Output (25 - 75 Watts) Single Ended - HI-FI (1627-1642 Series) - Hammond Mfg.
You can use three different solutions
Walter
Regulation of g2 makes a huge difference, whether you use a simple zener regulated dividers the difference is noteworthy, compared with a bypassed resistor divider.
No doubt, something could be achieved with regulator tubes, or gas discharge tube.
No doubt, something could be achieved with regulator tubes, or gas discharge tube.