This is my latest single ended amp build, and an outstanding performer, TYPE RH7591SE (Special Edition, because it has 3 inductors in the power supply) this and other unique features which are unavailable on any commercial type SE amps and certainly other amps at this price level. Please read the entire text for all the details. The detailed explanation are for those less familiar with single ended amp construction.
It is always important for single ended amps that the power supply receives extra attention. For SE amps, current delivery is paramount and low residual circuit noise. For this and all of my SE builds i use 2 inductors or chokes in a LCLC or CLCLC layout. Chokes are a simple "old school" device that is designed to deliver current by means of a magnetic field. It is simply a spool of copper wire wound around an iron core and there is no simpler device than that.
The basic circuit design type is based on the "RH 84" amp which employs Schade style or plate to plate feedback instead of global negative feedback that more than 90% of tube amps use. The critical difference is that the output transformer with its well known non linear behavior, is left out of the fb loop.
The heart of any amp, its power supply, consists of a voltage doubler circuit featuring 2 FRED, Fast Recovery Epitaxial Diodes. The capacitors have been upgraded to 2 x Panasonic 470uf x 250vdc feeding a 4 Henry choke, followed by a rare Siemens 390uf x 385 vdc LL (Long Life) cap into a 4 Henry choke and followed by another Siemens 390 x 385vdc cap which is also bypassed by a 10uf x 400vdc film cap.
The sound from one of these single ended amps is truly amazing. Don't take my word. Here is the latest testimonials from a buyer of a similarly designed 6l6 SE RH amp.
T4L, from California, wrote;
Well seasoned and broken in 6L6GB output tubes, 5AR4 rectifier, 6SL7GT with Cornwall speakers sound real nice. Listening to CSNY 4 Way Street, an album I've been listening to for years, using the Mac Mini playing iTunes. The detail is amazing. I just realized that there are some type of wooden percussion instrument on the song "Southern Man." All the times I've listened to the song, I never heard this detail. "Find the Cost of Freedom" caused chills on the back of my neck. I can hear the singers taking breaths between the lyrics. It startled me several times and I know the songs, have listened to the album at least 100 times. Now listening to "Street Life" by The Crusaders. Female vocals sound great, the bass is slamming, drums sound great, percussion is beautiful, horns/wind instruments are bright, soundstage sounds like a live performance. There's no noise between tracks, the tambourine sounds clear and detailed, I'm listening to music!
ALL USA MADE TUBES!
The power tubes are USA made 7591, which are like an 6bq5 or el84 on steroids. Tube collectors know that the USA made ones even if used, are far superior to the currently made types. The driver tube is RCA 12at7wa, which is a military version of the the venerable 12at7.
AMP Construction details
This amp is not a quick and dirty hack job only quality parts used. It has all new capacitors , resistors, wiring, sockets, input and output jacks . The only parts that have been reused and recycled (to save you money, but not quality!) is the power transformer, output transformer,d chokes and the chassis. The amp has modern convenience and safety features such as on/off switch and indicator light, 2 amp fuse, safety capacitors on the AC input, and gold plated 5 way speaker binding posts and rca input jacks. So, essentially, the amp has been totally rebuilt with all new parts and is very much a new amp.
Unique features not found on ordinary amps!
Another area of refinement is the use of a choke combined with a zener and a 10uf x 400v film cap for voltage regulation of the G2 supply (note; The 7591 is a beam pentode which means it has 3 grids. In pentode mode Grid 2 or G2 is supplied ideally, from an independent source). The use of the choke supplied by the 5 watt zener greatly helps to regulate the G2 supply. This yields a very dynamic sound where instruments bloom and crescendos reach realistic levels.
A short word about sound quality from a single ended amp. If I would have to give one word it would be INVOLVING. It has the ability to draw you into the music. Voices and instruments are suspended out from the speakers and seem to be playing a personal concert just for you. It is this ability that all high end amplifiers aspire to. What sets Single ended tube amps, whether they use very expensive triodes like a 300B or 845 or even a 2A3, or if they use classic pentodes like 6V6, EL84, 7591, 6L6, 6550, KT88, EL34, etc. is the uncanny ability to achieve a very realistic sound presentation. Voices, instruments, sound effects, have an uncanny you are there quality that can evoke a genuine emotional response to the music. This aspect of home audio is usually available only in big bucks audiophile systems.
A buyer from Texas wrote back his experience with a similar 6L6 rh amp.
Rudy from Texas wrote back; "did the quickest setup for me. am listening to youtube videos on roku. optical out from TV to teradak NOS dac to audionote one pre-amp to your amp. old audioquest emerald interconnects. clear day speaker wires (thin guage solid wire (silver, I think) to 1970's klipsch heritage speakers ( I have had for more than 10 years, don't think they have ever been opened) the sound is amazing! the amp and speakers disappear. getting the same feeling I had when first listened to audionote meishu. I know my audio memory is fleeting but difficult to say what difference there is between these tubes and 300B. have heard push pull el 34 amps before but this is way different, and way better. acoustic piano and bass sound exceptional"
this amp has the same ability to reproduce the unique single ended sound quality at a fraction of the price of the name brands.
TECHNICALLY SPEAKING; Single Ended Tube Amplifiers explained. Very, very, briefly the signal goes into the 12at7 is amplified, then goes into the power 7591 tube which increases the signal into high voltage of about 300vdc. This voltage when fed into the output transformer is converted into high current for the speakers. This simple circuit results in about 8+ watts of pure class A output. Thus the somewhat simple circuit is neither adding or subtracting from the original signal source. The result is a much more dynamic and visceral, for a "you are there" audio experience.
All the brand new components in the amp are hardwired, point to point, and still breaking in. Check the pics of the underside showing the meticulous, time consuming point to point wiring, and the high quality capacitors and resistors. The power tubes are operating in class A with cathode bias for about 7 to 8 watts of super clean sound. This little amp has amazing sound quality equal to or better than other SE amps such as Decware at less than half the price! Operating in Single Ended Pentode Class A with ultra short signal path for minimal alteration of the sound.
Please remember that this amp is sold strictly as is. Caution is required as tubes are hot and there is no bottom cover to the amplifier. Just remember if you are into headbanging, window rattling, neighbors phoning the police, loudness, this amp is definitely not your cup of tea. But if you are looking for a great sounding little amp for your den or bedroom this will make a Bose sound like pocket transistor radio in comparison and probably cost less and have a better resale value. Although this amp is built to extremely high standards and with the utmost of care it is sold strictly as is. Thank you very much for reading my ad.