“Evoke” - 6N7 preamp with remote

 

This is my third 6N7 preamp and this time with remote and glass tubes. The other two have metal 6N7 tubes. These are also Russian tubes from early 60s. The external PS is tube rectified and is one of my “Universal” supllies which work with my “Xfi” and EL3N power amp. My intention is to build a new PS and use an 80 rec. tube. But for now this combo works perfectly. My 6V6 power amp - “Rococo” - and this preamp make beautiful music. 

Chassis here is cast Al with an Ironstone finish matching the PS. As mentioned the tubes are NOS Russian  6N7 dual triodes. Plates and grids are paralleled because the tubes may have two triodes but share a common cathode. A combination of wire wound, metal film and carbon film resistors are used and cathode bypass caps are 100V NPs. Output caps are Mundorf EVO Oil caps and as usual sound excellent. Tube sockets are gold and ceramic types. They look flash and work well. 

Because of the external PS the heater voltage is DC using two 3A fast diodes, 2X 47000uf caps and snubbing polies. The preamp is very quiet has extended bass to 30hZ and clean, sweet highs. The remote is an Alps blue velvet and is powered from the 6.3V heater voltage. There are two selectable inputs with one output. Wiring is solid core Cat5 and fine silver plated wire. The knob is a sculpture 4oz solid brass type with a gold finish. This is a great looking and even better sounding preamp. 

“Rococo” - 5961/6V6 two stage power amp

“Rococo” ;- 5961/6V6 amp complete and playing very nicely. Tubes, as I mentioned, RCA 5961 red base and currently Tung-Sol 6V6GT (matched - 2009) ). I have other classy 6V6s but Ill listen to these a while. All tubes new.

Asian OPTs and blue CDC coupling caps. I have noticed these caps in some very expensive high-end power amps. PS is two 3A Fast diodes and double Pi filtering. HT feed to the driver is split into two single feeds with each a 22uf LESR electro for better separation and sound stage. Noise with RCAs open is 1.4mV. Thats quiet.

Big clear, very dynamic sound leaning toward the bright side emphasising voice. Tubes need 50 hours to burn in from new. Worked at first on. I played the new amp over the afternoon and into the very late evening. Watched a movie with it providing the sound and up in volume.

A few more details for those interested;- the timbre base is the last I purchased from my amp building octogenarian Don. He doesn’t make amps or bases any more. So a fitting tribute to his skill. The finish is a spray lacquer which went on well getting three coats all at once with no runs. 

The power tranni, as usual, is Hammond, ceramic sockets and all wiring is solid core Cat5. No shielded wire and noise is 1.4mV. 306V on the 6V6 plate and 160V on the 5961. Bias is 1.4V and 18V, all as the schematic. CDC interstage caps Ive had for years and sound excellent, WBT silver base solder used. The double Pi filtering adds upto 350uF of 400V caps and snubbed - 0.1uf poly. 

Mostly 1W film carbon film and 5W wire wound Rs throughout with a few metal films. Quality gold plated RCAs and heavy solid brass speaker posts also gold flashed. Ck(s) are all NP 100V types. 

Beautifully clear transparent midrange from the tube compliment and well presented through my horns. Bass sounds well extended and balanced against the other frequencies. Still smiling. Love the look

“Automony” - small signal preamplifier

 

Completed the cct. brds. thirty years ago and they have sat around until recently. There is no pcb but just a pad brd. There is no hookup wire on the brds. Each component is wired to the next directly with no other connection between. This I call component-2-component wiring, better the point-2-point wiring which uses hookup wire. To add to this there is six very expensive Jensen copper foil, paper and oil caps. Also two Solen caps plus a mix of carbon and metal film resistors.

Recently I discovered high voltage SMPS which I have successfully powered other preamps with. Here it also powers this preamp, the same “Universal” PS. The brds. plus a remote control Alps blue velvet pot fit snuggly into the Hammond wood cheek chassis. The preamp was designed for 12AX7s but here Im using LinLai 12AU7s. 

The finish colour is Ironstone and a heavy sculptured brass gold plated knob finishes the look. There is two inputs selected by a switch at the back. The sound is smooth and romantic. This maybe due to the both local and global negative feedback. This is old school design and has a lot to do with the smooth, creamy audio presentation. A fitting completion to what started thirty years go.

“Dadirri” - 71a power amp.

 

Every now and then you build an amp which stands out from all the other builds you have done in the past. Of the 71a amps I have built there is one for me and now two for others. Though there is a list of standard parts used in this build for some reason it sounds way better than it should. I did use new driver tubes - Tung-Sol 6SN7 - but the other tubes, 71a Cunningham and RCA 80 rectifier tube are vintage and I have used them before. I guess just accept it, listen and enjoy and don’t over think it. I know the new owner will be very pleased. He is using his own tubes. 

The timber chassis I am now buying from Aliexpress and though pricey they are solid and very good. In this build I left the top plate natural low sheen Al. It would be a shame to paint this one. An oversize Hammond power tranni and Asian OPTs round out the iron. Carbon film 1W Rs, wire wounds and a few metal film Rs were used. Interstage caps are Russian PIO in glass and metal envelope. I wired 4 and 8ohm speaker connections in this build. 

The 5V DC heater voltage for the 71a tubes is provided by a 3A bridge and two 4700uf caps and taps off from the 6.3V AC filament voltage for the 6SN7s. All wiring is with solid core Cat5 and no shielded wire is used. Noise is less than 1mV. HT is rectified by the 80 tube and a double Pi filter cleans up the 220V DC reaching the 71a tubes. There is 247uf of storage and smoothing caps. The HT feeding the driver tubes is split in two and 2X 10uf 450V caps hold a fast and individual power storage. The stereo imaging of this amp is extremely good and it may be due to this HT split to the drivers. 

I’m extremely pleased with the overall appearance of this amp. Matching the good looks is the most beguiling sound I have heard from a tube amp which only supplies about 300mW of power but in my system plays quite loud with my 93db efficient speakers. This one should have been a keeper.

50W Class A Holton based power amp

 

For a long time friend, who already has two of my power amps, one SS and one tube, I was requested to build this Class A power amp. Holton Precision of Tasmania had developed some new Class A 50W modules. That’s 50W pure Class A before sliding across to B. Amp should produce 90W in Class B. 

The PS consisted of a 300W tranni and 132,000uf of Mundorf Mlytic audio grade caps. Dual 35A rectifier bridges round out the PS. The caps were heavily snubbed with high voltage polies. With a result the amp has near zero AC noise. But better than that, the amp produces beguiling music like I’d not heard before. Its ability to dig out inner detail and bring it to the front was uncanny. The new owner liked it also. 

The amp runs extremely hot and to help control the heat two silent running fans were installed. The fans sat on rubber grommets for isolation and were run on low voltages. With a result they could not be heard. Though this build produced many challenges, over months of construction, it was worth it. 

“Immerse” - headphone amplifier using 5W chip amps.

I had two 5W chip amps (TDA1905) in my collection for many years but did not need just another low wattage power amp to drive speakers. The end result is a headphone amp. With the chips capable of driving eight ohm speakers to 5W driving 32 ohm head phones to just part of a watt should be easy. The manufacture of the chips claim 0.1% THD at 3W. That means the distortion levels into phones will be very low. And plenty of good drive power.

Using a similar enclosure I have used many times I hoped the amp would work with batteries but it drew too match current. Batteries were out. I have a few DC wall warts and a 12VDC 880mA unit was perfect for the job. I added another 1500uf of filtering in the amp some snubbing caps to keep noise low. Noise is less than 1uV. A mix of carbon and metal film Rs used throughout.

The headphone amp is dead quiet, sounds distortion free on both 250and 32ohm HPs and is clear and very detailed. The amp was constructed on a piece of vero-brd and solid Cat 5 wire used for hookup. And because I had a well preserved antique bakerlight knob on hand this dressed the front. Apart from a little too much gain the amp works perfectly and I have enjoyed many hours of music driven by it. A good outcome.

“Five” - Pass inspired F5 Class A power amp with SMPS.

 

For some reason, still unknown, I had chronic hum issues with this build. I tried two different F5 cct. bds. and one Class AB module. Even modding the PS with an additional rec. bridge didn’t fix the problem. With large tranni and 132,000uf of high grade Mundorf caps there should be no hum. The other seven or so F5s I built were dead quiet. 

Replacing the PS, tranni, caps, diodes etc with a SMPS of suitable power fixed the hum. But the SMPS would overheat and shut down. By adding a larger heatsink and a 12V silent fan running on 9V fixed the problem. The fan cannot be heard and now with large tranni removed the amp is much lighter. 

The amp stays a Pass F5 build and does sound very, very good with good power, dynamics and bass extension. Usually I use it with one of my many tube preamps. A great combination and has given me many hours of enjoyment. It took many months of trial and error to get to this point but glad I persisted. 

The enclosure I engineered from scratch around two very large heatsinks I had had for many years. My local metal supplier did all the plate cutting then I did a hell of a lot of drilling and assembling and re-assembling to get things right. The finished amp looks good and sounds better, once again, glad I persisted.