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.

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Tuesday, April 14, 2015

VinylSavor at the Munich High End Fair 2015


Time flies! The next High End show opens in a month in Munich, May 14 - 17. I will exhibit again with the same partners as last year, Wolf von Langa and PrimaryControl.

We will exhibit in the same room as last year: F231c / Atrium 4.

There will be different 300B amplifiers on demo using the Elrog ER300B tubes. Preamplifiers will be an updated version of the 10Y line stage and the latest LCR phono with EC8020 tubes.

See you in Munich!


Thursday, April 9, 2015

Tube of the Month : The E55L (revisited)


Since I used the E55L in a headphone amp recently, this is a good opportunity to have a closer look at the tube again. The first tube of the month post about the E55L did not show any photos of the internals, so it is time to revisit it.

Technical details of the tube have already been covered in the first post. So this one will just show photos.

Philips Miniwatt E55L:


Another Amperex:



For closer inspection of the internals I picked the Amperex with green letters. A close up before it is getting destroyed:

The glass removed:

Peeking into the side opening of the pate already gives an idea of the fine structures of the grids:

The top with the getter ring:

Side view:

A close up showing the pins going through the glass:

The plate removed from the system:

This leaves the remaining assembly exposed, cathode, control and screen grids and beam forming plate:

A close up to the rod which holds the screen grid:

The heater wire inside the cathode:

Heater wire partially pulled out:

Close up:

The heater:

Cathode and control grid:

The control grid wires are extremely fine and barely visible:

A human hair in comparison:

A close up shows what a marvellous piece of engineering the control grid structure is:

Cathode and control grid separated:

More views of the grid:

And lastly a few photos of glowing EL55s:

Best regards


Friday, April 3, 2015

The Headphone Amplifier


In most cases my line preamplifiers can drive headphones without any problem. But certain headphones with 32 Ohms impedance are a too heavy load for a preamp. Typically they are too sensitive to be connected to a power amp, even if it is a flea power single ended one. So in such cases a dedicated headphone amp which acts as buffer after the preamp is the ticket.

This is how the E55L single ended headphone amp was born. It is meant to drive the Grado RS1 which is very sensitive (1mW for 96dB SPL) and has a 32 Ohms impedance.  The E55L triode connected delivers more than enough power for that and has just the right gain. So the amp can be kept rather simple with just a single E55L stage per channel.

The circuit follows my usual approach in power amps. Output transformers are Hashimoto. The E55L runs at a moderate 30mA. The power supply is tube rectified with a 6BY5 augmented with UF1007 diodes to create a full wave bridge. Several LC filter stages after rectification. This guarantees a hum free operation even with these sensitive headphones.

Top view:

There are 3 outputs connected to the 4, 8 and 16 Ohm taps of the output transformers. The headphones work on either of them. Selecting different output provides some additional gain control.

Just one tube per channel:

View from the back:

The E55Ls proved to be just right for this application.

Best regards


Sunday, March 29, 2015

The ultimate 6CB5A amplifier


In this post I will show the single ended 6CB5A power amp which was built to be used together with the recently shown Octal Preamplifier Mk2.

This amp is built based on the same circuit and similar parts quality as the 'no compromise 6CB5A amp' presented in 2013. Instead of the Tango transformers in the 2013 amp this one is built with Hashimoto interstage and output transformers.

The external power supply is built in the same design as that of the preamplifier. It also uses a pair 816 mercury vapour rectifiers in conjunction with two 6AX4 TV damper diodes. This hybrid bridge arrangement givse a nice blue glow in operation:

The power supply has panel meters to monitor B+ voltage and total current through the amp. The same style on both amp and preamp. The latter now also in it's final housings:

Like the preamp, this type of power amp is a smart choice if maximum sound quality within a given budget is the goal, rather than forcing the use of a certain tube. The budget which is saved on the output tubes went into the parts quality of the rest of the amp. The result justifies this approach. Even with the rise of the Elrog 300B, I still love the 6CB5A. This amp represents the ultimate level of the 6CB5A concept. While my entry level 300B is 50% more expensive, this 6CB5A amp uses even  higher quality interstage and output transformers.

The matching preamplifier and power amplifier combo:

No directly heated triode anywhere, yet super smooth sound with tons of tone colors. High resolution and very quiet operation. I have been listening with this combination for a couple of days now and am amazed how beautiful it sounds. No urge to switch to a 300B amp or 10Y line stage.

Of course a DHT power amp and line stage do provide more resolution, even more tone colors and a separate LCR phono stage does improve on articulation of voices. So if the budget allows, DHT and LCR are the way to go. But rather than forcing the use of DHTs or LCR RIAA into a certain budget, the Octal preamp and 6CB5A power amp give much more satisfactory results!

Top views of amp and PSU:

 Mercury glow:

I cannot repeat it often enough that the tube type alone does not guarantee good sound. It is always the entire concept and the balance of the quality of parts and circuit. Yet many audiophiles just want a 300B or must have a directly heated preamp or a LCR phono. It is important to understand that DHTs need high quality surrounding circuits to perform at their best. While indirectly heated tubes don't require a lot of attention in the heater supply, DHTs are very sensitive and need the best possible filament supplies. That's why I recommend to use the 6CB5A over the 300B below a certain budget.I'd rather listen to a max'ed out 6CB5A amp like this than a compromised 300B.

Best regards