I wanted to set up a circuit and see what happens.
Previously I was trying to do something different and after gathering a few components my calculations showed a voltage drop across the collector resistor of 23.9 when Vcc was 24 volts :grr
So today I wanted to put together a circuit with a lower base resistor and see 🙈 if it would melt or blow up the transistor I had no idea what it would do.
Here is the schematic
IMG_20250927_003005623 (1).jpg
So I put it together and dialed up the voltage and kept watching for smoke but really nothing bad happened (I don't think) :loco
Also I measured emitter current
IMG_20250927_002925935 (1).jpg
And here are my results
IMG_20250927_003743405 (1).jpg
One thing I am noticing is the lower beta value seems iirc in all the book experiments i did beta was about 170 xP
Seems like the base emitter voltage drop looks good so maybe I was nowhere near Chernobyl territory idk and that wasn't what I was trying to do. I tried to feel if the transistor was getting warm/hot but it's tiny and I couldn't really tell.
My main interest was with the suspected huge voltage drop across the collector how much was gonna be left for the emitter resistor :grr
The classic "universal" values for these ultra simple gain stages is:
3k3 to 4k7 load resistor with 1M Base>Collector. NOT Base>+V as you show.
or
10k load resistor with 3M3 Base>Collector.
The beauty is that it is self-adjusting so it works with almost any transistor, no need for careful selection or trimming.
Try it and post results.
You will see Collector self biases *near* V/2 which is what we want.
Back in the day (in the 80s) I designed and published a series of Magazine articles showing how to DIY a ton of projects, from a single transistor Guitar booster to 6-12 channel mixers.
Many still in use today, 40 years later!!!!
Hey JM are any of those articles/projects around anywhere online? <3)
No Internet in the 80s for the average Joe but now and then some devoted reader scans and uploads one.
I do have a few in some OLD hard disks, pulled from dead computers.
Not promising anything but IF I find one, or two, I´ll post them here.
This is one from the series, easy to find because of, you know, "TOOBZ" ::) , but there are many others, mostly SS.
When I was a kid , "everybody and his brother" had a basic record player, WINCO brand, so pawnshops and old attics are choke full of them, everywhere.
So I published how to turn one of them into a Guitar amp.
This is the modded schematic:
Fahey 5W Musiquero.png
It has *one* error, easy to solve.
To save space, one PCB track goes through EL84/6BQ5 pin 1.
According to datasheet, there is nothing there, and pin is labelled NC, meaning "not connected" .... but on *some* tube brands, they use that "spare" pin to mechanically support things inside the tube.
That support wire grounds signal and mutes tube :(
Mind you, only on *some* brands.
Solution is to, after drilling PCB, using a 5-6-7 mm drill to gently "shave" some copper around the 1 mm socket leg hole so track "ring" copper foil does not touch socket pin.
Veroboards do the same to cleanly cut tracks where needed.
Of course, you can also build it PTP.
Hundreds were made , used in recordings, etc.
This is the El Musiquero magazine, today at the cult/collectible status:
Musiquero 75.jpg
Quote from: J M Fahey on October 02, 2025, 11:28:00 AMThe classic "universal" values for these ultra simple gain stages is:
3k3 to 4k7 load resistor with 1M Base>Collector. NOT Base>+V as you show.
or
10k load resistor with 3M3 Base>Collector.
Try it and post results.
You will see Collector self biases *near* V/2 which is what we want.
Yes sir thanks :dbtu:
I want to do this but alas my apologies I don't know what this means specifically ">"
:'(
I was lucky to figure out or look up what 3k3 and 4k7 means :lmao:
I think they mean 3300 ohm and 4700 ohm ?
xP
Yes.
Dots as decimal separators can easily be lost or added at random when photocopying , so in European notation k=1000 or M=1 Million are used.
Hard to miss those.
3k3=3300
3M3=3.3 Million
nd so on
Also: 2.2 nF = 2.2 nanoFarads=2200 pF is written 2n2
And instead of the Omega symbol which most keyboards do not have, we write Ohms (duh) or simplify it to "r" (resistance) for low-ish values (less than 1k) so, say, 820 ohms becomes 820r, 10 ohms=10 r and so on.
Once you catch where names come from, it becomes natural.
I´ll draw a schematic showing these basic but useful gain stages, a LOT can be done around them.
EDIT: another writing convention, to save space in small caps:
2n2 = 2200 pF is also written as:
222
which is read as
two , two, two zeros = 2 2 00
(https://rees52.com/cdn/shop/products/21068.jpg?v=1702155136&width=493)
definitely compact and easy to read.
Some add extra data:
(https://topsoil.co.in/wp-content/uploads/2022/11/222m-1kv.webp)
They added Voltage (1 kV) and tolerance "M"=20%
We common folks normally find K (10%) and M (20%)
I find it very hard to place a dot in a value these days, it has become such a habit to always stick the denominator where the dot or comma should be in a value.
I cant remember the last time I drew a schematic or made a PCB where I used a dot or a comma in a value of a component, even in voltages which is not that common. I am not sure if it is normal to write 4V5 instead of 4.5V, it looks wrong but I still do it when I design PCB's and stuff.
All one has to do is look up an old Marshall guitar amplifier schematic and it becomes obvious why the dot or commas are no longer used in a value of a component on a drawing.
It is hard enough to make out the numbers on some of the old prints.
Quote from: Tassieviking on October 10, 2025, 08:34:52 AMI find it very hard to place a dot in a value these days, it has become such a habit to always stick the denominator where the dot or comma should be in a value.
I cant remember the last time I drew a schematic or made a PCB where I used a dot or a comma in a value of a component, even in voltages which is not that common. I am not sure if it is normal to write 4V5 instead of 4.5V, it looks wrong but I still do it when I design PCB's and stuff.
All one has to do is look up an old Marshall guitar amplifier schematic and it becomes obvious why the dot or commas are no longer used in a value of a component on a drawing.
It is hard enough to make out the numbers on some of the old prints.
^^^^ THAT
For a long time now I label my Zeners, say, 3V9 instead of 3.9V and so on
The potential fpr trouble is immense.
*Some* values are easy to detect from function or position; others not at all.
And yes, old schematics, such as from VOX are a mess.