Tube Amp Power Supply & How To Hook Up

The Wiring Diagram for the typical Power Supply looks simple - but it is anything but.

It is also a dangerous thing and NOT for Children, but for adults aware of the risk of lethal voltages - 720 VAC Peak to Peak. Skilled Technicians have an insulated wire with alligator clips/and or insulated leads. Between these is soldered a 1K, 1 Watt Resistor. Before anything is touched in the amp at all; power is turned off, and amplifier is unplugged...then one clip goes to circuit ground, and, very carefully,  the other end of your "slow shorting lead" goes  to the hot wire. A voltmeter connected in this way will indicated a rapidly dropping voltage, indicating that the big capacitors are bleeding off to ground. Only after this is it safe to do any further work on the circuit with one's hand. Skilled Technicians also get in the habit of working with one hand while taking voltage readings with the amp powered on. This will reduce the chance of a lethal voltage streaming from one hand to the other, through your heart, which is the killer path. Never forget this.

I fabricate a piece of blank circuit board, and label connections  with a marking pen so as to reduce possibility of error. ( click on images for a full size image )

Pay careful attention here: Red wires from PS Xformer, one each go to the black end of the Diodes. The Silver ends of the Diodes are connected together, and one wire from that connection is fed to the 7 henry "Choke ". And from the Choke it's other black wire goes to the "+" lug of the  100 Microfarad, 500 volt "Can Capacitor".

The red and yellow wire from the PS Xformer goes to the "-" lug of the Can Capacitor- the ground circuit for the entire amp. From off the  same  "+" lug of the can capacitor  comes your 330 VDC for both channels.

Your "B+", or 330 VDC is fed by four wires to your amplifier circuit . An ORANGE wire from each output Transformer is connected to the 330VDC, and these two output transformers have a BLUE wire each...these go directly to the Anodes of your output tubes. Not shown here, but 330VDC goes THROUGH the output Transformers first, THEN the 330VDC goes to the output tubes.

Two Bright Red wires shown in the drawing are 330 VDC, one for each channel, going directly to the "Load Resistors "Anodes, or "Plates"

P.S.   yes I see that I have labled the orange and red wires with 330 VDC in the above two drawings opposite ways...it is basically the same...330 vDC goes to both the load resistors of the first  stage; and 330 vDC also goes to the output transformer THEN to the plates of the output tube...no Load resistor for the output tubes; the transformer IS the "Load". It simply serves to drop the high voltage low current to low voltage high current, which is what speakers need.

Lighted Rocker Switches are very helpful to remind you that the amp is still powered on for those times when the music has stopped, and you might forget the amp is "ON".

These switches have a BRASS LUG to which the white neutral wire from your 115 VAC goes . The HOT WIRE is always BLACK, and the NEUTRAL WIRE is always WHITE  in household circuitry. The BLACK wire goes to the opposite side of the rocker switch . Then connect one black wire from your 720VAC power supply transformer to the BRASS LUG , together with the Neutral white wire. The other black wire from the 720 VAC Power Supply Transformer is soldered to the  MIDDLE LUG of the lighted rocker switch. 

Let me perfectly clear...NO power is on any of these wires at any time..no 115 VAC shall be applied until all connections are completed, and thoroughly examined for error. As mentioned on another page, a VARIAC is a good idea, so as to gradually apply 115 VAC from , say 20VAC, and gradually turn it up watching for smoke or spark. You should, of course, have the FUSED power jack installed before any power on test...or "smoke test" it is called, jokingly - for often there is a mistake in wiring. Avoid that at all costs.

Front and Backside view of the Fused 115VAC Power Jack .  Pay careful attention to the back view here, and connect the Black Wire to the Hot ; and the White Neutral Wire to the Neutral side of the Jack...the silver "L" shaped strip is at "top". The Neutral wire from household power is the lower lug toward you...the black behind that...and behind that is the third lug for the "AMP GROUND" -  which connects your amp ground all the way out to your outside - household "Earth Ground". This is a safety issue and cannot be ignored. It is common to forget an amp ground connection:  in part owing to the fact that "ground" symbols on schematics sit there in "mid air" it would seem...no these all connect together through the entire amp. Missing a ground connection is a common error.

One last reminder of the lethal voltage on the amp, throughout the amp. I cannot emphasize too strongly that only a sober responsible adult can manage building a vacuum tube amp with such high voltages. Now that I have powered it up to show the lethality of this power..I have shut it off, and will now apply my insulated wire with the insulated alligator clips, with 1K, 1 Watt resistor between the clips, and will bleed off the capacitors in the power supply and also throughout the amp circuit with other capacitors, all of which are holding a whopping charge - and bleed it down until my voltmeter reads a few volts at most. 

 I failed to do this once- just cut the amp off. Some time later, I came back and noticed a nut loose that holds the circuit board in place, and put my finger on it to spin it down...and got hit with what seemed like a baseball bat really hard. Luckily I touched something accidentally with one hand only...otherwise I would not be here today to warn you about this. I will NEVER fail to bleed off the capacitors while the bottom is off, and the circuits exposed.  I will Never take a chance like that again. I strongly urge anyone new to this hobby to take this warning dead seriously. This is not a joke.

Here the HP "Nixie Tube" multimeter is reading 337 volts DC