KT88 SE UL tube power amp

This my second SE UL two stage power amp. This time the top plate was brushed Al and Sovtek KT88s were installed right from the start. The base is Mirbeu and the front-end valve is a 6N1P. Edcor XSE OPTs and a 10H Hammond choke with X2 caps make this a very pleasant amp to listen to. Mids are exceptionally clear and highs extended (46khz @ -3db point). In this build all connections are on the back and just the attenuator on the front.

Twinings Tea Box preamp with remote valve PS

This was the first of the remote, valve rectified Twinings Tea Box preamps I made. I have just recently completed another, commissioned by a supporter of DIY gear in Denver. In this build I used the original Jupiter, beeswax and paper capacitors. Sadly these caps are no longer made and a more modern beeswax cap has replaced them. In this build, as in the latest, silver wire and silver solder is used throughout the audio path.

The cct. is the original Silcon Chip two stage valve preamp employing 12AX7s. I replaced the Sovteks with Golden Dragons. The rec. tube is a very old 5Y3 which visually appeared in good condition. A 10H Hammond choke and Hammond power tranny supply plenty of power to the amp. Alps blue velvet attenuator and quality passive components lift the basic build to a higher level of performance. A 4oz solid brass knob gives this retro-thermionic two part preamp an old world "dad's gramophone" look.

The preamp was sold within a few weeks of completion to a couple who grew up with "dad's gramophone" which resembled a science experiment but conveyed the passion of the music. Not much has changed where passionate reproduction is concerned. And it may still look a little like a science experiment.

Woody Pro - under the bonnet

Not hard to see Woody Pro. is constructed of base components. Base components form modules which are then interconnected to form the whole buffer/driver. The output caps made from 20 X 10uf polypropylene caps (20 in all) can be easily seen with the aluminium and tar rapped PS to the left. A two stage filter is used comprising of 2 X 10,000uf Nichicon electrolytic caps per channel (total 40,000uf) which are snubbed. The single 2N3055 per channel bolted to the timber is on the far left. All of this in a 1U 19"case. The case is fully earthed and fused and the ferrite chokes use used to filter RFI\EMI.

All internal wiring is via pure silver wire and all internal power connections are via medium gauge OFC speaker wire. A 4oz solid brass knob tops off the attenuator\volume control. Woody Pro. is sleek and very quiet partly due to UF4003 Ultra-fact diodes (which are all individually snubbed) and encapsulated twin toroids. Wood Pro. is dual mono construction. The frequency response is below 10Hz to over 135Khz. Harmonic distortion is extremely low.

Woody Pro.

I had built two head phone drivers (HPs) for my low impedance Grado and Audio-technica head phones. I also discovered they were very good line buffer\drivers due to their low output impedance and high input impedance. They are named Woody and Woody Pro. due to the fact the the single transistor per channel is bolted hard to a block of Asian timber.

In Woody Pro. dual encapsulated mini-toroid transformers drive ultra-fast diodes and 40,000uf of filtering plus resistive ripple reduction to produce two very clean supplies. Twenty 10uf polypropylene capacitors are paralleled to produce 2 X 100uf output caps. There are two selectable inputs. The first input and output have both RCA and 6.5mm phone jacks connected.

Each channel has one 2N3055 in an emitter follower configuration. The sound is immediate, clean, with good bass extension bass and fast. Because Woody Pro. is an emitter follower 10% of the input signal is lost. This has never been a problem with most sources deliver around 2V.