Saturday, December 5, 2009


Merlot-entry level valve audio.

The build criteria for the Merlot valve amplifier was to construct a simple and excellent sounding valve amplifier from inexpensive parts. But this amplifier had to set an example of what can be expected from any valve amplifier.

Merlot's goal was to demonstrate to those listening to their first valve amplifier that, in a number of areas of quality audio, valve amplifiers can challenge, at a musical level, not only solid state amplifiers but inexpensive commercial designs. The design is single end (SE) and ultra linear (UL) with diode rectification.

Merlot uses two common valves: the 6N1P and KT88. The output valve can be replaced by a number of other valves: EL34, 5881, 6550, 6L6, 6V6 etc. I encourage "tube rolling". Feel free to replace the two output valves. Very different timbres and tonal balances can be obtained by tube rolling. This amplifier supports that practice.

If Merlot looks like this amplifier was hand built completely from scratch that is because it is. From the very solid Mirbeu timber base to hand assembled modules. There are no printed cct. brds. or commercially prepared modules Incorporated in construction. There is no additional wire used in the hand made modules, on component wires joined to other components. This is a technique I have used extensively here called component-2-component wiring. Fewer solder joints and less "hook-up" wire than point-to-point wiring. Individual modules are available.

retro-thermionic attempts to bring back some of the look and sound of early valve amplifiers. The use of heavy timbers, metal, large transformers and protruding valves is purposely done to produce a retro look and to reproduce music as it was meant to sound. Like music.

The sound of the Merlot is excellent mid-range tones, clean clear highs extending to 46khz and a balanced bass down to 35hz. Merlot's greatest strengths lay in its mid-range. Human voice and acoustic instruments are rended with great transparency, natural tone, real depth and immediacy. Output is 6.5W RMS per channel so efficient speakers are required.

This amplifier can be ordered and built with minor modifications should you require. Other models include: Cabernet and Shiraz which use more expensive parts but still the same retro look, more refind and detailed sound. These amplifiers will feature on this page.

Monday, November 30, 2009

Merlot - rear panel

The rear of the Merlot amplifier carries all connections. These include: two switchable RCA inputs, speaker binding posts which will take spades, banana plugs or captured wire, power cord outlet, fuse and on/off switch. The Merlot can be configured for 11oV. A standby switch is atop the the amplifier. This allows you to switch off the high tension but leave the heaters on for immediate listening, during short breaks. This saves power and stops cathode stripping by applying the HT after the tubes have warmed.

Sunday, November 29, 2009

Merlot with JJ KT88 Blue Glass

A number of different power valves can be fitted to the Merlot. It is one of the great strengths of an open valve amplifier, that different tubes can be "rolled" for different tonal balances. In this instance a matched pair of JJ KT88 Blue Glass have been fitted. This has increased the low end weight and brought the mid-range forward slightly. Apart from the different tonality the Blue Glassed JJs look stunning. Many other valves and speciality tubes can be rolled into the one basic power amp. Have a favourite power tube which has the same pin outs and specs as a common KT88? Then roll it into a Merlot. Plug and play-your way!

Saturday, November 28, 2009

Merlot - Black Top and Black Sable EL34

This is the first of the Merlot range I constructed. In this build all switches, controls and connections are on the top plate. The paint used is an epoxy enamul and forms a tough and textured finish. Modular design was developed in this first "proof of concept" build. Once again component-2-component construction was used in forming the modules.

This amplifier diplays all the mid-range fine grain clarity of the second build (above). A number of different valves can replace the EL34s used in this amplifier. Matched Black Sable EL34s are installed in the amplifier above.

Friday, November 27, 2009

Merlot - Black Top EL34

With the Merlot - Black Top build the valve sockets were recessed into the top plate.Therefore valves with large basses e.g. KT88 could not be installed. This issue has been corrected with the second build and now all bases sizes can be accommodated. Fortunately the amplifier sounded excellent with the EL34 Back Sables. This amplifier has also delivered excellent music with 6V6 Black Glass (original Australian made valves).

Wednesday, November 25, 2009

Merlot - Diode Rectification Module

As with all retro-thermionic amplifier sections each part is modularised but no module contains any wire other than the component wire. The Diode Rectification Module is a full wave rectifier employing the centre tap of the large power transformer. A large 10H choke is also used as part of the rectifying and power smoothing network. When a large choke is used to reduce hum and noise in the amplifier smaller filtering capacitors can be used. Smaller power capacitors produce a better detailed mid-range this is one of the better traits of a SE UL design.

Wiring between modules is of the free style method. Copper hook-up wire runs the shortest and safest path to the next module. Internal wiring is loosely banded together for safety and to ensure minimum cross talk. By using the shortest wiring path, total signal path length is kept to a minimum.

I can provide these rectifier modules, or any other of the retro-thermionic modules, for the individual who would like to assemble their own valve amp. E-mail me for a quote.

Tuesday, November 24, 2009

Twinings Tea Box Preamp with Remote PS

The Twinings Tea Box preamp is very much retro-thermionic. Always the mix of timber, metal and valves presents, not only a strong retro feel and unique images but very much a desire to get back to listening to good music the way it was meant to be. Controlled resonance qualities in natural materials can add a certain earthiness or natural tone often amiss in modern, commercial audio equipment. One of retro-thermionic's goals is to construct audio components in a novel and organic way, most often using timber, Bakelite or metal in audio component construction.

The inexpensive Twinings Tea Box provides a natural looking enclosure in which to construct a preamplifier using high-end and carefully chosen components. To further add to the lofty concept of the build a remote, valve rectified, power supply was added. In the image you can see not only was valve rectification and enclosed choke filtering used but a rare Australian made 5Y3 rectifier valve was also employed.

The chassis, on which the remote power supply is constructed, is die-cast Al. Hammond enclosed power transformer and 10H choke sits atop. Other electronics are housed beneath the solid chassis, which, like the preamp itself, reside on solid brass cones. Connection between preamp and associated power supply is via a high voltaqge short cord and XLR plug.

The Jensen copper, paper and oil capacitors and associated components (including the enclosures) make this a unique sounding andlooking preamplifier. Either coupled with a solid state power amplifier or a valve power amplifier this original almost conceptional preamplifier offers an exceptionally unique insight into electronics and audio reproduction equipment not seen in commercial units. And for the engineers amounsgt us the distortion figures fall below 0.05%. The musical rating figures: 99+. Listen and be convinced.

Monday, November 23, 2009

Twinings/Jensen Tea Box Preamp

Jensen copper, paper and oil capacitors from Denmark, large and all as they are, fill the small timber Twinings Tea box preamplifier. Two preamp component-2-component modules are joined to the input and output gold RCA connections via pure silver wire. The wire is prepared by covering pure silver wire with heat shrink. French Solen capacitors form part of the feed back network. Both capacitors have pure silver leads. Expensive components to produce a very natural sounding, high detail valve preamplifier.

The timber enclosure is lined with bituminous Al foil. Alps attenuator is topped off with a heavy 4oz solid brass knob. An external valve rectified power supply delivers a very quiet 260 volts to the Tea Box components. Golden Dragon 12AX7 valves are installed but any similar valve can take its place. A truly unique preamplifier and part of the retro-thermionic range.

Sunday, November 22, 2009

Twinings Tea Box Preamp PS and 5Y3

Fortunately I have been able to acquire a number of Australian made rectifier tubes. This one being a 5Y3. When purchased today a much difererent looking tube. The 5Y3 and 5U4G(s) I now own are all in excellent working conditon. Most looking at 50 years of age with many years of service behind them.

If any single component is going to make an impact on the overall sound eminating from your speakers, it is your preamp. Many hard core audiophiles "roll" (change) thier rectifier valves to change the tonal balance and voicing of their system. This may engender a more natural and sonic balance.

Well aged Australian made valves and exceptional sounding Danish capacitors, in a light timber box, with a remote valve rectified power supply. Not only good sounding but who else has one. retro-thermionic.

Saturday, November 21, 2009

Twinings Tea Box Preamp rear view

As with the Merlot power amplifier the Tea Box preamplifier can have switchable inputs. The power from the remote power supply is delivered by a fix cord which terminals on a metal XLR plug. The power supply has a XLR socket to connect the two sections: preamplifier and remote power supply.

Monday, November 9, 2009

Twinings Tea Box Preamp

Twinings Tea Box preamps are genuinely made from Twinings Tea boxes. Four fine and lightly scented teas come with the well presented box. Though the box timber is light weight and velvet lined, the adding of bituminous Al foil to the inside increases box weight and provides a RFI and EMI shielding.

No screws scar the the timber box top by the use of internal adhesive "stand offs" to mount the component boards. The two circuit boards are component-2-component wired. In a preamplifier, keeping the signal path as short as possible is essential. Only clean DC power enters the preamplifier section. With a remote power supply and valve rectification a very quite and detailed sound reproduction can be ensured. Not to mention the addition of a very cool looking timber preamplifier.

Friday, November 6, 2009

Fostex FE206E back loaded horn

Retro-thermionic not only produces valve amplifiers and preamplifiers but also some finished speakers. Currently retro-thermionic is having constructed the back loaded enclosures to accommodate the Fostex FE206E drivers. After evaluating the the Fostex driver in a simpler two chamber enclosure, retro-thermionic, decided to have the more complex labyrinth style enclosures made. A CNC cutting machine was employed to make the most efficient cuts from the expensive and heavy 21mm multiply timber. Some panels are double layers of 21mm multiply. Panel bracing is extensively carried-out to control box colouration.

Sandbags can be layed in the bottom of the horn to tailor the bass to the listening room. Sandbagging can also be performed in the driver chamber to alter the level of other low frequencies. With efficiencies of the drivers reaching 96db the retro-thermionic amplifiers can produce high sound levels easily.

Thursday, November 5, 2009

Fostex FE206E back loaded horn

At this point the enclosures have not been stained. It is easy to see the excessive bracing which goes into these speakers. A large amount of internal dampening is used and the cabinets are held together with stainless steel screws, doweling and glue. Large clamps were used when two panels were attached to ensure a rigid and tight fit of all panels. These speakers will be stained a dark teak.

Sound stage is pin-point. Stage depth is is very evident. Bass weight can be tuned by placing the speakers closure or further from the wall. Placement is critical.