Microphone With A Low Impedance Tube

YoungFred · 11th March 2007, 08:31 AM

Hi
I am building a high output tube mic and would like suggestions about tubes to use. I am leaning towards pentodes mostly but triodes I'l consider also.

I'm looking for tubes that have as low grid leak as possible, are low impedance (hopefully 2k or less in pentode but a little more might be ok), low capacitance, decent amplification (hopefully about 25 or more) and sound great.

I am really looking forward to everyones suggestions. So far I have used 12a-7's, 6au6 and ef86. I know they are fine tubes but what will be even better for low grid leak, low ra and sound.

Thank you! Have a great day,

Jor

Geek · 11th March 2007, 09:43 AM

Hi,

What microphone element will you be using for your tube mic?

Of those you listed, EF86 would be the best choice.

Cheers!

EC8010 · 11th March 2007, 12:39 PM

6BS7.

kevinkr · 11th March 2007, 02:36 PM

D3A!! Very high transconductance, and when triode connected internal noise generator impedance equivalent to about 60 ohms. (johnson noise equivalent) You probably won't find a quieter tube.. Mu = 77 so plently of gain as well.. RP well b below 2K

Brian Beck · 11th March 2007, 03:26 PM

Quote:

Originally posted by kevinkr
D3A!!

Or the E810F/7788 triode-connected. However, the trouble with these high-gm hot rods is that grid current will be a problem if the grid is directly connected to a high-Z capacitor mike element. I think this is why EC8010 suggested an electrometer tube with grid current in the picoamp range. "YoungFred" hasn't told us enough about his application to know for sure what he needs.

EC8010 · 11th March 2007, 03:47 PM

Yes, I'm assuming from the "low grid leak" requirement that this is to be the head amplifier for a condenser capsule. A valve that has a little of the E180F's properties and some of the 6BS7 is the EC1000.

grhughes · 11th March 2007, 07:08 PM

You haven't said what type of capsule or transducer element you're gona use. There are a bunch of tubes you could use but why re-invent the wheel. The 6688/E180F is a pentode you could use. A 6au6wa/7543 is not sloppy either. The 6DL4/8255 is a triode. The 6J4/8532 is a good triode.

YoungFred · 11th March 2007, 09:43 PM

Hi

I'm going to use an m7 capsule. I've also used vf14's and ef14's in u47's that I have restored or built. Those are large tubes. I was looking for something that is even better because lots of times people use the best tubes they know of and might not know about great tubes that have been made. Does the 6ej7 have low grid leak? I would guess not.

The EC1000 sounds like it might fit the bill. What is the plate resistance?

When I look for at tube specs how does one know if it has low grid leak? I would like this mic to be fairly high gain and use a tube that has low plate resistance, they sound more open to me. All input welcome! Thank you so much! Have a great day! Talk with you soon,

Jor

aletheian · 11th March 2007, 10:06 PM

EC1000 are fantstic tubes, but not many were made, so thy rare and very expensive if you get a good one. i have had an eye out on e bay for a long time for one.

EC8010 · 11th March 2007, 10:22 PM

ra is likely to be around 2k in use.

11th March 2007, 08:31 AM	#1
YoungFred diyAudio Member Join Date: Sep 2006	Microphone With A Low Impedance Tube Hi I am building a high output tube mic and would like suggestions about tubes to use. I am leaning towards pentodes mostly but triodes I'l consider also. I'm looking for tubes that have as low grid leak as possible, are low impedance (hopefully 2k or less in pentode but a little more might be ok), low capacitance, decent amplification (hopefully about 25 or more) and sound great. I am really looking forward to everyones suggestions. So far I have used 12a-7's, 6au6 and ef86. I know they are fine tubes but what will be even better for low grid leak, low ra and sound. Thank you! Have a great day, Jor

11th March 2007, 12:39 PM	#3
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	6BS7. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

11th March 2007, 02:36 PM	#4
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	D3A!! Very high transconductance, and when triode connected internal noise generator impedance equivalent to about 60 ohms. (johnson noise equivalent) You probably won't find a quieter tube.. Mu = 77 so plently of gain as well.. RP well b below 2K __________________ www.kta-hifi.net

11th March 2007, 03:47 PM	#6
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Yes, I'm assuming from the "low grid leak" requirement that this is to be the head amplifier for a condenser capsule. A valve that has a little of the E180F's properties and some of the 6BS7 is the EC1000. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

11th March 2007, 07:08 PM	#7
grhughes diyAudio Member Join Date: Mar 2005 Location: Cubicle Sweet Cubicle, SW, MO, USA	6688 You haven't said what type of capsule or transducer element you're gona use. There are a bunch of tubes you could use but why re-invent the wheel. The 6688/E180F is a pentode you could use. A 6au6wa/7543 is not sloppy either. The 6DL4/8255 is a triode. The 6J4/8532 is a good triode. __________________ "The gift of imagination is the gift of the gods imparted to a few for which they receive innumerable kicks in the a$$ their entire life." Le Corbusier (Edward Jenneret)

11th March 2007, 09:43 AM	#2
Geek diyAudio Member Join Date: Sep 2004	Hi, What microphone element will you be using for your tube mic? Of those you listed, EF86 would be the best choice. Cheers!

11th March 2007, 09:43 PM	#8
YoungFred diyAudio Member Join Date: Sep 2006	Thank you for all the advice so far! Hi I'm going to use an m7 capsule. I've also used vf14's and ef14's in u47's that I have restored or built. Those are large tubes. I was looking for something that is even better because lots of times people use the best tubes they know of and might not know about great tubes that have been made. Does the 6ej7 have low grid leak? I would guess not. The EC1000 sounds like it might fit the bill. What is the plate resistance? When I look for at tube specs how does one know if it has low grid leak? I would like this mic to be fairly high gain and use a tube that has low plate resistance, they sound more open to me. All input welcome! Thank you so much! Have a great day! Talk with you soon, Jor

11th March 2007, 10:06 PM	#9
aletheian diyAudio Member Join Date: Apr 2004 Location: Philly	EC1000 are fantstic tubes, but not many were made, so thy rare and very expensive if you get a good one. i have had an eye out on e bay for a long time for one. __________________ Heghlu'meH QaQ jajvam!

11th March 2007, 10:22 PM	#10
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	ra is likely to be around 2k in use. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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