WAVAC MD-300B Amplifier

Details: Written by: Grzegorz Makarewicz; Category: Tube equipment; Last Updated: 15 December 2025; Hits: 923

Grzegorz 'gsmok' Makarewicz (January 8, 2016)

A very interesting and exclusive design. I must admit that until I received the amplifier, I didn't even realize that any of its models were in Poland. And suddenly, such a pleasant surprise. I invite you to view the photos showing the design details.

Basic parameters of the amplifier

Tubes: 12AT7, 6Y6, 300B
Output power: 10W/channel
Load impedance: 8 (4/16)Ω
Frequency band: 40Hz-50kHz
Input sensitivity: 1.0Vrms
Input impedance: 100KΩ
Signal/Noise Ratio: 80dB
Power consumption: 250W
External dimensions: 265mm (width) x 420mm (depth) x 200mm (height)
Weight: 17kg

A nice glass cover. I like it. It's typical of WAVAC amplifiers. The downside is that it's not attached to the chassis. It simply sits there, pleasing to the listener's eye.

After removing the power tubes (300B), you can see how much effort was put into beautifying the sockets. Wow!

The feet have rubber shock absorbers that prevent any vibrations from the floor from being transferred to the amplifier.

Opening the casing is not easy and requires a lot of gymnastic skills.

The unsightly burn in the center of the printed circuit board, visible in the photo below and elsewhere, isn't an optical illusion—it's the reason the amplifier came to me. The cause of the fault was simple, but it caused me considerable trouble locating it.

I haven't been able to find a schematic for the WAVAC MD-300B amplifier anywhere. Several websites only mention that the topology is similar to that used in the Shishido amplifier. The schematic for this amplifier, based on an 811A output tube, is shown below.

I decided to test it out, and here's the result. For those interested, here's a natural-drawn schematic of the power supply and amplification sections.

As is likely the case in all WAVAC amplifiers (I say likely because I don't know the schematics for all WAVAC amplifiers), there are no coupling capacitors in the signal path. The 12AT7 stage is connected directly to the 6Y6 tube, which drives the output tube via an interstage transformer.

The side view shows a strange structure made of transformers and a choke.

View of the interior after removing the printed circuit board.

And here is the printed circuit board itself with components.

Interstage transformer housed in a sturdy box.

Updated on April 8, 2016.

Only a few weeks passed, and to my surprise and happiness, I had the opportunity to examine the second amplifier. I noticed a few interesting differences, consisting of places where someone (the manufacturer?) had cut the ground trace. This was likely done during the amplifiers' startup phase to eliminate hum. This "technology" doesn't exactly paint the manufacturer in a favorable light (unless, of course, these "modifications" were made after these amplifiers were released).

Let's take a look at what it looks like. First, a general view of the board and enlarged sections with cut traces from the first amplifier: