WAD 2A3 PSE Tweaks - Part 3

[FAQ Team]

Power Supply

Rectifier to NOS Brimar 1940's U52/5U4G. Also good is Westinghouse 5U4G or NOS RCA 5V3A (The WAD design pushes the 5U4 to the limit and the 5V3A has an increased current and voltage capability).
C13 to Arcotronic 40uF motor run cap (377-9153).
C14, 15 to Rifa 150uF low ESR caps (434-0964).

C13 bypassed with 2 x 0.22uF Arcotronic polyprops (114-610) in parallel, and also paralleled with 2 x Rifa PHE428 2200pF polyprop (240-5621).

C14 bypassed with 2 x Ampohm 1.0uF polyprop (365-7463) each paralleled with a 10nF Rifa polyprop (240-5435). Application is as close to the relative component as possible so connect one end to O/P Tx tag shared with feed from choke and other to star earth tag on end of amp tag board.

C15 bypassed with 2 x Rifa 1.0uF polyprop (240-5429) each paralleled with a 10nF Rifa polyprop (240-5435). Application is as close to the relative component as possible, therefore fitted on the amplifier tag board.

R14 dropper to 2K74 5W Mills owing to it's non-inductive qualities (available from <http://www.percyaudio.com/> ) NOTE. The value of this resistor will vary according to your mains voltage. The object is to arrive as close as possible to 300vdc at point B, so you may have to adjust accordingly.

2A3 Heater supply

Remove BR2,3,4,5 and construct a bridge from individual diodes on tag board. 16 x Schottky 80Q045 (254-0730).

Because of their increased efficiency, R31,32,33,34 change to 0.33R (Maplin LO.33). Again this may vary according to your mains and you may need to adjust to arrive at 2.5vdc. Both Tony and I consider this has a minimal effect on the quality of sound and would suggest you only go for it if you're into some very serious fine tuning.

Amplifier Tag boards

Remove C1,2,5,6 and R7,8,13,14. Convert 6SN7s to battery bias. Fit 4 x Nickel-Cadmium continuous charge AAA batteries (378-3304), wired in series, per stage, totalling 16 batteries for these valves. A bit fiddly to do, but heaps better in sound than the Nickel Metal Hydride batteries used by some of us previously.

C3,4,7,8 coupling caps to 0.22uF 630v E Dynamicaps.

C9,10,11,12 cathode bypass to 100uF 100v Blackgates.

Above available from <http://www.percyaudio.com/>

R5,6,11,12 Anode Load resistors to Kiwame 5W 36K. Apart from the component upgrade quality, this is about increasing the anode current from 2.6 to 3.9 mA to improve the loadline gradient, thus improving linearity and therefore reduced distortion. Expect to have to burn in for a few hours. Sounds awful when first fitted.

R3,4,17,18,19,20 Gridstoppers to Kiwame 2W 4.7K.
R9,10 Grid leak to Kiwame 2W 470K.
R15,16 Grid Leak to Kiwame 2W 150K.
R25,26,27,28 cathode resistors to non-inductive 1K 12W Mills. (Again available from Michael Percy). Once again, these need a burn in period. Will sound awful for a few hours after fitting.

All Kiwame resistors are available from Michael Percy and an order to him including postage is cheaper than buying these in the UK.

VR2/3 removed from rear of chassis and remounted on 'L' brackets attached to mounting bolts for V5/6 valve bases, to bring them close to the point of application.

Other bits

Richard's mains filter to back of IEC socket.
IPL Acoustics IC2 wire for internal signal wire.
6SN7s are NOS Brimar.

Thanks to Greg, Tony and Neal.