Compaq Deskpro EP, 1998 Windows 95 PC, factory installed software

     A Compaq Deskpro EP factory Windows 95 factory software restored. 4.3gb hard drive, cdtom, Diamond viper V550 video card, Compaq Soundblaster 128, modem & 3com network card. This PC ran a hospital nurse call system 20 years without being shut down other than when I shut it down every few years to blow out the dust and replace the UPS battery. It ran faithfully  all those years never shutting down as it was connected to an emergency power generator circuit.

20 Years Of Computer History

     20 years of computer history, upgrading and tweaking on a shoestring budget 1980 to 2000. Many things that my friends and I experienced while having fun with the hobby including hardware, software, networks, etc. that may have been forgotten. We experimented and learned about computers from the Commodore 64, to x86 personal computers.

Audio Note 6V6 Kit 4 Clone

     This is a clone of a Audio Note 6v6 Kit 4 stereo amplifier. I have wanted to build this circuit for about 5 years. It is a vast improvement over the Dynaco 6v6 clone that I had built some years ago. The tube complement is two 12AX7, two 6SN7, and four 6V6.

Audio Note Kit 4 Clone Front
Audio Note Kit 4 Schematic

       The circuit is practically identical to the original with a few changes, but of course a different PCB  layout. The ordinal circuit did not use  ultralinear transformers. I used a Hammond 159S choke in the power supply and had to tweak the dropping resistor in the DC filament supply to obtain the proper voltage.

Audio Note Kit 4 Clone Chassis

    The board is of a similar size to the original. Audio Cap PPT Theta’s are use throughout for coupling capacitors. The electrolytic caps directly in the signal path are Elna Audio SILMIC II. Power Supply capacitors are Cornell Dubilier SLP. Cathode resistors on the output tubes are Ohmite Audio Gold series. Unlike the original this board is easily removed if necessary. I used plug in screw terminal block connectors for easy disconnection. Also you will notice the orange/white plug in connectors. Those are standard power connectors used in lighting ballast connections. They are available at your local electrical supply store or Lowes and rated up to 600 volts. I used those on the ultralinear screen taps since the screw terminal block connectors would not work for that situation.

Chassis top Kit 4

      I wanted to use something different other than a standard Hammond or Bud chassis. This one came from China and for some reason it is built like a tank! The top chassis plate is around a 1/4″ thick. It was a real bugger getting the holes in it. I had to use carbide tipped hole saws then finished with a step drill bit. The silver transformer cover houses the Hammond 159S 4hy 225ma power supply choke.  The output transformers are oversized compared to what you would find for a 6V6 scenario weighing in at 4.5 lbs each. The UL taps are wound at 23%. Why? –  David Hafler and Herbert Keroes did extensive research to determine the optimal set-point for ultralinear transformers for various vacuum tubes and according to their research the optimal for a pair of 6V6 is 23%. The vacuum tubes are JJ ECC83S, NOS Sylvaina 6SN7GTB, and interestingly enough I tried some of the Chinese Apex matched 6V6GT’s from Antique Electronic Supply which actually sound nice!

Audioamp.eu autobias board

     Sometime after my original build, I decided to experiment with a fixed autobias board from audioamp.eu. The dealer for these in the USA is Erhard Audio. You can see where I mounted the autobias board. Being that I did not have a bias supply tap on the power transformer, the board I used has a built in power supply which supplies 6.3v to power the board and also the bias B+ voltage. These boards are really nice, set and forget. Once you set the bias it will auto adjust and keep the bias voltage set for the life of the tube. Also there is no need to use matched tubes because the autobias board keeps the tubes perfectly balanced. also there are LED indicators on the board which will indicate if the tube had failed. You can read about them HERE at Erhard audio. That being said, the amplifier is now of a fixed bias amplifier with a higher output and a better bottom end.

Three Band Vacuum Tube Tone Control

        Being my ears are not what they used to be, I built a three band vacuum tube tone control. This circuit was designed by Max over at Fun with Tubes.  (A 3 Band tone control that you could love) . It is a unity gain three band control using two 12AX7’s and one 12AU7. I removed the Glassware attenuator I had originally installed in the EL34 amp and installed it in the tone control.

# band Tone Control
Tone control Schematic

Schematic as Max has designed it. you can read a description here , scroll down the page to find it. he has recently revised the schematic.

3 band tone top inside
3 band tone top inside 2

The board is single sided cut out on a CNC.

180 Watt Stereo Amplifier

     I’m sure like me all of us have alot of parts laying around. Ideas are always running around and I decided to make use of an output transistor array that was pulled from a vintage Realistic Sta-2290 receiver.

     My goal was to re-create the vintage sound from those late 70,s early 80’s receivers that I remember using a combination of vintage and new parts.  I notice the vintage late 70’s Pioneer SX-1980 receivers are going for up to $4000.00 on ebay.  The Realistic Sta-2290 early 80’s receiver I found was trashed when I came across it. It had been butchered by someone  damaging a good part of one of the main boards that looked like it was on purpose. I salvaged the output array which contained pairs of Sanken 2SC291 / 2SA1215  Silicon Epitaxial Planar Transistors rated for 15 amps at 150 watts dissipation.

     I am suspicious of those tiny amplifiers advertising a zillion watts using a small power supply.  As far as I have found, any amplifier whether it be a vacuum tube, transistor, or a chip amp that puts out a respectable power needs a respectable power supply.  Can today’s new receivers keep up with the vintage ones?  I’ve read where the SX-1980 can go toe to toe with some of the new equipment in tests. When purchasing new equipment today and the sales specs are 300 to 400 watts per 7 channels. Ask one question. If seven channels are supposed to be putting out 2100 watts, cant happen. A good solid 120v 20 amp circuit can supply 1800 watts of power so how can you have more out than in. Even a well designed efficient digital amp has losses and its power supply has losses.  So a good sized power transformer / power supply is first required.

        I used an Antek AN-4435 400va toroidal power transformer that was actually a pull from a CNC machine. Then a combination 3-band tone/preamp circuit  utilizing 2604 op amps, and finally a driver board from Elliot Sound to drive the Sanken transistor output array along with a speaker protection board also from Elliot Sound.  All this is coupled to some vintage Realistic Mach Two 3 way speakers that each contain a 15″ woofer for that 70’s / 80’s sound. This amp was a little to much for my Bowers & Wilkins vintage 602-S2 speakers that I use on my tube amps, as they tend to distort at the higher power  that this amp can produce.

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amplifier driver board
sta-180 heatsink

     Here you can see where I mounted Rod’s driver board to the back of the output transistor heat sink.  The thermal protector is mounted in the middle between the output transistors. The output transistors are vintage Sanken 2SC2921, and 2SA1215 transistors.

SS1 amplifier top

     Top view of the amplifier with everything mounted including the power transformer and power supply pc board. Additional power supply circuitry is to the front of the pc board..

ss1 amplifier chassis

     Bottom view of the chassis shows location of the relays  preamp/tone board and speaker protection board.