Single Ended EF37A / 45 with Patridge transformers

Here we have a very unusual single ended type 45 amplifier, hand made by a hobbyist in South Korea, with an antique Raytheon power transformer and choke, and the coveted and superb sounding Partridge 1663 output transformers. And like icing on the cake, this one is driven by the strange and archaic EF37A pentode, a new one for me and an exciting tube that I had never even heard of. A new circuit, and a new driver tube. I love it. What a package!

Arriving from Korea in just a few days, the amp was set up and ready to go with a pair of new in their boxes Mullard EF37A tubes arriving on my doorstep the very same day as the amp. Of course I really love the aesthetics of this amplifier, with the panel meter, the large antique transformers and the strange driver tube. The coated red glass EF37A with plate caps, and my blue glass Arcturus 45 are the perfect match. Powering up with a 5U4 in place reveals a bit of background hum at 110V on my 100 db/wm speakers, maybe a bit more than I’m used to, but also a strongly engaging toe-tapping performance. Using a step down transformer to bring the voltage down to 100V makes the amp much quieter while still preserving most of the lively open sound, but it becomes a little less aggressive.

This amp has a fabulous presence that is very energized and dynamic. It has brightness but is also deep. The Partridge transformers definitely have a house sound, and it was familiar right away after having lived for a few years with another set of this iron on an Oliver Sayes 46 amplifier. Heavy bass seems to move through the room (and seemingly across the ceiling) differently through the Partridge transformers. Its incredibly palpable and full of nuances and depth; there is just a lot of articulation in the bass with this amplifier. Especially at 120V, this amp seems more “badass” than normal 45 amps, and that impression held up in direct back to back comparison to both Richard Becker’s Aum Acoustics 45 and Don Garber’s 2A3/45 monos running the same pair of 45 tubes. This amp has perhaps a little less detail and space than those uber amps, a slightly narrower presentation, but its big bold character and tonality is just wonderful.

Overall this is a really engaging sounding amplifier, and is once again a great example of what I consider to be good choices in a new single ended amp; high quality vintage parts used in a new circuit. This amp is made of superb vintage parts, the production of which are maybe impossible to equal today. And it was built as a personal project; a one of a kind statement by a talented and dedicated craftsman, without sale factors like marketing and markup in mind. To me this makes it a special piece indeed. Amps like this are why I’m in this hobby, and why I made this website. Creations like this deserve to be showcased. What a pleasure it has been to hear and have this superb amplifier in my room for a while.

What a cool looking amplifier, it definitely has a classic look to it.

The pentode driver provides a nicely aggressive saturation to the sound. This amp is light on its feet but it can sound downright evil when the program material warrants that. Delicious.

It would be hard to argue that these weren't the most beautiful 45 tubes ever made.

One downside to the Partridge 1663 transformer set is that it is 4 or 16 ohm only. I prefer the 4 ohm taps (farther apart) on my 8 ohm Lii Audio F18 panels as well as on the 6 ohm Visaton B200.

Being AC heated this amp does have a bit of hum, but it also has the wide open and free feeling sound that is unique to an AC heated triode. DC heating makes a quieter amp but kills some of the life.

There is something so pleasing about a genuine DHT tube run in AC: its open and effortless and so alive feeling. This is a very emotional sounding amplifier.

Here with 1940s National Union tubes. Through the step down transformer the meter reads around 70 ma.

I really like what I’m hearing from the EF37A as a driver for the 45 and hope to see more of this tube in the future.

Sophia’s mesh plate Princess tubes are always a good choice.