Bob's EML 20B One Tube Single Ended Amp

Emission Labs 20B Single Ended Directly Heated Triode Stereo Amp

Tube complement: 2x EML 20B and 1x EML 5U4G

Designed by Min

One output tube per channel amp (OTA)

Lundahl 7903 high level mic transformers, 20W Hashimoto SE OPTs (H-20-3.5U), Hashimoto power transformer (PT-220F),

Hashimoto choke (C-10-200W), teflon tube sockets, Audio Note RCA input jacks, Audio Note binding posts,

all ASC oil caps in the filter stage

Built for Bob Meegan

For more information on the EML 20B tubes check out: http://www.emissionlabs.com/datasheets/EML20B.htm

Toplogy similar to TRON Voyager One tube amplifer

I got these tubes from Jac at Jac Music. He also sells other high quality components - I got those Lundahls from him as well. The 20B is originally designed to be used as a driver tube, but its high gain of 18 and low output impedance make it possible for it to be used as an output tube.

It's a well known fact that Lundahls make some nice irons, but it wasn't until I used one that I realized how nice. Typical of Swedish practicality, these 7903's offer various impedance matching options - 1:2, 1:4, and 1:8. I went for 1:4 with +22 dBU. Here is the datasheet for the 7903.

The amp sports all Hashimoto irons - power transformer, choke, and 20W potted output transformer. I get mine from Isao Akasura, the CEO of Sound Tradition, who I find to be one of the most reliable and trustworthy vendors I have yet encountered.

Notice all the Audio Note silverware. I also used IEC power socket with a built-in filter.

Here is the finished product. I had to do away with those large ASC oil caps since I found that the FT multisection electrolytic provided better filtering. The heaters are rectified and the amp runs super quiet. I found that those 20Bs have excessive hum if heated by AC volts. This could be due to the fact that they are DHTs with high gain.

The amp sounds great. One of the things that stands out about the amp is transparency. The simplicity of the design really accentuates sonic quality of the 20B - there is no preamp tube to interfere with the sound of the 20B. I think the phrase "wire with gain" seems to best describe the sound of the amp. The tube and the circuit necessary to run it seem to showcase the strength of the components that are used, which boast impressive spec (remember I used Hashimotos and Lundahls). There is a plenty of tight bass and the highs are extended but not too shrill. The mids are warm and easy on the ears. Interestingly, I found that the amp sounds better when driven directly by a source. When I used it with an active preamp, the sound felt a bit "colored". Maybe I am just hearing the preamp since the amp is so transparent. It's a nice sounding amp that I would hope to build again if someone funds it. - Min

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