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EL36 / 6CM5 TESLA tube tubes store. TESLA EL36 / 6CM5 high power amp tube. Customers who bought this product also purchased. Class, Va, Vg2, Vg1, Ia, Ig2, Zout, Pout, THD. Line output, , , , B ( idle), , , , 36, 1, B, , , , , 38, 3,, , He offers a 6CM5/EL36 based 2 x 22 Watt Stereo Class AB1 triode amplifier, the fuss was about tube sound, while their solid-state amp’s are being repaired.

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I have spent a lot of time on this point, and can’t argue enough to add these to every valve amplifier you make. But after quite a bit of experimentation with other output valves I used 6CM5’s, based on the large amount of information now available on these dime-a-dozen valves. Additionally, the method of bias and voltage regulation also bears some importance tjbe maximum power output.

Note that the control-grid and cathode are connected together so there is no bias; the cathode resistor is used for a DC stabilisation circuit. The results were looking promising but still less than the requisite 4W was forthcoming.

But the comparison between the completely different nature of the two valves is apparent; the EL36 is about half the power rating of an EL34, but this is achieved using directly comparable currents and tubee less voltage; the r a of the EL36 is relatively low.

The cathode follower has only current gain, so we need a grounded cathode stage to obtain some voltage gain.

That’s a matter of personal preference; in fact I probably gube include any negative feedback for my first application of this circuit; that of a car radio for my Model T Ford.

Data obtained from different sources indicate different limits; from 10 to 18 Watts dissipation for the anode and 4 Watts for the screen.

As with all electronic experimentation, there are components hanging out everywhere. I have tried unpacking these transformers and adding an air gap; this is okay if you want a small Watt output transformer, but as the primary inductance falls from around 50 Henries to around 10 Henries at best tuge tested and optimisedit will effect the low frequency response markedly.


For someone who wants to get into valve technology these days, TV valves are ideal! I intend to go ahead and use the 6CM5 in single-ended Class A applications but only where heater current isn’t a problem and a couple of Watts is acceptable output.

One of these is the propensity for the valve to self oscillate, which has been traced in the case of my prototypes to the screen grid. There is a perforated steel cover which fastens down over the top of the amp to prevent anyone coming into contact with high voltage terminals”. Notice that adjustment of DC feedback is achieved with a kOhm preset pot potentiometer. The 6CM5 could obviously be replaced with a 25E5 if it’s convenient to obtain 25V mA for it’s heater.

The 6AV6 is really half a 12AX7, but just about anything could be used for this stage. El6 was to the best of my knowledge the only Geloso model to use a quad of output tubes. Only the DC biassing cathode resistor is decoupled for audio variations by a 22uF electrolytic cap’.

Q1 provides this function.

EL Applications in Audio

For someone who grew up in the ‘s, it’s ironic that I learnt about valves before solid state. Looking at the circuit now, to start with the output stage, the supply used was V 50mA. FIG 3 The total valve filament current requirement is: Many of these valves made in Australia were re-badged for other vendors. These are designed to work with no DC component in the windings and are ideal for these applications.

Be aware of the fact, that the power transformer is wired rather oddly in these amp’s. The amp itself had only a swing of volts for the negative bias, so my first move was to change this for a volts swing through two 20 turn pots; one for each tube. I didn’t need them in my prototype as a regulated power supply was being used a BWD with very low output impedance. I acknowledge inspiration for my design came heavily from the following web pages; http: Very little is published on this, so take heed!


However, screen grids draw current, which does not suit the relatively high impedance of RC coupling. It was so totally different from my EL84 amp, comparing mono to mono.


These days people tend not to use filter chokes in power supplies as there are plenty of high tubd electrolytics available at reasonable prices.

The primary impedance of the output transformers would be something like 3. I have done this many times before with other valves with great success; try an and you will never use any other method again. This is an advantage when you ek36 to build up a power supply with modern transformers.

The input transformer is from Altronics and is a nice low cost mu-metal screened one. Following a number of reader enquiries, Graham noted that there seemed to be very little published on the internet on the subject of grounded grid amplifiers in audio.

6P31S / 6P31C = EL36 = 6CM5 tube. Beam tetrode

Note that far more practical and realistic is application in Class AB, rather than Class B, where about one third of these power levels can be expected. The big problem with these amplifiers is low efficiency due to fighting the internal anode resistance of the valve R tbe.

Grid and screen grid stopper resistors are a must if you want the ELCM5 to be stable and not go into parasitic oscillations. I have developed a completely new simple topology for the EL36 I have also tested it with 6V6 and 6L6 valves as wellthat El6 have never seen before.