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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EL Applications in Audio

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.

Triode Mode Although a plot of EL36 curves in triode mode appeared reasonably linear, the EL36 was found to perform relatively poorly in a simple single-ended tub configuration, exhibiting very obviously poor linearity. I have brought the new 40 volt bias winding out on fly leads, no more tags left!

If the thought of 4 mains thbe seems and sounds a bit off-putting, just bare this in mind – the transformer for the screens supply need only be about 50 ma this is enough even for 4 tubes and will be small.

So, why not get rid of the grid bias and just control the anode current with the screen grid voltage? An early direct coupled test circuit.

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

I have done this many times before with other valves with great success; try an and you will never use any other method again. Very little is published on this, so take heed! Lots of secondary taps for various impedances, including 70V and V line driving windings. 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.

It was so totally different from my EL84 amp, comparing mono to mono.

Most companies that used the EL output tube the Belgian company Faylon and the German Dynacord being just two examples most probably chose this tube for its short, stubby, fairly beefy, relatively low voltage specifications enabling a smaller overall height of their amplifiers?


Recently, I’ve further been privileged tkbe have highly esteemed South Australian tubf Graham Dicker offer the following most valuable and extensive research report. This in turn makes the anode voltage decrease, thus reducing the DC on the cathode follower output and tuge reducing the 6CM5 screen voltage which in turn reduces anode current. Feedback isn’t applied to the 6AV6 as it’s a triode handling low voltage and in my opinion it isn’t necessary.

Either transformer or cathode follower drive would have to be used.

The Soviet 6pi31 6P31 is a direct equivalent, and the well regarded Sveltana branded type can be purchased cheap and in quantity. This I have yet to play around with. Best output power was achieved in the triode-connected mode, using a high anode supply voltage of Volts and a 10kOhm anode load. I have spent a lot of time on this point, and can’t argue enough to add these to every valve amplifier you make.

These are an old TV horizontal deflection tube with a plate dissipation of 11 watts. The anode voltage should be V when tue 6CM5 anode is drawing 45mA. It seems to be working tybe the EL36, maybe EL84’s would like it too. Furthermore, tuhe is my first experiment with enhanced triode mode. The operating conditions are most bizarre no bias and 25V for the screen gridbut it really does work, giving about 4W output.

Remember we a forcing a switching valve to work as a linear amplifier.

More valves in parallel will give more output power, but you will need to take out shares in the local electricity supply utility. In reality the actual power to the voice coil will be less due to transformer losses. One other point here. Click on the image to enlarge and view the circuit properly. Really nice reverb, 2 x 12 speakers, uses two EL36 output valves, about 40Wcombo style, but not open back – the speakers are fully enclosed. Also, the very simple independent screen supply can be clearly seen.


Philips got around the height problem by mounting them horizontally with generous ventilation. Then after putting the tubes in, work backwards checking cathode current at each tube cathode 1 ohm resistor pin 8. This means that for Class A audio, the 6CM5 is one of the worst valves you could use.

TDSL Tube data [EL36]

These tests were done with a regulated valve power supply, a BWD model At first it seemed to be a lost cause, trying to use this valve as an audio amplifier.

They seem to be quite happy at this, and in class AB1 too! The Williamson Amplifier Revisited. The EL36 family of tubes were originally designed for TV line output usage although Philips did make an amplifier using them for audio in class AB1, even though their own data shows them as class B for audio!? The 6CM5 is not a plug in equivalent, although it might have the same or similar connections. US, UK and European data books often do not show it. There is clearly a getter inside, but it is not flashed as it is of a type that doesn’t need to be, and cannot beflashed, but outperforms traditional getters.

The results aren’t really surprising, and after looking at the STC manufacturer data on the 6CD6 when used as a single-ended Class A output stage, it just confirms what I suspected. All is determined at which current you measure ra, as this can make a difference of a factor three with no problems. The bias is set by the 68 Ohm cathode resistors to around mA. As I build a lot of valve projects requiring an audio stage the 6CM5 has been of interest, especially as I have a huge quantity of them!