Now the secret of this ECH4A is yet to be solved.
Because of the straight bulb shape the ECH4A may probably be an Octal version of the E1R ?
Can anybody confirm this, e.g. by comparing the data ? Even checking the heater current will give some evidence, since the heater current of the E1R is only 0.2 A, while the heater current of the normal ECH4 is about 0.35 A.
Ravalico gives the E1R as an ECH3 with modified base connections that are the same of ECH4. The ECH4A is given as electrically identical to ECH4, with octal base and cylindrical bulb. The two tubes, E1R and ECH4A, seem to have different origin according to the above source.
Best regards, Emilio
thank you for this useful information.
About the same matter, I found additional information on this site: Le valvole convertitrici di frequenza .
After some research I could get more clarity about the ECH4 family, particularly about their octal versions. I hope, any open questions before, are now answered.
Since the Ex3x- series is the most common series of red-series octal tubes, I'll call the ECH34 as reference tube.
As usual in this series, the heater connections are on pins 2 & 7, according to the normal (American) octal standard.
The other ECH4 octal versions are in relation to the ECH34 as follows:
ECH4G = Australian version of the ECH34. Equivalent to the ECH34, but with golden painted bulb.
ECH4A = Italian version of the ECH34. Equivalent to the ECH34, but with straight GT-style bulb.
ECH4K = By now only found in some Swiss radios. Equivalent to the ECH34, with exception of the base diagram, which is the same as of the UCH4, with heater connections on pins 1 & 8.