I am trying to produce3 5volts from a 8.something voltage source.
I have tried 3 7805 regulators (2 different types) and they all produce 3.7 volts??
These are 1A Voltage regulators if that makes a difference. Also from 2 different suppliers
Am I missing something?
(pins in order as they appear on the regulator)
Pin 1 in input @ 8volts
pin 3 is common ground
Pin 2 is output @ 3.7volts and I expect 5 volts
I had capacitors etc as recommended by the datasheet and removed them in case they were dodgy.
I have no load on either the supply side nor the output side.
Can anyone advise?
For the questions asked - I am sure it is a 7805 - as per my earlier links. My multimeter is accurate.
With my dodgy power source I was measuring 8.1 volts on the input side and 3.4volts on the output when I had the red LED and a 150Ohm resistor attached.
You have a wall-wart supply that says 8 Volts. I bet it puts out is closer to 6 volts... which is not enough input voltage for the 7805 to work correctly.
My supply voltage is what I have directly measured it as (a repurposed ghetto blaster power supply) using my multimeter. It initially read 11.something but I attached an LED & resistor in parallel to indicate power on ... don't know if that caused it to drop the voltage to 8.something but I am sure it should not. ??
As others are pointing out, there is a potential issue with your pinout. The two datasheets for the parts you link to are slightly different.
The "7805CV" lists the pin out like you do in your post, which is leading people to suggest something there is wrong. Here's the key: how they label as pin 1, pin 2, and pin 3 is different how the industry typically labels a 7805 (or TO-220). Their pin function is in the correct order, but the numbers are nonsense. (They made the middle pin 3, instead of 2 even though the function is still GROUND.)
Use the pinout and pictures of the "MC7805" which shows the pin out people expect to see.
As for the 3.7V are you placing any kind of load on the regulator or measuring it open? You might put a 100K resistor on the output to see if it stabilizes.
The datasheet shows that output voltage is only specified when the output current is >5mA. So with no load, I don't think you can determine if it is regulating or not.
As an aside, what happens if you swap your input and output pins?
Well if you have spare parts, you can always try it and see.
As an aside, what happens if you swap your input and output pins?
It has been my experience that miswiring the 1a 7805 chips can make them very hot, start to smell, and burn the finger tips. Amazingly when rewired correctly it still worked normally.
Probably because they have high-temperature shutdown - or you have good luck. Silicon devices survive till about 175C, fingertips suffer from about 50C. Heat damage can be degradation rather than outright failure - basically the doped areas of silicon start to diffuse their dopant atoms around and drift out-of-spec - it may still work but it might not work well...
Basical rule with electronic circuits is check all the wiring twice - once as you go and once before powering up - saves a lot of money!
But regardless of pin numbering, the middle pin is GND, the first pin (reading from left to right) is INPUT and last pin is output.
This is ambiguous unless you state where the tab is and whether you are looking at the top or the bottom. That's why most data sheets use a diagram to identify the pins.
I placed a 100kOhm resistor across the (expected) 5volt side and measured 3.4volts.
I placed a red resistor (apparently pulls 20mA) and a 150 Ohm resistor across the (expected) 5volt side and measured 3.4volts.
Flipping the regulator so input was attached to the output pin and output to the input pin resulted in a no load voltage of roughly 7 volts on each side.
With the 100kOhm resistor the output dropped to about 6.4 volts.
Surely it is not that difficult to get 5volts from a 5v regulator??
When you have the resistor/load applied to the output and wired properly, what does your input voltage measure? (Now we are testing the loaded voltage of your input supply.)
"I placed a red resistor (apparently pulls 20mA) and a 150 Ohm resistor across the (expected) 5volt side "
I think you mean red LED. The LED will draw whatever current it can, once the forward bias voltage is applied. If it is a 2V forward bias, then there is 3V on the resistor which means 20mA flows through the resistor which means 20mA flows through the resistor. Well that all holds true when you have 5V... Make sure you connected the LED in the correct way.
For the record, the 150ohm resistor alone as a load would be a good test load.
Since nothing else seems to be working, how about a "duh" check - have you verified that your multimeter is accurate? Maybe check the voltage on a fresh 9V battery just to make sure it's not a meter problem?
I decided to try a different power source. The one I was using I had ripped out of an old ghetto blaster and when first measured, was producing 11.7 volts or thereabouts.
I then printed a custom box with necessary groves for the circuit board (holding some diodes and a fuse) and mounts to ensure the transformer did not shift.
I attached a 56Ohm resistor with a red LED (not resistor lol) in parallel with the output and since have measured a little over 8 volts on the output. It is this that I was using as my power source.
(FWIW - it is an interesting build process where I designed a 3D model, sent it to the printer and ended up with a nice box
Anyway - I have just tried using a 12v supply from my ATX power supply (reading 12.3 volts or thereabouts.) The output of the 7805 is now 4.98volts, which is close enough to 5v to set my mind at ease.
So is it possible that the ex ghetto-blaster power supply is the problem?
The LED's lit up well enough.
Anyway - I guess my custom power supply will need to be tossed
So is it possible that the ex ghetto-blaster power supply is the problem?
Yes.
The LED didn't light up well enough, it's tiny load reduced the voltage output massively, that power supply sounds well and truly fuct (further use completely terminated)
some wall wort power supplies don't do any filtering. some are no more then a transformer and a few diodes so the power you were getting might have been more of a half sine wave then DC.
The LED will draw whatever current it can, once the forward bias voltage is applied. If it is a 2V forward bias, then there is 3V on the resistor which means 20mA flows through the resistor which means 20mA flows through the resistor. Well that all holds true when you have 5V... 
Make sure you connected the LED in the correct way.