EF42 for audio applications

[TonyTecson]

i have a bunch of these, are they usable for audio?

 

[jerluwoo]

http://www.r-type.org/pdfs/ef42.pdf

 

[kevinkr]

It was designed for broadband RF applications, and is stated to make a good cathode follower.

Given the spread in the curves I would keep bias and signal inside the range of -2V to -1V for pentode connection.. (Bias at -1.5V to start?)

No triode curves are given, but given a Ug2g1 of 83 it might have usefully high gain triode connected.

More here: http://www.mif.pg.gda.pl/homepages/frank/sheets/046/e/EF42.pdf

 

[kevinkr]

I see jer and I referenced the same document from two different sources.. lol

I would breadboard a circuit and give it a try. Might work well in the first stage of a phono pre..

 

[TonyTecson]

thanks, i was looking at the ef40 data and to me they look the same....
i wonder if anyone have used them before for audio....

 

[Keit]

Being high-slope and semi-remote cutoff (ie gain varies with grid bias), it will be necessary to keep signal levels low to avoid distortion. It's best application in audio would be as a preamplifier input stage and should have good low noise performance unless gassy or worn out.

As these tubes have been obsolete for >60 years, your tubes are likely to have been storage for decades, unless taken from long service. I would suggest getter conditioning before putting into service - cook in an oven at 120 C for a while. Old tubes get gassy, cooking often fixes it.

 

[rotaspec]

i have a bunch of these, are they usable for audio?

Just a heads-up:
These are rim lock 8-pin tubes, and new sockets are not that common any more.
You can get Chinese ones, but they don't have the skirt which means the tube can be inserted multiple ways around.

 

[v4lve lover]

There are still a lot of these sockets floating around.