Friday, March 22, 2019

Using general purpose components -OR- TUN TUP DUG DUS circuits

This 1974 magazine uses general purpose parts to design and build circuits. A reader could build the circuits with whatever they had on hand and not be trying to locate and buy parts specified in the magazine.
It is a good plan so I'm posting the article. The names are a little strange and it doesn't allow for Germanium transistors but it is a start.

I use this ohmmeter test but use a 1K resistor.The skin resistance can vary quite a bit. The 1K resistor gives repeatable results.

A sample circuit from the same source.

The amps I've been building have been using Germanium transistors. I've used GSS109, MP40, MP16, MP39 and P416 with good results.

Saturday, March 16, 2019

Where to buy Variable Air capacitors

Variable Air Capacitors

Follow the link and you will find these for sale:

Good product and good service. The V- Cap is the hard to find item today but Mike has them. Now you know you can get one and get building.

Monday, March 11, 2019

What's it - part 2

I found some boards being sold as scrap. Harvest the gold......
The gold I see is the old components that are not being made any longer. A little research lead me to believe they are the first junction transistors made by TI. The story line goes like this. TI bought a license and the machine to make them from IBM. TI produced them for IBM. The numbers should have a date and component ID in them. In that day they even gave each device a serial number (some not all). So I make a giant leap and say it is an IBM device made by TI and excess IBM couldn't use was sold to GE. So what's in that TO5 can?
WOW! It took good eyes to set them up to be soldered? Maybe the machine did it??
A little more detail. The die is mounted over a hole in the base plate and the wire passes thru the hole to be soldered on.
The can is the base and the leads are emitter and collector.
I removed the top on a couple I had in the parts bin to see how they compare to the IBM.

My pictures are not as good as theirs. They probably used a real camera. I'm using a cell phone. They do appear to be made using the same design.

* The ones I disassembled are Russia 39B PNP.

** The boards arrived. I found four transistors with different marking. They all tested good. They were all PNP types with different ß and forward voltage. The Transistor Museum had an article showing some like mine and noted they have different colored epoxy filler. They questioned if the color was a code, maybe type ID? I tested some green and black ones. They were all PNP but did have different ß and forward voltage. If there is a code I failed to see it.

Friday, March 8, 2019

What's It?

What I know.
It's a 1960s circuit board.
Probably IBM (patent) transistors, made by TI for GE.

Thursday, March 7, 2019

Plate Bend or Square Law detection.

That dog gone knee again. I saw a post equating Plate Bend detection to class B operation. Study the graph and you can see it is not. Below the knee the signal distorts and distortions = detection.

Tuesday, March 5, 2019

Voltage gain Vs Power Gain

You can use the amp for headphone or earbud. I designed it for my earbud. I buy them at dollar tree for a $1 each. They have headphones too, I like the ear bud better. Any way I ran the sim for both so you can see how that works.
With my earbud I get 175mv-pk.
With the headphone I get over 400 mv-pk. So which is better? The one you have of course. Oh well if you have a choice which would perform better with this amp?
Wow 75 uw should drive the headphone well. Actually 1 or 2 uw will drive a sound powered phone well.
But look at the ear bud. Close to 500 uw. Yes the ear bud will produce as much sound as the headphone. The earbuds are rated 90dbm - 110dbm and the phone is rated up to 120dbm. The phone is a little more sensitive but the amp will drive the earbud harder with a smaller input.
I have been using this amp to drive a single earbud. The plug was bad on the bud so I split the cord and made 2 singles. The little amp drives the single bud very well.