Hybrid issues

[Alexdlss]

Anyone can help!!

I bought two hybrid+ from generoso cozza.

I build the supply for the heating, and the time delay and the ps for the PowerMosfets myself and they work, when i switch on the hybrid+, the mosfets and the resistors in front are burning, I dont know how to adjust, and find out where the problem lies. The only thing Mr. Generoso tells to me is: "it must work".

I should say, that i have build several mos fet amps without problems.

Can anyone help me ?

 

[jcalvarez]

This?

 

[NickKUK]

Can you measure with a 300V capable multimeter:
a) the voltage across R5 - gives us the idle current through the power stage
b) the voltage across R14 - gives us the idle current through the LTP
c) the voltage from Ground to the upper and lower base.

 

[huggygood]

 

[Sorento]

There is something fundamentally wrong with how the n-channel FET Q4 IRF940 is connected.
The drain of a n-channel should have a positive voltage relative to its drain.
In your diagram the drain of Q4 sits at the most negative -35V rail ... !?!
I'm pretty shure, q4 is connected upside down, should be like this:
https://www.tubecad.com/march2001/Erno Borbely Amplifier Readmade.png

 

[nigelwright7557]

There is something fundamentally wrong with how the n-channel FET Q4 IRF940 is connected.
The drain of a n-channel should have a positive voltage relative to its drain.
In your diagram the drain of Q4 sits at the most negative -35V rail ... !?!
I'm pretty shure, q4 is connected upside down, should be like this:
https://www.tubecad.com/march2001/Erno Borbely Amplifier Readmade.png

Yes, the arrow is pointing wrong direction in Q4 mosfet.
Arrow is usually reverse biased.

They dont usually have valves driving output stages as valves take 30 seconds to warm up and so output is up at positive rail to start with !
This will drive 35v into your speaker if no output capacitor.

 

[rayma]

https://audioxpress.com/article/Build-a-Hybrid-Tube-MOSFET-SE-Amp

 

[nigelwright7557]

https://audioxpress.com/article/Build-a-Hybrid-Tube-MOSFET-SE-Amp

Wouldnt be first circuit on the internet to be wrong.
They have to catch out those crafty Chinese copiers somehow !

Q4 has a body diode and Q4 is currently acting as a diode.
D and S need swapping.

 

[rayma]

Yes, the Q4 device N type is right, but the D and S are reversed. That may be why he has heating problems.
Try the drain connected to the output instead. Notify the author of the schematic error.

 

[tikiroo]

The Tubecad schematic linked by Sorento is accompanied by an excellent write-up and suggestions of improvement of the original circuit:

https://www.tubecad.com/march2001/page19.html

 

[huggygood]

Banned member !!??