Skip to main content

je2a3 amp

Twenty three years ago, I built my first 2A3 amp in the basement of the very same house I'm staying in right now. This was a pair of PP2A3 amps with a Mullard-Style driver circuit pumping 8W per channel of pure Class A to drive 82dB/1W/1M (in)efficient BBC LS3/5As, with external preamplification.

As I enter another phase in life, I am back in the same house, mellower with age but hopefully wiser, building a single channel, single-ended 2A3 amp with 3.5W output to drive a 99dB/1M/1W efficient Altec 2-way horn system, with a phono and line stage on board.

This project started with a chassis and choke (amongst other things) handed over by Joe Roberts at the Capital Audio Fest last July. Additional parts were either donated by my hamfest/radio show buddy, Chong Ong or ordered online, like the Hammond 272X power transformer, which came from Steve at Angela Instruments. Back in the 90s, I could have built this amp (except for the output transformer) using parts sourced from hamfests and radio shows. But times have changed, sadly for this project, the only parts I got from a hamfest were the tube sockets ;(

I had been exchanging emails with J-Rob regarding the WE/Altec 32, Emilar horns/drivers, ROK idler TTs, viscous damped tonearms, vintage cartridges like GE RPX, Shure M3D, etc. Among the tubes he suggested I try in lieu of my favorite octal 6SL/SN7s and 5-pin 27/37 and 56/76s, which are getting quite expensive, are the Loktal equivalents + the "Mickey Mouse" plate and grid-capped 2C22/7193 med-mu triode.
WARNING: the 2C22 is not for the faint-hearted, there is over 200VDC in the plate cap if accidentally disconnected while the amp is operating!!!

As depicted in the above block diagram, this is classic (nothing new = boring) JE Labs ;) I used 2 x 7B6 loktals in the RCA derived RIAA phono stage sans variable EQ. A stereo > mono mixer via a WE111C repeat coil to process digital sources was integrated into the chassis, then a single medium-mu triode 2C22/7193 acts as a line stage preamp cap coupled to a Radiotron SE2A3 amp.

The chassis was painted in Silver Hammerite, but wiring had to wait due to actual music making and more important projects ;)

Fancy-schmanzy boutique parts were not used in this amp - just plain old carbon resistors, paper in oil caps and electrolytics in the tube rectified/choke filtered power supply.

The amp section is currently fitted with a Noguchi PMF-15WS OPT I got in Akihabara. It sounds really good! You just have to take my word for it since I don't have a scope and audio generator to prove it ;)

At a later date I might swap in the PMF-10Ws, but ultimately I'd like to permanently install an American made OPT, maybe an Edcor or ask/beg Mike L. at Magnequest to wind a single TFA204 OPT just to keep the amp an ALL American classic ;)

Time Out

ala  Turk


Popular posts from this blog

Altec 2-way horn system redux

Truth be told, I was never fully satisfied with the performance of the Altec 2-way which is why I never uploaded the old article in the Arkiv.
Let's recap how the 2-way horn system evolved...

The project was conceived in mid 1998 because I needed a monitor system that was more efficient than the OB/755 so I could listen to SE amps with 2 watts output and below.
I commissioned my cabinet maker neighbor to build 614 bass reflex cabinets and loaded them with Altec 419A 12" drivers + 811 horns (early version/heavy sand cast) and 804A compression drivers gathered from hamfests and radio shows. Crossover was a textbook 1st order/6dB/octave hinged at 900 hz and the horn padded down to match the sensitivity of the low frequency driver.

Eventually I acquired proper 12" woofers - Altec 414As, which lack the upper midrange nasties of the 419As. The 414As have great midrange quality even if they lack the bass end of their larger 416/515 brethren.

802D compression drivers replaced t…

2017 Update: Hi-Fi Room

One year progress report

Garrard 301 + Ortofon RMG 309/SPU GME or SME 3012 + Denon DL103 Altec 4722 MC step-up
Digital line level sources processed  through UTC A20 transformers

JEL Stereo Preamp DX
JEL Stereo SE2A3 DX amp with Tango NY15S OPTs
Altec 2-way Altec 414As in 3.5 cf bass reflex enclosures + Altec 32A horns with 802D compression drivers
Mono Neat P58H 4 speed idler turntable + Velvet Touch viscous damped tonearm with Denon DL102 or GE RPX cartridges

je2a3 mono integrated amp

Stereo > Mono Line Level Mixer

Mixing line level stereophonic signals into full dimensional monophonic ;)
Here's a DIY project for mono aficionados that's so basic, I should have uploaded it many years ago. But other things got in the way.

Just like an MC step-up, these are entirely passive devices. 

The simplest way to convert stereo to mono is to connect left and right channels via a Y connector. But there's a more elegant way than just shorting two channels.

Resistors can blend two signals into one better by...

...using Allen-Bradley carbon composition for warmer sound ;)
We can end the mixing quest here but...

...the most elegant way of mixing two channels as was done in the studios by audio pros of yesteryears was through transformers.

This single UTC A-20 transformer was in a box lot of tubes and parts I picked up at a radio show. It's a high quality transformer designed for mic, mixer or line matching applications. Instead of trying to find a mate for MC step-up duty, I repurposed it for a g…