12ax7 trouble

[i am sparticus]

this is an absolute noob question but i just want to check;

The schematic i have doesnt have the 4,5,or 9 legs on the 12ax7 tubes connected to anything, the heater connections, do i hoot then up to the 300v power?

Thankeees

[defaced]

No, that will turn them into fuses. Connect them to the heaters. It is common, but sloppy, practice to leave those unconnected in a schematic for readability - especially in DIY schems. In professional schems, the heaters are often called out explicitly - not with the tube symbol in the preamp circuit - on the power supply schem.

[i am sparticus]

on the schematic there is a 12v 'heater supply' just hook it up with this?

[Enzo]

How about you either post the schematic or link us to it. That way we know what amp you are talking about, and we can refer to specific points on it.

Heater wiring is often just understood to be there. And as defaced points out, a lot of times the audio circuits show the tubes without the heaters wired, but in the power supply section, there will be the row of heaters.

[stingray_65]

if you are supplying the heaters to a 12AX7 with 12v, you connect to pins 4 and 5.

if you are supplying the heaters with 6v, you connect pins 4 and 5 with a jumper and hook up to 4,5 and 9

as simple as that may sound, a schematic would be of great help, there are other considderations depending on your layout.

if for example you have multiple 12AX7's you need to keep your wiring in phase. the same heater wire that connects pins 4,5 on your first 12AX7 should connect with pins 4,5 on the next stage and so on

also the way the wires are routed can make a tremendous difference in reducing hum.

Ray

[i am sparticus]

ah ok, this is the schematic.

there is also a psu and lfo bit but i they shouldnt matter for this be methinks

thanks
matthew

[Enzo]

Well, the psu or power supply unit would be exactly where this information is likely to be.

Looking at the schematic you have posted here, we see the tube heaters are drawn on the tubes without connections. In this case we can assume the connections are meant to be understood or are drawn out on another page.

Note that not only are there no heater connections drawn, there is no power supply for the tubes. It shows 300v up top, but doesn;t show where that comes from. SO it too would be understood or part of a second page.

[i am sparticus]

this is the power circuit then

[Enzo]

Yep, on the power supply, it says right on the page "heater supply." The 7812 is a "three terminal voltage regulator" and it makes a steady 12v DC. That 12v is then fed to each 12AX7 tube between pins 4 and 5. Pin 9 will be left unconnected.

Every tube in an amp needs heater voltage, so it often is not drawn in because it is understood to be there. To make a dumb analogy, it is kind like telling the guitarist to play an A-minor chord. You don;t tell him to tune his strings to E_A_D_G_B_E first, because that is understood, it is a given. If you wanted him to tune the guitar a half step low, that would be a special case and you would spell it out for him. And that would be like Running ten 12v tube heaters wired in series across 120v. That would be special and not expected, so it would have to be spelled out.