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Thursday, September 22, 2016

The Differential Power Amplifier - Part 1


After the successful completion of fully differential line stage and phono stage, here comes the matching set of mono power amps.

I have often been asked why I have no push pull amps in my line up. Finally someone commissioned a set of push pull mono blocks, so no more excuse!

Like the matching line and phono stages they will be fully differential throughout. Nut just a PP output stage but also a differential input stage. Of course they can also be used with single ended preamps. Phase splifting is done via input transformers.

Output tubes will be a pair Elrog 300Bs per channel, driven by a pair 10Y. Alternatively 801A can be used as well. These should be good for a solid 15W per channel. Operation will be pure Class A.

Construction has just begun, so not much more to show than the top plates with the tubes at this  point.

The power supply will be using my favourite rectifiers, 4 6AX4 in full wave bridge configuration. Choke input filtered and with oil caps. Filaments will be purely DC fed as in my other DHT amplifiers.

Once the concept is proven with this first set of amps, an all silver ultimate version will follow to complete the series with the ultimate phono and line stage.

Stay tuned for updates on this project!

Best regards


Wednesday, September 14, 2016

News from the ELROG Tube Factory


Last month I already reported the news about the ELROG tubes. I plan a series of posts with news from the factory floor. And also general news about tube availability.

The production line is in good shape and has been overhauled to get a better vacuum than ever. We are currently producing 845 tubes as well as 300B. Some 211 tubes are still in stock. The photo above shows a 845 with an RF induction coil around it to heat up the interior for de-gassing.

The entrance to the factory floor with new company logo:

And a sign at the street to mark the way to the company location:

Another photo of tubes on the vacuum pump:

In the meantime price calculations have been done and the distribution scheme has been set up. In order to keep pricing reasonable all sales within the European Union will be direct. I am happy to announce that George Lenz of tubesusa.com continues to represent the Elrog brand in Northern America. We are seeking distributors for other regions but have not come to agreements yet. Any new distributor will be announced. Until further notice sales to all other regions besides USA and Canada will be directly from the factory.


Export prices outside the European Union, including shipping cost per matched pair:

ER300B : 900,- Euros
ER211 and ER845 : 999,- Euros

Prices per pair inside the European Union including sales tax and shipping:

ER300B : 1060,- Euros
ER211 and ER845 : 1185,- Euros

Prices per pair within Germany including sales tax and shipping:

ER300B : 1050,- Euros
ER211 and ER845 : 1175,- Euros

Payments can be received by bank transfer or PayPal. To place an order please send an email to the address given on elrog.com. That site will be updated with the prices soon.

The tubes carry a 1 year warranty.

Please inquire for volume discounts.

Stay tuned for updates from the tube factory. I plan to post regularly with photos and videos of the tube making process.

Best regards


Thursday, September 8, 2016

The Ultimate Phono Stage - Part 3


A quick update on the ultimate version of my phono stages.

As shown on Part 2, the phono was already pretty much finished last month. Due to some other tasks I only now found the time to do the last touch ups.

The signal section.

Signal section and power supply together:

The wood has been changed to the dark smoked eucalyptus for a better contrast to the gold coloured metal plates.

When I started this project I though the gold anodised metal with the maroon metallic red transformer covers might be a bit too gaudy. But since it is finished I like this color combination a lot.

Of course it can be built in any other color combination as well.

Close up the the rectifiers on the power supply:

The phono is playing right now. Stay tuned for part 4 with some sound impressions and more photos.

Best regards


Friday, September 2, 2016

The 6J5 Line Preamplifier


Earlier this year I showed a version of my single chassis entry level line preamplifier with the 27 triode. Here is a variant of this with the 6J5.

They basically share the same circuit only with slight adaptions and parts selection for the tubes used.

The 27 preamp pretty much only has unity gain which is sufficient in most systems with sources with high output levels.

When some gain is needed, this version fits the bill with a bit over 12dB gain at full volume.

This particular unit has 3 inputs (more would be possible of course. It uses transformer volume controls like all my preamps. In this case Intactaudio units driven by Lundahl line output transformers.

The same arrangement on the top plate has been carried over from the 27 version. In this case also the same white color for the capacitors and transformer covers.

Gold color for the front and top plates as seen on the recent EC8020 phono stage. The wood is 'maple carbon effect' to match the stereo 300B amp with which it will be used.

Of course both  glass versions of the 6J5 can be used as well as metal versions:

View from the top:

A nice alternative if the 2 chassis versions of the line stage are too costly or the available space permits only a single chassis.

Best regards


Sunday, August 28, 2016

Tube of the Month : The 30

Here is another small directly heated triode which probably deserves more attention than it gets. The 30:

The 30 was intended as detector or amplifier tube in portable radio receivers. It is a battery tube like the 31 which was the tube of the month in January.

It has the same UX4 base and pinout as the 31 and also the same size bottle, ST-12. Being intended for battery powered equipment it's oxide coated filament was designed to operate at as little power as possible. The filament voltage is only 2V and needs a measly 60mA to operate! That's only 120 milliwatts of filament power. The 30 is typically operated at 135V plate voltage (180V max) and at around 3mA bias current. It has a plate resistance of 10k Ohms which makes it still usable with an interstage or line out transformer if they have enough primary inductance. It is more easily usable with LC or RC coupling. The amplification factor is 9.3. I never used the 30 myself. It could be an ideal companion for the 31 in a nifty flea power SET amp to drive ultra efficient speakers, or as tweeter amp in active set ups, or maybe a nice little all DHT headphone amp. The plate curves show the typical excellent linearity of directly heated triodes:

Which look just as nice in real life:

Since I never used the 30 in any project, I do not have a lot of samples. It was made in globe shape as well as ST shape. Unfortunately I have no globe 30s which were named UX-230. But I do have some rather nice ST shaped tubes. Let's start with the most beautiful ones. Sylvania VT-67, a variant of the 30 made for the military.

These have beautiful white ceramic bases.

Some close up shots:

The base with leaf-logo:

The top:

The plate:

There had been two military variants of the 30 with different VT-numbers. Initially it was introduced as VT-27:

The VT-27 had a black phenolic base which was upgraded to low loss bases for the VT-67. The latter could be micanol or ceramic. Here a micanol base:

A phenolic base:

The base above is from a tube made by Tung-Sol:

The top:

Side view:

Another VT-27 made by Sylvania:


Side view:

Hytron type 30 / VT-67:

Another angle:

Side view:


And of course the 30 was also made by RCA:

And as last example a 30 from National Union:

A beautiful little tube with excellent linearity.

Best regards