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

News from the ELROG Tube Factory 4

Hi!

While production of the 300B, 211 and 845 tubes is in full swing, the next ELROG tube type is in development.

The first prototypes are being made. The tube will be launched at the High End fair in Munich this May. Here another teaser photo:

More abut this new ELROG tube in upcoming posts.

In a previous post I showed some photos and video clips of the assembly of the filaments of a ER300B. Today I will show the next steps in the process of vacuum tube making.

Here we see the electrode system of a 300B with filaments and grid. Only the plate is still missing. Each assembly goes through careful inspection and alignment.

Proper alignment of the grid ensures that the finished tube will meet the specifications and pass final tests.

Here we see Olena carefully inspecting and adjusting this vital part of an ELROG 300B:

Next the glass base is prepared...

... and the electrode system is welded to the metal rods in the glass base:

Now the system gets washed in a special solution before the plates are mounted.

Here we see Matthias inspecting one piece of the plate which is made of two halves.

Adding the plates to the system...

... welding the plates to the support rods which run at either side of the tube:

This is the result from this step:

Now the two halves are welded together so that there is no gap remaining between them:

The only part missing before the internal construction is complete is the getter. The getter is stored in a little ring:

This ring is mounted at the top of the system. Here it holds the getter material which gets flashed and creates the silver mirror surface later in the production process.

Now the internal structure is ready to be sealed within the glass envelope.

This step will be shown in an upcoming post. Stay tuned!

Best regards

Thomas

The Ultimate Line Preamplifier, Part 6

Hi!

Another ultimate line preamplifier is in the making.

It shares the same circuit and all silver transformers and plate chokes as the previous ones. The pre-wired top plate:

All silver transformers and chokes are on a separate sub assembly:

Which is mounted below the top plate:

The only parts missing are the silver AVC volume controls which will be mounted to the front plate and wired to the rest at the final assembly stage.

This one shares the same color combination as the ultimate phono stage.

Both will be on demo at the High End fair in May. Visit us in rooms F231c and F231e to listen to this preamplifier combo.

Best regards

Thomas

Integrated SE Amplifier with the 46

Hi!

Here is another single ended amp based on the 46. This time an integrated with input selector and volume control.

It is basically the same circuit as the recently shown 46 power amp.

A DACT stepped attenuator serves as volume control directly after the input selector which in this case only selects between two inputs. One RCA and one XLR. The latter goes through a pair of input transformers before it is routed to the input sect switch.

The parts on the top needed some rearrangement to make room for the input selector and volume control.

Since this the power transformer does not really need a large cover as on the previous amp this helped to free up enough space.

When tested with the volume control at maximum and with a line stage this amp sounds just like the last one. The 46 is absolute musical ecstasy.

Extremely rich tone colours almost to the point of exaggeration. Bass is surprisingly solid and well defined with the right speakers.

Not as much resolution as a thoriated tungsten output tube. But sheer fun to listen to.

This will certainly not be the last 46 amp built be me. Stay tuned!

Best regards


Thomas

The Ultimate 300B Amplifier - Part 1

Hi!

After the excellent results from the fully differential 300B amp an ultimate version with all silver transformers and plate chokes was the logical next step.

It shares the same circuit and chassis design of the previous one. All relevant transformers and chokes are upgraded to silver.

These are all the silver goodies which go into one channel. Like the copper version the amp will have 4 chassis. Two mono blocks and each with it's separate power supply.

The sub assembly with all signal relevant transformers and chokes, except the input transformer which is directly mounted to the top plate near the input stage:

These mono amps are meant to complement the ultimate phono and line stage for a fully differential system without caps in the signal path. A set of these power amps together with the phono and line will be demoed at the High End fair in Munich this year.

Stay tuned for updates as the amps get completed.

Best regards

Thomas