Toob to transistor conversion

[Neurotic Norman]

Hello all! I'm having a little trouble with a circuit I've found. You see, it was originally designed for vacuum tubes. Since they aren't exactly easy to find or work with, I found a version that has been converted for use with transistors. Here's the caveat: It's untested and the values have been unconverted. Onto my questions:

1. How might one take the values like resistors and capacitors from the original vacuum tube circuit and convert it to the solid state?
2. What would be the best way to prototype circuits?
3. Does it matter if one uses an N Channel JFET or a MOSFET transistor?

Here are some of the sites from which I have drawn the theory of operation and schematics.

The theory of operation: http://www.beam-wiki.org/wiki/Grey's_Turtles

The Original Vacuum tube Schematic: http://www.beam-wiki.org/wiki/Image:Anotated_speculatrix_-1.GIF

The solid state modified version: http://www.beam-wiki.org/w/images/2/2c/Speculatrix_redux.gif

Thanks in advance!

 

[KrisBlueNZ]

Hello Neurotic Norman and welcome to Electronics Point

I suspect this project is really mostly a huge time sink. But I'll try to answer your direct questions.

1. Generally, solid state circuitry works at lower voltages and higher currents than toob circuitry. This generally means that resistor values are lower, and capacitor values are higher. An HT voltage of 45V is no problem for most semiconductors, apart from modern devices that are designed for battery power only, but you may want to reduce it to around 30V so you can use commonly available JFETs such as (2S)J11x devices which are rated for 40V maximum.

2. Prototyping can be done on solderless breadboards. That circuit does not operate at high speed, so stray capacitance is not a problem, nor does it operate at particularly high voltages. Standard breadboards should be fine.

3. Yes. MOSFETs are not an appropriate equivalent. Toobs are functionally similar to N-channel JFETs, but toobs have multiple grids, whereas JFETs only have one - the gate, which is equivalent to the control grid of a toob, i.e. the grid closest to the cathode. JFETs don't have an equivalent of the suppressor grid or the screen grid.

The designs in the articles you've linked to are not fully defined. For example, if you gave that to an engineer and said "build that for me", he/she would say "there's not enough detail". In my experience, this attitude of providing a vague design idea is common among folks who are more enamoured with the vague possiblities for interesting behaviours of an idea than with the practicalities of construction, and in my opinion, it is a symptom of a lack of discipline combined with an attitude of "try it and see what you can make it do", which is antithetical to the engineering approach of "make it exactly like this and be sure it performs according to these clearly defined criteria".

This is nowhere more in evidence than in the last link you posted, where a schematic is shown with no component values! Personally I think that if you're interested in making a "sentient" turtle, you would have more success getting involved with microcontrollers, where behaviour is clearly determined, rather than being interpreted "after the fact" to fit into a vague perceived "complex physical behaviour" (to quote one of those links).

 

[bigrededge65]

Hello all! I'm having a little trouble with a circuit I've found. You see, it was originally designed for vacuum tubes. Since they aren't exactly easy to find or work with, I found a version that has been converted for use with transistors. Here's the caveat: It's untested and the values have been unconverted. Onto my questions:

1. How might one take the values like resistors and capacitors from the original vacuum tube circuit and convert it to the solid state?
2. What would be the best way to prototype circuits?
3. Does it matter if one uses an N Channel JFET or a MOSFET transistor?

Here are some of the sites from which I have drawn the theory of operation and schematics.

The theory of operation: http://www.beam-wiki.org/wiki/Grey's_Turtles

The Original Vacuum tube Schematic: http://www.beam-wiki.org/wiki/Image:Anotated_speculatrix_-1.GIF

The solid state modified version: http://www.beam-wiki.org/w/images/2/2c/Speculatrix_redux.gif

Thanks in advance!

It is sad that the only other person to answer you has died. I too am interested in your question. May or may not be for the same reason. I like the look of some of the old radios but want to be free from tubes. Also, I would like to add modern things like CD, USB, and newer turntable. Sure, I could put 100% new items in the cabinet or radio but would it fit the tuning and volume locations? That is why I'd want to convert the old chassis to transistor; so I keep the old chassis with its tuner but with new parts. Probably clear as mud but that is my desire.

 

[hevans1944]

It is sad that the only other person to answer you has died. I too am interested in your question. May or may not be for the same reason. I like the look of some of the old radios but want to be free from tubes. Also, I would like to add modern things like CD, USB, and newer turntable. Sure, I could put 100% new items in the cabinet or radio but would it fit the tuning and volume locations? That is why I'd want to convert the old chassis to transistor; so I keep the old chassis with its tuner but with new parts. Probably clear as mud but that is my desire.

Please look at the posting date before responding to an ancient thread. The original poster was only seventeen years old and posted here only once. Obviously a "drive by" poster who just wanted a quick answer. When he didn't get it he moved on. Maybe he will see these "recent" posts and respond, but I doubt it. Perhaps a moderator will close this thread.

 

[bigrededge65]

Please look at the posting date before responding to an ancient thread. The original poster was only seventeen years old and posted here only once. Obviously a "drive by" poster who just wanted a quick answer. When he didn't get it he moved on. Maybe he will see these "recent" posts and respond, but I doubt it. Perhaps a moderator will close this thread.

I understand. The thing I was really talking about was the fact that the fellow had died. I was thinking of taking some old cab radios that had little value in the repaired state and putting in solid state. I was wondering if any part of the original parts could be reused in a solid state conversion. I have since found some circuits for building a solid state AM radio from scratch. Seems like a much easier task than conversion and potentially less costly.

 

[hevans1944]

The thing I was really talking about was the fact that the fellow had died.

I briefly knew Kris before he suddenly died at much too young of an age. He was truly remarkable and is much missed in these forums. Kris would answer a question in considerable detail, including an annotated schematic and parts list with his response. And he did it for free! I have never met anyone quite like Kris, although a current member, @danadak comes close in the quality of his responses.

At one time I rescued a large console radio that was probably manufactured in the 1930s. This was in the 1950s and tubes were available everywhere, especially in drug stores, for servicing television sets. So I was able to get it working again, but it still was POS compared to a modern (1950s) radio. I once repaired my grandmother's All American 5-tube AM/FM radio, after which she considered me to be some sort of electronics genius. Her husband was a retired electrician, so I doubt she was much surprised.

Anyhhoo... welcome to MakerPro. I hope you enjoy visiting us and sharing in the dialog.

 

[danadak]

There are folks in Amatuer radio that have converted shortwave receivers to transistor using
some of the components (but few), like IF Transormers and tuning caps and some coils.

But it really is a ground up design, not a simple task, to do it right.

This gent has done seval :

Example

In the old electronics mags there were articles creating a pin for pin drop in replacement for
a tube, maybe Radio Electronics or Electronics world as I recall. You can get old copies here
for free. This place has an enourmous collection of magazines :

WorldRadioHistory: Radio Music Electronics Publications ALL FREE

WorldRadioHistory: Thousands of Radio Music Electronics Publications ALL FREE

worldradiohistory.com

Regards, Dana.

 

[Harald Kapp]

thread from 2014 -> closed.