• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

12b4a

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Brett,

if do not let a CCS let it lift to 285V, i loose direct coupling.
This is a phono preamp with dc coupling over 3 stages. Converted into a line amp with input transformer by the input selector switch (this is a real comlex switch, cut off from the pix i posted as i intended the pix for another purpose).

But you are right, on always can use a nice low voltage MosFET CCS and hook it in series with a resistor. The CCS determines the current and is within comfortable voltage limits itself and the resitor handles the voltage drop and heat dissipation. Resistor on top, CCS on bottom.

The 12A4 link you posted leadds to the 12B4A. Do you have a link to 12A4?

Jennifer Conelly in leather: good idea :up: . :) but do i get you right? you would enjoy it? ;)
Sin bin isn't meant to be pleasant :devilr: ... :)
 
diyAudio Senior Member
Joined 2002
12A4

Bernhard,

Don't know if it is still of any use to you but you can consider 12A4 and 12B4A as electrical equivalents.Think the 12B4A has controlled filament warm up whereas the A4 hasn't.
Also the 12A4 may have a slightly lower Rp (ain't sure) which I think is what grabbed your attention in the first place.
When I get my tube stuff back in Belgium I'll doublecheck it.

Greetz,
 
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