• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6C33C-B on 8W


2021-10-11 6:43 pm
I guess you already have seen this datasheet: http://www.jogis-roehrenbude.de/Russian/6C33C/6C33C-B-6S33S-VExtendedDatasheetMB.pdf

Stay below 45W (for both anodes) and below 250V and service life will be a lot better. Go for a Ra between 800-1200 Ohm (preferable a transformer with an Rdc lower then 15 Ohm)

I personally like fixed bias for this tube but that is not the easiest way (steep tube, 1 volt differance on the grid makes a huge difference in current)
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In this amplifier, I use the mode of 300-320 V, 55-56 W of anode power.
The maximum output power of the amplifier is more than 18 W, the output resistance is 1.25 Ohms at a load of 4 Ohms.
I can get an output of more than 20 watts, but I have to choose the tubes.
The sound is great.


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2021-10-11 6:43 pm
It is recommended to try to work with a half heater (half cathode), which can reduce the heat generation and the anode characteristics are more linear.
Did you measered the linearity your self? From the datasheets it’s hard to tell.
The difference cannot be great anyway because almost nothing changes, only 1 or 2 heaters are on the rest is the same. (Ri changes)


2021-10-11 6:43 pm
Several amplifiers have been working for about 10 years without problems. Electronic bias and soft start extend the life of the tubes many times over.
Very good job!

I am also very happy with this tube, very reliable. I used about 200-220V and 50W dissipation. Never had a broken tube (exept when i made a mistake myself). However, after 1000h i checked the amplifier with a new tube and i discovered that a new tube sound a little bit fresher. Just a little bit. The older tube was still good enough in my opinion.