Chassis lay out:

• Before determining the lay out of the chassis, collect each component to be sure about its measures. This saves unneccesary work if component size seems to be different in the rear.

• Locate the power supply transformer as far as possible from the most sensitive input, try by turning to determine the least effective magnetic field.

• Place supply chokes always 90 degrees with respect to the supply transformer.

• Try to establish the ideal lay-out by following the electrical schematic literally, this to create as short as possible connections between each component.

• Keep AC apart from DC if possible.

• Keep AC wiring far from signal wiring, if crossing is inavoidable, keep the angle at 90 degrees.

• Place AC wiring tight to the chassis.

• AC wiring is made out of three separate wires, 2 for zero and 1 for phase. These are braided together.

• When distributing the filament voltage, never wire the tubesockets in series. Use a terminal from which each tubesocket gets its own wiring.

Chassis material:

• Non ferro materials have the preference here. Not only easier to work with, but also non sensitive for magnetism.... Stanless steel is an option too, only harder to work with. Copper is an excellent choice, aluminum cheaper. If power- and outputtransformers are placed on the chassis, go for a minimum of 3 mm thickness depending on surface size.

• It is practical to bend the upperplate at a 90 degrees angle, creating the backside for easy mounting of RCA receptacles, binding posts and power inlet. The angle can be used to place the transformers on/nearby. The rest of the chassis can be made out of wood. 

Earthing method:

• Use "one-point-earthing". This means that only at one point the electrical schematic contacts the chassis. Each earthing point is to be connected to this point separately. A good spot for "one-point-earthing" can be one the power transformers' atachment bolts.

• Create an earthing point for each amplifying stage apart. These are to be connected to the chassis earthing point. ie: earthing from RCA input, girdresistor, kathoderesistor/capacitor make one earthing point (not to chassis). In the next stage these components have also their own earthing point and so on. All these points are separately connected to the chassis earthing point.

• The neagative of the first power supply capacitor is directly connected to the chassis earth, each capacitor following is to be connected separately except from the last (before the tubes' load), this one is to be connected to the earthing point of that stage.This is done to shorten the signal path through the supply..

• If a multiple capacitor with common negative is used, this negative is put to the chassis. The first capacitor negative, is to be connected to this point. For all the accessory stages, this will be the earthing point. Click here for schematics to clarify this..

• Do not "gurdle in" a component or tubesocket using the earthing wires. If possible, tie them together.

• A "one-point-earth" can easily be made of multiple solderlugs, bolted circular to the chassis.

• Do not use thick wiring for earthing purposes. The biggest currents are seen by the first supply capacitor - a 0.8mm diameter is sufficient.

• If your power transformer is mounted on rubber grommets, don't forget to connect it to the chassis. This is also done with supply chokes.

• Try always if you can do without earth screens (like coax aso). Without screen you'll get an opener sound. If these have to be used (humm), connect them at one point only to the earthing point.

• Do not connect your installation to the earth connection of your mains. This earth connection is commonly used for all kinds of signalling.

• Do not forget to connect the secondary of the output transformer to the earting point. This can save your speakers!

Wiring:

• Don't use thick wiring, 0.4mm in diameter is my standard. Only for filament thicker wiring can be used. 1.8mm in diameter can be used for filaments up to 4 Ampère.

• If possible, use wiring with heath withstanding insulation, like teflon. I prefer cotton. If higher voltages in combination with cotton insulation are used, watch out for jump over! 

• Do not use stranded wire! Better (sonically) results can be obtained in using solid core. Solid core can also better shaped into place (hook-up).

• Use copper or silver, silver as preference. Don't use silverplated copper. If bare silver is used, insulation with PTFE-tape (gaztape) will do just fine. You can also use teflon tubing but, again, cotton sounds better! (for cotton something like a shoe-lace can be used!)

DC-current regulators for DHT's.

• The best way to feed the filaments of a DHT is with a battery... If not applicable, you can best use DC-regulators They are very silent and sound very good! You can use them, if welladjusted, up to RIAA-correction level! Click here for extensive schematics and calculations to DC-regulation (top schematic Tom Ronan, bottom schematic Phil Sieg).

Mounting:

• Mount the transformers on rubber grommets to keep possible humming from the chassis. You can put these in the larger drilled holes for the bolts, insulating the transformer from the chassis. A self-securing nut is used to tighten the bolts. Use washers to prevent the grommets against the pressure of the transformers. Don't forget to connect the transformer to the chassis' earthing.

• Silicon cement is an easy and secure manner to mount components to the chassis. It is strong and insulates them from the chassis. If you're into tweaking, industrial can be used. I've used it to mount batteries upto 4 kgs!

• Use, if possible, non-ferro bolts/nuts and washers. Stainless steel is easily obtainable and is looking good!

Series attenuator:

• Search for a nice switch, 2 decks each with a minimum of 23 positions, check if the switch makes contact before breaking the preceding contact!. Elna is a good choice, in older equipment nice old stock switches can be found... If there are more positions, these can be connected to the last stage (0dB).

• The resistors are soldered from position to position, in series.

• Use 0.1% resistors (metalfilm). This to create identical impedance.

• You can see here the resistor values and connection diagram.

Good Luck!

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