"Thirty-four" - EL34 SE UL amp

 

Again using up expensive parts on hand another SE UL tube amp. This time using a tweaked schematic which favors EL34s. I have a number of brands of EL34s on hand including:- Svetalan, Siemens, Black Sable, Tung-Sol and Electro Harmonix. Some quad matched sets like the Tang-Sol and Black Sables. With a mix of carbon and metal film resistors, mustard caps as snubbers on Ck and Jensen copper foil paper and oil inter-stage caps this is a real mixed build. Once more the whole idea is to use up what is on hand. KT88s can also be rolled for a different sonic presentation.

On hand I had the big Hammond 600V 200mA power tranni, open frame Edcor OPTs (under the bonnet), the wood base and top plate, inter-stage caps most resistors, ceramic and resin tube sockets, tubes and all components for the SS rectification cct. and smoothing caps. The PS is a triple Pi config but this time no choke. CRCRCRC with 100uf caps and 330ohm 5W Rs has produced an extremely quiet amp with only 0.9mV of noise. Total caps is 750uf.

The base is Australian Spotted Gum and after being sanded smooth and oiled was re-prepped with "0000" steel wool and re-oiled. The timber looks rich and is extremely smooth. The top plate is sprayed with Hammertone epoxy enamel after being sanded and etch primed. The finish looks lush and the Hammertone hides any dust particles or blemishes. The top plate is 2mm Al and the Tranni is isolation mounted to it to reduce vibration to the tubes. 

Cat5 solid core wire for the audio path and HT is delivered with either twisted pairs of Cat5 or heavier wire. There is no shielded wire and the audio is delivered to the 6N1P via Cat5 twisted pair. Where I found the sound of the KT88 amp - Toccata - very open with a huge sound stage this amp sounds a solid and grounded again with a large sound stage. Once more a very transparent earthy presentation and now with the Siemens tubes in place a cleaner open sound. Bass is full on and extends down to 30hZ.

"Toccata" - KT88 SE UL amplifier

This simple two stage power amp was built from 95% parts on hand. I had all the expensive parts, tubes, OPTs, power tranni, base etc. Inter-stage caps also on hand and are Russian PIO greens. I have used these in so many builds and always sound excellent. Only a handful of cheap components required purchase. Most of the parts on-hand I've had for nearly twenty years. Time to put them to good use and I haven't made a tube power for a while. Included in the parts I have had for a while were a pair of mustard caps (0.1uf) which I used as bypass caps (across Ck) on the 6N1P driver tube.

The power tube in the image is a JJ Blue Glass KT88 of which I have had - and never really used - for a long while. I bought them as a quad matched set for a PP amp I had years ago. The power tube can be swapped out for 6L6, EL34 and others with no bias tweak. The 6N1P is Silvania. Power tranni and choke are Hammond and OPTs Edcor. Ceramic sockets. Base is Australia Spotted Gum rubbed with a finishing oil and top plate paint Epoxy Enamel. Top plate is 2mm Al and the tranni is isolation mounted to reduce HF vibration to the tubes.

As is my usual practice there is no PCB or shielded wire. Cat5 solid core used throughout. Most P2P wiring uses a large tag brd. with components aboard then wired P2P from the brd. This results in a lot of hookup wire. A better solution is small 5 tag tag brds at each tube, two brds. each then mount components to them. Far less hookup wire, parts are right at the tube.

I'd built a SS rec. brd. with two SF 3A diodes and 150uf of 400V filtering a long way back. Using it here with a 5H choke and another 470uf in double Pi configuration (CLCRC) resulted in a dead quiet robust PS. Noise at the speaker post is 0V with the meter on the 200mV scale. That's quiet!

The amp only produces 3.5W RMS into eight ohms but sounds louder on my 90db+ sensitive speakers. Bass tests down to 20hZ and upper frequency is 70KhZ. Bass in my room is heavier and deeper than my DIY SS amps and there is a real sparkle at the top end. Best I've heard so far. Very transparent amp to listen to. Gain is 15db low for a power amp but only requires 300mV for full output. 

 

“Empire” - my super F5

The last and possibly the best F5 ever. There was another F5 which also appeared to exceed the others with performance. It also had the Mundorf MLytic audio grade caps. In this build I increased the filter caps to 132,000uf and upped the power tranni to 300VA. Keeping the Cat5 solid core twisted pair for hookup wire and the standard compact enclosure. This build is very similar to the others with the filter caps well snubbed with larger and small poly caps. 

The BIG difference here is the use of 1W carbon film resistors. The Jim's kit comes with Fishey and Dale resistors which normally I would use. Not this time. Also this Jim's board, like the build before, uses his double weight brd. with two 100uf Elnas on board and other components. The sound is hyper 3D and incredibly transparent with extended deep bass and startling dynamics. The whole sound is one of earthiness and richness. The use of carbon film is a controversial one. All negative comments about the use of carbon film Rs come from those who have never used them in a build or/and have never heard them. I like to buck the trend especially when I know what I build will exceed what others can contemplate. And exceed in performance.

“Mimic-Magic” - MM phono stage

 

Yet another Mimic and this time combining all the components I thought have sounded good in other Mimics. That’s what makes it “Magic”. Another in these more hobby looking enclosures mainly because I had them on hand. 1/4W carbon film resistors, PIO output caps, MKP and poly caps and the same OPA2134 chip as in all Mimics. Smooth and warm sounding with my Garrett P77i. 

“Mundor/F5” - Pass F5 inspired with advanced boards

 

I was vey impressed with last F5 I built using Jim Audio boards. The amp sold before a I could start construction. The build was a big step up from the F5 before by upgrading the filter caps to 88,000uf of Mundorf MLytics and the toroid tranni upgrade from 160W to 300W. The total presentation of that amp was beguiling.

Here is my build based on what I thought maybe the best amp I have ever heard. Ounce more 88,000uf of Mundorf MLytics audio grade caps at over $300 for caps alone. Same upgraded Jims brds. and as before all Cat5 twisted pair hookup wire. This amp shines. Given the right music you are challenged to think something so compact and unassuming can generate such presentation. It’s a 25W Class A simple amp. Bass goes easy to 30Hz, mids are transparent and treble clean and controlled. Compact and astounding. 

“3D” - Three channel Class D amplifier

 

I completed a three channel Class D power amp for another SNA member. 1X 150W and 2X 180W Tripath amp modules, 500W PS with Mundorf MLytic caps - 2X 22,000uf and EVO oils on the input. I sent the amp off without taking any images and had to ask the new owner for a few picks.

"Shadow" - SRPP 12AX7WA Sovtek preamp

 

Just finished this compact tube preamp with Sovtek NOS NIB 7025 (12AX7WA). Again on a jiffy box - “Shadow” - this time is an ironstone epoxy enamel finish. All metal film Rs and PIO output caps with silver plated fine copper hookup wire. Two inputs. SRPP topology. External PS is a Radi0kit kit for 12V and  250V DC. The preamp is absolutely dead quiet. No snap, crackle or pop.