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 NEW    Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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DIY-Two-Way-Speaker-VoXDeuX.jpg
DIY-Two-Way-Speaker-VoXDeuX.jpg2697 viewsUsing inexpensive components from the local electronics shop I constructed these small bookshelf two-way speakers. They comprise a 5” paper cone mid-woofer and dampened silk done tweeter. On the sides and back is wide internal vertical bracing and bitumanised heavy aluminum foil. This forms bass chambers within the box to control rear reflection. The passive crossover sits external to the speakers and is a Linkwitz-Riley 2nd order with a crossover point set at 3 kHz. The boxes and crossovers are bi-wired using Cat5 cable from the amp to driver. They sound excellent for an AU$350 build.

For more info, see the Simple and Cheap Two Way Speakers thread in the forum.

Mark Houston – retro-thermionic
12inch-60L-DIY-Subwoofer.jpg
12inch-60L-DIY-Subwoofer.jpg12-inch 60L Subwoofer2693 viewsThese 60ltr sub-woofers were built to complement my 2-way speakers "VoXDeuX". The drivers are 12" polycones with a free air resonance of 25 Hz. In the box they go down to 31 Hz where they are very active. The drivers are very efficient and are being powered by a compact 50W Class-D amplifier. A stereo feed is taken from the preamp and passed through an electronic filter. The filter has a -3 dB point of 52 Hz and but employs only a -12 dB slope. The internals of the box comprise of six vertical braces. Bitumanised heavy Aluminum foil covers most surfaces. Pockets and chambers are formed at the rear by the bracing which carries additional dampening. These are then covered by a single layer of damping.

Mark Houston – retro-thermionic
6N7-Tube-Preamp-Heavy-Metal.jpg
6N7-Tube-Preamp-Heavy-Metal.jpg6N7 tube preamp (Heavy Metal)2678 viewsConstruction is in a timber box. There are three switchable RCA inputs and power is supplied by an external 18V 2.2A AC power pack. Internally 255V is developed with a linear PS and regulated 12VDC for the heaters which are wired in series.

An Alps blue velvet potentiometer is fitted at the output for attenuation control with a fine solid brass knob to compliment the gold right-angle RCA jacks, name plate and ventilation holes. Wire wrap wire is used in the signal path. The power supply and amplifier are on separate circuit boards. Bitumanised heavy aluminum foil is used to line sections of the timber box for resonance control.

For more info, see the 6N7 metal tube preamp thread on the discussion forum.

Mark Houston – retro-thermionic
TeaBoxII.JPG
TeaBoxII.JPGTea Box 12AX7 Valve Preamp II2655 viewsSee the previous photo for more detail. In this image you can see the solid brass cones, 4oz brass knob and another view of the preamp. The SMPS is contained inside making one very neat and attractive looking valve preamp. Golden Dragons replace standard 12AX7 valves.
PhonoFront.JPG
PhonoFront.JPGPhono Preamp Kit with RIAA Equalization2641 viewsAfter resurrecting the Rega TT and RB300 tone arm with a Grado Sonata wood body cartridge I went on the hunt for a phono preamp. The Pro-Ject PhonoBox SE preamp was a value for money purchase, a neat and good sounding unit. This phono premp kit cost under $AU100 to build (including AC adapter) and challenges the Pro-Ject on a the sonic level. I can find no fault musically with the kit which has no hiss or hum and a natural sound quality. It is available from Jaycar Australia. Better than the Pro-Ject by provide the facility to have three different selectable compensations including RIAA and early DECCA (ffrr) and a host of others to select from. And to go one step better again there is a gain control to balance between CD and phono input levels. The case is ABS plastic and tar and foil lined. Gold RCAs used (see other photos). A +/- 12V regulated PS is include on the one peace cct. brd. The PS is shielded. Distortion is rated at .014% and RIAA accuracy is better than 1db. Signal to noise is -84dB.
00005.jpg
00005.jpg25EH5 / 50EH5 Tube Amplifier2637 viewsAnother view of the amplifier from the top. As you can see, I was using headphones as I took the effort of adding a jack with impedance matching resistors so I could listen to my music in peace. The funny thing is that I can apply just about any load to the amplifier without any audible change other than volume.
DIY-6V6-Push-Pull-Tube-Amp.jpg
DIY-6V6-Push-Pull-Tube-Amp.jpgDIY 6V6 Push-Pull Tube Amplifier2634 viewsA photo of a 10W 6V6 Push-Pull Tube Amplifier put together by Michael S. Holden. Michael has put together a detailed set of instructions for this tube amplifier project:

10W 6V6 Push-Pull Vacuum Tube Amplifier (Class-AB) - Michael S. Holden - (PDF 3.4MB)
Beyma-12XA30Nd-Speaker.jpg
Beyma-12XA30Nd-Speaker.jpgBeyma 12XA30Nd Speaker2633 viewsThese are the most expensive speakers I have made. Drivers are Beyma 12” with a titanium\polyester concentric 2” dome – 12XA30Nd. Efficiency is 98db\1W\1M for the woofer section and 105db for the tweeter. The drivers can handle 700W! Box is 33ltr and heavily braced with 4” rear port. Finish is heavily stippled and applied with a roller. Xover is at 2KHz. Bass is not super low and requires a subwoofer for better bass. Speakers work extremely well with my 0.5W 1920s tubed amp. See the forum thread Beyma, a Spanish coaxial driver for more information.

Mark Houston – retro-thermionic
5751-SRPP-EL84-6BQ5-Push-Pull-Tube-Amp.jpg
5751-SRPP-EL84-6BQ5-Push-Pull-Tube-Amp.jpg5751 SRPP / EL84 (6BQ5) Push-Pull Tube Amp (PoddWatt)2624 viewsAnother OddWatt tube amplifier. This one uses EL84 / 6BQ5 tubes in a self-inverting push-pull topology for the output stage driven by a 5751 SRPP. The gain is sufficient to allow direct connection to a portable mp3 player. As will all the OddWatt amplifiers, it measures very well and Bruce reports that it sounds very good. See the 5751 SRPP / EL84 (6BQ5) Push-Pull DIY Tube Amplifier project page for full details.
PhonoRear.JPG
PhonoRear.JPGDIY Phono Preamplifier Kit2611 viewsThe finished kit (see other photos) can be assembled in an afternoon. I used insulated gold plated RCAs but on an ABS plastic case like this insulated RCAs are not required. Keeping all connections on the rear makes for a simple front panel with gain control and recessed red led. I used thick silicon stick-on feet to ensure vibration into the unit is kept to a minimum. Stick down computer stand-off hold the cct. brd. to the bottom of the case and also help with vibration control. The case is lined with heavy sticky tar and foil. Base, sides and lid and are lined but not earth. This helps with shielding the low voltage levels and case dampening also. Shielded wiring is used internally and silver solder used throughout.
Jan6418JewelBoxInside.jpg
Jan6418JewelBoxInside.jpgInside the sub-mini Jewelery box preamp2607 viewsI have a weakness for "cute" enclosures, particularly timber ones. The mirror is just a bonus. The circuit board is part of a kit from Oatley Electronics Australia. I have replaced the carbon resistors in the kit with metal film, the 0.1uF MKT caps with 0.47uF polypropylene types, the 220uF electrolytic caps (output) with 470uF low ESR types. Also the PT2308 headphone driver chip was replaced with a Burr-Brown OPA2134 OP amp chip. 2 X 9V lithium batteries provide 9V to a L4949 regulator which controls filament current to the Raytheon JAN6418 sub-mini valves. Attenuation is trim set and volume controlled by external devices.

Three grommets are used as valve dampeners. These tiny valves can be extremely microphonic. Three grommets stops the microphonic problems dead! The amp is extremely quiet. See the JAN6418 Valve (Tube) Preamplifier Kit page for full details.
rectifier_tube_150_amp_6_phase.jpg
rectifier_tube_150_amp_6_phase.jpgMassive Rectifier Vacuum Tube (Valve)2604 viewsWhat a tube! This is a vacuum tube rectifier. 150 Amps with 6 channels.
BoydSmall.jpg
BoydSmall.jpgJAN6418 sub-mini valve preamp kit MKII2596 viewsYet another build of the Oatley JAN6418 valve preamplifier / headphone amplifier kit. This one was built to order. An Alps blue velvet pot and 4oz brass knob and pure silver hook-up wire add to the build quality.
IMG_2678.JPG
IMG_2678.JPG50EH5 / 25EH5 Tube Ampr with 12AU7 Mini Tube Preamp2582 viewsYet another picture of the 50EH5 Tube amp in action along side with the Mini 12AU7 tube preamp.
mag02.jpg
mag02.jpgMagnavox 93 Series Tube Amp Rebuild2580 viewsThe cloaked and stunning 93 Magnavox 93 Series Tube Amp ready for service! For more information, see the Magnavox Stereo tube amplifier model 9304-20 rebuild thread on the forum.
KitAmpTopSmall.jpg
KitAmpTopSmall.jpgKT88 SE UL Tube Power Amplifier2580 viewsI had put the partially finished amp in the gallery some weeks back. Now finished not a lot of difference on the outside except for the many silver colored screws on the top plate and some feet. See the other image for the underside shot. After a number of hours of careful listening and listening to it though others CD players, pre-amps and speakers I can say that most liked the sound. SE tube amps produce absolute and exquisite mid-range and silky highs and deep sound stage but this amp has a slightly narrow sound stage presentation. Bass improved and hum vanished with additional PS filter caps. With a brushed Al top plate and Mirabue timber thick timber base, Edcor XSE OPTs and component-2-component wiring on all circuit boards (including rectifier broard) this amp represents a clean and easy build with in-expensive parts. Though low powered (6W+) for a few hundred dollars you can experience the benefits of a tube SE UL design. So easy, so nice!

Here is a link to the KT88 Single-Ended (SE) Schematic I followed.
EL84-CCS-Push-Pull-Tube-Amp.jpg
EL84-CCS-Push-Pull-Tube-Amp.jpgEL84 / 6BQ5 Push Pull Tube Amplifier2566 viewsThe "OddWatt", a EL84 / 6BQ5 Push Pull (PP) Tube Amp project. SRPP input stage and ultra linear output stage with LM317 Regulators CCS. Tube heaters are 12VDC.
PreProduction-Odd-Block-Tube-Amps.jpg
PreProduction-Odd-Block-Tube-Amps.jpgOddWatt / OddBlock KT88 Push-Pull Tube Amp Kit2563 viewsThis is a pre-production photo of the OddWatt / OddBlock KT88 Push-Pull Tube Amplifier kits that are available from OddWattAudio.com.

Full details of the tube amplifier topology along with complete DIY instructions are available on the 12SL7 SRPP / KT88 SIPP (Push-Pull) DIY Tube Amplifier project page.
retro-EL34-SE-UL.jpg
retro-EL34-SE-UL.jpg2558 viewsThe enclosure base is made using Australian Spotted Gum and the power transformers and choke are from Hammond. The audio output transformers (OPT) are from Edcor (15W XSE open frame type series) and reside in the base and are shock mounted. The feet are filled with lead sinkers for resonance control. A CLCRC filter network ensures the amp performs dead quietly and has an extremely high head room. Frequency response is to 40kHz and power is 5W RMS into 8ohms. Russian paper in oil caps are used in the inter-stage and bipolar caps and low ESR caps are used in the cathode bypass. Silver plated wire-wrap wire hooks up the gold plated RCAs to the nearby 6N1P and connects the secondary of the OPTs to the binding post. The paint work is epoxy enamel on 2mm high grade Al plate and component-2-component wiring. This is a fast amp with a huge sound stage and a rich lush EL34 sound.

For more info, see the Pimp my tube amp thread on the discussion forum.

Mark Houston – retro-thermionic
OPA2134-opamp-Headphone-Amplifier.jpg
OPA2134-opamp-Headphone-Amplifier.jpgOPA2134 CMoy Style Portable Headphone Amplifier2554 viewsThis simple headphone amplifier is based on the high performance OPA2134 opamp chip. This headphone amp\driver is good sounding and portable. The schematic is based on the very popular CMoy headphone amp design with some changes in passive parts values. For the power supply I elected to power the amp from two 9V batteries (18V) which provides longer playback time and greater dynamics.

There is only 100 mm of hookup wire in the signal path and all connections are component-2-component on the protoboard. Low ESR 200uF caps and a resistive network provide the differential voltages required to operate the chip without an output capacitor. The brd. is silver soldered with Mil. spec machined chip socket and Russian PIO caps on the input. Power only comes on when both phone jacks have plugs in them and the power switch (at the back) is on. The enclosure is impact resistant and lined with heavy aluminum foil for shielding and enclosure resonance control. The sound is clean and bright with good volume and dynamics. The amp is dead quiet with no signal.
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