Self designed tube amp problem

[pdf64]

...Are you talking about the rc filters at the power supply rail for ripple minimization or the rc filters formed by the coupling capacitor and the grid leak resistor of each stage

I was thinking of the the RC interstage coupling, but thinking about your query, it kinda works for a PFB loop via a poorly decoupled HT too (motorboating).

[Helmholtz]

I designed it for light loading of the previous stage because the ecc83(previous stage)has high plate impedance.So do I remove it?

A µ-follower consists of a common cathode stage with a cathode follower as load on top. So the cathode follower is already built in. Output impedance is low, so loading is no concern.

[Manowar1985]

I thought of something else to avoid global feedback


I am thinking of trying correct local feedback configuration of each stage .What do you think of this. Will I achieve similar results as the global feedback

[Helmholtz]

I thought of something else to avoid global feedback


I am thinking of trying correct local feedback configuration of each stage .What do you think of this. Will I achieve similar results as the global feedback

Your µ- follower, PI and driver stages already use local FB.
While you could go class A with cathode biasing in the power stage (sacrificing some output power), a global NFB as recommended will be much more effective and it includes linearizing the OT.
And only global NFB allows to significantly lower the amp's output impedance which is desirable for hifi use.

[Manowar1985]

So to conclude. I remove the one μ follower and the cathode follower. I add rc filter for ripple in each stage and when applying global nfb I should have no more than 2 rc interstage networks within the loop. Is this right?

[Helmholtz]

So to conclude. I remove the one μ follower and the cathode follower. I add rc filter for ripple in each stage and when applying global nfb I should have no more than 2 rc interstage networks within the loop. Is this right?

Start with connecting the global NFB to the driver tube as said above and adding one more RC supply filter for the remaining µ-follower..

[Manowar1985]

Thanks a lot

[Manowar1985]

And about safety I have a question if anyone can help me.
First of all,correct me if I am wrong, grounding the chassis prevents electric shock because if the live wire touches the chassis or any metallic part including the input device(strings of a guitar) the fuse of the house blows because current flows from chassis(accidentally unconnected to ground)to ground causing a short instead of flowing through our body right?(if the ground of the house is really ground).Thank you

[Manowar1985]

Hi all once again.
I was just wondering if it is normal to have 5 watts rms max of clean signal from 2 el84's.Isnt it too little.Thanks a lot

[Helmholtz]

I was just wondering if it is normal to have 5 watts rms max of clean signal from 2 el84's.Isnt it too little.Thanks a lot

2xEL84 should give you more than 15W before clipping with a B+ of 300V at full output and an OT primary impedance around 8k.
What is the max. undistorted EL84 grid signal voltage?

[The Dude]

Both of those are mostly true, but there are other factors.

Regarding the ground question: Depending on where the short is, the amp's fuse may blow- not the house fuse.
Regarding the power question: That's typically true, but there are factors other than "2 el84's" such as B+ level, OT impedance matching, etc.

[The Dude]

2xEL84 should give you more than 15W before clipping with a B+ of 300V. What is the max. undistorted EL84 grid signal voltage?

Good point. Clipping may be occurring before signal even gets to the output stage.

[Helmholtz]

The EL84s will need around 10Vrms or 29Vpp at the grids for full output.

How do you measure output power?

[Manowar1985]

I tested the output stage alone having isolated it from the other stages.I used an external amplifier being able to provide very large output voltage.In my oscilloscope the output of the output stage was being distorted while the input was still clean.The maximum output undistorted voltage was 4 or 4.5 volts rms on 3.9 ohms ( a 15 watt resistor) and this is a little more than 4 watts rms I don't think this is normal.
The transformer was hand wired and when I measured it was 9.6kOhms anode to anode to 4 ohms at secondary. Thank you

[The Dude]

What is your measured B+?