The Black 300B Mono Amplifiers - Part 2

 Hi!

The all black single ended 300B mono amplifiers are finished.

This set consists of 4 portrait style chassis.

Two mono blocks, each with outboard power supply.

The driver tube is an ELROG ER801A, old production 801A tubes can of course be used as well.

The output tube is ELROG ER300B which can be substituted by any other 300B tube.

The output tube is placed between interstage and output transformer for short signal wiring.

All signal transformers are silver wound on finemet cores, made for me by Tribute.

Of course both the driver and output tubes are DC heated for hum free operation and best sound. This is done by separate elaborate choke filtered filament supplies for each tube.

The power supplies use a bridge rectifier scheme with two 866A mercury vapour tubes, augmented by a pair of 6AX4 TV dampers for slow ramp up of the high voltage. 836 vacuum rectifiers can be used instead of the 866As as well.

The 866As have an eerie blue glow when in operation.

Together with the bright light from the thoriated tungsten filaments of the ELROG tubes this is quite a show.

Email me if you are interested in such an amplifier.

Best regards

Thomas

211 drives 211 Monos with Mercury Vapour rectified Power Supplies

Hi!

In the last post I showed some 211 amps under test. Here some photos of one of the sets finished.

The power supplies use a hybrid rectifier bridge with two 866A and two 6AU4 tubes. Alternatively the 836 vacuum rectifiers can be used instead of the 866s.

The amps are single ended 211 with another 211 as driver. The tubes used are of course ELROG ER211.

Mercury vapour tubes need to go through some conditioning procedure when they are used for the first time. They need to be preheated without the high voltage applied for about 30 minutes.

For this the top caps and 6AU4 can simply be removed.

The mercury vaporises and condenses at the glass.

And then settles art the bottom. This procedure ensures that there are no mercury droplets between filament and plate which could potentially creating a short. After this the top caps and 6AU4 get reinstalled and the PSU is ready to be fired up:

As the 6AU4 heat up and start to conduct the current starts to flow and the blue glow comes on. In real life the glow is much more visible as in this clip. Therefor another one with the lights of:

As the B+ builds up the music comes on.

The 866As give an incredible atmosphere.

Best regards

Thomas

Power Supplies Tower Style

Hi!

The recently presented 211 amps in tower style received some good feedback for their design. Someone commissioned a set of 300B monos and a 10Y preamp in the same chassis style. The power supplies are already finished.

This time in a light coloured wood body. The power supplies use a full tube Graetz bridge with a mix of 1616 and 6AX4 tubes. Similar to the PSUs for a previous 300B amp and also similar to the PSUs of the 211/211 amps.

Like those the new PSUs can also operate 866A tubes:

The signal chassis will use silver finemet transformers for which I am still waiting. They will share the same circuit as the silver 300B amps and silver 10Y line stage built earlier this year.

Top view, showing the tubes and the rotary type on off switch:

The back side showing the connection terminal:

There is also a version of the Stereo 300B amp planned in the same tower style.

Best regards

Thomas