Tremolo

[Bill Layer]

Hi Mark / All,

>I don't know that much about Tubes (or anything) but after look at info
>on the 12AX7 tube I have some questions.
>
>1. I am assuming two of the circled bits equals one tube. Does It matter
>which two go together? Oh wait, I get it, V1, V2, & V3?

Well... not really, BUT: It's nice to keep signals of roughly the same size
in a single package, just for the sake of keeping impinged noise low. Also,
it's nice to use a single two-section device for a diff-amp, to take
advantage of common-mode cancellations.

>
>2. I've never built a 300V power supply, (sounds dangerous) does anyone
>have a schematic? Anything I should know before I kill myself?

I can find or draw you a schematic for whatever type of supply you'd like.
But if you are running only small-signal devices like the 12AX7, a 165-185V
supply would be fine. Consider using vacuum tube rectifiers; it affects the
sound, and solves another issue which I'll discuss in a moment.
>
>3. Where do the heaters go? AC?

The heaters could be run from AC, due to a unique feature of the 12A?7
series of tubes. The heater is a 12 volt fiament, center tapped. By tying
the ends of the filament together, and applying power to the center tap,
the tube may be operated at 6 volts. Now the AC on the filament is
comon-mode, and should be cancelled. The power supply may need to employ
some hum bucking as well.
>
>4. Should all Resisters be 1W?

Most old circuits use 1/2W, but it's become common practice among
audiophiles to use 2W-10W everywhere. Larger wattages are not a bad thing,
when voltages are high, and potential power is large.

>5. Are all caps uf (micro-farads) except for the one with the p? The
>numbers under some of the caps, are they the voltage rating? What about
>the rest of the caps?

Dunno. Can't read the schemos due to local proxy firewall. BUT: All signal
path caps should be rated to withstand the FULL voltage of the supply,
UNLOADED. The power supply electrolytics should have a reasonable safety
margin as well. Remember, that in a tube circuit, nothing draws current
until the tubes are hot. This means, that if you use solid-state rectifiers
in your supply, switching-on presents every point in the circuit with the
FULL supply voltage, until the heaters come up. That point in the circuit
that only measures 65 volts in operation, is now seeing 2,3, or 400 volts!>

This is where the tube rectifier helps. The delay in heating the rectifier
allows the other tubes to heat as well, and reduces the shock to the
circuit that ocurrs with a solid-state supply. Certain tubes (like the
5AR4) are specifically engineered for this characteristic. But I doubt you
(or I) feel like springing for a 5AR4...

>Thanks

Quite welcome. 


Bill Layer
Sales Technician
<b.layer at vikingelectronics.com>

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