This is Thomas Mayer's blog about vacuum tube audio, to share updates about new amplifiers and preamplifiers and ELROG vacuum tubes.
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These amps got finished in the last week of 2014. Another set of 300B mono blocks with 10Y as driver tube. The same configuration as the previously shown 10Y/300B. Only this time with Tamura F-5003 amorphous core output transformers.
I was never very fond of amorphous core transformers. Maybe this was mainly due to some listening sessions with systems which overly used amorphous core transformers throughout. So I decided to give it a try with just the output transformers on amorphous cores.
The driver stage is again a 10Y, transformer coupled with a Tango NC20 to the 300B grid. The amps can be operated from the same power supplies. But these new monos will later get a matching set of PSUs of their own.
Those Tamura transformers have a nice white/light grey finish. Unfortunately Tamura stopped production of a major part of their transformers last year, among them this line of amorphous core transformers. As was the case when Tango decided that they will go out of business, I also secured a stock of the Tamura types which were announced to be discontinued.
Stay tuned for an update on the sound of these amps and especially the amorphous core transformers.
2014 is coming to it's end and this is the time to look back at what happened throughout this year and also to look ahead into 2015. It's been another great year filled with music, great sound and many exciting projects.
Rereading last years Happy New Year post, I realised that many projects which had been planned got done. Others had not and are still awaiting to be brought to life.
The highlight of 2014 was the introduction of the Elrog ER300B. It surpassed the expectations and enabled a new level of sound quality from 300B amps. I finished 3 different 300B amps using this tube and more will follow next year. I will continue to post user feedbacks from the tube and hope to visit the Elrog factory again soon. Of course I will share a report about it.
The 801A amps which I announced end of last year got finished. See a post about them here.
Also silver was indeed an important topic of 2014 with several amplifiers and preamplifiers built using silver wound transformers. The pure 45 bliss silver amps are still holding the title of my best sounding amps so far, if used with the right speakers.For more demanding speakers and louder listening levels, it is the silver 211/211. This ranking may be a surprise since I wrote such glorious reviews about the ER300B. It is still the overall amp and parts quality which determines the final result. The output tube is only one part of the picture. The ranking will surely change once an all silver 300B amp has been built.
On the preamp side the silver/finemet 10Y line stage was a highlight and again proved the sound qualities of silver wound transformers. This was also the first time I was using finemet core transformers and this will be a big topic in 2015 with several amps using finemet interstage and output transformers in the planning.
Another topic which had been pending and finally proceeded in 2014 was differential/balanced circuits. Not in form of the differential EC8020 phono stage as mentioned end of last year, but I began with the differential 10Y line stage. It turned out great and showed the potential of the concept. So a differential phono has to follow and this will hopefully happen in 2015. But before that I will finish a single ended EC8020 phono with an improved biasing scheme. This is in progress and should get completed in January.
I am often asked about push pull power amps. Although by far the most amps I built are single ended, I am not dogmatic about this topology and will also explore this field further. The differential preamps will get their counterparts in form of push pull/differential power amps. Not sure if this will happen in 2015 or rather in 2016.
On the lower cost side there were also some new things. First the cost optimised D3a LCR phonos. Then I digged out some sleeper tubes: The 6GE5 for use as power tube, the 6AG9 as suitable driver for it and the 6BE3 as matching rectifier. Two different amps have been shown with these tubes.
There had been some great events this year. The High End in Munich was a great experience. I will be exhibiting again in Munich in 2015 with Wolf and Bernd and hope to meet and talk to some of you there. The ETF in Berlin was an absolute blast and I am looking forward to ETF.15 in Denmark.
And finally there was the journey through the world of 78rpm Shellac records which culminated in the Shellac presentation at the ETF hosted by my friend Frank whom I am thankful for introducing me to this.
The webshop for parts and kits which I wanted to set up got postponed a bit but is definitely going online soon. This year I started to upload some videos which seem to be quite popular. I need to work on my skills however and improve them. Here a short video from the lake, with some waves hitting the small island called Hoy.
Many thanks to all of you for a great year and all the best to you and your families for 2015!
In previous posts schematic and assembly steps of transformer coupled mono blocks with the 6GE5 as output tube have been shown. As promised a cost optimised version will also be presented in form of a stereo amplifier.
Going stereo instead of two mono blocks is already a considerable cost saving measure with minimal impact on sound quality. To reduce cost further we need to let go of the interstage transformer and use RC coupling in the driver stage instead. Next is the reduction of the number of chokes which requires to go for a cap input filter instead of choke input. And lastly the exchange of oil caps with electrolytics. Here is the schematic:
I wanted to keep the ultra path connection in the output stage, hence two separate chokes for each channel to isolate them. All other capacitors are electrolytic. The first cap after the rectifier sees the highest voltage peaks, hence two 22uF/350V caps in series. This results in 11uF capacitance which is still reasonably low and does not stress the rectifiers too much. The two 150uF caps after the chokes can be implemented with 3 47uF in parallel as I did. These caps can also be increased but the 150uF proved sufficient for quiet operation. The bypass caps at the cathode resistors of the 6GE5 are needed to suppress any residual ripple which would otherwise be coupled from the high voltage to the cathode. The driver stage is a standard RC coupled stage.
A rather simple circuit which is easy to build. I will show the completed amp in the second part and will also offer this version as a kit. Stay tuned!
Part 1 about the 6GE5 Monos showed the circuit. In this post I am presenting the assembly steps of the amplifiers.
So far the amps which received the most positive feedback for the design are my 211/6HS5 mono blocks. So I reused some of the design aspects of those 211 amps for the layout of the 6GE5 Monos:
All the capacitors in the circuit are place in a single row on the left side. The 6GE5 output tube at the front in the middle and the 6AG9 driver beside it. Two separate power transformers are hidden under the black covers. Since the heater windings of the power transformer used does not supply enough current for all the tubes, I used a separate heater transformer for the signal tubes. The 6BE3 rectifiers are placed at the back side.
This is the top mounting plate with just the 12-Pin tube sockets installed:
Most of the resistors in the design are directly mounted to the bottom side of the plate:
All remaining resistors are soldered to the terminal strip.
Mounting of the power transformers:
Most of the wiring done:
Adding the capacitors:
The chokes, output and interstage transformers go inside the chassis:
The finished amp:
The two monos side by side:
Top view:
I have been using these amps for some time and am very happy with the result. Power output is about 4W. Solid frequency response. As mentioned in part 1, I am making a parts kits available for these.
Iron set (power transformers, chokes, output and interstage transformers):
Too expensive? Stay tuned for the entry level version of this amp with just a single choke and RC coupled driver instead of the interstage transformer.
