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O.U.D.D.C (Otomon Ultimate Direct heat tube Drive Circuit ) the new approach for DHT (Patient pending)
What is difference between Direct Heat Tube and inDirect Heat Tube ?
Direct Heat Tube is tube that has cathode come together with heater and indirect Heat tube is not. Most of the DHT has lower output impedance and big current flow in its plate. Most of DHT is Triode, there is very very few penthode tube that is DHT.
Because in DHT heater and cathode comes together so it has disadvantage is very easy to get hum and distortion, but in opposite site, it bring a very special note in low frequency and musical sound. That is why people like using DHT as power tube although most of them does not have much of power.
Why do people want to use DHT as driver tube
Physically, DHT has low output impedance so it is very good to use as a drive stage connect to power stage. And because of its special sound, many audio mania uses DHT as driver tube although using it is not easy because of the hum and distortion as characteristic of DHT.
Direct Heat Tube is tube that has cathode come together with heater and indirect Heat tube is not. Most of the DHT has lower output impedance and big current flow in its plate. Most of DHT is Triode, there is very very few penthode tube that is DHT.
Because in DHT heater and cathode comes together so it has disadvantage is very easy to get hum and distortion, but in opposite site, it bring a very special note in low frequency and musical sound. That is why people like using DHT as power tube although most of them does not have much of power.
Why do people want to use DHT as driver tube
Physically, DHT has low output impedance so it is very good to use as a drive stage connect to power stage. And because of its special sound, many audio mania uses DHT as driver tube although using it is not easy because of the hum and distortion as characteristic of DHT.
Traditional DHT driving method
1. Using resistor
This is good for a small DHT which require few mA of current, but most of DHT has much current flow in plate, so using resistor will make voltage drop too much and you need to use a very big resistor which is not easy to get and guarantee of quality. A resistor also make loss much in sound signal, so it is considered as the worst method for driving a DHT.
2. Using a plate choke to drive tube.
Using choke to drive plate of a DHT has advantage that you can handle the current flow in plate, a choke plate always has very little DCR and high AC impedance so it is very good for driving a DHT. Using a plate choke to drive a DHT also bring a very good control for the low frequency. But its disadvantage is it need a big coupling condenser to connect to power tube. Because the output impedance of DHT tube is very low and plate voltage is high so you need a good coupling condener that can handle high voltage with big value. The sound of driver stage will be effected by quality of coupling condenser.
3. Cathode follower method.
Cathode follower is very good method for a driving stage. It connect drirectly cathode of driver stage to grid of power stage. You can use a choke in cathode to drive a DHT in this case. Current flowing in plate of driver tube will be used to driver the power tube. This method resolve the disadvantage of plate choke driver method. It connects directly from driver stage to power stage without using coupling condenser or any other devices so the sound is purely brought to power stage.
But the disadvantage of this method is cathode follower method has gain in voltage about 1:1, so you can only get rid of big current from driver tube only. The sound is almost not changed. Because there is no gain in driver stage so you have to design amplifier gain in the first stage which make thing more complicated.
4. Using interstage transformers.
This is consider as the best method until now, it resolve all problems of methods that mentioned above. A big advantage of using interstage transformer is it has low DRC value and high AC impedance, the signal lost is very low but driver ability is very high, the sound is also very good quality with musical sound. But the disadvantage is physical limitation of an interstage transformer.
The response frequency is narrow. However a good transformer it is , it has limitation in output response frequency and the distortion of sound. The low frequency is not as good as cathode follower method. You will never resolve this problem eventhough you pay much money for the transformer.
The high quality of interstage transformer cost much of money.
Due to above problems, most of amplifier manufacturer dont use interstage transformer, the technical data of the amp will be not good and not give impact to customer.
OUDDC, the new approach
Due to the characteristic of DHT tube that has cathode and heater come together, Otomon Lab researched and developed and new driving method called Otomon Ultimate Direct Heat tube Circuit.
This method resolved all problem of traditional methods above, drive tube will connect directly to power stage from plate with a driving plate choke. The gain in driver stage is gain of drive tube. The sound is purely brought from driver stage.
The big feather of this method compare to another method is special sound in low frequency that you can not enjoy from another method. The low distortion in sound output with open wide sound stage.
5. Hybird Bias
Generally, we use fixed bias or auto-bias for bias setting for tube amp. Both of method has advantage and disadvantage itself.
With fixed bias, you can set the good point of working point in tube, the driving current to grid is big, it help the sound more powerful. But the disadvantage of fixed-bias is the bias is easily changed after time of playing due to the heat of parts as resistor or capacitors.
Vice versa, the advantage of auto-bias is you dont need to worry about the changing of bias voltage. You dont need to care to bias of tube but driver current to grid is not as much as fixed bias.
The bias in O.U.D.D.C is neither fixed-bias nor auto-bias, it is hybrid bias which get the advantage of 2 method, user does not need to care to amplifier bias and the driver current to grid of tube is very much, so the sound of low frequency is very good.
1. Using resistor
This is good for a small DHT which require few mA of current, but most of DHT has much current flow in plate, so using resistor will make voltage drop too much and you need to use a very big resistor which is not easy to get and guarantee of quality. A resistor also make loss much in sound signal, so it is considered as the worst method for driving a DHT.
2. Using a plate choke to drive tube.
Using choke to drive plate of a DHT has advantage that you can handle the current flow in plate, a choke plate always has very little DCR and high AC impedance so it is very good for driving a DHT. Using a plate choke to drive a DHT also bring a very good control for the low frequency. But its disadvantage is it need a big coupling condenser to connect to power tube. Because the output impedance of DHT tube is very low and plate voltage is high so you need a good coupling condener that can handle high voltage with big value. The sound of driver stage will be effected by quality of coupling condenser.
3. Cathode follower method.
Cathode follower is very good method for a driving stage. It connect drirectly cathode of driver stage to grid of power stage. You can use a choke in cathode to drive a DHT in this case. Current flowing in plate of driver tube will be used to driver the power tube. This method resolve the disadvantage of plate choke driver method. It connects directly from driver stage to power stage without using coupling condenser or any other devices so the sound is purely brought to power stage.
But the disadvantage of this method is cathode follower method has gain in voltage about 1:1, so you can only get rid of big current from driver tube only. The sound is almost not changed. Because there is no gain in driver stage so you have to design amplifier gain in the first stage which make thing more complicated.
4. Using interstage transformers.
This is consider as the best method until now, it resolve all problems of methods that mentioned above. A big advantage of using interstage transformer is it has low DRC value and high AC impedance, the signal lost is very low but driver ability is very high, the sound is also very good quality with musical sound. But the disadvantage is physical limitation of an interstage transformer.
The response frequency is narrow. However a good transformer it is , it has limitation in output response frequency and the distortion of sound. The low frequency is not as good as cathode follower method. You will never resolve this problem eventhough you pay much money for the transformer.
The high quality of interstage transformer cost much of money.
Due to above problems, most of amplifier manufacturer dont use interstage transformer, the technical data of the amp will be not good and not give impact to customer.
OUDDC, the new approach
Due to the characteristic of DHT tube that has cathode and heater come together, Otomon Lab researched and developed and new driving method called Otomon Ultimate Direct Heat tube Circuit.
This method resolved all problem of traditional methods above, drive tube will connect directly to power stage from plate with a driving plate choke. The gain in driver stage is gain of drive tube. The sound is purely brought from driver stage.
The big feather of this method compare to another method is special sound in low frequency that you can not enjoy from another method. The low distortion in sound output with open wide sound stage.
5. Hybird Bias
Generally, we use fixed bias or auto-bias for bias setting for tube amp. Both of method has advantage and disadvantage itself.
With fixed bias, you can set the good point of working point in tube, the driving current to grid is big, it help the sound more powerful. But the disadvantage of fixed-bias is the bias is easily changed after time of playing due to the heat of parts as resistor or capacitors.
Vice versa, the advantage of auto-bias is you dont need to worry about the changing of bias voltage. You dont need to care to bias of tube but driver current to grid is not as much as fixed bias.
The bias in O.U.D.D.C is neither fixed-bias nor auto-bias, it is hybrid bias which get the advantage of 2 method, user does not need to care to amplifier bias and the driver current to grid of tube is very much, so the sound of low frequency is very good.
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