Amp and preamp gallery
These friends of mine at SETUP have been prolific in building amplifiers. The front pair is set-up with WE300Bs, Tango choke and Tango NY15s OPTs with a 76-DC-6SN7 input/driver circuit, the middle pair also has WE300Bs but uses Tamura F5002 Amorphous core OPTs and matching Tamura choke with a 327-DC-6SN7 input/driver circuit, while the back pair sports RCA/Cunningham 2A3 monoplates with Tamura F7001 permalloys and matching Tamura choke with a 76-DC-6SN7 front end. All three pairs were built using the chassis, universal power transformers and polypropylene in oil PS caps from Angela Instruments.
Amplifiers
This is the amp that got me into single-ended using directly heated triodes [DHT] as output devices. Although the Simple 45/2A3 may not be the last word in ultimate resolution, I still think it's a very forgiving and musical sounding amplifier. After all, it may well be just the amplifier for a music lover with a good pair of efficient speakers.
I think this is the most deluxe interpretation I've seen, built by my good friend Ding in his basement one cold winter week-end.
Frankenstein the bread board wherein I conducted extensive experiments on voltage amp/driver tubes like 12AX7,12AU7, 5687, WE417/5842, 7788, 6CG7, etc. and confirmed that I was on the right track using Art Deco period tubes - 76, 56, 27, 37 in combination with octal 6SN7, 6SF5, 6SL7 whenever possible or feasible.
I assembled and serviced several Audio Note Kit 1 amps and although it is arguably a well engineered design, I never could find myself enjoying its sonic qualities. I think it is the combination of SRPP driver stage and the high gm 5687. It may provide a lot of high-end detail but lacks musicality....but that's my opinion.
Those AN UK output transformers were nice sounding and I built a stereo SE 300B amp using the 2.5K OPTs from the Kit 1 for a friend in exchange for a Leica M3 outfit that needed servicing. Essentially this is the same circuit as the JE Labs SE 300B.
Since we are already talking about the original cascaded direct coupled 6SN7GTB input/driver stage, take a look at Ding's 300B monoblocks using Tamura F2007, a hefty beast of iron he hand carried from Akihabara.
I also built a stereo version using Tango U808s.
I had to convince myself that it may well be the 5687 being a later 9-pin design that was designed at the dawn of the solid-state era that was causing the grainy/gritty sound I perceived from the AN Kit 1.
So I configured a 6SL7 in SRPP as a driver for an SE 245 amp with Tamura F475 OPTs and realized that SRPP indeed has it's own merits as long as you choose the tube wisely and from my experience, it works best with hi-mu, low gm signal tubes.
After this I built another SRPP circircuit based 45 amp for my friend William using Tango U708 OPTs, which evolved to this when they installed Tango 10429 hi-nickel OPTs with a matching choke.
Did you notice all the Kimber silver cables connected to this amp?
When I recorded a CD of violin encore pieces in Manila, I needed a good monitor amp to listen to session takes. I found a rusty ST70 chassis from an aborted project 10 years ago, cleaned it up and whipped out an SE2A3 amp using the classic TFA 204 OPTs from Mike's Philadelphia workshop hooked to Altec 408 Bi-Flexes in 622 cabinets.
Here's another SE 2A3 I built using Magnequest RS025 OPTs. According to Mike LeFevre, he made very few of these. Basically it is exactly the same size as a DS025, but uses higher grade M4 laminations and the secondary is wound with more interleaving and is similar in geometry to the FS030. In fact Mike sent me the FS030 sheet for the secondary wiring diagram. The chassis and wooden base is unashamedly a rip-off of master craftsman Don Garber in his earlier Fi 2A3 effort, prior to the sleek looking Fi -X. However the similarity ends there. I configured the layout so that the audio stage is farthest away from the power supply which I felt was necessary given the relatively small 11" x 14" aluminum chassis plate I had available.
My SE 300B deluxe monoblocks uses Tamura 7002 permalloy OPTs, Angela/Jensen copper foils, Riken 1% carbon composition resistors, Cerafine and Black Gate caps and silver wiring for the signal path, perhaps the only time I splurged on boutique parts. Most of my projects use Allen-Bradleys, LCR, Cerafine, Sprague "Atoms", Kimber TCSS and other solid time proven parts that you will see very often in MJ or Stereo Sound projects because our Japanese friends consider them exotic. These are good quality parts that just lacks snob appeal because in the they are common in the USA. The circuit evolved from the classic cascaded 6SN7GTB front-end design using 1930s med-mu 5-pin triode, type 76 (or 56) direct coupled to 1/2 section of a 6SN7GTB driver capacitor coupled to the grid of the DHT output tube. I also improved the power supply so that maximum voltage swing can be had from the 2nd stage. To my ears the sound of this circuit is so much more refined and consider this to be a whole new design.
Stereo 300B version of this amp fitted with Tango XE60-3.5S OPTs but my friend Mike twisted my arm and took it back to Manila to drive his LS3/5As.....he's very happy with the combination so who am I to argue?
At one point this amp was re-configured to use WE 205D output tubes, so that I can make sure my buddies, Joel, Nonong and William in SETUP [Single-Ended Triode Users of the Philippines] did not end up with duds after coughing up all that dough for this extremely scarce and fine tube. This was an experience Ding and I relished shortly before we packed them carefully for shipment.
Eventually Joel was persuaded by William [over a few bottles of San Miguel beer in a Karaoke Bar] to build the ultimate statement WE205D amplifier. This amp is built on a 1/8" thick copper chassis using Tamura F7004 Permalloys, Tamura chokes and a custom wound Tamgo power transformer. Only premium Black Gates, Rikens, Shinkohs, Cerafines and silver wire were used in creating this amp. Last time I heard, William upgraded the OPTs to Tamura F5004 Amorphous. I'm still waiting for Joel or Nonong to send me better pics taken through their fine optics from Leitz, Wetzlar.
JEL SE10 amp
Back in the east coast, Ding and I still could not get over the experience from the WE205D so we kept ourselves busy and investigated other DHT possibilities yet to be tried. After a few months of drilling and sawing I came up with an SEVT25/10 with Tango FW20-7S. When the picture was taken, I had large globe 410s installed which has oxide filaments. This early version of the 10 actually looks very similar to a type UX250 or CX350 and not many have survived compared to the thoriated equivalent.
To this day I have yet to try the type 50 output tube, aside from their rarity and high cost I'm deterred by the fact that it requires a very low grid leak resistor [10K], which is almost impossible to drive with an R-C coupled circuit. I've considered direct coupling, but the voltages involved will be over 500V and admit to being scared to cross that line. Another way around this is by using an interstage transformer. But this is a scheme I'm not very fond of because interstage transformers that have the wide bandwidth are usually too low in impedance for use with my favorite Deco era driver tubes. Anyway I prefer minimizing the amount of iron in the signal chain. Perhaps someday I might be persuaded to use a plate load choke, we will see.
It is the first watt that counts.....
Ding was busy toying around with some cheap DHTs we found at a radio show. He has so much surplus iron pulled out of integrateds in his basement and had to put them into good use. On one of my NYC trips he surprised me with this SE71A amp using iron pulled from an old Pioneer integrated [looks like Tango to me].
Not to be out done in our friendly competition, the next time I drove up, I brought this SE171A with Tango H-5S OPTs.These amps put out less than 1 watt, in fact more like .79W or 790 milliwatts.
But they have sonic qualities I never found in other DHTs which my friend Sherwin recognized which led to his commission of this ultimate 71A amp.
Before we close the subject on amplifiers for the moment, I'd like to show you Class A PP 2A3 amplifiers I built using a Mullard style input driver circuit shortly before my foray into single ended amplifiers.
A pair of PP 2A3 monoblocks built on a Heath W4 chassis and a stereo version on an ST70.
For more information on amplifiers check out Shop Talk.
This preamp is an example of an RCA phono circuit adapted to a PAS chassis, The stock PAS power transformer limited my linestage tube choice to a 12AU7, so I opted for a power transformer hacked from a beyond repair Heath Audio Generator for the outboard PS.
Interior shot of PAS chassis with the RCA phono circuit and 6SN7s for the linestage.
JEL protoptype preamp with octals
The next step was to use octals on the phono stage which was possible in a PAS chassis, however I wanted a full function control unit with as many switching facilities as I can squeeze in plus a balance control so I had to resort to a painted bud box complete with legends as my prototype with an external power supply beefy enough to power an SE 45 amp.
The balance control led to some impedance matching problems, since the highest value for a quality volume control I could acquire was the ALPS 250K. So far so good, but wait, put this in parallel with a 100K or even a 250K balance control, it is still way below RCA's recommended 220K minimum load. I thought the smart way around the problem was a cathode follower. I spent several sleepless nights experimenting with various 6SN7 or 6SL7 CF configurations I could muster and they all sounded inferior to my PAS mod which has no CF (on the phono stage) nor balance control. Finally, I had to compromise and removed the CF then connected the balance pot in series with the volume control. Now the main drawback is reduced sensitivity - turning the balance control all the way to the right or left will not cut the signal out completely, just a bit of attenuation. After all this trouble I took away the balance control.
Keep these tips in mind before being turned off by hearsay that the RCA circuit sounds tired, dull or lifeless. Make sure that it is driving the proper load and do not use a cathode follower. The beauty of this simple design is in the passive RIAA EQ therefore there is no global negative feedback to choke the sound. Actually the Ni-Cad cathode bias tweak alters the sound in such a way that you might be fooled into thinking it's a totally different circuit.
After Ding heard it, he immediately commissioned me to build another unit providing a Cary chassis and other bits.
Soon after, William ordered an all out version using boutique quality parts, like Black Gate Caps, copper foils, Shinkoh tantalum resistors, Kimber AGSS wiring in a 1/8" thick copper chassis on maple base.
Eventually I discovered the 76 tube and realized that it will not be to difficult to graft this into my 1/2 6SN7 direct coupled to the other half as cathode follower, so one afternoon I built this prototype. The topology is very similar to Bruce Berman's however I'm operating mine at lower plate dissipation and sonically prefer the cathode resistor bypassed with a cap.
The JE Labs preamp and outboard power supply has remained virtually unchanged since I wrote the Home Brewer SP article in '98. I've yet to find another circuit that suits my taste and requirements since I'm really satisfied with its performance.
I briefly owned a pair of Tango NP216N preamp output transformers and after trying to drive it with a 76, 6SN7, 417A/5842 and 5687, I just could not develop an affinity for the sound. It is a matter of personal taste since my other friends in SETUP use this high nickel iron in their line stage and have fine tuned their systems to it.
Take a look at what Joel did to his PAS, ain't that sumthin'? He managed to squeeze in octals (12SL7s and 12SN7s) and the NP216Ns were mounted horizontally at the back of the chassis. In case you're wondering, those are Tango MCT999 MC transformers on the left.
For more preamp information check out Shop Talk.
Updated: 08/12/07, JE Labs all rights reserved.
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