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Hybrid amp

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Hi there


I need a tube with mu is 10 and 10 mA for the mosfet driving.

There are so much tubes I thought I ask .

thanks in advance.
 

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6DE7 has a triode with µ ≈ 6 and another in the order of 20, if I don't remember bad.

But why such low µ?

This mosfet driver do get to much, when mu is 20 then I get full power with 0,3 volts, I did want that lower, this high is because there is no feedback.

Maybe a penthode can be adjusted for lower mu.

The high supply for mosfets is not such serious, but when put 1 volts in it clips, power, well, I do just better not say.

6DE7 has two different triodes.

thanks for respons.

regards
 
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A cap and resistor from plate to grid of the 6SN7 would give you local negative feedback for reducing gain. If you are at the build stage and looking for a dual low-mu triode in a single octal package your number of tubes is extremely limited. How is that phase inverter supposed to work? To me it looks like the upper triode does all the work and the lower triode is biased via DC from the 6SN7 but is essentially grounded for AC so it just sits there?
 
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As I am busy with the circlotron with tube driving I did a time ago this, idea was a amp without cathode followers because some people say that this do sound better, well it did, I had a amp who is still not beated yet, but this one is more complicted and has a dual mu stage on top op tubes.
 

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For the people, I have lone the schematic from a guy here in Holland who do make tube amps, Triode Dick's Page this schematic a Paraphase fasedraaier is from him, but did already excist in 1959, and maybe this is a way to get lower amplification, because the mosfet output is a compound pair with 100 % feedback it do lot loose efficienty what happens with normal source follower.
 

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Oke, I managed it this way as a test, because of no feedback and wish of low HD I did use mosfet gyrator from a russian guy from here, name lost, and a mirror current source with mosfets making a nice fase shift who drive the mosfets, a tube with a MU of 60 do well.

regards
 

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I have now try some things, there are much possibility's out there, but with one tube I have more freedom, valve who has mu of 60 or 80 is oke, a penthode 6J51P do nice here.

So when I am ready with allfet circlotron I go try it.

For the tube experienced here, who do you like best as a fase shifter, I have here use mu loaded one for low impedance to mosfets..

regarerds.
 

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Hi All


I do not understand why in ltspice this happens, it has to be opposite fase in stead I get distortion, but in multisim it is fine, when delete the mu follower mosfet it did go right, but the mosfet is a source follower so it do not flip fase, strange behavior of ltspice or I do something wrong.
 

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Yes, you set a voltage on the grid of the phase splitter too high, saturating the tube.

Ahh thank you mayborn, I did have the schematic from internet, I did saw that sometimes a diode is used between grid and cathode as a flashover protection?


I have just restore a jukebox amplifier of a friend, making it quit (mosfet supply regulator) and replace some resistors, replace all the tubes like 2 x 6L6 12AU7 12AX7, now it has only some noise what is normal for a dynamic pickup amplifier, a lot different when it came it make my friend happy again, it is a AMI jukebox who did play well but did humm a lot.

Oke have change the voltage, it did has to be as low as 80 volts to get it working properly, the voltage amp tube has for this reason now a quite low voltage?

However distortion is quite high now.
 
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Yes, you set a voltage on the grid of the phase splitter too high, saturating the tube.

I use a gyrator now from your design, I hope you don't mind in stead of the mustage I did use, the gyrator has lower capacitance and give lower distortion I do like the distortion as it is with only first higher and the rest very low.

I have put 104 volts on the fasesplitter, lower voltage do let voltage stage work less like I want.

I have change the gyrator so it puts out 104 volts.

regards
 

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Ahh thank you mayborn, I did have the schematic from internet, I did saw that sometimes a diode is used between grid and cathode as a flashover protection?


I have just restore a jukebox amplifier of a friend, making it quit (mosfet supply regulator) and replace some resistors, replace all the tubes like 2 x 6L6 12AU7 12AX7, now it has only some noise what is normal for a dynamic pickup amplifier, a lot different when it came it make my friend happy again, it is a AMI jukebox who did play well but did humm a lot.

Oke have change the voltage, it did has to be as low as 80 volts to get it working properly, the voltage amp tube has for this reason now a quite low voltage?

However distortion is quite high now.

You can use a voltage divider between them to make both tubes happy. I do that pretty often. The upper resistor of the divider shunt by a cap. Here is the example, a couple of 2M2 resistors.
 

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