Bandpass filters using Tubes

[Headbuttking2]

Anyone know how this is done?
I want to make a 5 band all tube equalizer..
The only thing I came up with so far was using 4 high pass filters and a low pass filter using 12AU7 tubes as cathode followers to buffer the signal, but it didn't get very good results when I put it through PSPICE, and technically when you think about it, it wouldn't really work..

So my problem here is coming up with a 2nd-Order bandpass filter using tubes, without inductors.

I am fairly new to tubes....so anything will be helpful.

[Headbuttking2]

I believe I figured it out with the most obvious way....a high pass and low pass in series....
Wow I'm an idiot..

Oh well...I will post a schematic when I get this together..
Its goin to be pushing 7 or more tubes though..

[R.G.]

Well - you could use two tubes set up as an opamp, then use the old LC network across the inputs to do that.

[davebungo]

I believe I figured it out with the most obvious way....a high pass and low pass in series....
Wow I'm an idiot..

Oh well...I will post a schematic when I get this together..
Its goin to be pushing 7 or more tubes though..

It seems a little inefficient to use 7 valves with each one providing a simple low pass or high pass.  There must be a better way but I'm not a valve expert.  BTW cascading a low pass and a high pass filter in the way described will provide a bandpass filter but it won't be 2nd order as you said you wanted.  It will still be first order.  Cascading two low pass filters is 2nd order but overdamped and possibly not what you are after?  I think you will need to generate some gain to do this so source or cathode followers are not very useful in  that respect. 

[Headbuttking2]

R.G. - How do you set 2 tubes in the form of an opamp?  Differential amp?

Also I do have a series of 12AX7s on the output to provide gain.
I think 1st order will suit this fine because I am only looking to highten the selected frequencies.

[toneman]

googling  "bandpass filter tubes schematic"  resulted in---

http://www.cgs.synth.net/tube/vcf.html

http://www.tubecad.com/articles_2001/Tube-Based_Crossovers/page9.html

http://www.endino.com/photo9.html

http://home.netcarrier.com/~rstevens/aa-100.html

http://www.headwize.com/projects/opamp_prj.htm

Hope this is enough 2 get U started....(?)

have fun!!
T

[lovekraft0]

Here's a tube opamp setup:
TUBE-BASED EQUALIZER

For more info, read the whole article:
Designing A Pocket Equalizer For Headphone Listening

[Headbuttking2]

Thanks..

I just redid the circuit using the Tube-base equalizer there as a reference..

I found a cirucit using an EF86 pentode as a bandpass filter with adjustable Q and frequency like Electro-Harmonix TubeEQ...
But the SPICE tube models I have don't include any 3 grid pentodes, so I am out of luck testing it and all I would be able to do is build it and hope for a good outvcome (which I will probably never get around to doing).