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Tuesday, September 30, 2014

SE 45 amp made switchable to 300B


Last year I showed a 45 amplifier with a driver stage which could accept either another 45 or a 10Y. The owner of the amps requested them to be modified so they can also use the 300B as output tube.

It is relatively simple to make an amplifier such that it can accept either a 45 or 2A3 output tube as was done in this amp. The 45 and 2A3 use similar operating voltages. While the 300B could be run at a low operating point using the same voltage as the 45, this would not use it's full potential. So a more elaborate switching scheme is necessary to set the amp correctly for either tube, hence two switches. To easily monitor filament voltage, two measurement jacks were added as well. The switchability of the driver stage was kept.

Filament measurement jacks were added for the driver as well. The power supply also received a switch to set the different supply voltages:

And finally for covering to all kinds of situations, a set of switch was added to the back for adjustment of filament voltages over a wide range. This allows to adjust the filaments by accessing different taps of the filament transformer, in case some tubes are used with filament specs that do not match the originals. There are cases of new production tubes which draw much higher filament current. The filament voltages are DC for driver and output tubes for hum free operation.

The complete set of mono blocks with their power supplies, here equipped with ceramic base 801 in the driver sockets and Electro Harmonix 300B output tubes.

These amplifiers allow a variety of combinations. A tube rollers dream. Here one of my favourites, 10Y drives 300B, in this case an old production Western Electric:

The 10Y driving a 45:

45 drives 45:

Globe 45s:

EML makes ridiculously large 45s. Here a mesh plate in the driver position and a solid plate output tube:

The EML 45 is even larger than the Western Electric 300B:

The Tango XE20S output transformer allows a wide flexibility in primary impedance to cover this variety of tubes. To make use of it's full potential, all taps of the output transformer are brought out to speaker jacks:

As soon as the new Elrog 300Bs arrive these will also be evaluated in this amp. Please don't expect me to give sound descriptions of all these combinations. This is highly subjective and I learned that different users of such switchable amps seem to develop different preferences. I will run some listening sessions during the next days and report my impressions on some of the combinations. Stay tuned.

Best regards


Friday, September 26, 2014

It is finally coming!


Great news! The new german made tube many people are eagerly waiting for is finally coming!

I expect the first tubes to arrive next week. Stay tuned for photos and the first listening tests. I will also start to accept preorders next week. Availability will be very limited until the end of the year. Deliveries will be done based on the pre order queue.

Best regards


Endlich ist es soweit, die Röhre auf die so viele warten kommt! Ich erwarte erste Röhren nächste Woche. Es wird natürlich Berichte mit Fotos und Klangeindrücken geben. Ich werde dann auch Vorbestellungen annehmen. Die Verfügbarkeit wird zunächst sehr begrenzt sein. Die Auslieferung erfolgt in der Reihenfolge der Vorbestellungen.

Viele Grüße


Saturday, September 20, 2014

Tube of the Month : The 83V


Due to my preference for TV Damper tubes like the 6AX4, classic rectifier tubes haven't received a lot of attention on my blog so far. Except for the 5X4 which was presented last year, none of those classic two diode rectifier tubes with 5V filaments/heaters have been covered. This doesn't mean that I don't consider them as useful. I'll give them some more attention in the future not only on the blog but also in actual projects. This months tube is a type many of you probably never heard of: The 83V.

The 83V is not to be confused with the 83, a mercury vapour rectifier tube. As the appendix 'V' indicates, the 83V is a vacuum tube. It was introduced in 1934.  It was probably meant as an alternative to the 83 which avoids the hazards of a potential mercury spill in case a tube breaks.

But the 83V cannot replace a 83 in every application since it has lower ratings. Both tubes have the UX4 base in common (pinout shown on the left). But that is where the similarities end already. While the 83 is directly heated, the 83V has an indirectly heated cathode. The cathode is connected to one end of the heater inside the tube to avoid the need for a fifth pin. Sometimes this is referred to as half indirectly heated. With the indirectly heated cathode, the 83V has a rather low internal voltage drop which mimics the mercury vapour tubes, the drop is not as constant but rises with current draw. While the 83 filament consumes a hefty 3A, the 83V only requires 2A. Peak inverse voltage is the same 1400V for both, but the vacuum variant has a lower current rating of 200mA max versus 250mA of the 83. A big advantage of the 83V is the slow voltage rise as the heater warms up.
It also doesn't require a preheating procedure. Both types also differ in terms of size. The 83V has a ST14 bulb while the 83 comes in the larger ST16 glass. The 83V has the same size as a 45 which would make a good fit on a 45 amp. Current and voltage capabilities are more than adequate for a stereo SE 45 amplifier. That will probably be an application for which I might use the 83V in the future. also powering a stereo 2A3 amp would be possible, while the current rating would be too low for a Stereo 300B amp. A mono 300B would be possible however. While the 83V is quite different to the 83, it has a much closer equivalent, the 5V4 which is basically the same tube with an Octal base. Both of these will also be covered in some future Tube of the Month posts. Although this rectifier is quite capable for such a small bulb, it has not been used a lot in audio. Nowadays it seems to be forgotten among amplifier builders. Thus it is still available from tube dealers at reasonable prices, albeit not as cheap as TV dampers.

Let's have a look at the tube:

I only have RCA 83-v in my collection, so can't show any other brands.

Views from the side showing the plate structures:

Detail at the bottom:

This shows the heater wire going into one of the two cathodes which are internally connected:

The top:

Close up to the upper end of a cathode:

Tube marking on the glass:

The UX4 base:

As mentioned above, the 83v is electrically identical to the 5V4. Here both tubes side by side:

The top of both tubes:

The only difference is the base, the 5V4 is a Octal tube:

Now let's see the tube in operation:

The cathodes give off a nice orange glow.

A close up to one of the cathodes:

The bottom part of the tube:

More close ups:

Can't get enough of that beautiful glow. That's why the color scheme of the logo at the top of the blog resembles the glow of tubes.

I hope you enjoyed this expedition into the world of 'classic' rectifier tubes.

Best regards


Thursday, September 18, 2014

Tube Box Art, Part 16 : Delco


Delco was a subsidiary of General Motors which developed car electronics and radios. They also supplied tubes under their own brand.

As far as I am aware they did not have tube manufacturing of their own, so these were rebranded tubes from the major suppliers.

As with most tube boxes the earlier one had beautiful logos :

And got simplified over time:

The latest boxes had the most bland design:

I found this tube box branded General Motors Parts Corp. Not sure if that was part of Delco or if this box is from a time prior to the formation of Delco.

Best regards


Friday, September 12, 2014

Tribute OPTVC, Silver Windings on Finemet Core


More cool stuff just arrived! A pair of line output transformers with TVC (transformer volume control) secondary. Same style as used already in the 10Y line stage. Only this time with silver wire and Finemet (nano crystalline) core material.

I think the 10Y line stage performs already on an extremely high level as is. No matter if equipped with Tribute OPTVC or a combination of Lundahl line out transformers and Intactaudio AVCs (auto former volume control). Several versions of the line stage have been built with both and they work nicely for the people who use them. Yet occasionally I am asked if it is possible to even improve on this. One result of such a request was the differential 10Y preamp. The other possibility is to use silver windings in the transformers.

So I commissioned a pair of silver wound line output transformers with TVC secondaries (dubbed OPTC) to Pieter Treurniet. Besides silver these also use a nano crystalline core material called 'finemet'.

The cases also got a special finish in metallic white, which was applied by the paint shop who treats my transformer covers.

Stay tuned for updates as the assembly of this over the top version of the line stage progresses.

Best regards


Wednesday, September 10, 2014

New Lundahl Interstage transformer for 845 amps


During my visit at Lundahl in Sweden, we discussed some new products which would be worthwhile to add to the line up. I suggested a 1:1 interstage transformer, capable of enough voltage swing to drive a 845 output tube and for use with powerful driver tubes which draw a lot of current.

Last week I received prototypes of the new LL2753 interstage transformer. It is capable to swing 330V peak to peak at 30Hz. Like most Lundahl products the air gap can be chosen for a wide range of bias currents. My sample pair came gapped for 20mA with a primary inductance of approximately 60Hy.

Initial measurements on the bench look very promising with a nice flat frequency response and a smooth roll off without severe resonance peaks.

The LL2753 comes on a larger core than the widely used LL1660. Here both of them in comparison:

Measurements in an actual tube circuit will be done soon. Stay tuned for more results. Also a SE 845 amp with these might be coming up in the near future.

Best regards


Monday, September 8, 2014

Tube Box Art, Part 15 : Raytheon


It's been a while since the last tube box art post. So here is a new one. This time covering the tube boxes of Raytheon.

Raytheon has a long history spanning back more than 90 years. The company was founded 1922 under the name American Appliance Company and initially worked on refrigeration technology. They got into the electron tube business with the development of rectifiers, which were an essential part in their 'battery eliminator' which enabled powering radio sets from the AC mains rather than from expensive batteries. They marketed their tubes under the name Raytheon which means 'light from the gods'. In 1925 they changed the name of the firm to Raytheon Manufacturing Company.

Raytheon was very successful and grew quickly and acquired other companies. By the 1930ies they were among the largest tube manufacturers. During World War II Raytheon got involved in developments for the military. The company diversified a lot throughout it's history. The company still exists and is now mainly working in aviation and Defense technology.

Raytheon's tube box art changed during the years. Shown above is an early box design. These are boxes containing a 56 and a 45. The top flaps:

Later they changed the style to this one:

They maintained the red/blue color scheme but the design got simpler. This is a box with a 46 tube.

Another version of that design:

Which then turned into a red/white design:

Top and bottom flaps:

Stay tuned for more tube art posts coming up.

Best regards