What test equipment do you use?

[gonzothegreat]

I've been working on fixing gear that has been gathering dust in storage for a while and I was wondering if I should get a distortion analyzer. The only person I've seen mention a DA is (trumpets) Echowars in a bias tweaking thread.

Aside from a DMM, audio oscillator, oscilloscope and a good dummy load, what else is on the "must-have" list? I have a cap ESR checker and a transistorized VTVM but most people probably don't need those.

I need to put together a good dummy load that will take 250W and keep smiling. I don't think the one in a Sencore stereo analyzer will be up to the task. It would probably end up like a famous smoke filled scene from Fast Times At Ridgemont High

 

[Chad Hauris]

I have been able to fix all problems in audio equipment with a digital multimeter and a tube tester. For an audio test signal source I use a portable radio with alligator clip leads from the headphone jack and just use my ear to the speaker as the output indicator! Also I have a pair of test speakers on the bench.

The ESR tester I've heard is good for checking caps in switching power supplies...do not have one so can't personally testify to its results.

If there is a problem that is causing distortion it usually shows up as incorrect voltage readings...so as long as it sounds good, and bias voltage, etc. are at proper levels, I don't feel the need for more analysis.

The only times I have used the scope is to check oscillators like the chroma oscillator in color TV...have not really found the need for it in audio. The one time I think it could be useful is if you have an ultrasonic oscillation in an audio circuit that could destroy tweeters/cause an overload...the scope would let you see it.

The most important piece of test equipment I have found is the manufacturer's service literature or the Photofact folder. I've found that especially on transistorized equipment, its almost impossible to do a professional, successful repair job without it, unless the problem is very simple like a shorted diode, noisy controls, etc.

 

[Morden2004]

Hey, great thread.

And, just in time as I'm assembling test gear to do future DIY projects.

Over the past 3 months I have purchased a lot of test equipment - most thru eBay.

I have a tight buget so I have had to pass on a lot of really great gear at terrific prices but when 1 item is $200 or greater I have to pass.

I have the following:

1. Tektronics 465B Dual Channel Oscilloscope (100 Mhz)
2. Fluke 8060A True RMS Digital Multimeter
3. RCA WA-44C Audio Generator
4. Philips PM5324 HF Signal Sweep Generator (100 Khz - 110 Mhz)
5. Fluke 1910A Multi-Counter
6. Realistic Sound Lever Meter

I asked some very knowledgeable techs over in the FMTuners Group on Yahoo! for suggestions on Signal Generators and they suggested the following models suitable to do alignments on FM tuners (one of the missions I have in the future); HP 8654A, HP 8654B, HP 8640A, HP 8640B, HP 8601A, and HP 102X. However, the Philips HF Generator came up (and local too) and they agreed that the specs were fine for my needs - so I grabbed that one.

Still on my list of items to own is a Distortion Meter. For distortion analysis the HP 331A was recommended by the Yahoo! group.

As for cost, here are the prices I paid for some of those items above;

1. $81
2. $62
3. (donated by a friend)
4. $140
5. $72
6. (bought new many years ago)

Paul

 

[Morden2004]

I forgot all about the dummy load.

I recently lucked into a batch of high power wire-wound resistors (on eBay, of course! ) and I now have a set of 8 ohm 300 watt resistors - enough to build a 2 channel dummy load.

Cost - about $20.

Paul

 

[Lefty]

I also have a pretty good stock of test equipment that I have aquired over the years. Scope, DVMs, audio generator, LCR tester, resistor decade box, etc. I do lack the specialized types that would allow for FM tuner alignments and lack a distortion analyzer. Always thought I might build a DA if I needed one.

One type I would like to have or build is a good semiconductor tester. I just use the ohm meter method to look for gross shorted or open devices, but always thought a decent tester would be nice to check for leakage, beta valves, etc. Any suggestions on nice semiconductor tests or DIY plans for one?

Lefty

 

[Dan ʕ•ᴥ•ʔ]

Mine is fairly basic, but serves my needs.

Fluke 79 Series II Digital Multimeter
Fluke 80TK Thermocouple Module
Temna 72-505 Portable Audio Generator
Bias King Pro Dual Digital Bias Meter
These items all fit snugly into a Fluke hard-case.

And:
Micronta 22-220 FET Analog Multitester
Weller WLC-100 Soldering Station
Bulova Instrument Demagnitizer
Realistic 33-2050 Analog SPL Meter
Hoyt Analog AC Voltmeter (old, but spec on)
Eico 'Silly-Scope (very old, not very reliable and out on loan)
H-P Audio Generator (very old and out on loan)

 

[House de Kris]

I too have barely the basics. My humble list:

-Fluke 199 Scope/meter, wish I'd waited for the 199C with color display, but B&W good enough for me.
-Lots of adapters to convert between BNC/SMA/SMB/SMC/RCA/F/banana.
-HP 339A Distortion Measurement Set, very touchy, but usually can make a good measurement.
-Philips CD player and test CD for general purpose test tones.
-HK40 test speakers.

Currently building a dummy load. I find it amazing several of us are doing similar things at the same time. I'm also trying to decide if I should pick up an HP4284A precision LCR meter for winding my own inductors.

 

[Mr Natural]

VariAC's..?????
Anyone still use one? Man, I just cringe at the thought that you guys are turning on unknown equipment at full ac voltages And don't forget a big ole ammeter to go along with it. That was SOP 30 years ago, working on tube stuff.
Now that I do RF stuff these days, BIG current draws don't scare me anymore...so when I fry a $300 space qualifed FET

 

[RocknRoll]

Lots of great advice here. A multimeter is all you really need. All the rest is really usefull for those hard to diagnose problems. The hands, eyes and brain are about the finest tuned instrument one might have. Everything else is just a 'tool' :headscrat

 

[Rob]

I have two portable variacs with power cord and outlet on them constantly on the go around here. They are "no bout a doub't it"one of the most useful pieces of lab gear I ever owned!

 

[Dan ʕ•ᴥ•ʔ]

Nah, everything I work on has just come out of service. The amps may show up broken, but only became so recently.

 

[gonzothegreat]

Originally posted by Lefty
One type I would like to have or build is a good semiconductor tester. I just use the ohm meter method to look for gross shorted or open devices, but always thought a decent tester would be nice to check for leakage, beta valves, etc. Any suggestions on nice semiconductor tests or DIY plans for one?

I have one of those Sencore dedicated semi testers somewhere in this mess (I think its in the kitchen...). Bought it for $5 at the Princeton hamfest years ago. I've also thought of building one of those x-y scope semi tracers. Used to have a Tek tubed semi tracer but I had to sell it. Some bottlehead cherrypicked the tubes and left the rest to rot

As for plans, I thought there was a set of plans on the web for a semi curve tracer that you could hook up to a scope w/x-y inputs.
I have an old Radio Electronics by my bed with plans. I'll look at it this weekend. I think it was just a 6.3 VAC transformer and some resistors to limit current.

I have a combo variac/iso for TV work but it doesn't get much use. Usually when I'm turning on something for the first time, the previous owner already let the smoke out (i.e. it won't get any worse)

 

[Morden2004]

Lets talk 'variacs' and current limiting those untested units.

Way back in my teen years and before I graduated in my Electronics course I worked for a terrific Dutch guy who repaired TV's. It was a HOT business back in the 50's and 60's.

He was a self-taught (meaning he took a correspondence course in TV repair - but he was a natural) and very penny wise. He built his own 'variac', sort of.

We wired a standard screw-base lamp socket to a chassis and wired it in series with the power line powering the TV under test.

For maximum current limiting he'd screw in a 250 watt light bulb.

As units burned-in and aged, he'd step down thru 150 watt, 100 watt, 60 watt etc. bulbs.

For "no current limiting" (fill power) he'd screw in a 15 amp fuse.

Kinda neat, eh?

Paul

 

[bolly]

Paul, Excellent...

... variation of the old lightbulb trick!

Greg

 

[dshoaf]

Work on a stereo bench in the 70s...

and discovered one of the most-used pieces of equipment was the old receiver and speakers on the bench. Most audio problems required a quck way of tracing a signal so I used the tape outputs of the bench receiver into the amp under repair and then used the tape input and a modified interconnect cable with a test probe on the end to trace where the signal stopped.

Adjustments for things like DC offset and idle current in the power amp required an FET VOM. Generally FM problems weren't that frequent so the cost of an extensive set of sig gens didn't cover the times I would actually use it.

You'll have to remember that I was paid by the repaired piece so time was money. That tends to have you focusing on the things you could repair rather than doing an extensive checkout of things that were clearly working fine.

The second most important piece of gear was the service manuals. As this old TV tech told me once, "You can't play the game if you don't have a score card."

Cheers,

David

 

[Morden2004]

Dave:

Yes, I recall that the tech I worked for was very practical and cost conscious and we didn't have RF generators or anything elaborate. Just basic test gear.

Paul

 

[bolly]

a modified interconnect cable with a test probe on the end to trace where the signal

...stopped.

What type of meter did you hook the other end to? Has to be a scope, no??

Greg

 

[RocknRoll]

The probe probably just went to a speaker for sound indication and used for simple signal injection or tracing.

 

[Mr Natural]

Re: Work on a stereo bench in the 70s...

Originally posted by dshoaf
The second most important piece of gear was the service manuals. As this old TV tech told me once, "You can't play the game if you don't have a score card."

Cheers,

David

How could I've forgotten the old Sam's Fotofax's??:bash: an absolute life saver...
and must not forget the HP audio generator. the one with the gigantic dial, what was the range, like 20 to 2khz or something?

 

[oldmarantz]

As I like test equipment and Hifi vintage I bought some good stuffs but the prices was right

I ve got:

FM/AM SIGNAL GENERATOR NATIONAL VP-8190A
FM MULTIPLEX SIGNAL GENERATOR PANASONIC VP-7635A
SCOPE TEKTRONIX 2X50 Mhz 2225
AC VOLTMETER KIKUSUI AVM 25R
MULTIMETER FLUKE 77 , BECKMAN TECH 300 and a taiwan crap
WELLER WS 50
and I just buy DISTORTION METER NATIONAL VP-7705A

Now my tuners and receivers are always perfect