- This topic has 9 replies, 3 voices, and was last updated 3 months, 4 weeks ago by LectronFan.
February 19, 2020 at 15:01 #8311LectronFanModerator
When browsing through the circuits posted on this forum, I noticed we’ve forgotten the Wien Bridge oscillator !
Time to gather our Lectron set and build one in a blink of an eye !
Here’s the setup :
After pressing the switch, we hear a warm sounding low tone. This tone is a sine wave.
You’d probably wonder how this works.
Well, we have a 2-stage amplifier consisting of T1 & T2.
The “Wien bridge” consists of the components R1-R4 and C1-C2.
The output and the input of this amplifier is connected to this circuit, so oscillations occur.
We will later get in detail about this circuit and also propose this circuit build with the modern transistors.
February 22, 2020 at 14:03 #8312LectronFanModerator
This is the same circuit with the modern silicon transistors.
To build this circuit, you’ll need a few more connection blocks then included with the base and expansion set.
If you compare the 2 versions, you’ll see the advantage that the legacy transistors have : they have the bias resistor incorporated which saves a lot of connections.
We also have used for R7 a 100K resistor instead of the 330K for biasing T1. Do you think the sound produced will be the same ?
Try it out and compare the results !
May 11, 2020 at 23:30 #8651bodgerParticipant
Those are great builds! I’m trying to make a vacuum tube version, but it’s tricky to get the gain just right.
What did you use to make the good-looking diagrams?
May 12, 2020 at 01:24 #8655LectronFanModerator
A radio tube version would be awesome ! I hope you will succeed in finding the right circuit setup.
The first stage should be an amplifier with enough gain to overcome the losses from the Wien RC network
The 2nd stage must have a low gain to drive the speaker without distorting the sine wave.
For the diagrams, I use Splan from Abacom software. It’s very easy to use. I’ve created a whole Lectron library with many components. I can share it with you.
Here is the link : Splan 7
Splan has enough editing tools like a snap grid and 2 layers.
The snap grid is very easy, When you place a component, it automatically connects to an adjacent component to align.
What I also like is, when placing a resistor or capacitor, it automatically asks you for the value and it will place this inside the symbol.
Also other things like automatic numbering is cool .
May 12, 2020 at 09:02 #8656mwpeters75Keymaster
Thanks as always Frank for all the contributions. Your Splan blocks are especially helpful and your diagrams look like they are out of an Egger/Braun instruction manual. Wonderful!
May 12, 2020 at 21:48 #8659bodgerParticipant
I would be interested in your component library, that would be a real help in creating nice looking diagrams.
May 13, 2020 at 11:27 #8660LectronFanModerator
I’d love to share the Splan libraries I’ve build so far around the Lectron system.
I will make a new sticky post where you can find these and this can also be the place where users can add their own.
Check it out in a while !
May 25, 2020 at 08:07 #8704bodgerParticipant
I built your transistor design, but didn’t have a 300kΩ transistor block without the emitter grounded, so I used two 100kΩ ones. I also didn’t have a 2.2kΩ resistor, so substituted a 3.9kΩ one. I’m making some progress on the vacuum tube version. The triode one didn’t want to work, so I’m using pentodes now. I’m taking some cues from Bill Hewlett’s original 1939 thesis, your design, and some reading. It’s oscillating, but not very stably yet. I’m still working on it.
May 25, 2020 at 08:12 #8706mwpeters75Keymaster
Bill Hewlett of Hewlett-Packard fame. I wonder what he would have thought of the Lectron System. How great that you are using his design specs and building something new, using tubes no less! Very retro and cool!
May 25, 2020 at 15:27 #8731LectronFanModerator
Thumbs up for what you achieve with the Lectron tubes !
I’m sure you will succeed in making the circuit stable.
A sine wave is always delicate. Too much amplification and it will distort.
Too little and will fade out.
I have experienced this too with the phase shift oscillator posted in this forum.
Man must tweak those circuits to have a stable sine output.
I’m sure you will find it !
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