B+ question

[iknowjohnny]

In running the B+ rail in the new amp i'm just completing, i have a question regarding how i will wire the B+ to all the preamp points. What if any are the areas i should keep the supply wire away from to lower the possibility of any issues? And secondly, what if any ARE the issues you may run into if the B+ is very close to certain parts of the circuit? Thanks.

[tubeswell]

IMHO be careful about which signal wires to have nearby and keep hi current AC wires away (any pairs should be twisted anyhow). Most other stuff should be okay, that B+ itself is filtered after all is said and done, so it is pretty stable. I mention the signal wires because the signal at subsequent conventional triode stages' plates will be inverted, and if there is any backwobble on the B+ due to excessive signal (or intermittent insufficient filtering) and it can randomly couple with the signal. So much for my wisdom. Interested to hear what others have to say.

[paulster]

In the preamp the B+ rails won't generally be modulated* because they are driving triodes operated in class A which are constant current, and so long as they are well filtered they will be very quiet because they are very low impedance, so functionally very similar to ground in your amp.

* It is possible to get inter-stage modulation across the plate resistors when you've got multiple gain stages sharing a single B+ capacitor but it isn't usually a problem when you've got a properly designed power supply.

[iknowjohnny]

So assuming the PSU is well designed you're saying the rail wires can be right up against anything w/o and tonal issues? I'm not worried about noise, as the amps i've built so far have been very quiet. Just about tonal issues that may cause the tone to not quite right. I mainly want to know if that could potentially happen and if so what areas to avoid close relation to the B+ wires.

[Firestorm]

B+1 and maybe B+2 deserve a little extra respect because they still have fairly high ripple and will radiate it. In two-channel Fender amps, because of the location of the filter caps, the B+1 and B+2 hot and ground wires all run right behind the Channel 2 tone, volume and reverb controls, which are all on grid circuits. The hum in this channel decreases significantly when these leads are shielded. My 2 cents.