• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Anti-Triode SEPP, how to do best?

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#81
These are the circuits.

The recommended BJT has a tad higher THD but more important, it has LOWER 3rd and uneven harmonics.

.SUBCKT 6V6 P S G K
Esp 2 0 VALUE={V(P,K)+13.49*V(S,K)+130.4*V(G,K)}
E1 3 2 VALUE={5.521E-7*(PWR(V(2),1.5)+PWRS(V(2),1.5))/2}
E2 3 4 VALUE={5.521E-7*PWR(13.49*V(S,K),1.5)*V(P,K)/25}
E3 5 4 VALUE={(1-V(4,2)/ABS(V(4,2)+0.001))/2}
R1 5 0 1.0K
Gk S K VALUE={V(3,2)}
Gp P S VALUE={0.92*(V(3,4)*(1-V(5,4))+V(3,2)*V(5,4))}
Cgk G K 4.5P
Cgs G S 4.5P
Cgp G P 0.7P
Cpk P K 7.5P
.ENDS 6V6
 

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#88
We normally shoot for half B+ on anode. So in your example is (140V - LEDs drop) + VGS or Vbe. That is for Q2.

For using a Darlington, I don't know. But it may be more prone to oscillation in practice?
 
#92
Roughly 10V for the upper, and roughly (B+/2)-10 for the lower, plus sink for it if enough current is running. That is the ballpark for choosing max V ratings of the semiconductor parts IMO.
 
#93
SY said:


Longer tube life? Do you mean because of the inability of the bias voltage to adjust itself as the tube ages and starts getting gassier?
Click to expand...


Yes, I mean that negative feedback on DC that we loose stabilizing an absolute value of a bias voltage.

I missed this thread before, sorry. Otherwise I would have commented on your very clever circuit. That's an interesting variation on a CCS. I use gyrators for active crossovers, but never have as a plate load. Excellent idea!
Click to expand...

Thanks! It was a logical evolution of this servo (a first, I decided to load the tube on a CCS, and then decided to shorten the servo path so it's impact on the signal will be less audible):

micpre.gif
 
#94
As I mentioned earlier you must use the Ua/Ia-curves to decide workingpoint.

With 6V6-trioded, B+ 300V , Ia 20mA, load above 10k and the BJT/Mosfet version, we can swing between 65-70V and 290V. This means the workingpoint should be choosen at ca 180V. This is where you will get symmetric clipping and max output.
 
#97
For valves with a lot of voltage swing, such as your examples, I guess you would need to drop quite a bit of B+ across the transistors, but what about a preamp with only a few volts swing?

In post 55, Revintage quotes an equivalence to about a 60H choke. One of the great advantages of loading an anode with inductance is that it allows you to run off a lower B+ while still maintaining your voltage swing. Does this not also apply with this circuit?
 
#98
hihopes said:


In post 55, Revintage quotes an equivalence to about a 60H choke. One of the great advantages of loading an anode with inductance is that it allows you to run off a lower B+ while still maintaining your voltage swing. Does this not also apply with this circuit?
Click to expand...

No, it is not a real coil that saves an energy in a magnetic field, it is an electronic simulation of a coil that spends an extra energy to work. But it dissipates much less of an energy than a plain resistor would do for the same results.
 
#100
I have downloaded the datasheet for irf9610 from International Rectifier, but it doesn't show the pinout - just says it is a TO220AB package. As far as I can find out, this seems to have a pinout of G,D,S (looking from the front). Can anyone confirm this? I am drawing up a PCB and obviously need to get this right. I can post a jpg of the PCB if anyone is interested, or would like to give feedback on it.
 
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