pucho812

check out this mic schematic. dual tube transformerless output
« on: February 10, 2010, 06:00:02 PM »
dual tube transformerless design. Variable pattern... Hmmmmm?








You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.


abbey road d enfer

Re: check out this mic schematic. dual tube transformerless output
« Reply #1 on: February 10, 2010, 06:31:21 PM »
It seems to be workable. However, the dynamic range is going to be very limited because of the output stage. The first stage is probably capable of developping several volts p-p but the output stage is limited to about 100mVp-p. The max current in the output tube is limited to ca. 2mA by the plate resistor, so basically, the voltage across the 82R ohm cathode resistor is 160mV. You could try to run the tubes with more current, reduce the plate resistors, but you would need to run them with 10mA idle to gain 20dB of output, which would not be enough, and that's really pushing the design's limits.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

PRR

Re: check out this mic schematic. dual tube transformerless output
« Reply #2 on: February 10, 2010, 08:40:25 PM »
There's no bias reference to the output tube grids.

Output stage far-side is not driven.

V1b has no real function; if it were a Cathodyne it could drive the far-side nice.

V2 each side would have some THD; driven push-pull most of this would cancel.

Maybe they like it as-drawn, maybe there are a few mis-transcriptions.

There's "200dB" of B+ filtering before the Zener. If it needs anywhere near that much, the PS layout will be critical. (But it may just be an over-supply of 22u caps.)

Lot of heat to put under a capsule.

Gus

Re: check out this mic schematic. dual tube transformerless output
« Reply #3 on: February 11, 2010, 08:28:33 AM »
search for "transformerless tube microphone" at this site there are some old posts.

I would use EFs or SFs at the output not a tube

wz5q

    Deep Down in the Dark Dismal Swamps
  • Posts: 1
Re: check out this mic schematic. dual tube transformerless output New
« Reply #4 on: May 12, 2012, 05:44:35 AM »
Howdy Y'all,
I just came across this posting and even though it is very old, I would like to let you know that there were some errors in the original schematic which have been corrected. It looks like the pics above now reflect the changes I have made on my site.
http://www.wz5q.net/index/shack_data/muneo.htm

The Valves were originally listed backwards. They are as corrected as...

V1 is a 12AX7B used as a Constant Current Draw Amplifier (CCDA) which is using V1a as Grounded Cathode amplifier followed by V1b in a Cathode Follower configuration. 

V2 is a 12AU7 used as an impedance matching device.
The factory later added a 2M resister on each Grid on either side of the 510K resistor having an effective 1.113M resistance to ground on each of the Grids.
I had originally transcribed the wrong resistance as 82 ohms for each of the V2 Cathode resistors on the previous schematic. The correct resistance is 820 ohms for each cathode resistor.

The factory lifted the Front Capsule element from chassis ground and added a 51M Resistor in parallel with a .022uf capacitor in between the chassis ground and the Front Element.

The mic works great and has wonderful sonics.
Take Care,
WZ5Q
« Last Edit: May 12, 2012, 05:53:32 AM by wz5q »


 

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