Monday, June 2, 2014

"Black Lace" all Ozzie valve 6V6 power amp.

Ozzie, Ozzie, Ozzie. All Australian made Miniwatt tubes (at least 50 years old) on a Murbue base. "Black Lace" was always going to be a very Ozzie build. All tubes: 6V6, 6SN7 and 5U4 are Ozzie Miniwatt made. The 6V6s are black glass and spent 40 years under a house nearby uncovered. To keep with the old school feel carbon film resistors are use throughout except for the cathode Rk which are 5W wire wounds.

The PS is split at a Russian 4uf PIO first cap. The power tranni is rubber mounted to stop vibration reaching the tubes also on the top plate. Domed chromed nuts, securing the power tranni, sit on copper and brass washers purely for looks. The bottom plate has a heavy strip of bitumanised Al foil for dampening.

Two 5H Hammond chokes split the PS to pass through C-R-C filters. 100uf-6.8ohms (carbon film)-100uf. Even at the driver tube the PS remains split in two for two drop down resistors each with a 47uf snubbed electros for storage and further filtering. As you can see a dual PS stream right from the first cap all the way through. Most filter electros are snubbed with 0.1uf high voltage polies. Russian Military PIO caps are used for the inter-stage. The amp is exceedingly quiet.

All hook-up wire was off-cuts from the power tranni and OPTs. The solder was from the 60s or 70s - lead, tin and copper and Ozzie made. The sockets are a resin style, no ceramics around here! OPTs - Edcors - strayed black. The bypass caps on the 6SN7 are bypolar and the bypass caps (Ck) on the 6V6s are low ESR electros. The black lace with the amp (Black Lace) has been photographed on will be cut to for a dust cover when the amp is not in use and will be weighted down with clear and emerald glass beads. All tubes should be run in but all other components are new. The sound for now playing laid-back jazz is crisp, fast and un-coloured.

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