My ultimate intention would be to make the amps by myself, but lack of time and poor skills in metalworking caused me to retire this wish and rely on others.
For past 15 years I used to collaborate with the great people of ARG company from Ukraine and we worked hard to make together the best amp.
The history of this can be found in the link below.
Now with the totally new situation - tube amps being made in China and costing next to nothing, my advice to the people needing an amp is to shop in china on ebay and re-work the amp to make it decent.
Chinese amps coming to us via Hong Kong look great and sound HORRIBLE. I mean Hor-ri-ble.
But the price justifies that we buy them, use the beautiful bodies and all, and just change a little the schematics. In the end - they sing like a dream.
The link is  to be found below.

ARG amplifiers

SET XD 845 Music Angel from CHINA

SET 845 Mr. Liang amp from CHINA

SET 300B Music Angel from CHINA

P-P Music Angel KT88

Mini amp from China 

Cayin T35 PushPull amplifier

VTL from USA 

Bewitch amp from Chinabewitch

TRIPATH Class D ampstripath

Balanced Audio Technology BAT VK-3i

BAT VK-60 power amps

My new GM-70 Mono Block SET ampsGM-70

New Fikus PREAMPLIFIER 1.0 with a remote

New Mikro Pre Sheng Xiang  project

Ming-DA Meixing amps (300B and 805)mingda

Audio Note M-Zero preamp   M-Zero

Audioromy 813 power amp 

My amp story

General note about the tweaking process

It is hard for me to describe every amp and every possible schematics - how we want things to be modified.
In general - western schematics are usually a  result of a very long period of preparations, testing and optimization. They are finished and optimized.
Chinese amps are strange animals. Good looking, with good parts, but totally strange schematics.
The circuits look like a result of un-qualified copying plus some "original creativity" plus unknown factors. All in all, the Chinese products have too many parts and unnecessary components scattered all over the place.
My short list of mods is this:

1. In pentode tube amps ALLWAYS make a triode mode conversion (unless there is a switch to change the modes). This applies to ultralinear circuits etc.
Triode mode pentodes sound great, but in pentode mode - they sound really BAD. Bad bad bad. The mod is easy and costs nothing.

2. In the input section - remove and short all series resistors - we don't need any of them. Tubes are happy when coupled to each other directly.

3. sometimes there is too many paralell resistors which form - together with series resistors - some signal attenuators. Get rid of all of them except the resistor which goes from tube grid to ground. Every small tube needs grid grounding resistor, value between 200K to 1 M.
The first input tube may use the volume pot as a resistor - so the paralell R can go out.

4. I like triodes without the cathode capacitor. Most amps use an electrolytic cap across the cathode resistor. Remove it and maybe you can decrease the cathode resistor by half. This sounds much cleaner.

5. Coupling caps: all tubes connect to the next tube by a series cap. Use sizes like 0,47 uF or more in the first stage, and over 1 uF in driver stage. use the RADIAL wound, round type not the box type and not the oval. Radial is the way to wind a good cap.
The best type is paper in oil (PIO) type, copper foil is the best electrode material. (jensen or audionote) or any decent MKP.

6. I routinely remove the global feedback loop and never I found it to be a problem. Without feedback EVERY amp that I know - performed better - more open, louder, with deeper bass, more magic, more what I like.

Thats basically all we need to do. The improvement depends on the circuit but usually the mods open up the sound a great deal. Triode mode is most important of them all. Theoretically we "loose power" but subjectively the sound is louder, more spacious and free. Wery well worth doing.

This is an EXAMPLE of VERY DETAILED modification process of a super amplifier - Music Angel KT88 (price circa 300 USD !!!)


The most basic and simple test of an amp is to run a generator vawe through it and see if it shows on the scope.
By using the sine vave we can learn a great deal about the condition of an amp.
1. Is it alive?
2. Does it distort the sine visibly? Does the both phaces of an amp work equally (symmetrical sine versus a "W" letter wave. )
3. What is the amplification coefficient of each stage and the whole amp
4. When (in volume) the clipping begins. (finding the real maximum power, not advertised power )

The biggest problem is that that test has no real value unless we can run the power near the maximum.
It is NOT ALLOWED to play the amplifier without the load, just silently.
Especially tube amplifiers hate to be run at max volume without speakers or load connected to the outputs.

A human can not possibly spend any time testing speakers and playing say a 1 kHz tone at 50 Watts in the same room.

So the BIG ISSUE is to find a load capable of dissipating up to 100 Watts of power at 8 Ohms or close.

Here comes my own Fikus solution: Immerse the load in Water. You have an unlimited power, silent, cheap and lasting infinitely load.

The resistor (in my case a wirewound 20 Watts / 10 Ohms) can be immersed in a bowl of tap water and the water takes up all the heat. I tested 60 WPC for half an hour without any noticeable temperature rise ).

Just look:

the dry resistor measures 10.8 Ohms plus 1 Ohm for the probe wires.

The resistor gets immersed in the room temp tap water

Wet resistor measures slightly more - 11,2 Ohms plus probes. That is still a perfect test load for the 8 Ohm amplifier output.

Contrary to popular belief, water does not short the electrical circuit easily. (the lights stay on in a sinking car or on the Titanic). Especially that we are dealing with only a few volts AC here. Of course a prolonged application og DC would lead to the water electrolysis (still harmless for the purpose of testing as a load).

Happy testing !!!


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