I´ve built a 3A5 preamp

[euro21]

3A5 plate resistance is 8k3.
If you paralleled two halves, the resultant is 4k15.

The optimal load is -at least- 2x (rather 4x) source impedance, so rather 16k6.

150H impedance at 20Hz:
Z=2*pi*f*L
Z=2*3.14159*20*150
Z=18k85

So, the 18k85 load is appropriate for paralleled 3A5 at 20Hz.

 

[Ryssen]

Ok,thanks for the explanation.

 

[Ryssen]

An other question is: If you use CCS you get maximum amplifying factoring.
Does the induktor load get the same amplifying factor?

 

[euro21]

The CCS impedance is a few hundred kOhm ... few GOhm.




As you can see in #101 post, the 150H inductor impedance at 20Hz not reaches 20 kOhm.

 

[triode_al]

I've used the same board from aliexpress, with the same schematic as the output stage for a DAC - it sounds excellent in that role. The board parallels both triodes, I have mine running at 10mA per valve and ended up with about 90V or so at the anode.

Can you share the link from aliexpres?

 

[woodturner-fran]

https://www.aliexpress.com/item/400...1;30.21;-1;-1@salePrice;EUR;search-mainSearch
Of course its not SRPP!!!

 

[Ryssen]

https://www.aliexpress.com/item/400...1;30.21;-1;-1@salePrice;EUR;search-mainSearch
Of course its not SRPP!!!

No the 3A5 is connected in paralell.

 

[woodturner-fran]

Also - its not worth buying that for 30usd without the tubes. You can easily wire it on piece of perfboard.

 

[Ryssen]

Ive tried the induktor load now,but I came to the conclution that I like the Gyrator better.
Much more dynamic and you comes closer to the musik..

 

[woodturner-fran]

Nice result @Ryssen - did you go back to filament bias yet?

 

[Ryssen]

No I am still using the cathode bias as I dont hsve the spade for another trafo.