Minature Vaccum Tube Question

Mark A. Gulbrandsen · 26th May 2005, 07:25 PM

I am aware of the minature vacuum tubes(the ones with wires comming out the bottom) that were designed back in WW-2 for aircraft avionics and that these are used today in some of the Groove tubes microphones. Would any of these tubes be sutable for building a Grounded Grid line stage, were there medium-mu versions of these tubes, which is what is needed, and if so what are the numbers of these tubes. If anyone has any other info on them that might be of help I would greatly appreciate it.

Thanks,
Mark

agent.5 · 26th May 2005, 08:40 PM

check out www.tubecad.com. It has lineamp schematics with 6021W

nuvistor · 27th May 2005, 01:34 AM

Tubecad balance line preamp with 6021 , mentions plate voltage limitation

Mark A. Gulbrandsen · 27th May 2005, 02:27 AM

Thanks for the link guys! I can get some of these locally so I thought I'd see what they could be used for.......

Mark

Mark A. Gulbrandsen · 27th May 2005, 08:38 PM

I picked up a dozen 6021's today for 10 bucks apiece. Most are RCA and some are Sylvanias, all are NOS.

Mark

agent.5 · 30th May 2005, 04:00 AM

You may want to consider the Aikido amp

http://www.tubecad.com/2004/blog0011.htm

In the safer version, at the bottom of the page, you can replace the 5687 and 6N1P tubes with 6021, and just change all resistors with value of 430 to 181. The rest of the circuit remains the same.

My math is

Rk = rp (mu +1)
rp = 6500, and mu = 35. thus
Rk = 181

kevinkr · 30th May 2005, 10:06 PM

Note that the 6021 may not be happy with 300V applied to any of its elements as I found to my chagrin in my submini tube based phono stage. The 6021 has a maximum plate voltage rating of just 165V and although the voltage across either section does not exceed this value in the aikido design, the clearances are such that leakage paths across the mica can become a problem with anything over 250V.. Some 6021 work fine well above this value and others don't. I would use the version designed for 220V as agent.5 suggests - it ought to work well.
You may have to tune the cathode resistances in order to get the desired operating points, the equation he used is not usually all that accurate.

Kevin

RE 604 · 30th May 2005, 10:38 PM

Hello ,
this is my 6021 RIAA - pre with 6111 as line stage .
The circuit and pcb layout are on my homepage under "Vorverstaerker"" .
This is the pocket- version ;-)).
Regards , Alex .

P.S.: The resistor , feeding the riaa - network , must be 68 k if you use the 7963 tube ( difficult to find here in Germany ) .

Mark A. Gulbrandsen · 31st May 2005, 03:17 AM

What I am really after is a simple line stage to build. I was hoping that the 6021 might be sutable to use in a grounded grid line stage similar to Rosenbilts.... but these tubez may not be able to work at the voltages found in that preamp. Will have to do some more investigating on this.....

Mark

Robert Morin · 31st May 2005, 05:08 AM

Quote:

Originally posted by Mark A. Gulbrandsen
What I am really after is a simple line stage to build. I was hoping that the 6021 might be sutable to use in a grounded grid line stage similar to Rosenbilts.... but these tubez may not be able to work at the voltages found in that preamp. Will have to do some more investigating on this.....

Mark

I don't see why the Rosenbilts "grounded grid" (I put hat in quotes because the configuration Rosenbilt uses is a diff amp in my book" would not work but you will have to do some serious tweaking of voltages...

Tally ho!
Robert Morin

26th May 2005, 07:25 PM	#1
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Minature Vaccum Tube Question I am aware of the minature vacuum tubes(the ones with wires comming out the bottom) that were designed back in WW-2 for aircraft avionics and that these are used today in some of the Groove tubes microphones. Would any of these tubes be sutable for building a Grounded Grid line stage, were there medium-mu versions of these tubes, which is what is needed, and if so what are the numbers of these tubes. If anyone has any other info on them that might be of help I would greatly appreciate it. Thanks, Mark

30th May 2005, 10:38 PM	#8
RE 604 diyAudio Member Join Date: Oct 2003 Location: Germany	Hello , this is my 6021 RIAA - pre with 6111 as line stage . The circuit and pcb layout are on my homepage under "Vorverstaerker"" . This is the pocket- version ;-)). Regards , Alex . P.S.: The resistor , feeding the riaa - network , must be 68 k if you use the 7963 tube ( difficult to find here in Germany ) . __________________ No reason to get excited : Jimi Hendrix .

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26th May 2005, 08:40 PM	#2
agent.5 diyAudio Member Join Date: Aug 2003 Location: San Francisco, CA	check out www.tubecad.com. It has lineamp schematics with 6021W

27th May 2005, 01:34 AM	#3
nuvistor diyAudio Member Join Date: Jun 2004 Location: Richmond CA	Tubecad balance line preamp with 6021 , mentions plate voltage limitation

27th May 2005, 02:27 AM	#4
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Thanks for the link guys! I can get some of these locally so I thought I'd see what they could be used for....... Mark

27th May 2005, 08:38 PM	#5
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	I picked up a dozen 6021's today for 10 bucks apiece. Most are RCA and some are Sylvanias, all are NOS. Mark

30th May 2005, 04:00 AM	#6
agent.5 diyAudio Member Join Date: Aug 2003 Location: San Francisco, CA	You may want to consider the Aikido amp http://www.tubecad.com/2004/blog0011.htm In the safer version, at the bottom of the page, you can replace the 5687 and 6N1P tubes with 6021, and just change all resistors with value of 430 to 181. The rest of the circuit remains the same. My math is Rk = rp (mu +1) rp = 6500, and mu = 35. thus Rk = 181

30th May 2005, 10:06 PM	#7
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Note that the 6021 may not be happy with 300V applied to any of its elements as I found to my chagrin in my submini tube based phono stage. The 6021 has a maximum plate voltage rating of just 165V and although the voltage across either section does not exceed this value in the aikido design, the clearances are such that leakage paths across the mica can become a problem with anything over 250V.. Some 6021 work fine well above this value and others don't. I would use the version designed for 220V as agent.5 suggests - it ought to work well. You may have to tune the cathode resistances in order to get the desired operating points, the equation he used is not usually all that accurate. Kevin

31st May 2005, 03:17 AM	#9
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	What I am really after is a simple line stage to build. I was hoping that the 6021 might be sutable to use in a grounded grid line stage similar to Rosenbilts.... but these tubez may not be able to work at the voltages found in that preamp. Will have to do some more investigating on this..... Mark

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