Yaqin MS500B - 300b tube questions

Good looking amp.Can't believe no one is responding.

Grant Fidelity A534B appears to be exactly the same amp for$2K.They have reviews on their web site too.

Both models probably come from the same factor in China. Sometimes different brands are used for different markets. That is most llikely what's going on here.

As for the 300B, honestly, I don't have much experience with them. However, it seems that most headphone amps tend to use the 45 or 2A3 when building a DHT SET amp. Further, I've looked for schematics for 300B-based headphone amps to build myself, but there are very few of those.

I'm not sure why the 300B doesn't have wider use for headphones. I hope someone else can answer that.

Simple - it is an OEM design, manufactured in the Far East by a specific company then rebranded for various resellers (e.g., Grant Fidelity and Yaqin). If I recall correctly, this particular design is from Tonewin in China, who also sell it under their house-name brand as the Tonewin MS-300B:

In regards to the headphone out, I'd be a little weary (or at least cautious). Many integrated tube amps do not have the tube output connected to the HP jack at all; they often use a simple opamp in front of the jack to simply provide HP functionality.

This is primarily due to the high sensitivity of HP's and specific requirements (e.g. 120 ohm at the output) which needs to be achieved to clever use of circuits, resistors etc. to prevent major background noise levels and overpowering HP drivers.

In the review it said the headphone is directly coupled to the 300b's.I think with resistors.

ALSO, on e-bay 8plantshop site.They are selling buy it now price $899.00 PLUS free shipping.

They go on ebay for pretty cheap as the Yaqin "King", I think about $680 USD before shipping of course, and I think they have a free shipping option (surface, likely). I honestly doubt the headphone circuit uses all of those tubes, it would be way overkill, but I don't doubt it's directly coupled to the 300Bs. If you really spend on the 300Bs and get some Western Electrics it should be a pretty ridiculous amp. It would be fun to mod the King too, although it appears to be pretty well made.

There probably isn't an opamp on the headphone jack. It costs even less to put a couple of voltage dropping resistors there. That's the solution used by most integrated amps and receivers for their headphone jacks.

Also, cheap is not necessarily a good thing for tube amps. Most people only consider the tubes used when looking at an amp. However, the power supply is hugely important, as are the output transformers. To get a low price, companies often use the cheapest available while hoping that a prestigious tube will sell the model. You're much better off with quality transformers and ordinary tubes than you are the other way around.

I don't mean to bash this product - I am not familiar with it. It could be excellent for all I know.

headphone socket is connected directly to output transformer

I have the circuit diagram for the Yaqin MS 300b amplifier and this shows the headphone socket connected directly to the output transformer via a 470 ohm resistor (one for each channel) which according to the diagram and their manual is optimum for headphones around 32 ohms.

I have this amplifier myself and have used it to drive both my AKG 701 and Audio Technica AD1000 headphones. For my personal taste I found it drives the Audio Techica headphones the best and sounds very smooth and open with plenty of detail with these, an excellent combination, I didn't like the AKG combination as much, preferring these being driven by my MF Xcan V3 amp.

Going back to the Yaqin amp this is a great little (heavy) amp for driving efficient loudspeakers, probably best with 93db plus ones, I use it with my Tannoy DMT15's which are 98db with great success. The amp is also notably very quiet both electriclly and mechanically.

I have changed all the chinese valves for JJ300B's, russian 6H8C's, german RTF AT7's and 274b rectifier valve. The chinese 300B's actually aren't that bad although I do prefer the JJ's (not too dear to buy around £140 matched pair lovely thick glass with a taller glass envelope than the chinese version). The biggest change I found with the valves and the largest influence on the sound was changing the rectifier valve. I prefered either nos 5UG National's or similar, but found the 274B to be the best with excellent deep tight bass (in relative terms for 300B amps).

I think at ebay prices this amp is an excellent buy for headphone driving (32 ohm types) and very efficient speakers. Be aware however if anything goes wrong with the components on the board that repairs could be costly as the amp is based largely on a single printed circuit board which if it has to be removed will take some time due to the number of connections made to the board and no slack with the connecting wires (from my own experience).