Gonna try to make an oscillator based on this
IMG_20260803_233515614 (1) (2).jpg
I have no idea what values of resistors or capacitors to use
Nor do I even know what where the output is
I presume B+ is gonna be DC piped in to two places
Anyhow I looked in my box of junk and pulled out two ancient transistors hoping they were NPN and they are
IMG_20260804_194542166 (1).jpg
Should be cool 😎
Did it work?
I just assembled this rats nest
IMG_20260804_205530408 (1).jpg
Not knowing where to put the scope probe I attached it to the positive leg of C1
And it looks like the sum of all those randomly selected components has resulted in a malfunctioning diode
IMG_20260804_205537310.jpg
That being said hey I'm glad I got something
Maybe that "waveform" can tell me something xP
So the only cheating I did was glancing at the tube oscillator schematic xP
I noticed they were using much smaller capacitors
So I changed out the two 100 uf for 22 uf and played musical resistors for a while really no change but a cleaner rectified waveform xP
I have decent Vbe on each transistor 0.7 and 0.65
Also voltage across the resistors going to ground xP
So idk should be educational :tu:
So I'm gonna make some BOLD statements here
Some (or all) of them probably wrong
I think it's worth stating that we need the collector of each transistor more positive than the base and the emitter
Since the base of (call it) Q1 and the collector of Q1 get their voltage from the same place then I'm gonna say that R3 needs to drop less voltage so the collector will have more voltage leftover therefore R3<R1
Now looking at Q2 it's collector gets straight up B+ so of course whatever value R4 is the collector of Q1 will be more positive.
But I'm sure it's important what the value is I just don't know xP
And then I think we are good to go with the emitters since they both are at ground ok maybe not I have no idea what values those emitter resistors should be seems like I remember people liked to have em there because it made the circuit more stable.
Btw my condolences to anyone suffering through this i just didn't want to get some premade recipe online or YouTube xP
With that I think I'll meditate trying to see what kind of voltage I need on the base(s)
:'(
Ok time to start keeping records and analyzing results
First I redrew the circuit trying to make it easier to comprehend xP
Then rolled out another configuration
IMG_20260805_105256702.jpg
I feel a fusillade of erasers bouncing off my head as I report this because I should know what it means when an emitter has the same voltage as the collector (I think it means the transistor is in saturation mode). xP
Anyhow I'm gonna stick with CHANGING ONE THING AT A TIME so I don't induce myself or anyone reading this into despair xP :loco
Ugh ok nm
Just looked in some of my books and apparently saturation mode is the max collector current
And I have a bit of a voltage drop across the first collector resistor but hardly nada on the second
Oh well this is cool because it's making me have to think about stuff :lmao:
And whoops
How does a direct short from B+ to the base of Q2 result in a 1.5V drop
Doh 😣
From the looks of your re-drawn schematic, you have moved the resistor from the 'Q2' base to it's collector. We have no emoji for the 'shame shame' gesture we do with our index fingers. :lmao:
Ugh
Yeah I know I literally just discovered that
Ok another revision
IMG_20260805_135644396 (1).jpg
Which I already don't like because there is no collector resistor on Q2 :'(
Look up 'common collector' or 'emitter follower' circuit.
Ugh ok here we go
I'm gonna try to do this like I'm at a job interview or something
I know or think common emitter means the emitter is connected to the ground of the input voltage as well as the output measured voltage
And cathode means emitter
So dude where's my sin waves xP
Quote from: saturated on August 04, 2026, 09:07:55 PMGonna try to make an oscillator based on this
IMG_20260803_233515614 (1) (2).jpg
I have no idea what values of resistors or capacitors to use
Nor do I even know what where the output is
I presume B+ is gonna be DC piped in to two places
Anyhow I looked in my box of junk and pulled out two ancient transistors hoping they were NPN and they are
IMG_20260804_194542166 (1).jpg
Should be cool 😎
That one might be a relaxation oscillator, turning out a weird unsymmetrical "square wave".
For a sine wave oscillators you need THREE capacitors and resistors, like on tremolo oscillators
(https://circuitdigest.com/sites/default/files/circuitdiagram/Simple-Sine-Wave-Generator-Circuit-diagram-using-Transistor.png)
For the full article:
https://circuitdigest.com/electronic-circuits/sine-wave-generator-circuit Sinewave will probably clip a little on one or both peaks because there´s an excess of gain to guarantee it starts oscillating but is good enough.
Do the experiment, they even show a protoboard version, and post results.
That oscillator looks exactly like someone trying to build a two-stage amp, which ends up motorboating or otherwise oscillating. R2 and R5 represent the parasitic resistances due to bad grounding practices. :lmao:
C2 could be a parasitic capacitance between two long, parallel traces.
Ok wow I built that one esteemed Hermano JMF suggested
IMG_20260806_005001259 (1).jpg
:dbtu:
Pretty funny I was digging around trying to find the right stuff....the nearest resistors I had were some ancient Allen Bradley 680 ohm that measured 780 ohm
Then for capacitors I managed to find three 100 nf then used a 222 nf for the 200 then miraculously somehow dug in and found an 88 nf capacitor
I know I have some 2N222 around somewhere but ended up unboxing another rusty leg relic 2N3391A
So I just checked maybe because of the substitutions but if I decrease the voltage the sin wave collapses about 12.45V then comes back alive about 12.7V
I wanted to see how high I could go but my trusty PACO only got to 30V but the tips of the waves are starting to look funny.
IMG_20260806_010108223 (1).jpg
Here's the hastily assembled circuit
IMG_20260806_010141356.jpg
Anyhow wow thanks that was fun
I think the take home lesson for me now is there's gonna be a minimum voltage requirement xP
I decided to take a look at the circuits that used an op-amp to make an oscillator
So I grabbed a book and they used a 741
Ok cool let me take a look at what's going on there xP
IMG_20260806_202051958 (1).jpg
I'm gonna use an old phrase from the classic days of sports center
"It's deep and I don't think it's playable"
:grr
I do remain optimistic that perhaps one day like when I'm 93 might recognize some things in that menagerie xP
And I imagine the pros here break it down into sections xP
Btw sitting here doing some thinking
The circuit that worked utilized capacitors 100x smaller than what I tried xP
And the resistors that I tried were orders of magnitude larger xP
So going back to the original generic schematic that I could not get to work....it used the polarized capacitor symbol so hence I used electrolytic capacitors in my trial runs.
Also referring back to the schematic for the tube generator and I presume MFD means microfarads but idk
IMG_20260802_234407029 (2).jpg
But it could be that there's no reason to compare the two (SS vs tube) because they are completely different animals
At any rate I may try using the smaller capacitors and resistors and see if it works
So the original generic configuration that was attempted I made a big reduction in values for resistors and capacitors
Increasing the power supply slowly I noticed there was something that rapidly appeared and disappeared as voltage continued to increase
So I went back to the narrow range where it would appear and carefully dialed it in and got this
IMG_20260806_233927096 (1).jpg
What's wierd is if I decrease voltage the frequency decreases and if I increase voltage the frequency increases xP
Because it was bugging me that amplitude was not responding to voltage level :grr
Before I shut it down I decided to write down some voltages
The first set is taken when there was the visible waveform or apparition or more likely abberation xP
Then below that is when the voltage was increased to cause the abomination xP to collapse and become a straight line
IMG_20260806_235601209 (1).jpg
Hmm looking at this I don't think the base is supposed to be more positive than the collector but I'm not sure
Maybe I need to increase the Q1 base resistor
Base is not more positive than collector, you have huge voltage drop across that resistor connected to +B
In a working circuit, base is around 0.7V above emitter which is well below collector voltage.
Horrible waveform is typical of a "relaxation oscillator"
Those were much used in TVs, Radars and such, to generate sweep signals.
Think of it like a simplified multivibrator.
Frequency is NOT stable, changes a lot with voltage.
Also, what your meter is calling DC when there is a waveform present is not all DC.
Quote from: g1 on August 07, 2026, 11:17:55 AMAlso, what your meter is calling DC when there is a waveform present is not all DC.
The voice of sanity/reality has checked in :tu:
200w.gif
The "butterfly-like" transistor pair arrangements, where one of them has the base and collector tied together are "current mirrors". The transistors are made together on the same substrated by the same fabrication process and have nearly identical VBE curves. And that includes temperature behavior, plus: the transistors are close together on the same chip and so thermally linked: one won't be hotter than another with a different temperature gradient of its VBE curve.
The VBEs of the current mirror pair are tied together, so whatever VBE is one transistor is the same on the other and that drives the collector current. This relationship causes the collector currents to be nearly identical (i.e. mirrored). By setting up the collector current in one half of the current mirror, the other half generates the same collector current.
The schematic shows several current mirrors tied together: Q8/Q9, Q10/Q11 and Q12/Q13.
The main purpose of current mirrors in amps is that current sources look like very high impedances. It's like a trick for producing a very high resistor, that appears to be sitting on a high voltage. This is particularly valuable on a chip because it's hard to produce large resistors on a chip and takes up space. E.g. if we put a 1M resistor on a 10,000V supply, we would have a 10 mA current source. Provided we used the current source with loads much smaller than 1M, it would look stiff. If we make a similarly stiff 10 mA current source using transistors, it kind of looks like a 1M resistor on a 10,000V supply, in some ways. If we use that as a load resistor for an amplification stage, it produces a lot of gain. Using a current mirror (or other current source) as a load resistor is called "active loading".
You know like when you use a larger resistor for a tube plate, or BJT collector, you get more gain in the stage. But there is a limit; the bigger resistor you use, the more you choke off the current. You can make up for that with voltage to a point. One problem with that is if the transistor shuts off, current stops flowing and then the full voltage appears on the transistor, which may not be rated for it. Active loads will never generate a voltage in excess of the supply. While within their limits for current regulation, though, they look like a giant resistor with a large voltage behind it.
These current mirrors clutter the 741 representative schematic, making it twice as "scary" as a schematic in which resistors play similar roles. Once you understand the mirror pattern, you mentally treat it as one unit.
Hey thanks man that was very generous of you to take the time to offer that info I appreciate it
I need to start paying attention to impedance as it's obviously a major player in these systems
I was just reading about it here actually
IMG_20260809_015934477 (1).jpg
As G1 had me reading about it and this
IMG_20260808_162702614 (1).jpg
I did notice today that I had a pack of 741s also