Tube Op Amps Experience/Interests?

[BogeyBass]

Any members have experience
working with or building Tube Op
Amps.

Like to hear or see pictures of experience or projects.
Likewise if you have no experience if you have interests and thoughts on building one and what circuits interest you.

looking to build a 12ax7 or 12at7
based op amp with inverting and non inverting inputs. lower voltage rails possible 120 to 170 volts.

schematic shows general purpose computing Op-Amp from George A. Philbrick Researches. This type was first introduced in 1952/53 had inverting/ non inverting inputs.

 

[BassmanPaul]

It’s much easier to use a pentode such as an EF86 with feed back from plate to grid as a gain stage. There is a vast difference between a computer logic “switch” and an audio amplifier. Tube based op amps have been used for a long time and there are examples out on the Web.

 

[rufus.K]

what did i circle in red?

 

[agedhorse]

IIRC, inductor.

 

[cfsporn]

What's the advantage of using a tube as an op-amp?

 

[rufus.K]

I think is more in the area of novelty over advantage.

 

[cfsporn]

I think is more in the area of novelty over advantage.

I'm always cool with that!

 

[rufus.K]

I'm always cool with that!

I think you know where I stand too

 

[cfsporn]

I think you know where I stand too

 

[seamonkey]

Look at this!
An Op-Amp made with Transistors!
The XL741 Discrete Operational Amplifier | Evil Mad Scientist Laboratories

I heard they'll get smaller when we go to the moon.

 

[B-string]

Looks like a solution looking for a problem.

 

[BogeyBass]

there would be little advantage as far as input output impedance and yes more as a novelty.

Likewise I'm more interested in use for tone circuit, active crossover and distortion harmonics/ character if used for distortion.

It is a fairly simple circuit and good food for thought. always in need of something to read and research. be fun to bench test or discuss. it involves basic op amp topics/ history. high voltage and tubes

 

[B-string]

The world has been waiting for a high noise 741.

 

[BogeyBass]

Tubes can be noisy yes
and any simple audio circuit can be overdriven for distortion.
but we'll designed filters and gain stages become well-known musical distortion. Tube preamp and even all tube amplifiers are still used today. not because of there amazing lack of technology high cost,noise factor,high heat, and not efficient. it's because...of harmonics from low or high amounts of distortion lol. so if your familiar with the basic 2 types of distortion. Clipping diodes in feedback path. or basically driving a opamp/tube/transistor into its supply rail. without being cheesy on descriptions of distortion. emulating the sound of a beam tetrode tube amp being driven into its supply rail. is a certain type of crunch obtained by well known op amp circuits where a inverting amplifier is driven into distortion by hitting the supply rails.

 

[okcrum]

If you want to play with tube op amps you might find one of these; it has 9 of them:

 

[rufus.K]

If you want to play with tube op amps you might find one of these; it has 9 of them:

She's a beaut!

 

[agedhorse]

Tubes can be noisy yes
and any simple audio circuit can be overdriven for distortion.
but we'll designed filters and gain stages become well-known musical distortion. Tube preamp and even all tube amplifiers are still used today. not because of there amazing lack of technology high cost,noise factor,high heat, and not efficient. it's because...of harmonics from low or high amounts of distortion lol. so if your familiar with the basic 2 types of distortion. Clipping diodes in feedback path. or basically driving a opamp/tube/transistor into its supply rail. without being cheesy on descriptions of distortion. emulating the sound of a beam tetrode tube amp being driven into its supply rail. is a certain type of crunch obtained by well known op amp circuits where a inverting amplifier is driven into distortion by hitting the supply rails.

This is a very simplistic proposition IMO.

There are many different types of distortion, you listed 2 of maybe 10 or 15 commonly used forms. You haven't even considered the enormous difference between distortions generated by global feedback type circuits versus local feedback circuits. The transition between open loop and closed loop gain, and what happens with the loss and recovery of feedback in global feedback circuits is very much the elephant in the room when comparing many of these classic (or legendary, or whatever term you wish to use) amps (both pre amps and power amps)

 

[agedhorse]

If you want to play with tube op amps you might find one of these; it has 9 of them:

I used some form of analog computer like that (not Heathkit though) in one of my sophmore EE classes. Pretty amazing to be able to do realtime analog calculations.

 

[toomanyslurpees]

Geeze, I'm a licensed avionics tech turned biomedical tech that does some casual messing with tube amps and I didn't even know a tube op amp was a thing...

 

[Passinwind]

Geeze, I'm a licensed avionics tech turned biomedical tech that does some casual messing with tube amps and I didn't even know a tube op amp was a thing...

I remember looking at getting one of these for my Tek 500 series scope a zillion years ago: Invalid Link Removed

I've occasionally considered doing one with some Russian micro tubes that a friend gave me, but I just don't see the effort/expense/reward proposition lining up in any positive way for any of my current DIY build interests. The biploar HT supply in the original post would be a likely deal killer for me in any case. Never say never though, I guess.