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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If omitted there will be slight negative feedback from the 6CM5 cathode. Unfortunately the 12AX7 is highly revered by audiophiles and some brand names attract unusually high prices when sold at on-line auction.

Having said all that, the low anode voltage is of interest, as it may permit a valve amplifier to operate on modern low voltage power supplies. The anode voltage should be V when the 6CM5 anode is drawing 45mA. I am most grateful for John’s contribution of time, experience and knowledge as evidenced below. Regardless, the circuit in Figure 1 yields a nice, high quality, low tuge let’s make that ” really, really cheap “amplifier.

In theory this is not a practical thing to do as this would allow the pot to completely shut down the bias of the connected tube! Driving via the control grid g1 is not the way to use this valve for Class A audio, as much as I have tried. Then after putting the tubes in, work backwards checking cathode current at each tube cathode 1 ohm resistor pin 8. This is confirmed after repairing many Philips public address amplifiers, in never ever having to replace an output valve.

Grounded-grid mode with constant-current drive. In this configuration with low Volts and low impedance anode loads you are fighting the dynamic internal anode resistance of tkbe valve, making it almost impossible to match an anode load with reasonable output power and efficiency.

Listening in mono, the instruments didn’t come from the speaker, but rather from somewhere around it. The amp itself ek36 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.

One of the photos shows a re-wound power transformer with the extra screens tune 2 winding on two tags previously used for the 20 volt bias winding. Very little is published on this, so take heed! This in turn makes the anode voltage decrease, thus reducing the DC on the cathode follower output and therefore reducing the 6CM5 screen voltage which in turn reduces anode current. The anode is DC coupled into the grid of the cathode follower by a voltage divider which sets the 25V on the cathode.


The amp is by no means a state-of-the-art high-end unit in terms of style and finish, but it is amazing how much better it is than most other more powerful solid state amp’s. You may need to re-do this a couple of times as the tubes el336. Click on the image tue enlarge.

EL36 / 6CM5 TESLA tube – POWER / OUTPUT tubes –

The other method is of a much higher impedance, and also tends to sag as the main HT winding drops with currant drawn. I didn’t need them in my prototype as a regulated power supply was being used a BWD with very low output impedance. All is determined at which current you measure ra, as this can make a difference of a factor three with no problems. These had all cost me a fair bit of money and I still needed more! However, having the design knowledge and winding facilities for transformers myself, it is of course convenient for me to do this.

I probably won’t bother including it in future amplifiers. I wanted to try them in a tiny regulated power supply, and I just measured the triode characteristics of one specimen. So, any line output valve is going to need a very small voltage drop from anode to cathode when it is turned hard on.

6P31S = EL36 = 6CM5 tube. Beam tetrode

Having started at about the age of 9 and I am now The “Williamson” type circuit would set the standard in audio amps’ for many years to come. In practice it did seem to work better and a bit over 2W was available.

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. 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!?

At this point the 6CM5 had the screen grid at about V and the grid bias set to draw about 45mA tbue current. Puts out about 70W, according to Philips. I tested all valves and they are fine.


The main smoothing capacitors are even keeping the clipping point flat with no ringing coming over the top of the caps whatsoever! Screen grid drive seemed to be a better option, going on the theory that the gain of the valve would be less, and possibly more linear.

For a higher anode voltage, a 22kOhm 2 Watt series resistor and two 75V Zeners in series to ground form a nice regulated tueb supply. The scope photo shows it just clipping at The input transformer is from Altronics and is a nice low cost mu-metal screened one. I have also not done any experimenting with them in self cathode bias mode.

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

I’ve built numerous other AM and FM radios using only TV valves rather than comparatively rare and expensive GT and G style radio valves, which I’d rather keep for equipment made in that era. Allowing for the DC across the speaker transformer, the total supply will be more than this hence the V in my circuit.

In many respects the data for this valve indicates general similarity, but clearly the two are not immediately interchangeable.

This is done to get V for the screens, a voltage which, under no circumstances, may be exceeded. The pale coloured aluminium central box is a channel with solid-state components for regulating the anode supply instead of using a choke.

Also, separate feedback windings.

Needless to say after completion of the mod it should be powered first without the output tubes in place, by metering grid one negative volts on each tube base pin 5 and winding all the pots to maximum voltage first.

Before continuing to read on with this text please note the following: They don’t look bad at all!

The output transformers were made in in Sydney and the power transformer and chassis is a new one by T. Ratings for use in Class B push-pull are readily available from Philips datasheets available on the internet. They are still holding in there with no change in any way.