Hello, Radio Friends members,
It will be that la válvula EL33 (Mullard) it is equivalent to the valve KT61, (Marconi).
Retired data the book in Spanish of the author R. J. Darkness. 1.ª edition November 1956.
Hello Júlio Branco,
The EL33 (or 6M6) it is NOT equivalent to the KT61. This data book is not serious !
A Philips or Mullard data book would never make such recommendations.
The EL33 needs a cathode resistor of 150 ohms at least, while the KT61 needs a cathode resistor of only 90 ohms.
Without changing the cathode resistor the EL33 and the KT61 may never be used to replacing each other.
As a makeshift one can use a KT61 to replace an EL33, but the performance will decrease.
An EL33 should never be used as direct replacement for the KT61. Due to the wrong cathode resistor the EL33 will be severely overloaded and will give only low performance.
Best Regards, Jacob