Hi Guys,
Came across this : www.nataudio.com/products/vacuum-integrated-tube-amplifier/item/29-single-hps.html.
Wonder how they attain 50 watt using just 1 Gm70, is it possible ?
Came across this : www.nataudio.com/products/vacuum-integrated-tube-amplifier/item/29-single-hps.html.
Wonder how they attain 50 watt using just 1 Gm70, is it possible ?
In theory an SET can be as much as 50% efficient and the GM79 can dissipate 125W oi I guess it is just about possible.
Cheers
Ian
Cheers
Ian
It may have 5% THD, perhaps 10% THD at the 50 Watt level.
Or it may have very high global negative feedback, so it may be un-stable on some loudspeaker models.
High distortion - great for certain Guitar Amplifier Sound Effects.
Perhaps not good for Hi Fi (I know, this is an integrated Hi Fi amplifier).
It sounds too true to be good. Caveat Emptor.
On the other hand, it just might test out with flying colors.
It does suggest using: 'best amplifier performance with moderate efficiency speakers that have stable impedance between 4 and 16 Ohms'.
What is Stable Impedance? No varying impedance? non reactive impedance? Or what?
And the distortion is 0.15% At what power level?
It has Zero global feedback (perhaps uses Schade or similar negative feedback)?
Non global NFB has the advantage of not taking the feedback from the output transformer secondary, improving stability versus NFB from the OPT secondary.
In some former days of vacuum tubes, tube data sheets listed output power at 5% THD.
Some marketeers specified some ICs and some modularized solid state amplifier modules at 10% THD.
I used one of those solid state amp modules in a special featured guitar and microphone amplifier I designed that a friend and I built (I forgot that I ever did a guitar amp). Despite the 10% THD rating, it sounded good at reasonable volumes.
10% THD - "What an improvement", more power, less Hi Fi.
Just my opinions.
Or it may have very high global negative feedback, so it may be un-stable on some loudspeaker models.
High distortion - great for certain Guitar Amplifier Sound Effects.
Perhaps not good for Hi Fi (I know, this is an integrated Hi Fi amplifier).
It sounds too true to be good. Caveat Emptor.
On the other hand, it just might test out with flying colors.
It does suggest using: 'best amplifier performance with moderate efficiency speakers that have stable impedance between 4 and 16 Ohms'.
What is Stable Impedance? No varying impedance? non reactive impedance? Or what?
And the distortion is 0.15% At what power level?
It has Zero global feedback (perhaps uses Schade or similar negative feedback)?
Non global NFB has the advantage of not taking the feedback from the output transformer secondary, improving stability versus NFB from the OPT secondary.
In some former days of vacuum tubes, tube data sheets listed output power at 5% THD.
Some marketeers specified some ICs and some modularized solid state amplifier modules at 10% THD.
I used one of those solid state amp modules in a special featured guitar and microphone amplifier I designed that a friend and I built (I forgot that I ever did a guitar amp). Despite the 10% THD rating, it sounded good at reasonable volumes.
10% THD - "What an improvement", more power, less Hi Fi.
Just my opinions.
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Where does the 42% come from? It does not matter what version of class A you work in, the theoretical maximum output power is 50% of the dissipation.
Cheers
Ian
It is no bad at all.🙂.Remember of old days when 5% of tube distortion was rule.
In this design,A2 class set with DHT or DHP, OP must have aditional secundar winding for NFB.10-15db is suficient.
I agreed with all your remarks but topics is about max power tube can give.
And THD of 10% wake up ours adrenalin and we feel happy🙂
It is possible in a deep A2 operation mode, that means driver stage must deliver tenths mA of signal currents into GM70 grid. This is impossible from ECC88 tube, here it could operate only as two stage voltage amplifier. After the ECC88 stage they MUST use transistor source follower for delivering big signal currents into GM70 grid. So, in fact, this amp is not a tube amp, it is HYBRID amp. In the description below taken from the NAT site, they mention "last generation J-FET semiconductors", that explains the high output power.
"Quality of electronic components that is used inside Single HPS are at high level - military grade and N.O.S. tubes, Teflon and "in-oil" military grade capacitors, Caddock and Vishay 5ppm resistor, Ohmite Alumina HV type resistor, many electrolytic capacitors for 105C of operating temperature, last generation J-FET semiconductors, laboratory grade speaker connectors, Hammond mechanics, teflon isolated silver-ofc military grade wiring…"
Guess it would be running much hotter then normal Gm70 implentations.
I like to build a GM70 amp but having experienced the heat it produces &
the high voltage involved it's kind of holding me back. Came across a schema
that use's only 875v to produce 32 watts. This is confusing too as the voltage
used varies so greatly. Hasn't anyone found the sweet spot for the GM70 yet ???
I like to build a GM70 amp but having experienced the heat it produces &
the high voltage involved it's kind of holding me back. Came across a schema
that use's only 875v to produce 32 watts. This is confusing too as the voltage
used varies so greatly. Hasn't anyone found the sweet spot for the GM70 yet ???
That should also be with transistor driver at GM70 grid. If to build genuine tube GM70 amp, I would consider LAMM ML3 approach. Tube plate voltage rectifies, tube rectifiers for fixed bias voltage, 1100V, 125W. Expensive, but free cheese does not exist.