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

Amplifier Testing

Hi!

There are a bunch of amps lined up to run through their final test.

So I thought I give a glimpse into the workshop.

When amps are finished they first go through a set of standard measurements on the bench. If all tests as expected the amps get hooked up to the system.

For this they are left naked for easy access to the internals to take some measurements while the amps are running the whole day.

Here we see a set of single ended 211 mono amps with 211 drivers.

Of course each set of amps is also extensively listened to.

Some times amps pile up a bit if some material is missing to finish them as seen above. Thanks to all who are waiting for their amps for being patient.

Best regards

Thomas

Tube of the Month : The EY500A / 6EC4

Hi!

After the presentation of the 83 last month let's continue with another rectifier. This time something quite different. A TV damper / booster diode. For this month I picked a rather modern version of those which was used in Color TVs. The EY500A.

The EY500A has the American designation 6EC4. It is the 6,3V equivalent of the more common PY500A / 42EC4

The EY5400A has a 9 Pin Magnoval base, not to be confused with the very similar Novar base. The cathode connection is brought out at the top which is covered with a 6.35mm cap. The pinout is shown on the left. As mentioned above, this tube is quite modern and was developed for color TVs. It probably has the highest ratings for peak inverse voltage and current delivery capability of any of the TV dampers. The continuous current rating is a whopping 440mA. This is for a single tube. In a full wave rectification 2 of those would be used or 4 in a bridge arrangement. This would mean double that current which can be drawn. During the time I was still using 3-phase power supplies I was contemplating building a filament supply for the
10Y with a 3-phase bridge of 6 of these tubes. This would have been sufficient to deliver the 1.25A filament current of a 10Y. But that project was never started and would probably have been a bit too insane. So my stock of EY500A and PY500A has not found any use so far. Many people object tubes with a top cap but others find that especially attractive as I do as well. So I do hope some time I will find the right project to use this very special tube. So far tubes like the 6CG3 or 6CJ3 had been sufficient for power supplies which have to deliver a lot of current. But if something in the order of 750-800mA is needed, the EY500A can be used. The price which usually has to be paid for such high current capability is heater power. But the 2.1A heater current of the EY500A can still be considered moderate. See the Telefunken data sheet for all technical parameters. This tube is unusually tall compared to other TV-Dampers. This gives it a rather distinctive look. The PY500A is basically the same tube but with a 42V heater (American designation 42EC4). While the EY500A was intended for parallel heating, PY500A was for series connection, usually within a string which was directly connected to mains. A practice not recommended nowadays especially since isolation transformers can be found rather cheap. PY500A tubes seem to be more common and can be easily found at good prices.

Let's start with a tube made by PhilipsECG.

As can be seen the internals don't use all the available space. But the bulb had to be within spec so that the lead to the top cap connection would still reach the tube in a TV set. So a lot of space inside the tube was left empty.

Close ups to the top:

The top cap:

The Magnoval base:

Sylvania branded tube:

Close up to the cathode:

Another Sylvania with very different internal construction:

This one uses up most of the space inside and the large plate structure looks quite convincing.

This one I would trust more than the short version above.

The base:

Quite peculiar plate structure.

This tube was made in Great Britain.

Raytheon:

This one looks very similar to the Sylvania above.

Also made in Great Britain.

Probably from the same factory and just rebranded.

Two different versions by RCA:

Again very similar in construction as the tubes shown above.

General Electric:

This one was made in Germany

Here a sleeve of 5 tubes of Sylvania EY500A.

This time with a different internal construction.

Copper plate and several mica supports

Here a PY500A for comparison:

Not much different at first sight but a close up to the heater shows how it is folded several times for the 42V rating:

And lastly a Zenith EY500A, made by Sylvania:

Here a photo of a matching Magnoval socket for this tube:

And a top cap:

Now some photos with the heater lit up:

That's it for the EY500A / 6EC4. I hope you enjoyed it. Stay tuned for many more tubes to be covered in the Tube of the Month series!

Best regards

Thomas