Greetings. I built the transistor/capacitor/heatsink 5V output for my gauges. I hooked the assy. across a 12 V battery to test the output, and it was 7.0 V. I double-checked the transistor number, and it is correct (not to say the transistor is truly correct). I know the transistor got hot while soldering, but I'm pretty good at soldering, and it did not get hot too long. Questions:

Could the heat of soldering increased the V output 2.0 degrees? Kinda doubt it.

If I test the assy. by putting full car battery 12V through it briefly, would that destroy the components? A 7.0 V reading suggests the transistor is not destroyed by such a test.

I've built another assy, using the same transistor part no. 7805. I think the cap is only 10 uf. What would be a better way to check the assy's. output?

Could I run the gauges on 7V, or would they read falsley hi or low?

Super close to getting this 8 year project back on the road, so please help if you can. Thanks!!!!!!!!!!!!!!!

No, the heat should not increase the output by 2v. Melting the silicon or the internal bonding wires would pretty much be guranteed to have a much more damaging effect.

Double check your connections to the 7805 to make sure you don't have 2 of the leads reversed; I suspect that is the case. Do you have a diagram depicting the pins out of the 7805 package?

And, are you measuring the output voltage from ground to output? You could get 7 volts if you had your voltmeter connected between input and output.....

I am not sure what you mean by 'putting 12 volts through it'. The 12v goes from IN to Ground (pins 1 and 2) and the output is from OUT (pin 3) and is referenced to Ground (pin 2).

By the way, this is not just a transistor, it is a single packaged integrated circuit. This ought to produce a very stable 5V even down to no load current.

You were right on, nm9stheham.
I was measuring between the input and output pins. Made sense to me to measure between those, but I'm ignorant of what's inside that black little box. Measuring between pin 3 and ground gave a nice, 5.00V.

"Putting 12 V through it" should have said, "Applying 12 V to it."

A little more excitement to motivate me towards the goal line. THanks
for taking the time to help!!!!

Cool ! It's always good to find the 'problem' AND the reason!