Recently I posted about this amazing DHT. Although my original intent was to use them as part of my Parafeed headphone project, I decided to try them as first stage on my system. I have been playing lately with mid-mu DHTs with great success, and this valve didn’t let me down at all.
The EML-20A likes an operating point above 200V to get its best. If you want to use it as a driver, you should aim at 220V/16mA operating point. You can maximise output at minimum distortion, like I showed on my last post about this valve.
The Mule update
Best way to test this valve was to pick up my Mule breadboard and get the preamp up and running in a few hours. The hacking is pretty simple:
- The filament regulators are set to 1.4A and aiming a filament voltage equal of below 5V.
- The filament resistor is changed to 2.5Ω. In my case I paralleled 4 10Ω/20W Russian NOS wire-wound resistors.
- The gyrator is set to 205V anode and current is measured to be around 10mA. This is due to my limited HT. If you can, you can push it up more to 220-230V to achieve 15-16mA of anode current. You will need an HT of 280-300V to provide enough signal headroom as well as allow the MOSFETs to operate properly
Impressions
I was very impressed when I tested these. The linearity as well as the true-mesh anode makes this valve a fantastic device. The level of detail and sound of this valve is amazing, I put it just at the top of my list with the 01a and the VT25/801A ones. Despite not having thoriated tungsten filaments, it sounds superb. The dynamics and gain seems to match well with my 4P1L PSE output stage. Not microphonic at all! I was slightly concerned about potential hum pick up, but on my system is dead quiet.
I will keep these running for a while. I just returned the Elrog ER801a prototypes back to Thomas Mayer, so have good time to listen to these valves in detail.
I use a pair of EML center tapped 45s as my main amp output tubes and they sound very, very good. Would love to try an all-EML amp.
Indeed. I hope to get back to the 45 one day, may be an EML version 🙂
Can you characterize this one a bit more versus Thomas’ new creation (801a) ? Where do the differ or excel the other one ?
I would like to find out the same thing, basically what is the very best DHT for preamplification.
Hi Roland, there isn’t a “best” DHT. There are a few in my opinion who sound the best, but this is a subjective opinion and also will depend massively on the end to end system and circuit. These valves aren’t similar and may behave/perform differently in different circuits. So you may be labelling one valve to sound bad (or not as great) unnecessarily.
I’d like to see an EML-20A mesh with thoriated tungsten filaments, that would probably add the “thoriated” sound clarity which I love from the 801a and the 01a.
Either way, this is an absolutely great DHT. Only drawback is the hum pick up. You need to be careful with the design layout and proximity of transformers or other sourcing of EMF radiation.
Other than tat, when you need a gain of 20 (which is more than double that what the 801a or 01a can do) then is probably the “best” valve for the job.
Again, I don’t like making a “best” statement so judge it for yourself and hope this comments help making you a decision.
Cheers
Ale
Hi Ale,
I agree with your thoughts around best etc. That is why I asked differently: It would be nice to characteries the strengths. 801A with Th. TUngsten seems to be more clear. Ok. But where would you rate the EML stronger ? Typically you have always some strengths and weaknesses and to find the right mixture is the art we all look at.
I also built a preamplifier with a 20A tube but it is terribly microphonic.