Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => AmpTools/Tech Tips => Topic started by: sluckey on February 18, 2022, 06:28:37 am

Title: Cheap LCR meter
Post by: sluckey on February 18, 2022, 06:28:37 am

Cute meter. Even cheaper in the USA...

https://www.amazon.com/Proster-Multimeter-Capacitance-Resistance-Inductance/dp/B071WNNYQT/ref=sr_1_3?keywords=proster%2Blcr%2Bmeter&qid=1645187044&sprefix=proster%2Blcr%2Caps%2C93&sr=8-3&th=1

Title: Re: Cheap LCR meter
Post by: sluckey on February 19, 2022, 02:58:02 pm

So I decided to buy this little meter. Just got through testing it. I had no inductors handy, so I just checked resistors and capacitors, comparing to my Fluke 87V. It matched the Fluke on all resistance checks, 1Ω up to 10M. And it surpassed the Fluke on capacitance. My Fluke doesn't do caps below about 1000pF, but this cheap Proster LCR Meter accurately goes right on down to 10pF (smallest value in my bench stock). The largest cap I had was 250µF and the Proster and Fluke were right on.

This meter is not tough, so don't drop it. And there is no prop up stand, so it has to lay flat. But the display tilts up! The case is a bit tight, but you can put everything in it and still zip it up.

Well worth the money. I'm happy. BTW, you can find several demos on youtube.

Title: Re: Cheap LCR meter
Post by: pdf64 on February 19, 2022, 04:53:38 pm

No spare OT handy as an inductance test piece?

Title: Re: Cheap LCR meter
Post by: PRR on February 19, 2022, 04:57:38 pm

What is the frequency of the inductance test? (Meter a speaker and hear the pitch.) Iron-core chokes will be much smaller above 400Hz than below 200Hz. If it sings instead of growls, it's not telling the audio (or power ripple) value.

Title: Re: Cheap LCR meter
Post by: sluckey on February 22, 2022, 03:59:10 pm

I finally decided to test PRR's idea. Sure enough, I could barely hear the tone in a speaker so I looked at the meter output with a scope. The LCR meter uses a non symmetrical square wave, approx. 1200Hz for the 200µH scale and about 400Hz for all others.

The speaker really loaded the output and made the signal look terrible. These scope pics are just with the scope connected to the meter leads.

I did measure the inductance of several OT primaries, with similar results for each one. But I had no data to compare to see how accurate the measurements would be. The only inductor I have that has a value stamped on it is a 15µH. It measured at 18µH.

Title: Re: Cheap LCR meter
Post by: PRR on February 22, 2022, 04:49:13 pm

> only inductor I have that has a value stamped on it is a 15µH.

Probably not an iron core?

What does it say for a Champ/Valco/etc output transformer? 10 Henry is the expect ballpark for the bottom of the audio band, where it matters "to us". Maybe 300mH for the speaker winding.

Title: Re: Cheap LCR meter
Post by: shooter on February 22, 2022, 05:28:55 pm

the asymmetry may be to allow the electro-magnetic field to collapse before smacking it again.

Title: Re: Cheap LCR meter
Post by: 72Blazer on February 26, 2022, 06:55:45 pm

Just bought one.  None of my meters will test low pf value silver micahs.  Thanks for the info!

Title: Re: Cheap LCR meter
Post by: 72Blazer on March 01, 2022, 04:53:17 pm

Got it today.  Works great.  Even came with a battery.  I can finally test the pesky pFs!  Thanks Sluckey for the info.