KT77 Push-Pull DIY Tube Amplifier

Bruce has followed up his OddWatt tube amplifier project (a EL84/6BQ5 Push-Pull Tube Amp) with the Oddwatt 225 (a KT77 SIPP (Push-Pull) Tube Amplifier). The Oddwatt 225 is a scalable tube amplifier which will work with any octal tubes that share the base layout of a 6L6GC.


The driver stage uses 6SL7 tubes in a SRPP topology which feed the KT77 self-inverting push-pull (SIPP) output stage operating in Class A Ultra Linear (UL) mode. The constant current source (CCS) uses an LM317 regulator.


I was most impressed with the performance of the design. The SRPP and Push-Pull outpout stage combine to produce a very low noise floor. Distortion was measured to be less than 1/2% at 12W. The design can be scaled for use with other tubes by simply adjusting voltage and cathode current. My understanding is that KT88 versions of this design are in the process of being built.

For complete information about this project, see the Oddwatt 225 project page - DIY KT77 SIPP (Push-Pull) Tube Amplifier.

Related DIY Tube Amplifier Projects:

• Alex's DIY KT88 Single Ended Tube Amplifier Project

What's Playing: Joni Mitchell - Carey

Audio Paradox - S-5 Electronics K-8LS Tube Amp Kit

Bruce Heran writes:

As an avid diyer and fan of the S-5 Electronics K-12 tube amplifiers kits (I have 2) I thought it would be a good idea to get a K-8LS. This tube amp kit is a logical replacement for the S-5 Electronics K-12 and K-502 tube amplifier kits. It is about the same power and is aimed at the same budget tube amp market. The basic amplifier circuit topology of the K-8LS is the same as its predecessors. With the exception of an added preamplifier section, it is not a major redesign, and now uses somewhat more readily available vacuum tubes. The one big plus is that it now comes with a much larger power transformer. The original K-12 ones ran rather warm.


I really want to like this product, but as you will see in the following comments, mine is awful. Sine wave and square wave tests were conducted at several frequencies. The measurements were made at 1 volt output into an 8 ohm non-inductive resistor. This is an easy load for any amplifier. Frequencies checked were from 20 Hz to 40 kHz.

25 Hz Sine Wave

100 Hz Square Wave

There was a significant drop in output (sine wave) below 150 Hz and by 20 Hz there was not much left (about 9 dB down relative to 1000 Hz). The high frequencies were down around 3 dB at 18 kHz. Sine waves at 50 Hz showed clearly visible distortion. Square wave response at 1000 Hz was fair, but with some tilt. By 500 Hz the tilt was significant and below 150 Hz it was excessive. At frequencies below 50 Hz it no longer resembled a square wave at all. On the high side, rounding occurred from about 4 kHz up. By 10 kHz, square waves looked more like a sine wave! To be fair, there was no ringing or overshoot at any checked frequencies.

1 kHz Square Wave

10 kHz Square Wave

Now you can see the paradox. I want to like this product, but it is awful! So rather than jump all over the manufacturer, let’s start a dialogue and see if others have the same or different results. I’d like to give the K-8LS a chance, so let’s hear from you about your experience with this kit.

Good listening,
Bruce Heran




Other DIY Tube Amplifiers by Bruce:

• KT77 Push-Pull Tube Amplifier
• EL84 Push-Pull Tube Amplifier
  

EL84 Push Pull Tube Amplifier

Bruce's latest project, called the "OddWatt" is the EL84/6BQ5 Push-Pull Tube Amplifier shown below.


The driver stage is an SRPP circuit with ECC802S tubes, while ultra linear operation is used for the output stage with Sovtek EL84 tubes. LM317 Regulators are used to produce a constant current source (CCS) to set the bias of the output stage. The power and output transformers are from Edcor. 12VDC from a SMPS is used for the tube heater supply.

Bruce reports that performance from this amplifier is excellent. The low end extension is clean but not excessive. As expected, it has the characteristic tube warmth and is very easy to listen to.


For additional information, pictures and schematics, see the complete page of Bruce's EL84 Push-Pull Tube Amplifier Project.

Related Posts:

• Alex's DIY KT88 Single Ended Tube Amplifier Project
• Bruce's KT77 Push-Pull DIY Tube Amplifier Project
  

What's Playing: The Church - Metropolis

K-502 Valve Amplifier Kit

It is no surprise seeing another build of the S-5 Electronics Tube Amplifier Kits. These valve amplifier kits are inexpensive, simple to build, fun and best of all, they sound great.

Pictured below is Scott's build of the inexpensive and popular K-502 Tube Amplifier Kit and Enclosure. The enclosure for this tube amp looks fantastic. Great attention to detail.

Scott only made a few changes to the circuit board; replacing the stock 0.22 uF polyester film caps with good quality Orange Drop capacitors. I lived with a stock build of the S-5 Electronics K-12M Tube Amplifier Kit for a while and I can tell you that this kit does sound very good in stock form. Scott also replaced the standard volume potentiometer with a good quality stepped attenuator.

For additional information and pictures of this tube amp project, see Scott's K-502 Tube Amplifier Kit and Enclosure page.

Related Tube Amplifier Projects:

• Barry's DIY K-502 Tube Amplifier Kit

What's Playing: Echo & The Bunnymen - The Killing Moon

KT88 Single Ended Tube Amp

Alex has put together a single ended (SE) KT88 tube amp. His design was based around Mikael Abdellah's KT88 SE Tube Amplifier design from 2003. Alex has made some changes, such as the ability to switch the amplifier between triode and ultra-linear operation. A picture of his finished KT88 tube amp is shown below.


Alex has done some experimentation with different tubes. EL34 tubes can be used in place of the KT88 valves. The preamplifier tube is a 6N1P, but the 6DJ8 / ECC88 / E88CC family of tubes can be used instead. The power supply uses a 5U4-GB dual rectifier tube.

For additional information, pictures and schematics, see the complete page of Alex's DIY KT88 Single Ended (SE) Tube Amplifier project.

Related DIY Audio Tube Projects:

• Bruce's DIY EL84 Push Pull Tube Amplifier Project
• Bruce's DIY KT77 Push-Pull Tube Amplifier Project

What's Playing: The Alarm - Rain in the Summertime

"Beauty" - A 12AX7 Tube Preamplifier

To accompany his recent LM3875 DIY Chip Amplifier (gainclone) project, Bruce has put together a DIY 12AX7 Tube Preamplifier Kit to drive the chip amp. He has named the tube preamp "Beauty", as it sweetened the sound of his LM3875 Chip Amplifier.


For the enclosure, Bruce used a readily available plastic and aluminum project box from Radio Shack. This is the same enclosure he used for the LM3875 Chip Amp. The photograph below shows the Tube Preamp and Chip amp together.


Similar to what Mark discovered with this economical (read dirt cheap) tube preamplifier kit is that you get a very quiet preamp that can compete with ones that cost much more. For more information about this project, see Bruce's project page, "Beauty" - A DIY 12AX7 Tube Preamplifier Kit.

Related Post:

• Mark's DIY 12AX7 Tube Preamplifier Kit

What's Playing: The Cars - Bye Bye Love (Demo)

K-502 Tube Amplifier Kit & The DelSol Speaker

Barry has put together his first two DIY Audio Projects. A build of the inexpensive K-502 Tube Amplifier Kit and the DelSol Speaker.


The enclosure for the K-502 Tube Amp Kit is wood and plexiglass.


The DelSol projects uses the Aura NS3-194-8E fullrange driver. For the enclosure, Barry used 3/4" MDF and 1/2" oak.


Together these two simple DIY projects make a simple hi-fi unit. For more information, see Barry's project page the DIY K-502 Tube Amplifier Kit and Aura NS3-194-8E DelSol Speaker.

Related DIY Audio Projects:

• K-502 Valve (Vacuum Tube) Amplifier Kit
• Aura NS3-194-8E DIY Bookshelf Speaker Project

What's Playing: Duran Duran - Like An Angel

DIY 5687 Tube Preamplifier

The latest addition to the DIY Audio Projects website is a fine looking tube preamplifier constructed by Vincent Wong. The tube preamp is based around a pair of 5687 twin triodes. Each channel uses both sections of a 5687 tube and LED biasing is used on each section.


To keep hum at a minimum, the filaments are heated using DC. The power supply is external to the preamp section and consists of a RCA-83 mercury rectifier and two 50H chokes.


For more project details including schematics and an enclosure construction guide, see: DIY 5687 LED Biased Tube Preamplifier.

Related Tube Preamplifier Projects:

• Mark's build of the DIY 12AX7 Tube Preamplifier Kit
• Bruce's build of the DIY 12AX7 Tube Preamp Kit

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What's Playing: Fleetwood Mac - Landslide

12AX7 Tube Preamplifier Kit

This is Mark's build of a simple and inexpensive 12AX7 tube preamplifier kit from Silicon Chip magazine. What makes this kit inexpensive (and interesting) is that power comes a switch mode power supply, which is fed from a 17 volt DC wall wart! To silence the skeptics of a switch mode power supply in a tube circuit, Mark has completed a number of measurements on the power supply as well as the preamp. Mark's modifications to the preamp kit include the addition of snubbers and upgraded capacitors. The end result is a simple DIY tube preamplifier that sounds great and will keep some money in your pocket for your next DIY Audio project.

For more detailed information about Mark's latest project, see the project page, a DIY 12AX7 Tube Preamp kit.

Related Posts:

• Bruce's DIY 12AX7 Tube Preamplifier Kit
  

What's Playing: Pearl Jam - Glorified G

Another K-12M Tube Amp

Since building a S-5 Electronics K-12M Tube Amplifier Kit, I have received several emails with questions and comments about this inexpensive tube amplifier. Well, Bruce has also built one of these popular and inexpensive Tube Amplifier Kits. In addition to finishing the simple kit, Bruce has completed a number of Modifications for the S-5 Electronics K-12M Tube Amp Kit. His modifications include many of VoltSecond's mods, new input and coupling caps, a beefed up power supply and upgraded output transformers wired in Ultra Linear (UL) Mode.


For more information and pictures of Bruce's experience with this kit, see his project page, More Modifications for the S-5 Electronics K-12M Tube Amplifier Kit.

For additional information about these and other inexpensive vacuum tube kits, see: S-5 Electronics K-8LS, K-12 and K-16 Tube Amplifier Kits.

Related Tube Amplifier Kits

• S-5 Electronics K-8LS Tube Amplifier Kit
• K-502 Valve (Vacuum Tube) Amplifier Kit
• S-5 Electronics K-12M Tube Amplifier Kit

What's Playing: Robbie Robertson - Sonny Got Caught In The Moonlight

A Case for the K-12M Tube Amplifier

This is Mark's build of the inexpensive and popular S-5 Electronics K-12M Tube Amplifier Kit.

Actually, Mark has built three of these fantastic sounding tube amplifier kits! Mark has experimented quite a bit with these kits and his modifications include snubbers, a beefed up power supply, an upgraded power transformers and Hammond output transformers. I am always impressed with Mark's enclosure skills and look forward to seeing more of his diy audio projects.

For more information about these inexpensive tube amplifier kits, see: S-5 Electronics Tube Amplifier Kits.

Other S-5 Electronics Tube Amplifier Kits:

• S-5 Electronics K-8LS Tube Amplifier Kit
• More Modifications for the K-12M Tube Amplifier Kit
• S-5 Electronics K-12M Tube Amplifier Kit

What's Playing: The Velvet Underground - Sweet Jane