20W OTL with 6N5P, Opinions...

[tricomp]

Hi,

I got this off a Chinese forum where all sorts of electronic designs are discussed.
It seems rather simple to me; doesn't take much to build but will it work?
6N5P is of course the Russian 6H5П, data available on frank.pocnet.net
I had to stitch the schematic and I've added the data given on the forum in the pdf.

Your input highly appreciated,

rgds,

/tri-comp

 

[smoking-amp]

It is lacking a bootstrap (from the output) of the top 6N6 plate resistor, so will not have symmetrical grid drive signals for the 6N5P outputs. When the bottom bank of 6N5P's turn on, the top bank will not turn off enough to be complementary. So excessive current will flow thru both banks. Wasted energy, excess tube heating, high 2nd harmonic.

 

[tricomp]

It is lacking a bootstrap (from the output) of the top 6N6 plate resistor, so will not have symmetrical grid drive signals for the 6N5P outputs. When the bottom bank of 6N5P's turn on, the top bank will not turn off enough to be complementary. So excessive current will flow thru both banks. Wasted energy, excess tube heating, high 2nd harmonic.

OK, I get your point.
Even if this problem is dealt with the circuit still seems fairly simple.
The given Ra for 6N5P is 155R and 4 in parallel isn't going to get anywhere near 8 Ohm. How can they expect to lower Zout enough to be compatible with a common 8 ohm speaker? Doesn't it take more tubes in parallel?
Ik max is 25mA pr. triode which certainly isn't a lot for OTL.
Just a Chinaman's crazy dabblings or the basic design that can be developed into something usefull?

/tri-comp

 

[smoking-amp]

The product of the gains of the 6N11 and 6N6 can lower the output Z for small signal by that gain product. But not for large signal power delivery. With a 40 Ohm output Z the power transfer into 8 Ohms will be rather poor (same current thru the 40 Ohms as thru the 8 Ohms, so 20% efficient times 50% tube efficiency at best in class A => 10%). A headphone amplifier maybe. Or many more tubes needed.

 

[tricomp]

The product of the gains of the 6N11 and 6N6 can lower the output Z for small signal by that gain product. But not for large signal power delivery. With a 40 Ohm output Z the power transfer into 8 Ohms will be rather poor. A headphone amplifier maybe. Or many more tubes needed.

Thanks, it's what I thought.

I suppose it isn't the first time a 'High-End' tube-amp design slips out of China without the muscle to fill promises

rgds,

/tri-comp