Music Angel 300B - "The 300 Bucks amp"




It is a beauty, isn't it?
I mean - 300B tube is a legend. It has probably 10 times more cult status than it deserves.
But someone who was influential - 70 years ago said that 300B is THE TUBE - and the world took this as an 11th commandment.

The amps with 300B which I heard before were all very weak in power, but paired with "proper" speakers - were all very very good. The sound is nothing short of magical.
But I almost forgot to mention - they were all VERY expenceive. In the 5000 Euro range. Except the AudioNote 300B KIT which must be one of the best deals in all highend industry.

So how about our cute little Chinese "Miss Shenzen" ???
Can we peek behind the pretty dress?




Out of the box this amplifier played typical Music Angel sound. Booom Booom Biiig Bass and muddy everything else. (I think that the boomy bass in all Angels is a result of cathode bypass capacitor. Removing cathode capacitors ALWAYS cleans the sound a lot!)
The sound in fact perfectly matches the price tag - 300 bucks. Yes. This is a 300 B from 300 Bucks Sound.

Can we make it sound as GOOD AS IT LOOKS?

At least I tried.

First - I did not like the small septal double triode (3A5) in the input stage. I know nothing about it, it is rare, it has no easy replacement, is is very microphonic etc.
Out with it.
I installed a proper noval socket to be able to change different tubes freely.

My sweet 6H6P was too quiet here. I needed more amplification, so i decided for 6H1P in triode mode - one half is an input stage for every channel.
So far so good.
But the driver tube is wrongly chosen too - the very high amplification factor plus small current are not optimal here. We need high current.
So I exchanged the 6H9P with 6H8C (In "Chinese language" this is 6N8 replacing 6N9)
This tube is exatc equivalent - 1:1 with 6SN7GT (most popular tube in the world) and also with my little baby - 6H1P (except it is noval not octal).

After applying the SRPP circuit (lampizator) to the tube - I got just what I needed.
It took me 3 full evenings to find optimal operating points - mostly by trial and error.
First - I drop the power supply voltage from 420 V DC to a more suitable 250 V.
Then I adjust the anode current to be not too big, a conservative 2 mA.
Lastly, I had to rectify the heater circuits. The AC heaters of driver tubes is humming. Some other variants of this amp have DC heaters (like on my photos above - from e-shop internet). Also the schematics which is available on the net - ther heaters are DC. But my sample had only the input tube with DC heaters.
Last thing to do would be to at LEAST double all electrolytes in size and bypass them with a small MKP or better small PIO cap (observing minimum voltage ratings to be 600 V DC for all applications except 1000 V DC in 300B anode supply).
The caps in this amp are VERY VERY SMALL.
Of course - it goes without saying - that the coupling caps (2 per channel) must be replaced too, with a 1uF PIO or something like that.

IN THE END - the amp starts resembling areal 300B. It has a midrange slightly more charming than 845, very very clean and spacy trebles, and the bass - not too muscular, but rich in colors and vibrations. Nothing like the stock unit. The difference is really night-day.
If I was doing it again, I would install in the center the octal base and all 3 tubes would be 6SN7GT from NOS variety (same schematics is valid as below) - the best there are - "black glass" JAN NOS, maybe from Kenrad. It is worth investing 100-200 USD in these three tubes, while I would seriously hesitate before spending $$$ for the NOS 300B or JJ or any other exotica. But you may if you wish. In such case - the cheap small chinese output transformer will be the most serious bottleneck of this amp.
But wait a minute - these transformers can be raplaced too ....;-)


 

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