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Tuesday, February 28, 2017

Tube of the Month : The EY500A / 6EC4


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.


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