Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st June 2008, 06:19 PM   #11
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
Umm.... Ken,
Two inversions = piece of wire. Nice try though!

Maybe ground the grid of the output 1/Mu tube and take the output signal off the cathode. (probably get 1/(Mu-1) for inverted tube , so will end up with -Mu/(Mu-1) overall gain.

(Guess we posted at the same time)
Don
  Reply With Quote
Old 22nd June 2008, 02:45 PM   #12
oldeurope is offline oldeurope  Germany
diyAudio Member
 
Join Date: Mar 2008
Default searching for a unity triode ...

Quote:
Originally #11 posted by smoking-amp
... Maybe ground the grid of the output 1/Mu tube and take the output signal off the cathode. (probably get 1/(Mu-1) for inverted tube , so will end up with -Mu/(Mu-1) overall gain.
...
Don
Hello Don, hello forum
whow you mean the "triode transformer mode".
This isn't an "inverted" triode. I the "inverted mode" '<1/. See graph.

I am searching for a unity triode as a phase inverter.
Something like the triode section of the ECLL800 because
it is an inverter as simple as can be. It provides excellent
power supply riple rejection, low output impedance, no
negative feedback, very low input capacitance, excellent linearity and
a high well known factor.

I'll leave the 6080 in place, it takes much filament power
but it does this job very well.

Thanks for the replies,
Darius
Attached Images
File Type: jpg triode_transformer_mode.jpg (45.6 KB, 381 views)
  Reply With Quote
Old 22nd June 2008, 06:07 PM   #13
kenpeter is offline kenpeter  United States
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
You mean like this?
Attached Images
File Type: gif unity2.gif (22.6 KB, 359 views)
  Reply With Quote
Old 22nd June 2008, 11:13 PM   #14
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
"You mean like this?"

Yup!

"This isn't an "inverted" triode."

Oh. I see Steve Bench uses opposite DC voltages for his inverted triode. But the AC operation is nearly the same either way. I think Frederick Terman came up with the scheme using reversed DC voltages a long way back: (Electronic and Radio Engineering, 4th edition, page 209 or "The Inverted Vacuum Tube ..." Proc. IRE vol 16, p 447, April 1928)

As Ken has it drawn now, I think the second tube gives 1/(Mu-1) voltage gain at it's cathode output if loaded by a CCS instead of a cathode resistor. But reduced gain with a resistor load of course.

Unfortunately, the first tube won't be getting near its ideal Mu voltage gain though with the low input impedance of the 2nd tube's plate loading it down.

Using a pentode (for V2) with screen grid input and cathode output (grounded grid1) would give higher input impedance. (plate at B+)

Going even further out on a limb, how about running the screen grid at some negative voltage to get very high input impedance there, with the plate at B+, and a CCS pulling down (negative) on the cathode output. (Grid1 grounded. The CCS would pull the cathode down enough to make the grid1 to cathode positive enough to cancel out the negative screen grid bias) Now it looks like a REAL 1/(Mu-1) triode.

Now lets see. Get rid of the 1st inverting Mu gain tube and use a pentode for the sole gain stage. Input at the negative screen grid with output at the plate (pulled positive to B+ by load resistor). CCS pulling down (negative) on the cathode with grid 1 grounded. Adjust plate load resistor for unity gain.

Darn...., puts out constant current on the plate. Maybe use a cathode resistor instead of CCS.



Don
  Reply With Quote
Old 22nd June 2008, 11:24 PM   #15
jon_010101 is offline jon_010101  United States
diyAudio Member
 
Join Date: Nov 2005
Quote:
Originally posted by smoking-amp
Going even further out on a limb, how about running the screen grid at some negative voltage to get very high input impedance there, with the plate at B+, and a CCS pulling down (negative) on the cathode output. (Grid1 grounded. The CCS would pull the cathode down enough to make the grid1 to cathode positive enough to cancel out the negative screen grid bias) Now it looks like a REAL 1/(Mu-1) triode.

I now wonder how a 1/(Mu-1) triode would perform with Mu=1
  Reply With Quote
Old 22nd June 2008, 11:58 PM   #16
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
"I now wonder how a 1/(Mu-1) triode would perform with Mu=1"

Oops.... Looks like all those 1/(Mu-1) 's above should be 1/(Mu+1) I was adding the cathode voltage shift effects into the plate to cathode voltage with the wrong polarity.

Tube Mu = 1 example:
Lets say the plate shifts positive by 2 delta (with respect to ground) and the cathode shifts positve (with respect to ground) by one delta. Then the final plate to cathode shift is 1 delta and the grounded grid to cathode shift is -1 delta. So internal to the tube (referenced to the cathode), the Mu of 1 (-1 actually since it is inverting internally) is observed, but externally (referenced to ground) Mu of +1/2 results (+2 delta in on plate for +1 delta out on cathode).

Don
  Reply With Quote
Old 23rd June 2008, 04:59 AM   #17
kenpeter is offline kenpeter  United States
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Well, the way I figured, as long as the voltage difference between
input and cathode(triode1) was matched by an inverse inbetween
output and grid(triode2)... And both share the same plate voltage.
Both triodes would conduct the same. Any AC at the plates would
represent only the power supply ripple...

As input differs from inverse at the output, we begin to see a very
large voltage swing at the common plates. How does this translate
impedance and Mu? I am not really sure...

I had reason to suspect it might be x*Mu/Mu close to 1, but the
cathode resistor at the output may be fighting me... I do not yet
fully understand the fourth (or fifth) topolgy.

Seems to me very similar to inverted triode, except the plate still
has the higher voltage, and the grid does not conduct. 1/(Mu+1)
instead of 1/Mu you say???

I am sure there are slightly mismatched triodes where this works
out to 1. And Mu lines of triodes are only constant if the current
is also held so. If one triode was deliberately run with a slightly
lesser idle current than its twin, the one starved of current would
have less Mu.

If your formula holds true. We only need a Mu of oh-say 15 on
the input triode and 1/(14+1) on the output. To have unity gain.

But does it really work like that, or am I just dreaming it?
One of these days I gotta figure out how LTSpice works.
Right now, I'm only using it to draw pictures...
  Reply With Quote
Old 23rd June 2008, 08:33 AM   #18
oldeurope is offline oldeurope  Germany
diyAudio Member
 
Join Date: Mar 2008
Default #14 #17

Quote:
Originally #17 posted by kenpeter

...
But does it really work like that, or am I just dreaming it?
One of these days I gotta figure out how LTSpice works.
Right now, I'm only using it to draw pictures...
Hello kenpeter,
no, you are not dreaming. You are discovering the "fourth circuit topology".
Be careful, this is against the forum rules.
I am using this topology to build DC coupled tube pre amps,
tube based operational amps and e.g. the RIAA 2007.

Quote:
Originally #14 posted by smoking-amp
"You mean like this?"
Yup!
"This isn't an "inverted" triode."
Oh. I see Steve Bench uses opposite DC voltages for his inverted triode. But the AC operation is nearly the same either way. ... Don
Hello Don,
it isn't. The "inverted" triode is a different kind of triode with grid outside.
In german the inverted mode is called "Aussensteuerung".
I don't know the english word for it.

Kind regards,
Darius
  Reply With Quote
Old 23rd June 2008, 04:26 PM   #19
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
Looking back at the schematic in post #13:
http://www.diyaudio.com/forums/showt...10#post1545510

I later commented that the plate input Z of the second tube would be loading down the Mu gain of the 1st tube. This is fixable by putting a CCS in for the pullup load resistor for the two plates up to B+, and by using a CCS of 1/2 that current for the output tube cathode load. The CCS in the cathode makes the plate Z go very high as long as no additional load Z is connected to the cathode output (so fine for driving the next tube's grid). So it would seem workable to get Mu1/(Mu2+1) overall gain. But two tubes, to do this, does seem a bit extravagent still.

"it isn't. The "inverted" triode is a different kind of triode with grid outside."

Well, DC wise, yes they look quite different, since the cathode current always goes to the positive electrode in each case. But AC wise, they are the same. The relative Mu factors just depend on electrode capacitances to the cathode. Output signal does however have to use an electrode with current thru it, so different there.

For a "really inverted" tube, look at the ionization gauge tubes that have a wire in the center for the plate (at neg. pot.) and the cathode filament is outside the spiral wound grid (wound around the "plate") with positive voltage on it. (positronic tube)

Looking back at the speculation at the end of post #14, using a pentode, this is looking workable and just uses one tube section:

Model:
Pentode with a plate load resistor to B+, and output from the plate. Grid1 grounded. Grid2 as input with moderate negative DC bias on it (high Z input). Cathode with an un-bypassed, fairly high value (maybe 100K) resistor to some negative B- (DC tube idle current set by the cathode resistor and B-). A pentode with lowish Rp would be best I think so as to get closer Mu ratings between grid2 and plate. The plate load resistor can then be used to adjust the final gain down to unity. (DC operating current would need checking as to whether the grid1 dissipation, from intercepted current, is being exceeded. ie, make sure grid1 is well below glowing level)

Don
  Reply With Quote
Old 23rd June 2008, 04:50 PM   #20
oldeurope is offline oldeurope  Germany
diyAudio Member
 
Join Date: Mar 2008
Default #19

I feel very sorry Don,
but I can't find anything that makes sense to me in your post #19.


Darius
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Unity gain inverter emogstad Chip Amps 1 10th June 2009 03:09 PM
Phase inverter ThSpeakerDude88 Tubes / Valves 37 29th August 2007 03:15 PM
6C8G phase inverter engels Tubes / Valves 4 4th February 2007 06:01 PM
Unity buffer from 7-pin triode? aletheian Tubes / Valves 11 16th December 2006 10:40 PM


New To Site? Need Help?

All times are GMT. The time now is 11:49 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki