As well as supplying premium grade iron for your amplifier project, we now offer a select range of components which may be difficult to source. Quotations for complete "sets" of components can be put together if you wish, it just leaves you looking for the chassis.
Over the past 10 years it has been well documented that the types of passive components used in constructing an audio amplifier can have a great effect on the final level of sound quality. This is no different for valve amplifiers than it is for solid state ones. In fact most valve amplifier builders would argue that it is more important because the number of components used is so much smaller that each individual item is more noticeable. In practical terms this comes down to the choices made for resistors, capacitors, wire, valve bases, solder and casework. The relative order of importance is outside the scope of this article, and will always be a very personal list.
Improving resistors can be one of the most cost effective upgrades in terms of performance per pound. Holco resistors offer a great improvement over the more usual types of metal films and for a comparatively small outlay. The H2 have a voltage rating of 350V which also makes them the best of the Holco range for valve amplifiers. Other types of resistors do offer improved performance, but normally at great cost. Vishay bulk foil resistors are probably the best sounding, should you require quantities of these please enquire for a quote. When handling resistors during construction, don't forget that they all require the leads to be bent a small distance away from the body of the resistor so as not to damage the joint between the lead and the resistive element.
The resistors we are now offering to supply is a small range of the Ohmite Brown Devils, Dale Precision Wire Wounds and a couple of Mills Non Inductive wire wound resistors. These can all be used for plate loads, cathode resistors and power supply bleeds. The Ohmite are built on a large hollow ceramic core with a ceramic glaze over, while the Mills and Dales have a ceramic inner core and a physically much smaller.
When constructing your amplifier care must be taken to suspend the audio circuit away from the amplifier chassis in order to control stray capacitance. Both channels should be laid out in the same manner for optimum channel balance. This can be a difficult operation and some form of hardware is usually required for assistance. Cheap compressed paper tag board is often used, however the poor dielectric absorption of this material and the magnetic steel tags normally used are a compromise when used with top quality components. A much better method is to use PTFE board. Both these methods facilitate good point to point wiring techniques, controlled component layout and the optimum in sonic performance.
PTFE board offers almost ideal properties for point to point wiring provided a thick enough board is used. The material can easily be drilled with a low speed drill and flat wood bits for large holes for valve bases. We have 4mm thick board available, which is thick enough for mounting preamplifier tubes providing the board is supported sufficiently. This then means the whole preamplifier stage may be constructed out of the box before final mounting. The PTFE board comes as standard in a 10cm x 10cm square for œ8.68 with increases in sheet size available a 5cm increments ie 15cm x 20cm etc with the cost increasing in proportion to area eg 15cm x 20cm would cost œ26.04
Solder tends to be a necessary evil when building amplifiers. At first sight it would seem silver solder would be the best type to use. There are, however, a few drawbacks to this. High silver content solder tends to have a high melting point, thus a high quality temperature controlled soldering iron is required to obtain a good joint. These tend to be expensive and not owned by many hobbyists. Another problem is associated with ageing effects. In the same way that unprotected silver oxidises over time, so will a silver solder joint. The only effective way to secure a performance which doesn't degrade with age is to protect the joint by lacquering it. For these reasons we make available the new Wonder Solder at £2.50 per metre; a high quality, good sounding solder which currently offers the best compromise between price, performance, usability and long term stability.
Gold plated ceramic valve bases:
UX4: £6.43
Octal: £4.57
B9A: £3.98
Alps volume pots:
27mm "blue beauty": 50K £11.55
40mm "black beauty": 20K £22.50
At some stage during construction a good quality hook up wire will be required to wire in power supplies or earthing arrangements, as well as the signal path. For this we have available:
0.6mm 99.99% pure solid silver wire which is PTFE insulated.
This is available in white or red at a cost of £9.73 per metre.
PTFE insulated silver plated copper cable
This is available in red, pink, black and yellow at a cost of £2.94 per metre.
Also available are a small range of pure silver interconnect and loudspeaker cables:
Interconnect Cable
1m pair terminated with Neutrik Profi phonos £145.00
2x0.6mm PTFE insulted screened £51.32 per mono metre
1x0.6mm PTFE screened 75ohm dac cable £49.38 per mono metre
Speaker Cable
2x1.0mm enamelled screened £45.75 per mono metre
3x1.0mm enamelled screened £80.24 per mono metre
4x1.0mm enamelled screened £104.29 per mono metre
5x1.0mm enamelled screened £136.29 per mono metre
With information and good advice on valve amplifier design generally quite difficult to come across we are have put together a few information packs to help on some of the more important or interesting aspects. Loudspeakers and amplifiers will eventually be covered, as many people are now wishing to construct sensitive, easy to drive, loudspeakers to really bring out the most in their amplifiers.
The information packs we have available at a cost of £5 per set cover:
1) Copies of Power amplifier section from Radio Designers Handbook
2) Copies of Rectification and filtering sections of Radio Designers Handbook
At £10 per set we have:
3) Pre and Power amplifier schematics, mainly low or zero feedback single ended, NEW
In-house designs
4) 6 Horn loudspeaker designs suitable for Lowther drive units.
5) Copies of Horn Speaker Design articles from Wireless World
6) Translation of Jaques Mahul's "L'Audiophile" article on mini-Onken bass
speaker.
An A4 sheet of answers to any specific written questions can be put together at a cost of £15.