Tube Amps Are Still Tubular In 2018

Our friend [Pete] was reminiscing over the golden days with his old and broken antique Grundig Majestic console when he realized it deserved proper refurbishing. Now, any generic stereo record player might not be worth the time and effort to fix, but this was not any generic stereo record player. [Pete’s] inherited Grundig Majestic was his childhood favorite due to the distinct sound it had from the tubes that were used as the active elements. So he set out to fix both tube amps inside of the system.

[Pete] has had some experience working with audio equipment in the past. He did what we all aspire to, and got paid for doing what he loves by creating tube amps as a side gig. When he had finally had enough of the sub-par quality of bluetooth speakers that we all put up with for convenience sake, he decided to finally fix his favorite radio that had been lying around for far too long. He got to work immediately in his notebook finding what parts would be necessary for the reboot. The build ended up consisting of a HT supply regulated at 350V, an LT supply half DC-regulated at 6.3V, a 12AX7 input/bass/treble section, 6922 concertina tubes, and an EL34 ultra-linear output section. The end results yielded one amp that sounded just like it did in his youth, and one that isn’t quite there yet.

The Grundig Majestic is not done with just yet though. [Pete] plans to add a couple of additional modifications to his beauty when he’s not too busy with the kids. Firstly, perfecting the second amp is a top priority. After that, installing red LEDs that illuminate underneath the tubes would indicate low voltage presence, whereas blue illumination would indicate HT was locked and loaded. Bias monitoring to keep him informed on the status of the circuit conditions would insure smooth sailing down the road. Adding a relay connection of the speakers to the output transformer would minimize a popping sound that is currently being made in the speakers when the HT is initially turned on. These small improvements are just that — small — but that is part of what makes home projects so rewarding. The more you use something at home, the more you realize what needs to be refined further, so you are constantly learning more. It is a gratifying experience that I hope all of our readers have the chance to come across.

Tube amps are no stranger to Hackaday. Some of us have even built a few ourselves.

Thanks [Sophi]

Via Sparkfun

11 thoughts on “Tube Amps Are Still Tubular In 2018

    1. You might try carefully taking the shell off and following the primary wires into it. The place that gets the most stress is often right where the outside wires connect to the magnet wire. You may not be that lucky but it is easy enough to check.

      I got my first good power drill after it’s first owner smoked it, and I do mean smoked. It no longer worked at all when I got it. I took it apart and discovered that the wire from the line to one of the field coils has burnt away. I had to take a turn off the coil. I was nervous when I put it back together but it ran fine for many more years after that. I put a lot of stuff together with that drill.

  1. If you want to find the qualities of a good tube system, start with something better. There are great examples that sound extremely good. The grundig equipment has a name and a look but nothing i would work hard to reproduce. You can find some consumer rca amplifiers and tuners that will run circles around it. Turntables in most of these systems are all sub par ase they use cartriges that are sub par

  2. If you want to witness the great qualities of tube equipment frpm the 50s you are starting too low with grundig. Not really good designs and quality to match the designs. Turntables in most consumer consoles of the time are substandard due to the use of ceramic/crystal cartridges. If you want an example of a better console from about 1960, look at RCA who made a series of consoles that at the apex, included class ab el84. There were some that had class a el84. Not as good. The good ones had 2 decent speaker systems that were bass limited with a subwoofer channel driving a 15. These systems were application notes in reality for their parts.

  3. (High power) tubes are still used in some broadcast applications, but the trend is toward arrays of solid state FET amplifiers wired in parallel.

    These same tubes are often used in ham radio power amplifiers, and since the broadcasters replace them on a schedule, they often find a second life at a ham radio station. As do the solid state modules. Or so I hear :-)

  4. I love tubes. got a small selection of them of various types and applications. Tough for audio atm i am mostly experimenting with very low plate voltage amplification. Mostly cause i lack a power supply for high-voltage audio circuitry. Really should get myself like a Hammond Transformer and wire a simple and preferably safe test bench.

  5. Pete, You’re asking for trouble if this “speaker relay” allows the output transformer to have an open secodary when HT is turned on; potential high voltage arcing at the output tube sockets between Plate & Filament pins. To eliminate the unwanted thump noise find a way to ramp-up the HT rather than an immediate application of HT. Never allow the output stage to see an open circuit when powered up. High voltage arcing is just the beginning of yet more damage.

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