Just another simple hybrid

It was my long time idea. Now I started to simulate it, and looks quite good on the simulation.
The topology based on Blameless, but with tube VAS. Simulation result is 0.000421% 8ohm, 50W, 1kHz and 0.006% 50W/8ohm, 20kHz.
This is just a basic idea, and all comments are welcome!

Sajti
 

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Hi Guys

DC stability through the tube may not be great and a servo might be required unless the sim shows otherwise.

The DC output is controlled by the input stage, and it should be stable. The only issue is the startup, because the output will be hang up to the positive rail, until the tube heating up. So DC output protection will be very important.

Sajti
 
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Hi Guys

In a lot of hybrid amps a relay is used to tie an internal point to ground during the tube warmup. Most of those hybrids are of the type with a tube gain stage and solid-state buffer, then the tie-down point is at the junction between the tube output and the SS input. In your amp, you could tie the anode of the tube to ground during warmup, or some other point.

The parameter keeping symmetric clipping from happening is likely rp of the tube. If the current through the tube is kept low then it should be easier to pull close to the rail, except the bias elements for the tube are "in the way". Boosted rails for the front end would leave clipping entirely to the output stage, which has its pros and cons.

Have fun
 
Hi Guys

In a lot of hybrid amps a relay is used to tie an internal point to ground during the tube warmup. Most of those hybrids are of the type with a tube gain stage and solid-state buffer, then the tie-down point is at the junction between the tube output and the SS input. In your amp, you could tie the anode of the tube to ground during warmup, or some other point.

That can be an option. I will check it! My original idea is to keep the output relay off during the warm up. DC protection combinated with the relay driver makes it easy.

The parameter keeping symmetric clipping from happening is likely rp of the tube. If the current through the tube is kept low then it should be easier to pull close to the rail, except the bias elements for the tube are "in the way". Boosted rails for the front end would leave clipping entirely to the output stage, which has its pros and cons.

Have fun

The E88CC running with about 4,5mA, which means 2,25mA/triode. Checking the tube datasheet I found, that it will results saturation (0V grid), at approx 10V a-c voltage. It would be a huge loss in the efficiency. But my surprise was, that the input stage can easily drives grid current to the triode. This reduce the loss, and increase the distortion, but only in the last dB.

Sajti
 
frontend worth considering

It was my long time idea. Now I started to simulate it, and looks quite good on the simulation.
The topology based on Blameless, but with tube VAS. Simulation result is 0.000421% 8ohm, 50W, 1kHz and 0.006% 50W/8ohm, 20kHz.
This is just a basic idea, and all comments are welcome!

Sajti

Hi Satji!
John Broskie in one of his blogs proposed such frontend for hybrid amp, maybe it will be helpfull for you?
 

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