[Mikey01]

As I had reported earlier this week, I have an Eddie Current "Dual Mono 2" headphone amplifier here to sample. I have only listened for one night so take that into account as also the BlackGate caps are probably not fully broken in either, let alone the rest of the amp. I am sure it matures well as it ages as most do. However, straight out of the box, with Russian tubes, it did sound very good.
The DM-2 is an OTL design and a true dual mono setup. Each channel has it's own power supply with absolutly no crosstalk bleedover between them. This should replace the HD 300. There are NO similarities in design between the two. The HD 300 was a straight forward very simple common design where as this DM-2 design is much more complex with a few rather complex engineering features installed.
The DM-2 has 2 12AU7 tubes. The 12AU7 is a medium-mu twin triode minature glass tube. A lot of you are familiar with this one. The DM-2 also uses 2 6B4G tubes. The 6B4G is an octal equivalent of 2A3 called 6B4G (Russian name is 6C4C). This is a 6.3V-filament DHT with octal base and 2A3 construction. I guess this is why I like the amp so much. Tube rolling should be a real joy with this amp having a 2A3 type of sound. Any faults the Russian tubes may have, I suspect, would be wiped away by tuberolling as was the case with my Eddie Current 2A3.
In brief, it has a very wide sound stage, extreme blackness, splended bold bass, melo midrange, and a high which is good but which I would temper with tube rolling and more breakin.
I will let the people at the upcomming New York meet expand on this as they see fit. OH, and also the music from this amp comes thru "thick". Another way to say it is that, like the DM-1, it is very musical and a bit different than any other OTL design I have listened to. This amp has great potential with it's tube compliment "upgradeability". This is a "must listen to" amp to have on your short list. I will compare the DM-1 and DM-2 in a later more indepth review.

[size=medium]The DM-2 will be available for audition at the New York meet June 18th.[/size]

 

[tanfenton]

After the stopover in New York, this amp will be on its way to me. All I need to remind myself is that it will be here in two short weeks.

Here is a picture Craig (Uthus) sent of the amplifier before it left California. Your guess is as good as mine as to what the final edition will look like:

NGF

 

[recstar24]

Wow, that looks gorgeous just the way it is! Im not sure what it is about his amps that attract me so much, its kind of like that old-school retro look, its the same reason i guess why i think grados look so good

 

[Mikey01]

The opening price should be quite attractive. I think this will make for a very high value purchase. The real prize is waiting for the soul that takes the time to invest in tubes for it and tuberoll. They will be very rewarded. The Russian 6B4G tube is a real turkey and a good NOS tube would be quite superior. Also, thanks for the picture.

 

[sacd lover]

Quote:

Originally Posted by Mikey01 The opening price should be quite attractive. I think this will make for a very high value purchase. The real prize is waiting for the soul that takes the time to invest in tubes for it and tuberoll. They will be very rewarded. The Russian 6B4G tube is a real turkey and a good NOS tube would be quite superior. Also, thanks for the picture.

I was researching this tube last summer and my understanding was the 6a3 is the 6 volt equivalent of the 2a3. The 6bg4 is the octal base equivalent of the 6a3. Both the 2a3 and 6a3 have four pin tube bases. The NOS 6bg4 is a seriously hard tube to find. You can track down 6a3's for $35-40 but other than the Russian 6bg4's I couldnt find any of this type. I was entertaining doing a singlepower 6a3 but I ended up going with the 5687's and the loctal 7n7's.

 

[bozebuttons]

Looking foward to putting a ear on this amp when it gets to NY as Graig was very enthused about how good it sounds.

 

[Mikey01]

Quote:

Originally Posted by sacd lover I was researching this tube last summer and my understanding was the 6a3 is the 6 volt equivalent of the 2a3. The 6bg4 is the octal base equivalent of the 6a3. Both the 2a3 and 6a3 have four pin tube bases. The NOS 6bg4 is a seriously hard tube to find. You can track down 6a3's for $35-40 but other than the Russian 6bg4's I couldnt find any of this type. I was entertaining doing a singlepower 6a3 but I ended up going with the 5687's and the loctal 7n7's.

Can't find 6B4G NOS tubes? Look harder. Their out there, not in great abundance but enough to suit. Most people will want two or three extra and thats available. I found Sylv. for $18. As for a 6B4G being the octal equivalent of a 2A3, that information came off of a tube suppliers page discription. I have seen it before elsewhere also. I am assuming the word "octal" means eight places or segments. In this case "pin outs". The 6B4G tube has a 2A3 internal construction with an "octal" or eight pin base. The part of the 6B4G tube, responsible for sound characteristics, is of a 2A3 construction. I am compileing an online reference list of URL's to back the quotes as well as places for the tubes. This will be in the master DM-1/DM-2 review. My DM-1 has been modded and is due back here this Tuesday. The DM-2 leaves this Monday.

 

[Mikey01]

I have here some reference pages I ran across related to the 6B4G tubes.:
Some reference:
http://www.geocities.com/dmitrynizh/hf60-dht.htm
Many other tubes can be used in place of EL34/6CA7: 6V6, 6L6, 6550, KT66, KT88, KT90... and there are more. This is so because all these tubes have the same pin-out and the bias can be adjusted.
Without doubts, HF-60 is a very fine amplifier, delivering powerful and refined classic penthode/ultralinear PP sound. Can it be converted to a DHT no-feedback, all-triode amplifier? Thoughts of drilling the chassis for 4 pin sockets, adding filaments transformers producing 5V (for 300B) or 2.5V (for 2A3) render this idea as very bad... until we realize that there is an octal equivalent of 2A3 called 6B4G (Russian name is 6C4C). This is a 6.3V-filament DHT with octal base and 2A3 construction.
Some reference from Machmat.com:

6B4G6.3 volt, octal version of the 2A3. Double black plates, extra support rods, Black coated glass, made in USA, pair measuring 44 and 48 mANOSTung-Sol1 pair98.00 (pair)
JAN-6B4G6.3 volt, octal version of the 2A3. Double black plates, extra support rods, made in USA, pair measuring 42 and 46 mANOSRaytheon1 pair94.00 (pair)
6B4G6.3 volt, octal version of the 2A3. Double grey square plates, extra support rods, brown base, made in England.NOSLabelled Haltron1 single1 pair34.0084.00 (pair)
JAN CHS 6B4G6.3 volt, octal version of the 2A3. Double black plates, extra support rods, made in USA, different versions, no pairNOSSylvania234.00
6B4G6.3 volt, octal version of the 2A3. Double black coated plates, extra support rods, made in USANOSSylvania1 single1 pair29.0072.00 (pair)
6B4G6.3 volt, octal version of the 2A3. Double black square plates, extra support rods, made in England. PictureNOSLabelled Haltron2 single1 pair29.0069.00 (pair)
6B4G6.3 volt, octal version of the 2A3. Double black square plates, extra support rods, made in England. In white box. PictureNEWLabelled Haltron126.00
6B4G6.3 volt, octal version of the 2A3. Double black square plates, extra support rods, made in England. One is a bit bent inside, but because of the mica it works fine (and will keep working fine). PictureNEWLabelled Haltron1 pair44.00 (pair)
6B4G6.3 volt, octal version of the 2A3. Double black rond plates, extra support rods, labelled made in Belgium. Probably Russian production. PictureNOSLabelled CEI3 pairs5 quads42.00 (pair)99.00(quad)

More reference: http://www.angelfire.com/ma2/AdamVon/project1.html
Since 6B4Gs are basically 2A3s with 6V filaments and octal bases, any 2A3/6A3 design can be modified to use cheaper 6B4Gs.

 

[GlowWorm]

I was wondering if there are any specs available on the Dual Mono 2?

 

[KenW]

Crap. Guess I got bumped off his list to audition the DM-2. That's disappointing. Oh well, life's too short to sweat the small stuff. Happy listening guys. Time to move on.

 

[recstar24]

Mikey,

Can you clarify the price point for the DM2? I am in the market for a tube amp and could use some OTL goodness for sure

 

[bozebuttons]

Quote:

Originally Posted by GlowWorm I was wondering if there are any specs available on the Dual Mono 2?

Here are the specs Graig sent with the DM2 for the NY meet.
The DM2 is a non inverting OTL topology
It has a 7 ohm AC source resistence.
The uncompensated bandwith driving Senn 600 ohm phones is 6-125khz +0.25dBb -0.5dB.
It will drive 30 ohm to 600ohm phones,with a slight loss in low frequency response driving 30 ohms.
It will drive 300 ohm loads to 15V peak,or 750mW peak.
Because of the true mono design,the channel seperation at 1 Khz is greater than 100db.
Price $695.00

All mumbo jumbo to me but it did sound good

 

[recstar24]

Thanks bozebuttons for the info! That is a killer price.

 

[Mikey01]

[size=large]HOWEVER[/size], that was revision "A" you heard and it's picture is posted above. Then there is revision "B" with the 6SN7 tubes which still was not good enough and never left the shop. Now, possibly, the final revision "C" is already on it's way to me for a final listen. Yes, I bought the amp feeling that it is in it's final version. It is sporting (2) 6J5 Jan Phillips drive tubes and (2) 6B4G's as output tubes. As Craig put it: [QUOTE: The DM-2 is close to being killer. Then component cost start to enter into the equation.] Supposidly the cost could exceed $1400 to have even a very minor sound improvement. A "killer amp" would be a EC/Moth 2A3/300B and the like. This amp gets as close to the EC 2A3/300B as it gets. So we shall see. Rev "C" departed from the original circuit, the output was also moved. The production price may change to $795, donno yet. Less parts in the OTL design (no heavy transformers to buy) so the cost should be less. But I think Craig is shooting for the sound level to be just as esoteric as the DM-1. Please keep posted on this and I will let you know more.

 

[TonyTripleA]

Mikey01 thanks for the news on the DM-2 and the DM-1 amps. Very interesting. In your view would the DM-2 or DM-1 best suit cans with a relatively low but not real low impedance (I'm thinking Sony SA5000 which I believe are about 70 ohm).

Thanks,

TonyAAA