EF72 in tube microphone?

Hi
My friend who have a lot of tubes gave me one CV465-EF72.
Does this tube used in tube microphone?
Thanks
Duka

Hi Duka,

EF72 or 5840/CV465 are a HF subminiature wire ended pentode, some application use was in IF amplifiers around 10 mHz.

Heater: 6,3V/150mA, Anode max: 100V/7mA
Pin: 1=g1 2,8=k,g3 3=h 4=h 5=a 6=h 7=g2

I don`t have more data, but if the g1 Cg/capasitance and Rg/resistance are enough low recpective high (it should be because it is a HF tube) maybe you can use this pentode as a cathode follower and drive a output transformer around 5:1/5k-200 ohm or maybe drive a high ratio transformer from the anode.

The funny is that the mostely of tubes can be used in audio amplification circuits, ok for the condenser microphones application it is important to match the capsule to a very hi-z input (100Mohm and up) but the grids on tubes is nearly as a gate on JFET transistor, so with some luck it can be ok.

--Bo

Hi
Thanks for reply
I find that CV72 -EF72 are similar to CV3929-EF732-5840. 5840 is used in some microphone and Royer modification where he said that 5840 is like AC701K.
Duka

Duka,

I think this is a missunderstand, because
the EF72/5840 are a HF pentode and AC701K are a NF triode, and particalary designed for condenser microphones, so the only common is that they are of subminiature type.

--Bo

[quote author="Bo Hansén"]Duka,

I think this is a missunderstand, because
the EF72/5840 are a HF pentode and AC701K are a NF triode, and particalary designed for condenser microphones, so the only common is that they are of subminiature type.

--Bo[/quote]
OK.
Wach on this site Royers modifcation "One tube Microphone from Berlin and one from Barstow"
Duka

[quote author="Bo Hansén"]I think this is a missunderstand, because the EF72/5840 are a HF pentode and AC701K are a NF triode[/quote]
But couldn't the EF72 in triode mode have similar data to the AC701K?

Best regards,

Mikkel C. Simonsen

Ok, I yield,

But give my one right, for that the one is a pentode and one is triode.
(and a half right that it is not direct equal to AC701K)

Put the tube in and try, it is a simple hook up.

--Bo

[quote author="Bo Hansén"]Ok, I yield,

But give my one right, for that the one is a pentode and one is triode.
(and a half right that it is not direct equal to AC701K)

Put the tube in and try, it is a simple hook up.

--Bo[/quote]
OK
But 6AU6, EF86 are pentode and they are used (truth, like a triode) in many microphone.
Duka

I've used 5840's in mics, they work quite well. The 5840 was used in the Altec 'Lipstick' mic (M20 and M30), and is also used in the Royer circuit (as was mentioned earlier). Pentodes are often used in mics - and often triode-connected. The Altec M11 used a 6AU6 pentode in a cathode follower, the M20 and M30 was an updated version of the same design but used a 5840 instead of the larger 6AU6. Sony C37 and C800 use a 6AU6, U47 used a VF14 pentode, U67 used an EF86 pentode. So try it - it'll likely work.

-Dale

Of course pentode`s are used in condenser microphones, they have good quality for that.

From first time we talk about the unknown EF72, it was a mistake to mix in the 5840, I should know better, I have the information on my microphone tech page http://w1.316.telia.com/~u31617585/

BTW,
There are also some nice subminiature tube that was used in hearing aid devices, Gefell U900 use one type there the filament draw very low current so they can drive the tube circuit from the phantom power.
(there are some sort of internal switching supply, but the tube must still have very little filment consumption)
I have ask Gefell about the tube, but they will not answer this question.

Are there somebody that know something about this tube ??

--Bo

The 5840 is like the 6AK5 http://www.mif.pg.gda.pl/homepages/frank/sheets/137/5/5840.pdf

There was some talk in the newsgoups about possible subs for the ac701k
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&q=ac701+5703