DIY Audio Projects - Hi-Fi Blog for DIY Audiophiles: November 2009

30 November 2009

KT88 Push-Pull Monoblock Tube Amp Kits

Back in the summer I purchased a pair of the new OddWatt monoblock KT88 vacuum tube amplifier kits. A photograph showing the contents of the tube amp kit is shown below.

DIY KT88 Push-Pull Monoblock Tube Amp Kit

The amplifier circuit is very simple and there are a minimal number of parts in the signal path. The input stage uses a 5751 dual triode in a Shunt-Regulated Push-Pull (SRPP) circuit. The output stage is a Self Inverting Push-Pull (SIPP) amplifier that uses KT88 power tubes. A constant current source (CCS) is used to force the output stage into class-A operation. The power supply is solid-state and there is a turn-on delay. The audio output transformers as well as the power transformers are from Edcor Electronics. The tube amp kit comes complete with a black powder coated steel chassis that includes a ventilated cover for safety. Following the thorough instructions provided with the tube amplifier kit construction of the amp was very straightforward and the kit went together without any difficult. The photo below shows the finished KT88 monoblock tube amplifier kits in use.

Shown in the photograph are the two monoblock KT88 tube amplifier kits, a NAD C521i cd-player, a Behringer SRC2494 used as an up-converting DAC and a DIY Lightspeed attenuator.

The tube amp kits have been in use for about 3 months now and I am very pleased with the monoblock amps. For a detailed review of the tube amp kits and additional notes on the construction of the kit, see the DIY monoblock KT88 Push-Pull Tube Amplifier Kit page.

Additional OddWatt Audio Amplifier Information

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19 November 2009

DIY Vacuum Tube Prototyping Board

by Bruce Heran USA Flag

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This is a project that I made to take care of an ever increasing need to prototype vacuum tube (valve) circuits. As you can see from the photos, it really is a test “board”. I do a lot of work with tubes and love to design and improve circuits. In the process I often use various CAD type programs to rough out the designs. I have frequently found that the models do not agree with the final build. Some are right on, but most are off enough to turn a good idea into a waste of time. Thus the need to quickly prototype designs. Now I could have created this board with many additional features - speakers, output transformers, LEDs... But what I needed was a simple way to test single stage tube circuits. So for simplicity I wired the tube pins together (pin 1 to pin 1 and so on). The leads from the pins are brought out to terminals on a “Euro” style terminal strip. I included several other “Euro” strips, a pair of RCA jacks, a 100 k-ohm variable resistor and solderless prototype breadboard. This solderless breadboard is available in various sizes from several sources. If you build one of these boards, feel free to use the idea to adapt it to your needs and use whatever parts you so desire.

The hardest part of the build was deciding on the layout of parts. I tried to figure out what kinds of parts would be connected to the various tube pins and place the terminal strips in locations where they would make it easy to swap parts in and out of circuits.

You will certainly notice that there is no power on the board. I have several external variable power supplies and decided they would be fine for prototyping. No need to reinvent the wheel. With a larger board you could easily add power supplies if you desired.

Good listening, Bruce

More DIY Audio Prototyping Tools

14 November 2009

Elekit Single-Ended 6L6 Tube Amp Kit

A little over a month ago TubeDepot added the OddWatt Audio KT77 monobloc tube amp kits to their growing line-up of HiFi tube amp kits and they have just added another. Their new tube amp kit is the single-ended Elekit TU-879S Stereo Tube Amplifier Kit which is available for $599.95US (November 2009).

From the TubeDepot OddBlock Elekit TU-879S Stereo Tube Amplifier Kit page:

With a simple, clean design this Elekit TU-879S single-ended, class-A vacuum tube amplifier kit echoes past greats like the Japanese made Audio Note Ongaku. Supplied with EH 6L6 tubes, this versatile amplifier is able to handle just about any octal based power tube on the current production market. We have tried it with JJ KT77, EH 6L6, Sovtek 6550 and SED KT88. They all sound great, but we favor the SED KT88 for its robust power and overall balanced tone. What’s even better is that you can download a highly detailed, easy to follow assembly manual. In just a few nights, you can be listening to some of the best audio you can imagine.

As evident from the photographs, the Elekit TU-879S Stereo Tube Amplifier Kit is a complete tube amplifier kit which includes a clean and functional enclosure. The power transformer is a thin R-Core type produced by Kitamura Kiden.

For those of you who like rolling tubes this kit will give you plenty of options between the 6L6 / KT66 / 5881, EL34 / KT77 and KT88 families of tubes. A comprehensive instruction manual which includes the schematic is available if you would like to have a closer look.

Link to the kit: Elekit TU-879S Stereo Tube Amplifier Kit

More Tube Amplifier Kits

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