[Abszero]

Here is my latest creation inspired by the beauty of a pair of EML300B that was lying unused.
As always, I try to create 2 stage SE amps for many reasons. Hard to do 2 stages with low gain power DHTs. One of the few tubes that have the advantage of high gain, great linearity and still a bit of headroom to be able to let the 300B signature be predominant. The 300B starts clipping at 8W or so and that corresponds to a 1.65Vrms input. The C3g starts clipping at 2.3Vrms input. This allows a headroom of 2.9dB which is not a lot, but still way better than no headroom. Anyway, the 300B will distort above 2% at 4.5W and in my opinion the listening levels for a 300B amp should be at 2-3W and that allows a 6-4.2 dB power headroom and therefore creates a more realistic 7.4 dB signal headroom for the C3g.
I was a bit reluctant to built it in one case, but many audiophile are looking for single enclosure amps as more convenient use of space. It ended up weighting more than 50lbs.
The big challenge, when building a tube rectified DHT amp in one enclosure, is to keep it quiet. This amp is dead quiet on my 96dB speakers and my 100dB headphones.
The power supply uses the LL1651 and two LL1673 10H chokes in common mode. The B+ is around 475V. This time I didn't use the famous Coleman regulators because of lack of space. The 300B filaments and the C3g filaments are powered using LD1085V regulators.
The amplifier is transformer coupled using the LL2753 and the output transformers are Jack Elliano's Electra-Print 3.5K to 8Ohms low IMD. The tubes are self-biased and decoupled with Elna Cerafine. All the resistors for biasing the 300B are Mills MRA-12. The 300B is biased at 380V/-80V/75mA and the C3g at 225V/-3.5V/17mA.
The amp has an input sensitivity of 1Vrms for 3W output. The frequency response is 20Hz to 25kHz at -0.8 dB and the damping factor of 2.3 which calls for easy to drive, full range drivers.
This amp sounds great on my TangBand and Mark Audio speakers. The bass is well defined and under control, the mids are superb and the high are clean and crisp.

I am asking $3,300 plus shipping of a 24x18x16" of 65 lbs from 06851. The amp itself weight about 57 lbs.
Also welcome to pick it up in Norwalk CT. It comes with new tubes except the EML300Bs which have about 500 hours.

[mca]

Beautiful work!

[FullRangeMan]

9 transformers in this amp

[ClefChef]

I follow your work with great interest and admire your craftsmanship. It is getting really hard finding finely crafted tube amplifier - the golden era is long gone.

I was wondering about LD1085 on 300B heaters - any comments?

Thanks

[FullRangeMan]

I follow your work with great interest and admire your craftsmanship. It is getting really hard finding finely crafted tube amplifier - the golden era is long gone.

I was wondering about LD1085 on 300B heaters - any comments?

Thanks

I think Radu should not reveal his secrets, suffice to say few builders use any heater regulartor or even post underside photos.

[ClefChef]

In tube amps there are few secrets, everything is available and discussed at length on various forums. DC heaters on DHT is a big topic with which Radu is familiar I'm sure. Thus my question.

[FullRangeMan]

In tube amps there are few secrets, everything is available and discussed at length on various forums. DC heaters on DHT is a big topic with which Radu is familiar I'm sure. Thus my question.

DC heaters on DHTs tubes is the only right way to heat cathode, AC heaters are cheap, use less than half dozen caps and polute cathode electrons with AC mains wall noises and some times Hum.
What do you want he say? He do the right thing.

[ClefChef]

DC heaters on DHTs tubes is the only right way to heat cathode, AC heaters are cheap, use less than half dozen caps and polute cathode electrons with AC mains wall noises and some times Hum.
What do you want he say? He do the right thing.

 

http://www.diyaudio.com/forums/tubes-valves/181184-300b-dc-heaters-confusion.html#post2434206 - for your reading pleasure.

[FullRangeMan]

 

http://www.diyaudio.com/forums/tubes-valves/181184-300b-dc-heaters-confusion.html#post2434206 - for your reading pleasure.

Thanks, this board is even useful to builders. Rod Coleman sell a nice regulated DC heater board, in some amps it even dont need hum pot.

[pocomo]

Beautiful work Radu!

Mike H.

[Abszero]

Bump.

[Abszero]

I follow your work with great interest and admire your craftsmanship. It is getting really hard finding finely crafted tube amplifier - the golden era is long gone.

I was wondering about LD1085 on 300B heaters - any comments?

Thanks

I forgot to notify myself of new posts, so apologize for this delayed response.
I do like Coleman regulators the most. In this amp, in order to keep things simple for the user and reduce the footprint a bit, I chose a voltage regulator for the 300B. Many of the Japanese designers are using this type of supply for the power DHT filaments. The output has low value resistors to reduce the start up current and prolong the life of the 300B. In order to keep the hum low, and limit the IM caused by a AC filament supply, I always choose to use DC for DHT filaments.  Going even further, I used DC for the C3g filaments too.
There is a slight difference between this regulator and the Coleman. Coleman isolates very well the filament ( whuich is in the signal path) from the DC raw power supply. The effect is a more refined and open sound. However, the differences are hard to tell and a A/B test is not an easy task.
Hope this helps

[hotube]

I own an amp of Radu Like this. Once you go transformer coupled you never go back

[Abszero]

The amp is not for sale anymore.
Thanks for all the praise.