Tube Operational Amplifier

[Osvaldo de Banfield]

Do anybody experimented or work around Operational Amplifiers made only with vacuum tubes/valves (No ss at all)?

I have some ideas, but mu brain is open to newer/different ones. What I need is a differential triode/pentode pair wit inverting and noninverting inputs, one or two inverted outputs.

Any suggestion or example is welcomed.

 

[phaselag]

The op-amp was developed and sold in 1952 by George Philbrick. It was tube based. Used for a number of years, mainly in analog computers.

paul

 

[Osvaldo de Banfield]

Thanks, Paul. I read something about it, but my doubt are the neon lamps in the signal path. Aren't they noisier?

I want to make 3 units to extrapolate an invention of a guy I know into the tube technology, he did it using SS and works pretty fine. By the moment, I reserve the basic idea of the thing.

My current idea is as follows: a (not exactly) differential pair made with a triode and a pentode inside the 8BU11 compactron tube. The last triode as a follower for the output. This tube with filaments grounded at 0VDC. A 6U8 tube, with the pentode as CCS for the pair, an the triode as CCS for the output triode. A neon lamp to give biasing for both CCS, with heaters near the negative rail (I called it Ekk).

 

[Ketje]

The op-amp was developed and sold in 1952 by George Philbrick. It was tube based. Used for a number of years, mainly in analog computers.

paul

He made also models with tubes+transistors.
Mona

 

[Ken Newton]

I think that the first question is why do you desire an op-amp, whether tube or transistor? What is the application?

 

[Osvaldo de Banfield]

He made also models with tubes+transistors.
Mona

Interesting readings.

The purpose: a novel sine wave RC oscillator that uses no classical frequency selective networks. As it isn't my idea, I still can't give further details.

 

[phaselag]

A classic phase shift oscillator uses 3 op-amps with simple RC networks. If you are going in this direction, it has already been done.

Paul

 

[Osvaldo de Banfield]

The project resembles this, but it is not equal to the showed below. It uses different array of passive elements. Nor it is of the Bubba topology.

Sorry, I still have no permission to give more details, because it is under development and perhaps it will be patented. It has been designed in the Campus of an University in Argentina and I am not the creator. Only a second test of the principle.

 

[stocktrader200]

if it is a true op-amp then the negative feedback required to reduce the gain to 10 will increase linearity to the point where it sounds solid state, so why bother.
properly used solid state parts increase the sonic performance of a tube amplifier

 

[tubetvr]

my doubt are the neon lamps in the signal path. Aren't they noisier?

Operational amplifiers was invented for and used to to perform matematical operations like integration or derivation in analog computers, in those applications noise was an issue but not as important as in low level audio amplifiers.

 

[Mark Johnson]

Check this out. link

 

[rayma]

my doubt are the neon lamps in the signal path. Aren't they noisier?

They're not in the signal path, they're over-voltage protection clamps.

 

[Wavebourn]

I spent many hours on this one solving differential equations. Probably it helped me a lot later to design things with nested feedbacks. ;-)

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[Jonathan Bright]

I think there is one on Nelson Pass "passdiy" site. Go to "projects" and hit "amplifiers" then on the Project categories list on the left hand side a number of articles will emerge. About a third of the way down. It is called "DIY op amps"
It is a 2 tube simple opamp. 12 AX7 I think.
Cheers
Jonathan

 

[smoking-amp]

There was the Heathkit EC-1 home analog computer.

Then some VT Op Amp circuits from the book "Analogue and Hybrid Computers" by Z. Nenadal and B. Mirtes 1962

Heathkit EC-1 manual:
http://www.analogmuseum.org/library/heathkit_ec1_operation_manual.pdf

There is a more complex Heathkit Analog Computer, the H-1 too:
Heath H-1 Analog Computer - neurotica.com

and the VT Op Amp for the H-1:
D. C. Amplifier ES-201 Misc Heathkit Brand, Heath Co.; Bento

..

 

[smoking-amp]

The Heathkit ES-201 OP Amplifier schematic (for the H-1 Analog Computer):

 

[Osvaldo de Banfield]

Many many thanks for all inputs. Briefly I will read and answer you all.

 

[smoking-amp]

Then there was the Tektronix Type "O" plug-in. A VT dual OP Amp. scope plug-in. I still have one of these around, nice for an integrator for xfmr. hysteresis curves.

O - TekWiki

 

[Osvaldo de Banfield]

I spent many hours on this one solving differential equations. Probably it helped me a lot later to design things with nested feedbacks. ;-)

Interesting apparatus. Call my attention the lighter, did you want to put it on fire?

 

[Osvaldo de Banfield]

Smoking amp: There was an analog computer like the one in the last pic, in the University I coursed my studies. They destroyed completely, because the chief of the cathedra didn't know what the thing was.