#26 pre amp

[DIYspaceW]

Please try plate reactor load instead of resistor! The 301 is far better sounding in this setting...
For resistor load you will need a resistance 3-5x higher than of the plate,

 

[euro21]

something around 20-30K

.... with B+: 250-280V.

 

[euro21]

But have CCS.

... before the shunt regulator!

 

[neskor]

.... with B+: 250-280V.

yes, he will need higher B+

 

[merlin el mago]

Yes, so can't add an anode load resistor in place of OPT?

 

[merlin el mago]

No problem power tx secondary 250VAC

 

[euro21]

Yes, so can't add an anode load resistor in place of OPT?

Why not....but the sound will be better?

 

[merlin el mago]

I don't know, I want to experiment, thanks for the schematic🙂.

 

[merlin el mago]

What's the output impedance?

 

[euro21]

What's the output impedance?

About 6k.
With CCS load Rout about 400R!

 

[merlin el mago]

Cascode DN2540 CCS load like this?

 

[neskor]

yes, something like that 😉
here is the complete schematic

 

[merlin el mago]

Thank you Neskor.

 

[merlin el mago]

Please try plate reactor load instead of resistor! The 301 is far better sounding in this setting...
For resistor load you will need a resistance 3-5x higher than of the plate,

Reactor load is tranformer load?
For resistor load: plate resistance 7.600 ohms x 3 or 5 times = 22K8 or 38k?

 

[merlin el mago]

Why not....but the sound will be better?

Used 23K5 (two paralleled 47K 2W) in place of 24K, one chanel 145V the other 150V, how can reduce 150V to 145V or increase 145V to 150V?

 

[euro21]

how can reduce 150V to 145V or increase 145V to 150V?

Unnecessary to deal with few volts difference (3%?).

These tubes are 70+ years old pieces.
If you have few dozens of old DHT (for example #26) and tested its for example mutual conductance, close pairs DC characteristic may differs.

 

[merlin el mago]

So can listen?

 

[euro21]

So can listen?

Why not?

 

[merlin el mago]

Works but with a lot of noise not volume related surely trafo mains hum & tube microphonics, placed again the LL1660 and zero noise trafo mains & microphonics.

 

[king4joy]

Merlin.....we are clear that the noise is not volume related.....on top of that, appreciate if you could give more details about the hum.....