DISCLAIMER: Vacuum tube circuits work with dangerously high voltages. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

All rights of photos and text reserved. Usage of photos or text from my blog on other websites or for any other purpose only with prior permission. If you want to use any material from my blog please contact me by email.

Wednesday, October 18, 2017

Power Supply with ELROG ER274A


Here some photos of the first power supply I built for the ER274A rectifier.

The owner of one of the sets of 211/211 amplifiers requested to convert the power supplies to use the new ELROG rectifier. How could I say no to that?

Two of the TV Dampers got replaced by the directly heated rectifiers. Two TV dampers remained for a slow ramp up of the high voltage.

Now not only the amplifier sections exhibit the bright thoriated tungsten glow, but the power supplies as well.

Not sure yet if I even prefer this to the blue glow of the mercury vapour PSUs.

Quite spectacular light show!

Amp section and PSU side by side:

The gap between the two plates gives a nice view to the filament.

Best regards


Friday, October 13, 2017

845 Mono Amplifiers - Part 1


Several different 845 mono blocks are in the planning stage for the next months. Here a sneak preview how the first ones will look like.

I will start with a pair of 'entry level' monos. These will be single chassis, one per channel. So the power supply is integrated. Driver tube is the 6HS5. A pair of 6CG3 TV damper tubes will take care of the rectification. All the tubes are placed on top of the chassis without anything else:

The chassis will be tower style, about 40cm high (plus feet and tubes). The same size as the chassis used in the 300B differential amps. This is a view from the top:

All the internal parts will be mounted on several stacked sub assemblies. This are all the metal plates for the internal construction of one amp:

Stay tuned for updates as the construction of these amps progresses and other more advanced 845 amplifiers will enter the planning stage. There are some cool things coming with a unique new driver stage for 845 tubes.

Best regards


Friday, October 6, 2017

300B Mono Amplifiers Landscape Style - Part 2


In part 1 about these amps I showed the initial construction steps. Here are some photos of the finished set of amplifiers and power supplies.

One of the monos blocks, amplifier chassis:

The 10Y input tube is on the back side to the left near the input connector. The signal is then routed through the interstage transformer at the front left to the output tube at the right and then through the output transformer to the backside and the speaker connectors.

Top view:

One of the power supplies:

Some more views:

Top view:

One channel, amplifier and PSU together:

The two amplifier chassis are mirrored:

The entire set of 4 chassis:

In part 1 I showed the assembly and wiring of the first tier. Here photos of the internals of the finished amp with the second level of components installed.

The power supply:

And now some photos of the amps in operation:

Nice glow in the dark:

Best regards


Wednesday, September 27, 2017

Tube of the Month : The 849


This month I am presenting something very different. A large air cooled transmitting triode. Meet the mighty 849.

Like many  tube amplifier designers at some point I was obsessed with large directly heated triodes and collected some of those beasts.

The 849 is one of them. It is a thoriated tungsten directly heated triode designed for audio amplifier and modulator use as well for RF amplification. It measures a massive 36cm in length and 10cm in diameter. Dimensions and connection terminals are shown in the drawing on the left. Connections are made to the tube from both ends. There is a large plate cap on one end and a terminal with 2 massive filament pins and a blade type connection for the grid between them. The 849 has a maximum plate dissipation of 300W. This comes with a relatively high amplification factor of 19 and a plate resistance of about 3 kOhms. The Amperex data sheet lists single ended Class A operating points up to 100W out of one tube! That should be enough to drive even some of the more power hungry speakers. What a beast! Of course such a power rating is not easily obtained. A DC supply voltage of 3kV would be needed and the filament consumes 11V @ 5A. No off the shelf output transformer is available for such a tube and would need to be custom wound. An amplifier with this tube would be a nice room heater. 300W plate dissipation plus 55W filament power equals to 355W of heat just from the tube. That's 700W for stereo. Add driver and rectifier tubes and losses in the power supply and the heat will be beyond 1kW. Maybe something for the winter time. But I bet it wold sound simply stunning. Have a look at the evenly spaced plate curves:

My curve tracer only operates up to 400V. But this limited region of the operating area of the tube looks great already:

Now let's see some tubes, here is a Amperex 849:

What a majestic tube!

Check out the internal construction details:

Unlike other tubes the 849 has a mesh like grid.

The plate structure is massive

Which it has to be to be able to dissipate 300W

The filament and grid terminals:

The tube is  normally mounted with this end up.

And the plate connection toward the bottom:

These are the original sockets for this tube:

Amperex logo and tube type designation:

Some more detail shots of the internals:

Close up to the grid:

Mounting on the filament/grid side:

Westinghouse 849:

Close Ups:

United Electronics 849:

Sylvania 849:

An interesting feature on this one, in addition to the common barium getter which leaves a silver mirror area on the glass, this tube also had a zirconium getter which leaves no visible mark after activation:

On the next photo we see the barium getter on the top and the zirconium getter was in the little mesh pouch on the bottom:

The construction of these tubes is simply stunning:

My collection of 849s:

Since these photos cannot really give a real impression of the size, here a 849 besides a 211:

Now a few photos of a 849 with the filament lit up:

These photos are a bit underexposed. In real life the filament is brighter.

The filaments create a hot fire inside the plate.

I hope you liked the presentation of this rather unusual triode.

Best regards