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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The pale coloured aluminium central box is a channel with solid-state components for regulating the anode supply instead of using a choke. The bias is set by the 68 Ohm cathode resistors to around mA.

The comparison chart lists the parameters of both valves in Class A and Class B applications. In series with your original transformer this will give you the volts DC plate supply on load. Lots of power at low anode voltages. The sound is clean, accurate, detailed, emotionally involving, with the typical smooth treble and precise bass with a warm midrange. Interesting they were, HiFi they weren’t! Only the DC biassing cathode resistor is decoupled for audio variations by a 22uF electrolytic cap’.


I wanted to try them in a tiny regulated power supply, and I just measured the triode characteristics of one specimen. Next job was to rip out the Magnavol bases and replace with a pair of good old octals.

RUwhere it says that it is a full EL36 analogue. They are getting very rare nowadays, though they turn up now and then on Ebay but the prices are extortionate. A lot of fixed bias circuits are usually quite high and are deliberately reduced accordingly. All is determined at which current you measure ra, as this can make a difference of a factor three with no problems. Best output power was achieved in the triode-connected mode, using a high anode supply voltage of Volts and a 10kOhm anode load.

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

The one I have here actually produces 36 watts quite easily before clipping! Note that if you build a stereo version then use a separate filament supply for each output valve and do not ground the supply.


Q1 provides this function. After having thought about some of the problems for a while I next tried a low impedance direct driven grid, with fixed bias, the cathode earthed, and tub valve in triode mode. 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.

I believe negative feedback gives the amplifier a substantially flatter frequency response, than otherwise would be. If you have 45 volts or more then that is fine.

TDSL Tube data [EL36]

Not HiFi but great robust workhorses that ran for decades without attention. In each channel, the 6CM5 TV line output output valves tubr connected as triodes and are driven by a long-tail pair using a 6CG7.

Before continuing to read on with this text please note the following: John contacted me in August – it quickly became evident that he had a much much greater knowledge of this interesting valve than I, and dl36 I am most appreciative of his willingness to allow me to repeat tub advice to me here.

They are still holding in there with no change in any way. Ratings are similar; same top cap and pin out. I simply re-wound mine to 40 volts. The pot is simply adjusted for a total current consumption of 50mA, or 45mA for the 6CM5 anode.

EL Applications in Audio

I was looking at about 50 watts with the volt plate option, and the plate load seemed to suit too. The eel36 transformer would be very small. 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.

I built five of these on the same chassis tubr a home theatre amplifier for the five main channels; the sound is glorious and a lot easier to listen to than a solid-state amp! With the road and engine noise in an open car, Hi-Fi is scarcely worth trying to attain! This is the purpose of the other half of the 6CG7. When using a low supply voltage of Volts the screen can be tied to the anode supply, thus not requiring its own regulated supply voltage.


At this point the 6CM5 had the screen grid at about V and the grid bias set to draw about 45mA anode current. Although sensitivity was tubee, again requiring 42V ppthe output was the greatest and distortion the lowest. Year of manufacture of my valves is and data for them is at Tubes.

The valve-data does include Class A operation, but that is for a V supply at mA. This helps ensure that you do not exceed the valve’s tibe potential rating limits. Grid and screen grid stopper resistors are a must if you want the ELCM5 to be stable and not go into parasitic oscillations.

Russian, Eastern European, and Chinese audio valves mean that we don’t need to make do with old non-audio types unless we want to. Also, separate feedback windings. Looking at how much power you need to get a cherry red anode around 40 Watts all I can conclude is that the tuge Watt tybe is conservative. The Williamson Amplifier Revisited.

Additionally the circuit design draws strongly on the famous “Williamson” design Amplifier, published in Wireless World magazine in 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 triode-strapped configuration, exhibiting very obviously poor linearity.

This is an advantage when you want to build up a power supply with modern transformers. After having taken a few of these apart it appears that the Philips made ones have similar anode dimensions and cathode size as the 6CA7 not the EL Driving via the control grid g1 is not the way to use this valve for Class A audio, as much as I have tried. If you feel uncomfortable with this, simply lift the ground of each pot through a 10k resistor per pot or a common grounded one of 2.