Blog Pages

11/21/13

VARIAC VOLT METER

I can't live without my variac. Every Line operated circuit I design gets powered up by slowly turning that big fat knob from 0 to 120V. The challenge, however, has always been knowing when to stop turning so you don't accidentally smoke your circuit.

Most inexpensive variacs don't give any indication of output level except a cheesy sticker on the top of the unit which isn't very accurate. Some mid level variacs may include a very small analog type volt meter. In my experience those cheap indicators don't have adequate resolution and are not always easy to monitor while powering up.

So, my solution in the past was to put a big ugly black mark on the top sticker to indicate where I needed to stop. Thankfully, those days are in the past because now there is a much better solution.

  Trenton Blizzard Variac DMM

While setting up for radiated emissions testing at Northwest EMC in Irvine, California, I noticed this cool looking blue LED readout they had plugged into their power outlet in the 10 meter chamber. It turned out that those little meters are made by Murata and are available in Red and Blue.






Trenton Blizzard Dual DMM

BLUE Part # DMS-20PC-1-LM-BF-C
RED Part # DMS-20PC-1-LM-F-C

They are available from electronics retailers such as Mouser and Digikey (see part numbers). They aren't exactly what I would call cheap at $65.00 each. However, the peace of mind they provide I feel is worth at least having one in the lab hooked up to the variac at all times.

Thanks for reading,
Trenton

11/16/13

POMONA TEST ADAPTERS

1/4" - BNC

Having the right tools for the job makes designing and testing audio equipment much more enjoyable. Test gear, such as function generators and oscilloscopes, typically use BNC connectors. Guitar amplifiers typically use 1/4" jacks for inputs as well as speaker outputs.

For connecting test equipment, with BNC connectors, to guitar amplifiers, with 1/4" jacks, I use Pomona 1/4" to BNC adapters.
 

These adapters connect right to a standard BNC-BNC cable. They are available at electronics retailers such as Mouser and Newark. The Pomona part number is 1297.

They can cost anywhere from $10-$15 each and they are totally worth the price. I highly recommend you get a couple for your test bench.







One note: these adapters are "unbalanced". So, keep that in mind when testing.
Thanks for reading,
Trenton

11/3/13

1176 DC MEASUREMENTS

1176 & NIXIE TUBE DMM

I started to measure the DC potentials inside my 1176 kit when I remembered I had this old nixie tube digital multimeter. After digging it out from underneath a small mountain of gear I proceeded to dust it off and see if the little beast even worked. After probing around for a while I discovering that it wasn't very accurate when it measured only 9 volts for the negative 10 volt source. So, I decided to abandon ship on that idea.

 CLASSIC VACUUM TUBE SCOPE

But, while I was busy reminiscing into the technical past I decided that I should also use my old Tektronix vacuum tube oscilloscope at the same time. I ran a few different signals through the 1176 until it made a good signal on the CRT.


THE GLOW OF TUBES

This older gear is just too cool! The scope is an absolute engineering work of art! The glow inside the cover was so enticing that I just had to take a quick shot of the tubes.






INSIDE THE NIXIE DMM

The Nixie tube DMM is also very cool inside. It's made up of logic IC's, open frame rotary
switches, carbon composition resistors and a pair of Nixie tubes. How cool is that.....






PROGRESS

Finally, after an hour or so of being completely distracted by all of the old test gear, I did actually manage to make some useful DC measurements inside the 1176. I will post them soon.

Please stay tuned,
Trenton