Tube audio related projects:

*** Guided Missile Amp *** - A cute little design based on the 6AR6 / 6384 beam tetrode originally designed by Western Electric for sweep amplifiers in airborne radar indicators.

The first time I saw a 6AR6 I thought it was a TungSol 5881. After fishing it out of a 2/$1 bin at a hamfest I wondered what I had located. I purchased a small handful and went home to hit the manual. The 6AR6 was designed by Bell Labs but apparently made primarily by TungSol. It is one tough little tube - take a look at the TungSol 6AR6 spec sheet (warning, large pdf file). The Bendix version of the tube is a premium version with hardened glass, a 30 watt rating and a ceramic octal base. The plate rating is an outragious 750 volts. Fortunately I picked up a few before Vacuum Tube Valley wrote an article on Bendix tubes.

Schematic of Amplifier is here. I haven't drawn up the power supply, but it is a simple design with 760vct transformer, 5AR4 rectifier choke loaded into 5H followed by 200uf/450v of filtering caps. Filament is 6.3vac. Bias circuitry makes use of a -55v tap on the power transformer, and is almost identical to the bias circuitry from a Dynaco ST70 (see Dyanco Schematics to see how that's done)

Images of Amplifier from the Front, Closeup of Tubes, Top, Bottom.

Also some Bendix tube Specifications.

JC Morrison's Stripped down Micro 3.5 2A3 Loftin-White from Sound Practices Issue #6.

I've just completed the first of a pair of Monoblock versions of this amp. Look - no electrolytic caps anywhere!

Special thanks to Alan Douglas for the beautiful UTC chokes, and to JC for sharing this design with all of us. I can't wait for the second amp to be done, but had to show off the first one!

Output transformers are Tango U808's Top photo Bottom photo

The pair is now done!! I decided to build the second monoblock as a "mirror image" of the first. I makes for a nice bookend appearance. I also picked up a plug cutter so that I could hide the corner screws used in the base. The wood for the base was a nicely figured piece of Bubinga. It is tough stuff - hard to cut and drill.

There's alway's one final change... I swapped the Tango U808's for a pair of Magnequest DS025's and am quite pleased. The DS025's are a bit more solid in the low end and I have another plan for the U808's. Here's now they look now.

Refurbishing Mcintosh Mc60 Amps.

I have 4 of the worse condition Mc60's in the world. I've disassembled two thus far and have had the chrome bases replated. The other two will follow shortly. I'm also making up silk screening masks and will have the set rescreened before assembly.

Single Ended 45/2A3 Amp

I assembled a 45/2A3 single ended amp based on: Angela Simple 45/2A3 Amplifiers.

The schematic is no longer on their website, so I've posted it here. Angela ships quickly, and carries a nice assortment of parts for DIY audio. Link to Angela Instruments

I used an inexpensive set of Hammond 125E universal output transformers ($28 each) and was very pleased with the results. The base is an aluminum case bottom that has been punched and painted with Rustoleum BBQ high temperature paint and baked. I added a 25 ohm hum potentiometer to the filament windings (hook the bias resistor/cap to the center tap of the potentiometer and don't use the center tap off of the filament transformer).

Top image

Bottom before final wiring

DC-Darling 1626 based amplifier

With a set of transformers from a very rusty Heathkit AA-151 Amplifier I built one of the DC-Darling Amplifiers amplifiers designed by Bob Danielak Although very limited in power, it sounds quite nice with a pair of Altec A-7 speakers. I made use of a surplus Radio Shack aluminum base, and more of my favorite BBQ paint.

Top image

Front image

See Steve Rochelin's write up of the "Boston Bash 99" with great photo's of the Angela SE '45 and DC-Darling!

Special thanks to James Melhuish for arranging and hosting the party.

HeathKit A-4 Amplifier

I was walking around a hamfest and spotted a chassis with 3 1626's sticking out. It turned out to be a Heathkit A-4 amplifier that also uses 1626 tube, but in the input section. Outputs are a pair of 12A6's - also vintage WWII surplus. This one is still awaiting restoration, but should be an interesting addition to the collection once it is completed! If anyone has a "real" schematic or manual please contact me!

Front image

Bottom image

Hand drawn schematic

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